View Full Version : Proportional Controller EMULATOR

01-19-2003, 11:18 PM
Got a few Bit-G clones for xmas and I gotta say they're nuts!
Took 'em around to a mates place and we raced them all night around a home made track on the living room floor.

During this time all I could hear was this incessant clicking sound from the RC controllers. None of us ever held down the steering buttons for very long since every turn on the race track varied in length / sharpness, etc... So how do you control a Bit-G that doesn't have a proportional control? Click the bloody left-right pads repeatedly depending on the shape/sharpness of the corner, ouch!

This gave me an idea. If I could control the left/right steering as a series of pulses instead of a constant on / off maybe, just maybe I could EMULATE a proportional controller! You could do this for forward/reverse as well, effectively giving you speed control in both directions.

At this point let me say that all I'm trying to achieve is to EMULATE a proportional controller to the best of my ability. There is no way known given the circuitry of the transmitter & receiver to be able to achieve a fully proportional controller since it has been well established that the custom RX/TX IC's use a pulse width encoding scheme that either outputs a 0 (OFF) or 1 (ON) to the motor / steering circuitry on the receiver board.

So, with all of that in mind I came up with a design that sends a pulse to the left/right switch (on the IC side) of the controller. This pulse pretty much emulates the action of clicking on the left/right button instead of the operator of the controller doing this himself. This pulse is controlled by a potentiometer (a variable resistor, found in many computer joysticks) that is used to control left/right functions. This is what you use to steer the Bit-G.

In layman’s terms what does this mean? Well, having the dial in the middle means steering is in its default state, centred with no action. Turning the dial to the left starts a pulse that is very “thin”, this causes the wheels on the Bit-G to turn to the left for a very short amount of time. As the dial is turned to the left even further, this pulse becomes “wider”, therefore the wheels stayed turned for a longer period of time. Turning the dial all the way to the left causes this pulse to stay “on” all the time, therefore keeping the wheels permanently turned to the left. This is the same as when the left button on the controller is pressed.

This is still in heavy testing and development, I’ve been able to get this to work but so far for one direction only. I will need to modify the circuit to add the extra “channel” to be able to turn the car left AND right. The schematic below is for the left. Notice that the circuit requires 6V. I use a 3.3V Zener diode to bring the voltage down the 3V for the controller circuit. I haven’t tried this part yet since charging the Bit-G “might” blow the diode due to excessive currents.

For you tech’s out there the circuit is a basic PWM (Pulse-Width- Modulator).

01-20-2003, 12:01 AM
i had thoughts to do this but for haven't had the time to really get into it so definetly keep us posted on you progress then with a little more modifications you could put it into a joystic and have a totaly proportional bit

Blue Raven
01-20-2003, 12:09 PM
This is a great idea. I had also thought of doing something like this but for the speed instead of the steering. Also for controlling both sides of the steering coils, why don't you duplicate u1d but in an inverting configuration. Then put an RC filter on the steering coils of the car. This might give you a crude analog voltage. But I'm not sure how you can drive only one coil at a time. Also I was wondering what frequency is the PWM running at?

01-20-2003, 04:10 PM
That's a good idea Blue Raven, you can use this for fwd and reverse. The PWM is running at about 10hz, I wanted to duplicate the manual pressing of the button first before I up'ed the frequency on the circuit. Once I get the second channel going for steering both ways I will stuff around with the frequency to get the best result. The values of the caps and resistors aren't final, if anything I've changed them since drawing the first design.

Your suggestion about using an RC filter is an interesting one, I take it you'd be utilising the charge rate combo of the RC network to "smooth" out the square wave pulses going to the steering coils. I "think" (not sure, anyone is free to correct me) that the coils in the steering arm must have some some of alternating pulse (Possibly simulating a sine wave) going into them to be able to generate a magnetic field (since a DC current won't do this). This field alternates depending on what direction you choose. Left charges one coil, Right charges the other. An RC network might smooth out this "alternating wave" so much as to negate any magnetic field being generated and therefore killing any steering action you might have.

The problem before me at the moment is being able to use just the one potentiometer (variable resistor) to vary both left and right signals. When the pot is centred both channels need to be outputting > 1.2 Volts (this is the quivalent to not pressing either left or right buttons). As the voltage approaches zero the channel is activated. I've found that at the input to the Comparator (U1D) the voltage varies between 0.8 and 1.5 volts. Inverting the other channel is worth a try , I will give it a go and find out if it works. Otherwise I was looking at a "dual-gang" pot where one half is used for left and the other half used for right. The advantage of this is that each variable resistor on the pot is electrically isolated for the other AND i can wire one in the opposite direction of the other. So turning one way increases the resistance of one resistor whilst decreasing the resistance of the other.

