New ''Dual Cell''
 

Just an idea to make a dual cell with out the second cell, we could use a regulator. I have a few of these ones which i think will work, Look for the 'TPS61015'. They are really small and could easily fit into a Bit. Of corse there would need to be other components but if we did it surface mount we could keep it really small. The PCB would just go inline between the battery and the RF board it would mount on top of the RF board. The increased voltage would also be able to operate a small PICmicro which would be able to control LEDs for headlamps, you would be able to program it so when you pressed forward twice then the front lamps come on etc. I also have a few PIC 12f675s that could do this job, they are also surface mount just to be small!

i dont get it

i think this chip takes in a low voltage, as low as .8 volts, and it will bump it up to 3.3 volts max

It simply takes in a small voltage and boosts it to something around 3v.

Two problems with that.

1) The extra components will make the car heavier, causing the motor to draw more current to do the work of getting it around.

2) The extra voltage is more than likely at the cost of, guess what? That's right, available current!

Interesting thought though.

True, but im still going to have a go just to see if it does work at all.

Please post your results if you can.
In theory it would only reduce your run time, if you can bring the rest of it together.

Teamoutburst, this is a great idea that I have been experimenting with as well.

Let's just get a few things straightend out first.

The car will increase in weight, BUT this will be less than adding another battery. The centre of gravity won't be affected as much as an internal daul cell bit, therefore keeping the car's handling in check. (Dual cell's with the batt piggybacked on the rear of the car is a waste of time, internal dual is the only way to go.)
The current WILL increase, not decrease. Ohms law will back this up.

The problem is one of supply current. I've done some tests and on a normal 1.2V battery the car pulls the following currents.

1) Fwd or Rev = approx 90mA
2) Fwd/Rev + Steering = approx 160mA
3) Car is idle = 7mA

I've designed a few converters that take 1.2V in and spit out 3.3V but none of them can supply the much needed output current for this motor and steering circuitry. The TPS61015 is only rated to 250mA for a input voltage greater than 1.8V. For a 1.2V input it would be approx 150mA. Again this is not enough. Keep in mind that increasing the voltage you increase the current. So the measurements above will probably double/triple for a 3.3V source.

I've been researching this pretty heavily and still on the lookout for a suitable DC-DC converter. Team, you can email me on ph2t@prahranpianos.com if you have any specific questions or just want to techo chat, lol! If you want I can post all the converters I've checked out to help you if you'd like. Most of them are available as free samples from all the major semiconductor component makers....

One possible application is to remove the 1.2V -> 3V converter on the RX PCB (This is used to drive the RX chip and AM receiver ONLY) and replace it with a 1.2V -> 5V step up converter. You should get a great increase in range with this mod, hmmm might go and try that tonight............

Best of luck.

ph2t.

ph2t, what is the best regulator that you tried or seen?

Great idea guys, let us know if there's anything we can do to help; keep us posted!

eh thats what 200mah batteries r 4 btrc

where can you get 200mah bats from?

WOW! thats pretty amzing to have 200mah cells in a 1/3 aaa battery, that would be perfect for testing this idea! The most ive seen is in the tiny rc shop which is 160mah (which is still an awlful lot!)

Hey team, good to see this thread where it belongs. I will post some info soon on what DCDC converters I've tested.

:)

ph2t.

I've had an idea!

Why dont i just put the convertor inline with the motor and rc board, then it will only draw 90mah as described in one of ph2t's posts, you might not get as good steering as in normal dual cell cars, but you would get the speed!

Also ph2t did you test the motor to stall when you found out the current ratings?

Tricky to do, it's not easy to be able to isolate the H-bridge transistors and run them at 3V/5V and leave the rest of the circuit untouched.

Motor when stallled (enough pressure on wheels to stop motor) was about 250mA, almost 100mA more that the car at normal operations.

ph2t.

Here's some of those DC-DC converters I've been checking out.

Here's the family!

http://www.prahranpianos.com/bit_g/conv1.jpg

http://www.prahranpianos.com/bit_g/conv2.jpg

http://www.prahranpianos.com/bit_g/conv3.jpg

http://www.prahranpianos.com/bit_g/conv4.jpg

http://www.prahranpianos.com/bit_g/conv5.jpg





Tired, gotta crash. Will post more information tomorrow.

ph2t.

Made my first version and it is allready for soldering tonight, will post some pictures later on.

I have managed to get pics of the PCB, I also chucked in two pictures, one of the car it is going to be fitted to, the other of the track it is going to speed around.
http://www12.brinkster.com/myrobotics/lightpcb.jpg
http://www12.brinkster.com/myrobotics/car.jpg
http://www12.brinkster.com/myrobotics/track.jpg

That pcb looks mad dude, did you use a riston covered board and expose it using an overlay? Pretty darn well detailed. I'd like to know your pcb making processs. specially when you're dealing with those TSSOP packages that are so #$%^& small it's not funny!
And show us the schematic as well.....