*sigh* To many nights out drinking during my uni days when I should of been studying!

01-20-2003, 06:10 PM
Hey Smokey, I should be so lucky! :cool:

You're probably right, it is a good idea. In testing the circuit I did notice that with the motor is was sputtering along. As the duty cylce of the pulse increases though it becomes a smooth ride.

Also increasing the frequency of the PWM will reduce the jerkiness of the motor, this is something I will try out. With this mod the motor will almost become a stepper motor at the lower end of the duty cycle of the pulse.

Keep in mind that the design is primarily for steering purposes so a clean square wave pulse (with a variable duty cycle) is sufficient for a variable steering control.

Great ideas guys, keep 'em coming.

01-21-2003, 02:28 AM
Well here is what i have been planning on using... since my electronic skills are on a somewhat basic level (two electronics classes a couple years ago in high school), i decided to use an already built circuit. Allelectronics.com has some pwm motor controllers for $4. They look to be small and it could be used as a means of pulsing the control buttons (taking out the microswitches and connect to the spot on the motor control board where it would open and close the circuit. I'd have to order and look at the thing to tell what exactly to do with it, but thats my basic idea.

on the same site, there are some "basic stamp" boards that can do all sorts of stuff, including pwm. I have a few from a robotics lab i did in highschool, but forgot a lot about how to use them. they retail for a tall $60

01-21-2003, 02:30 AM

here is the link to the motor controller

01-21-2003, 06:29 AM
Dude, not a bad suggestion, but the ciruit needs to be built from scratch. I've yet to work out how to tie both left and right steering into the same variable resistor (potentionmeter)

01-22-2003, 02:19 AM
f/b and l/r could be run from one basic stamp, and you could use the same pot for input on each. The function would just be inverse. I would recomend picking one up. They are fun to mess with and if you get tired of micro r/c for some reason, you can do many other cool things with them. Like automatic goldfish feeders.

01-22-2003, 12:32 PM
What about robbing the POT's out of an old RC Car "wheel" type Tx? Or, better yet, use the case with the wheel and trigger. That way, you will have the POT's, return springs, plenty of roon to drop in the electronics, and a long telescopic antenna!

01-22-2003, 03:49 PM
hey great idea.... I have a really old non operational futaba sport

01-22-2003, 03:59 PM
That is exactly what I was looking at when I got the idea.
I'm excited to hear if it works!

01-22-2003, 04:36 PM
That's a great idea and one I have trying to achieve. the only bugger is that I don't have any old R/C controllers lying around to do this mod in.:mad:

Also the other issue is the value (in Ohms) of the variable resistors in these R/C controllers. Unfortunately I can't just use any variable resistor for reasons explained below.

In the circuit I've posted I noticed that the PWM cycles between 0% and 100% duty cycle over a voltage range of approx 0.8v -> 1.5v. For a really smooth control the variable resistor (potentiometer) needs to be able to adjust over this range from it's centre position to rotated all the way to the left (or right).
I'm currently working out the V=IR calculations I need to select the correct values for R6, R7 & R8(pot).

I've been stuffing around with a "daul-gang" pot which is basically two variable resistors on the same rotating shaft. With each reference wired oppposite to the other. This means that when I rotated the pot to the left to output from the comparator (U1d in the schematic diagram) that "drives" the left channel is active, BUT the right channel (with an extra comparator driving the output for the right) is off. Turning the pot to the right causes the left to become inactive and the right active.

Once I've tested and finalised this I will post the updated schematic.

01-22-2003, 04:47 PM
Right. I think we should be able to use the same set-up, though. Just need to swap the POT's out for the impedence we need?

I know I'm simplifying, but I just wanted the general idea expressed.

01-22-2003, 08:07 PM
Hopefullly that will be it, just swapping the POT's to the correct values *SHOULD* do the trick.

I'm currently working on the maths involved to get some proper vaules. I've selected a 5K linear POT to use at the moment because they are widely available. I've pulled apart my old quickshot joystick and found that the X/Y axis POT's were 150K. This sux because there is too much potential (voltage across the resistor) drop which can be balanced by increasing the ohms of the other two resistors each side of the POT. Too high a resistance will create a very small current, possibly not enough to power the Comparator, dunno, not sure............

Hopefully during the next week the design will be finalised, tested and I should have some video to show the darn thing in action, hopefully!

01-23-2003, 02:07 AM
Sweet... This would be great for my latest project idea... Clone donor, full-length fiberglass chassis (not retaining any of the clone chassis), lexan slot car body (anybody know where to find these?), and either 2 1/3aaa or 3 of the cells used in the layman mod. Proportional control will be a must for getting the most out of it.

01-26-2003, 02:38 AM
Try here (http://www.scaleauto.com) for Lexan HO Slot bodies. Good luck with the mod, be sure to show some pics when you're done.

01-27-2003, 02:20 AM
AHHH thank you sooo much. I'm looking right now.

01-31-2003, 09:24 AM

What is your source for the dual-gang potentiometers you are talking about? I have been searching for these, and am trying a different approach to "pushing the buttons" on the controller (using a Low power 556 chip).

Also, I had found an analog joystick with what I think is the correct pot on a nintendo 64 control pad, but it is dual-axis, and I was hoping to find tiny single axis joysticks, with no luck.

Any ideas?

02-01-2003, 06:41 PM
hey ejaf..

here's a link to an aussie supplier, Jaycar (http://www1.jaycar.com.au/productView.asp?ID=RP3706&CATID=34&keywords=&SPECIAL=&form=CAT&ProdCodeOnly=&Keyword1=xxxxxxxxxx&Keyword2=xxxxxxxxxx&pageNumber=&priceMin=&priceMax=&SUBCATID=384)

I also tried using a 555 initialy, in astable mode as an oscillator. I tried using a pot on that to vary the duty cylce of the pulse, but I found that I could never achieve greater than %50 duty cylce on the square wave. ( The duty cylce equation backs this up, see page 8 of the 555 timer datasheet (http://www.national.com/ds/LM/LM555.pdf) )
This is why i switched to a PWM circuit.



02-01-2003, 11:48 PM
Hey ph2t, have you finalized anything? If you need some pots, i could send them to you. They are from an OLD airtronics 4ch plane radio.

02-03-2003, 06:09 PM
That would be great dustn, the only thing is I live in Australia!



02-03-2003, 10:22 PM

Thanks for that bit of info. I think I may have bought useless parts :-(

One question though. The basic astable circuit that I was looking at has the capicitor between pins 1 and 2, so the capacitor charges through R1 and R2, but discharges through R2.


formula given for t1 (time between pulses)
t1 = .693(R1+R2) * C1

fromula given for t2(pulse length)
t2 = .693(R2) * C1

Therefore, I was think of using a very high value for C1, with a lower value for R2, and using a 10K pot, which, I think, may increase the duty cycle.

Take that with a MAJOR grain of salt, since I only started looking at this a while ago, and I am NOT an EE by any stretch of the imagination.

If I have a chance, I will post the picture of the book I am looking at (from RS - Timer, Op Amp & Optoelectric Circuits by Forrest Mims), if anyone is interested.

Wait...here it is attached. Hope this isn't copyright infringement:

02-04-2003, 06:03 PM
ahhhh ejaf, I used to have that book! Also the one for TTL logic circuits. They were great books.

What you're doing is exactly what I set out to do initially. After experimenting for a while I found that I could never achieve a duty cycle greater than %50.

No matter what value combination you use for R1 / R2, when the pot is turned to zero ohms you'll get %50 duty. As the pot resistance increases (10K, 100K, 1M, etc...) the duty approaches zero.

The duty cycle equation is as follows..

D = -------------
R1 + 2*R2

when the pot is a max resistance (eg, R1=10K)

D = ------------ (assuming R1 value of 1K)
10 + 2

D = 0.0833 = 8.33% (pretty much zero)

when the pot is at zero resistance (eg, R1=0)

D = -----------
0 + 2

D= 0.5 = %50 duty.


02-04-2003, 06:55 PM
Also, here's the latest version of the mod. I have now both channels LEFT and RIGHT. Don't take the resistor values as kosher, they are no way final at the moment.


02-04-2003, 11:16 PM
Thanks for your insight...being a newbie to electronics, I might try it just to see the results anyway, but I will study that formula a little closer.

Also, I will definitely look at the one you are proposing a little harder now. ;-)

02-05-2003, 01:23 AM
Try increasing the frequency of the oscillator. I noticed
stepper-motor like results at low freqs, increasing this made the acceleration smoother. Even with the %50 duty cycle, at a high enough frequency it might just work.....

02-05-2003, 10:09 PM
Thanks...worth a try, just for fun.

FYI... found this, might come in handy for someone interested:


That page also mentions that there are PWM IC's, but the voltage requirements are too high for what I'm looking for.

Also, I guess the only way to truly test this would be with an o-scope, correct?

Also, this page mentions getting a 98% duty cycle out of a 556, and the circuit is totally different than the one I was looking at:


One other question...what is the maximum output current needed to actually push into the transmitter IC?

02-06-2003, 08:19 AM
You're right ejaf, a CRO (cathode ray oscilliscope) would be the best way to test and see the shape of the waveform you're putting out.