:)

ph2t.

BTW, the pics don't work. You need to load the URL into another browser to see.:cool:

I have access to a cnc pcb milling macgine, so i just design it then i can mill it out really nicely, this version just ahs headlamps nothing for the motor.......yet. Its only headlamps because i just want to see how well this conertor works.

You lucky @#$%^! :D

I've found good results for powering LEDS with the NCP1402 DC converter from onsemi.com. Datasheet is HERE .

I'm using the 5V converter, NCP1402SN50T1. I've run two high intensisty blue LEDS that need 3.6V to turn on in parallel with no problems. I think the current sink is about 50mA for the two LEDS in parallel, haven't measured it though. As with a lot of the DCDC converters a 1.2V input won't give you a great output current at the converted output. 2.4V+ input gives you more output current.

The beauty of the NCP1402 is minimal components.

http://www.prahranpianos.com/bit_g/hbridge/dcdcconv.jpg

There is also the NCP1450 series of converters that have a mosfet in the output stage. For a 2.4V input you can get up to 600mA, 5V output..!

Let us know how you go....

ph2t.

oh yeah, forgot to say that if you need web space for hosting pics, let me know, I can help ya.

ph2t.

This stuff is fascinating! BTW, do any of you have a line on a DC-DC converter that will turn 4VDC@60mA into an output of 2VDC@200mA? I've found a chip called a Buck Converter that may do the job. I'm getting some free samples in a couple of weeks so I can try it out then. But, I was wondering if you've found anything that you know will work already.

Azimov, I haven't used one personally but I know they do exist. Check out all the majors, they offer free samples as well (you prolly figured that out already).

Try:

www.ti.com
www.onsemi.com
www.national.com
www.maxim-ic.com
www.microchip.com

They all have DCDC converters, PFM, PWM, buck, Inductor boost, all the buzzwords, lol! :) All these sites offer free samples. It's harder to find sites for free samples for passive devices, eg caps, inductors, resistors. www.onsemi.com is also great from standard semis like, transistors, fets, diodes, etc....www.ti.com is great for logic, 74xx and cmos...

The bugger is being able to fabricate a pcb with the fine tracks to fit some of the crazy-arse packages these chips come in. Wish I had team's resources...

Anyone know of any manufactures' sites that provide free samples for passive components?

ph2t.

Using the schematic I posted earlier of the NCP1402, I achieved this:

http://www.prahranpianos.com/bit_g/5v_lights1.jpg

The output voltage (no LED load) is 4.97V and when I load it with 2 high intensity blue LEDs it drops to 4V. This is pretty good and I am happy with the result. The drain on the battery is about 20-30mA which is OK as well. The LEDs are wired in parallel. I didn't measure the output current from the NCP1402, only from the battery to the pcb, too slack ;).

Here's a closer picture of the pcb:

http://www.prahranpianos.com/bit_g/5v_lights2.jpg

This pcb has come from my
Custom FET H-Bridge projects over at bitpimps, you can check that for more info.....

ph2t.

Thats pretty cool, the diference with mine is it uses a PICMicro chip so it can turn on the lights when you press forward twice and when you turn the indicators flash etc. Nice PCB

That's great Team. I've got indicators going, it's in a thread somewhere on this site, too lazy to search, lol.

The idea of using the PIC micro is a great one, I myself have zero experience with these, post your results when you can.

I was invetigating a flip-flop/latch type of circuit that would do the same thing to be able to turn a circuit (be it lights, breaks, whatever...) on with 2 succesive clicks of the fwd button, but I'm still investigating...

Should of paid more attention in my uni days........

ph2t.

i havent got that much experience (i've only used them on my robots) but im learning basic so i can program them using PIC Basic plus, its simpler then i thought is was

oh, and here is the indicator lights: http://tinyrc.com/forums/showthread....threadid=11485

i tink two flip-flops in series will do it, if u use the output of the second flipflop to turn on the led's, then it shoudl require two input pulses to get the second flipflop to turn on the led's. wut u could also do is wire more led's on teh first flipflop so that the first pulse can turn on parkign lights, 2nd pulse turns on headlights. im just throwing ideas out there

We'll I've tried this and the range has decreased:(. I need to re-tune the ferrite core in the inductor and see how I go. This is called the POT mod (which is incorrect by the way since it's a variable inductor and not a variable resistor, aka pot)

ph2t.

it look slike a pot, anyway tell us if it works when youve tuned it.

J/K :D but i cant see it :(

ph2t i could use some free space as long as it has decent speeds(like say atleast 70KBps download speeds and decent bandwidth my current is only 30KBps down and 3gb of bandwidth which isnice for free)

And what do you have to offer me BK?

err you make me feel like buger king ahh

[Babykiller edit: BK you got it!]llooololll:D