As for current into the TX IC. Well when the button is pushed, the pin on the TX goes to ground. So the output of the PWM needs only to go to ground to turn the IC "on" so to speak.

I was thinking of a transistor-coupled circuit using a pullup resistor on the IC pin but in the end I didn't need it. I just connected the output of the PWM to the input pin on the IC.

Currently the controller is running at approx 10Hz for the steeering. I'm working on the speed control as well, but this circuit will be running at a higher speed (possibly > 30Hz??) to reduce the "stepping" effects of motors at this speed and duty cycle.


02-06-2003, 08:22 AM
Please forgive the quality of the pics, I know they are crap but you can see the birdsnest I've created trying to get this thing to work!!

02-06-2003, 08:23 AM
and another!

02-06-2003, 08:24 AM

02-06-2003, 08:25 AM
here you can see the POTentiometer in the background.

02-18-2003, 07:06 PM
Just wanted to say quickly that I haven't abandoned this project. I just bought a house so things are pretty busy at the moment!

Watch this space!


02-18-2003, 08:21 PM

02-28-2003, 02:12 PM
I'm on it too!

03-02-2003, 07:48 AM
coolies ejaf, let me know how you go!


03-04-2003, 03:26 PM
Well I've finally got some video of my exploits to show.:cool:

This first example shows how the speed varies. I don't have a long enough table to show the full range of speed but this is a good enough "proof of concept" thing.

Download the 900K AVI (DivX) here (http://www.prahranpianos.com/bit_g/speed_test1.avi)

The second video shows a close up of the rear wheels on the car and how the speed of them vary as I change the "pulse width" on the controller. You can see a green light that varies with intensity as more power goes to the motor. I've been using that as an indicator.

Download the 1.2M AVI (DivX) here (http://www.prahranpianos.com/bit_g/speed_test2.avi)

Now I need to confirm the stop/start voltages at the comparator stage and go off and buy some proper resistor values so I can update the schematic with the correct values. Once this is done I willl focus on getting reverse happening as well on the same POT ( as stated before I'll need a daul-gang POT for this).

Let me know what you think....



03-04-2003, 03:42 PM
Absolutely incredible.

03-04-2003, 03:57 PM

please keep the feedback coming, it's the only way I'll learn...



03-04-2003, 11:42 PM
Here's the layout of the points to be soldered on a clone (Bensu)transmitter board.


Closeup of Left / Right


Closeup of Forward / Backward


03-04-2003, 11:44 PM

03-04-2003, 11:57 PM
I managed to increase the sensitivity of the POT to allow for better control of power to the motor.

This video shows a closeup of the wheels and how the speed changes as I turn the POT.

Download the 570K AVI (DivX) here (http://www.prahranpianos.com/bit_g/speed_test4.avi)

Here's another shot of the car in motion, this time the speed control is definately evident.

Download the 640K AVI (DivX) here (http://www.prahranpianos.com/bit_g/speed_test3.avi)



03-05-2003, 10:19 AM
ph2t - you work for Agilent?

03-05-2003, 07:06 PM
no, my wife does..........

we're moving house at the moment, so we've got agilent & dell boxes everywhere :D


03-05-2003, 07:37 PM
I'm the shipping manager for Reid-Ashman Mfg. We make test head manipulators for some of the Agilent test systems.

I ship to Agilent all the time, but mostly Stateside, and Singapore.

03-06-2003, 01:18 AM
great work ph2t. you actually finished it:) and seeing it work is just sweet.

do you have anything finalized yet? i wanna start makin one:D .

also, did you consider using a joystick of some sort for the pot?

edit- woops, this thread was so long i must've missed the lines regarding the joysticks, my bad.

NOS man
03-07-2003, 10:58 PM

03-09-2003, 09:23 PM
Yo NOS, what are you on? ;)


NOS man
03-10-2003, 10:49 PM
what do u mean what ime on?

03-10-2003, 11:04 PM
Your post just says....what???????????



NOS man
03-10-2003, 11:20 PM
fr get it

03-12-2003, 08:15 AM
NOS, please make a constructive comment or nothing at all.....


03-12-2003, 09:41 AM
ph2t - any luck finding micro components to replace the standard ones? Would be great to fit into a standard controller.

NOS man
03-12-2003, 03:05 PM
dont edit my post!!!!!!!:mad:

03-12-2003, 03:55 PM
hey, did you know http://www.bitmod.tk has done a propo controller? it only works forwards though.

its called Stepless speed(translated) or Stufenlose Geschwindigkeit

i saw this a long time ago but never bothered to translate it.

03-12-2003, 05:13 PM
NOS man,

I'll ask you to NOT post nasty comments on our Forums.

03-12-2003, 07:17 PM
Modjo: This circuit is similar to what Ejaf is designing. You can get the translation here (http://babelfish.altavista.com/babelfish/urltrurl?tt=url&url=http%3A%2F%2Fwww.universalhost.de%2Fhtml_bit%2 Fstufenlos-vmax.htm&lp=de_en) .

It's a 555 timer setup as an astable oscillator, what's interesting is that the designer used an opto-coupler to ground the input from the IC. I might try that since it's tricky to be able to pull the pin from the TX2 IC to ground properly using my design.

Bencloned: Mate I've gotta get the design final yet before I microsize it! :D I would like to be able to fit it into my controller but with the use of POTS now for steering and accel it will be hard to maintain the original enclosure.

03-15-2003, 02:58 AM
Just a quick update:

I've gone a bought two daul-gang pots so finally I can now test the design for forwards AND backwards with full proportionality (emulation of course). These pots have a "centre-click" feature which will be usefull when calibrating them later..

Also, I went to buy some opto-couplers from Jaycar but the @#$% closed before I could get there :mad:, so I'm gonna have to wait on that.....

So Modjo and Efarel please be patient, I will have this finalised during the next few days and I'll update the schematic with the correct values soon....



03-15-2003, 10:36 PM
thank you for the update. take ur time. the more "finalized" it is the better. but don't feel obligated to finish it if ur busy with other stuff.

i'll just sit here staring at the screen till u post somethin:(


03-16-2003, 06:58 AM
No sweats Modjo;), I'd like to thank you for pointing me in the direction of that german mods page. I've been there before but never noticed that mod in particular. (Stufenlose Geschwindigkeit just rolls of the tounge, not!)

Anyways, I've got a bit of light reading to do (http://www.ee.mut.ac.th/datasheet/4N2X.pdf) . :eek:



03-18-2003, 08:00 AM
Well I've been testing the circuit using the 4N25 opto coupler and I gotta say that it works great!

The steering now holds itself well and i don't have any more issues with forcing the input pins for L, R, Fwd, Rev on the TX2 chip to ground. The advantage here is that the signal to the TX2 chip is better defined as being either ON or OFF. This should allow me to up the freq on the speed controller to allow for a smoother ride.

The big news is that I added the extra OPAMP in the comparator stage of the circuit (see schematic on 1st/2nd page, can't remember :) ) which has enabled me to use the dual gang POT.

What does this mean? I can now do Fwd and Rev with proportional controll(emu). I will then duplicate this circuit and run it at a lower frequency for Left & Right proportional steering(emu).

The video below shows two LEDS (one for each "channel") and how the brightness varies as I rotate the POT in either direction. At the moment both LEDS light up when the POT is centred. I just need to tweak the resistors each side of the POT so when it is centred both LEDS will be off. Turn one way causes the green LED to turn on and increase in power. Turn the other way causes the red LED to turn on and increase in power. Each LED could represent either L/R or Fwd/Rev.

Theses LEDS are a proof of concept thing. Once I sort the centre position issue out I will get some more video.

Download the 700K DivX here (http://www.prahranpianos.com/bit_g/dual_chan.avi) .

Time to sleep......:cool:


03-19-2003, 03:39 PM
that sounds awesome. u can actually make the wheels stay in one spot? i thought that would require a servo but i guess u can pulse it really fast.

to be honest, i only understand a little of what ur talkin about cuz my bro is the real engineer. :eek:

anyways, check out the new video on bitmod.tk of the propo speed controller. there's also a pic of the electronics linked to the controller and i think urs looks a lot easier to make.

03-19-2003, 05:21 PM
Yeah the wheels only stay centred. I'll have to make some video to be able to explain this better.

The steering is "pulsed", a short pulse means that the wheels only turn for a short time. A long pulse make to wheels stay turned for a longer time. This goes back to my first post in this thread where if you wan't to turn gradually you need to press the button on the controller repeatedly. If you wan't to turn as sharp as possible you hold the button down fully.

This idea only works because the car is moving in the fwd or backwards direction.

Again, pictures are worth a thousand words, I'll post some video tonight (hopefully).

The propo controller on bitmod.tk is quite exceptional, from what I could understand (babelfish translates like a 3 year old) the author uses the PIC microprocessor chip. One on the controller and one on the car. The original controller effectively becomes a RF transmitter and nothing more. The PIC chip encodes the signal, the controller transmits it. On the car the PIC chip decodes the signal and then uses some drive circuitry to spin the motor. The advantage of this design over mine is that it is a pure analogue voltage going to the motor on the car, not pulsed like mine is. Through this you can get better control of the car. He has a long way to go through, so far it seems to only work in one direction. Also this mod would be out of reach of the average joe (look at the circuit connected to the controller, wow!).

The advantage of my mod is that it is purely controller based, the car does't need anything changed.........

Then again, competition is good. ;) These krauts know their sh1t.



03-20-2003, 04:19 PM
PIC! those schweet. i was thinking of getting a microchip programmer. do u have one or have any suggestions on which one to get? particularly one that uses higher language.

also, shouldn't using a pic make the circuitry simpler? *oops

03-25-2003, 08:14 AM
OK, finally the circuit! :eek:

Modjo, Efaral, don't go blind!:cool:

View it in PDF format here (http://www.prahranpianos.com/bit_g/pce.pdf) .

Guys, I won't be able to do anymore development over the next week. We're moving house so I had to pack up all my electronics and Bits , *sigh*.

I thought I'd at least give you something to get your teeth into.


03-26-2003, 08:10 AM
You can omit R14, R16, R23 & R28 from the schematic and replace them with wire. They were a stuff up, not meant to be there.....


03-26-2003, 11:25 PM
Some of the dudes at ausmicro.com had some questions about this mod. I've answered them and thought I'd paste it here.

The throttle is proportional in both directions(Fwd & Rev).

When the pot is centred there is no signal (the trimpots R13/R15 are used to tweak the centre position for no signal). This is the same for the steering (in this case the trimpots R21/R29 are used to calibrate the centre, neutral position).

Looking at the schematic (http://www.prahranpianos.com/bit_g/pce.pdf) I will explain it in portions.

1) Triangle wave generator:

U1B & U1C (parts of the LM324 quad op-amp) form a triangle wave oscillator at a certain freq. This part drives the throttle so its freq is about 30-40Hz (I think). This can be set by capacitor C1.

U2B & U2C are a copy of the same osc, but in this case the value of the cap C2 is greater for a lower freq. This drives the steering, I found the steering more responsive at a lower freq (approx 6 - 10Hz)

U1A is just a reference voltage source @ 3V. This is needed because op-amps usually are run off +ve and -ve voltage sources.

2) Comparator / Pulse Width Modulator

U1D & U2A take the signal from the output of U1C and compare it against a voltage level set by the potentiometer R12. I won't go into too much detail here but when the voltage reaches a certain level @ the -ve input of U1D & U2A it outputs a positive voltage. (Bugger, this is hard to explain[xx(]. I might need to draw some pictures) This is why a triangle wave generator is used. As you turn the pot R12 it varies the width of the pulse seen at the output. Hence the name "pulse width" modulator.

The daul-gang pot (R12/R25) is the part that makes it all happen. You will see that each side of the pot is wired in opposite direction. ie: I turn the pot one way causes one voltage level to increase and the other to decrease. It is this that gives you both directions.

3) Output stage

The outputs of U1D & U2A both drive the opto-couplers which then in turn drives the transistor allowing for the pin for the TX2 chip on the controller to go to ground. At first I didn't have the opto-couplers and I was finding it hard to "pull" these pins to ground properly.

Stages 2 & 3 are duplicated for steering AND throttle. It is really stage 1 that differs (and then only in the value of caps C1 & C2).

Sorry for such a braindump, but you asked [;)].
I'm just waiting for uA to get back from his holiday so he can read this![:)]


03-30-2003, 08:31 PM
wow! over 2000 reads..... (massaging ego.....)



03-31-2003, 05:59 PM
:) i check this thread all the time, even if there aren't any new posts.

I'm currently searching for parts. luckily rs sold lm324 so i didn't have to order it. now all i need are some correct resistors.
did u use the exact values pht2? or did u just use one value and hook a bunch up to equal the resistance? i was also lucky enough to find dual gang pots at my local www.sciplus.com store.

03-31-2003, 06:25 PM
Yes mate, the vaules in the schematic are the values I read off the resistors once I concluded this was final. Standard 5% tolerance carbon film types, 0.25 Watt.

I have run into a problem though. Some germans contacted me and told me of a problem when trying to do steering AND throttle at the same time. Due to the way the TX2/TX2 chipsets encode the instructions of what to do (Fwd, Rev, L, R, L+Fwd, R+Fwd, L+Rev, etc....) the signal gets buggered (what a technical term!).

So I would hold off just yet on building it unless you want to help me ;) try and figure this issue out.

The post is explained in detail at http://www.ausmicro.com in the BCG-Technical forum, look for the thread "The true extent of my madness". Quite a fitting title methinks.............:cool:


04-20-2003, 07:46 AM
Well, I'm making some headway... Here are some pics to show you that I am still building this. Just ran out of solder *arghhhh*:mad: , so I gotta go 'n get some tomorrow. I knew there was an Easter break for a reason!





04-20-2003, 03:06 PM
Interview times:D

So you figured out the frequency problem? I read the ausmicro posts but wasn't sure. somebody posted you had to raise the frequencies rite after you posted the new ones.

What are those round things protruding out of the board and whats the 6 pin chip for?

Just have to express my curiousity. I hope ya finish it or else i'll have 3 lm324's layin around for nothing:)

Sorry about the lack of help from me, I don't know much about electronics.

04-20-2003, 06:58 PM
Hey Modjo,

I hope to figure out the freq problem. As long as I keep both the steering and throttle circuits in sync and driven by the same oscillator whos max freq is about 16Hz, then yes it should be OK. I gotta build one half of the circuit at the least so I can start testing. The circuit was getting too unwieldly on the white testing board (see the earlier pics...).

Yeah the raising of the freq's was micro_amps suggestion, and a good one too.;)

The round things sticking out of the board are known as trimpots, these are small potentiometers (variable resistors), they are R13 & R15 on the schematic diagram. I use them to calibrate the centre posistion on the POT (R12) so as to cancel out any signal for either Fwd or Rev, this way the car isn't active whilst the POT is in the ventre posistion.

The 6 pin chips are the 4N25 optocouplers that are used to isolate my circuit from the controllers circuit. Refer to U4/U5 on the schematic. This method was much better than just connecting the controllers pins straight to the output of the op-amps.

Don't worry about the lack of help part, I hope you are learning things as we go..........;)



04-30-2003, 12:53 PM
ph2t, I did that proportional control icon (http://tinyrc.com/forums/showthread.php?s=&threadid=8304) you were wanting. :)

Keep up the good work.

05-18-2003, 11:15 PM
Just a little update.

This project is still happening it's just that there are so many other cool (and quicker) projects to do that this one gets a bit sidelined......

Trust me, it will happen...............;)


05-25-2003, 11:06 PM
how hard is it to make

05-25-2003, 11:46 PM
It ain't rocket science. But if you're not into electronics then I wouldn't attempt it. I'm still developing it at the moment....

05-30-2003, 09:35 PM
I'm VERY interested in this and am holding my breath for a finalized schematic. A finalized component schematic would be even better so almost anyone could try their hand at building one. Please, by all means, keep us posted on this. I'm gonna be checking back here often to see how your project is progressing. Wonderful work!

06-02-2003, 10:37 PM
Hey Azimov, thanks for the interest.

The components in the schematic are final at the moment. You could build based on what I've got there and it will work.

The schematic is linked a few pages back in this thread if you want to review it.

Also some local boys are helping out at AUSMICRO.COM you can check the thread here (http://www.ausmicro.com/topic.asp?TOPIC_ID=418&FORUM_ID=9&CAT_ID=2&Topic_Title=The+true+extent+of+my+Madness%2E%2E%2E %2E%2E%2E&Forum_Title=BCG+%2D+Technical) .



06-03-2003, 01:05 AM
Thank you kindly mate. I'll dive in when I get time and see what's what. I've been thinking of trying my hand at the problem, but am glad someone sweated it out already.

06-15-2003, 03:38 PM
Hi all.
I've been following this thread with a great interest. I was wondering about something to make a "semi proportional" steering. We could use a motor for steering, and adapt the wheel of a PC mouse to the transmitter R & L contact. ie: each time the wheel turns to the right, an impulsion is given to the steering motor acting as a step motor that would turn the wheels to the right just a bit... I hope you see what I mean. That would give a more acurate controls to the wheels (while propulsion control could be done with your "potentiometer" system).
Tell me what you think about it.

08-14-2003, 02:35 AM
OK, it's official "pull my finger out of my arse" time....

Expect results over the next week.


09-16-2003, 05:52 AM
So, one month later, how is it going? :)

09-22-2003, 10:03 PM

I do a lot of electromagnetic actuation / oscillation for miniature movements - micro-robotics type stuff. I have a lot of practical experience with resonant oscillation of mechanical assemblies.

I think that the idea of a proportional controller emulator is probably the best way to get the effect, and it should be pretty straightforward to get proportionality from the drive motor.

However, the proportionality of the steering might be a bit trickier.

I would like anyone directly working on this project to read through this so that they are at least thinking about it beforehand.

The mechanical/manufacturing characteristics of bit steering assemblies do not look that precise to me in pictures (and I say that because I still have yet to receive the ones I ordered in the mail this week).

Since the steering assemblies are probably quite a bit different from car to car, with tight and loose tolerances, different wheel/tire setups, different springs, etc, the "resonant frequency" of the whole assembly will be different with each car.

In "stock" operation, the coils probably serve to overcome the restorative force from the central spring and slightly tip the balance past some breaking point, after which the motion of the car itself is enough to momentarily force the steering linkage to turn. It would be nice if we knew precisely what forces were applied by the coils under different electrical situations.

I bet that there is a fairly wide (but still critical) range of frequencies where PWM will work on the steering, but it may indeed be more of a coarse vibration around a central steering deflection angle, rather than a constant deflection.

I plan on taking some precise measurements of my bit chassis when it arrives, and I might make a more advanced chassis using my Prazi precision milling machine and lathe. I make mechanical parts smaller than watch works all the time, so bits should be a fun diversion. I also do some electronics work as well.

I will follow this forum. Just remember, nature abhors a change in flux.


09-22-2003, 11:35 PM
Jesse, welcome to the forums, and let us know what insight you get once you receive your cars, sounds like you know your stuff! :)

09-24-2003, 03:43 AM
I have been thinking a lot about the propo steering. I looked at some of the non-bit cars and decided I didn't like their setup.

I think I have a solution, but it will involve both electronic additions to the control and mechanical additions to the car. I don't like the idea of having to mess with the car, since ideally this would just be a sweet propo emu controller, but it is a different kind of setup than anything I have ever seen, so I think I will at least try it once.

I plan on making what I will refer to as a ratchet steering linkage.

It is basically quantized steering.

The steering mechanism will have a few stable positions that it can be in (such as dead-center, pegged at full left and right, and intermediate positions, although not necessarily spaced evenly).

This will be achieved by making a moderately tough spring with a rounded-off dimpled area on a flat end. This dimple/nub protrusion on the spring will be able to click into some holes (or perhaps depressions) that will be drilled into a thin disc of flat brass, aluminum, or stainless steel. It will look sort of like a record player stylus that can click into some pits on a tiny record.

To actuate the device, a forward or reverse pulse from the transmitter will hit a tiny DC motor with a small gear that meshes into a larger plastic gear that the metal disc with the pits or holes is glued to. This larger plastic gear can have the steering knuckles on it.

I have some 4mm dia by 10mm long ultra small pager motors that cost about a dollar each, which would be perfect.

I will post a schematic of the steering assembly soon.

To create the RF pulses from the transmitter, a computer mouse with a scrolling thumbwheel can be taken apart, and the scroll wheel can be built into the controller. The optical encoder disc setup can be rigged to send pulses on the Left and Right transmissions. The proper transmitted pulse length to kick the steering assembly over one click will need to be determined experimentally.

This isn't fully proportional, and it requires a lot of work, but I bet the performance and feel of the controls would be quite good, and I am sure that the whole thing can be made light, perhaps as light as the current coil setup. Also, we can eliminate those delicate wires to the coils. I bet those things are hard to solder. I have a giant 20lb roll of enamel wire that is finer than human hair. It makes a great low-current coil, but it is tough to solder.

One of the first mods I plan to make is to put pin connectors on multiple contact points of my receiver PCB so I can do quick connects to various electronic mods.

It shouldn't be a problem to get 20 different mechanical click positions into the steering mechanism, and they should each be stable enough that the force on the wheels as the car changes direction won't upset the balance too much. If the wheels start to straighten in an intense turn, just keep spinning that mouse thumbwheel as fast as you can. Unlike a standard trigger RC control, the controller steering wheel could be turned indefinitely in one direction, continuosly pulsing the steer motor.

There would, of course, be mechanical stops at the full left and right positions.

I will build it in the coming weeks, and report back. It might sound complex now, but I think I can design it so it is pretty buildable. Of course, people will need a scrap computer mouse to scavenge from, since new mice cost more than bits.

If anyone has any thoughts or knows if this has been tried, please post.

11-10-2003, 04:21 PM
Hi :)
I had the same idea (about using a mouse's scroll button) but with a stepper motor. I don't know if there are any stepper motor small enough for BCG though. A stepper motor would be much more simple than the setup you describe I think.
Anyway, I'm so dumb in electronics that I never tried anything (but thinking never hurt) :)

01-21-2004, 05:12 PM
The whole steering linkage thing is fine, but the ZZSE's already use it. It's a bit tricky, and I perpetually have to tune mine.
Why not use a variable resistor connected to a cap connected to the TX button leads to control it? The lower the resistance, the more the cap "fires", and the more the car turns. A similar system is used in RFFS controllers, and they work fine.
Alternately, just get a set of Cirrus Mj gear (~150.00) which includes a Rx, ESC, 2 servos. It's designed to use 3-4 cells, and, at 6 grams for the ESC,RX, and 1 servo, it should work nicely. Sure, it's expensive, but you'll have the best Bit in town.