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  #1  
Old 09-22-2003, 11:35 AM
slider69 slider69 is offline
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Mosfets?

Alright u guys...and MICROAMPS in particular if he is reading this...there has to be a way to mosfet the ZZ se. I looked at the PCB on my friend's, and there is a coating (looks like the black epoxy used to cover Mosfet mods on Microamp's cars) That coating is not to keep u from modding..It is to prevent short circuiting with the lights' PCB inside the body. But anyway, the coat should be removable, and the thing has to use those H-bridges at some point so....Anyone MOSFETTED one of these or got any ideas on that?
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  #2  
Old 09-22-2003, 11:55 AM
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First off mosfets are not a H-bridge. The H-bridge is the circuit that switches between foward and reverse in Bits, and the original Zip Zap. It is composed of NPN, and PNP transistors. The mosfets that we use are N-channel, so they can be directly swapped for the NPN trannies, and the have to be flipped to match polarities with the PNP.

Since the SE is digital proportional, there is no H-bridge, and I don't see any N-type transistors that seem related to to the drive.

I've already started scratching off the black stuff, it's just paint, chips right off, and at this point, as far as I can tell, that big black block right by the motor is what is controller the throttle. I deduced that because the connections to it are labeled forward and reverse. (see pic)



So the mosfets we've been using are not going to work, and until someone breaks down this circuit, and finds a compatible component, with better performance, mosfets ain't happening in these. Bummer too, because I'm used to my FET'ed cars now, and these seem really wimpy to me.
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  #3  
Old 09-22-2003, 02:18 PM
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Yeh...Im sorry i was unclear about the H-bridge...I did know it was the type of circuit. OH and i replaced the pnp transistors w pnp mosfets on my ZZ. But look at the front of the pcb where the black epoxy is on the PCB....There are transistors on the board but i guess they're for steering. I cant see the numbers on them..could there be transistors as a preamp for that large box?
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  #4  
Old 09-22-2003, 03:03 PM
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Quote:
Originally posted by slider69
..could there be transistors as a preamp for that large box?
That's what I'm wondering.

Since this is my only SE, I'm in no hurry to tear it apart. When I get another I'll get more aggresive about figuring out what i can do to the circuit.
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  #5  
Old 09-22-2003, 05:12 PM
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BTW, What are u using to take off the epoxy, and does it just peel of or is it stuck to the components pretty well? Oh, and what is the number on the part...maybe i could cross reference it with a manufacturer and find out exactly what it is. U could try to wire the mosfets between the box and motor (like u would wire a regular transistor as an amp) couldn't u. i dont think that would cause u to lose the propo control.....
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  #6  
Old 09-22-2003, 05:27 PM
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The paint chips right off, I'm taking it off with my finger nail

I can't read the part number on the box, because it came off with the paint.

Adding a mosfet where it don't belong wont do anything. Mosfets increase power because they have 1/10th the resistance of a transistor, and allow more current to flow, but they do have resistance, so if you're adding it, and not replacing something with it, it would only add resistance. Besides, it's a switching device, what would you be switching?
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  #7  
Old 09-22-2003, 05:41 PM
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On the contrary, most transistors can be wired as an amp if i am not mistaken....it usually involves wiring base to collector so the transistor immediately turns "on" when voltage is applied. And mosfets do amplify by other means than resistance change, otherwise "stacking" would be useless, right?
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  #8  
Old 09-22-2003, 07:17 PM
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A transistor or mosfet peform the same function. In an amp the transistor is just turning the signal rapidly off and on to pulse the speaker. So it's still being used as a switching device. Mosfets do not increase power, or 'amplify', as you are thinking, they are still acting as switching devices. I wish I could explain it better, but it's not like I went to school for this stuff or anything.

..and stacking works, because there is now 2 mosfets for the current to flow through, so you've cut the resistance in half.

I come from the angle of playing guitar, and I build my own effects, and know how to fix amps. The more I study the RC cars, the more I realize how many similarities there are.

Here, I'll even explain further. See transistors and mosfets have a power source. If there is magnetic interference around a coil (Such as a guitar string, magnet in a microphone, or a radio crystal) it will produce a very small current, when that hit the transistor it allow the current from the power source through, which powers your speaker, or motor.

Last edited by crazydave; 09-22-2003 at 07:26 PM.
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  #9  
Old 09-22-2003, 07:48 PM
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Sounds like ive been an idiot....Ah well... There has to be a way to amp that thing. I'll try to find out more tomorrow. And i did look at the board some... i got a partial number on the part... it was
15** and there is a symbol that could have been just a rectangle or might have had something more written on it... I scraped very carefully, too... u did really good with yours on that. I would be very careful on the board, as that involves shorting out with the LED's small PCB if u expose traces and solder pads...but i figure u knew that already....
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With mosfets for throttle and steering
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  #10  
Old 09-22-2003, 08:04 PM
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I've got it! Thanks man, you forced me to think about this, and I'm actually building off your idea.

Ok so you take a lead from the motors foward, you put some resistors on it so it keeps the current flowing to the motor, but(and here's the tricky part) you keep the resistance low enough that when you reach full throttle a little juice gets through creating a signal to switch on the mosfet, which then would turn on the juice straight from the battery bypassing the PCB leaving only a mosfet in the way.

In theory I don't see why it wont work, in reality I know there a lot I don't understand so it might not work.

I'm not gonna go killing my SE right away, but hopefully someone with better electronic knowledge than mine might see this and be able to build off of it. In the meantime I'll try to work it out in the back of my head.
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  #11  
Old 09-22-2003, 10:25 PM
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That's about how the zipzap NE (normal edition) dragster worked-it used a 2n22222-whatever transistor to pump current strait to the battery from 3 seperate cells. Of coursre, there's no reason why you couldn't use the stock battery instead. You need to know how much voltage the black box puts out, and how much current the mosfet can take to choose the appropriate resistor-the problem is the pulsing makes it hard to measure, unless you have an oscilliscope.


But, this idea would work, and has been done in other forms before (no reverse mod, 4.5v dragster...).
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Last edited by Nathan; 09-22-2003 at 10:29 PM.
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  #12  
Old 09-23-2003, 08:58 AM
slider69 slider69 is offline
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What does the black box look like to u? I dunno but i think it could be a coil of some kind like a relay or transformer....and i noticed something on the bottom of the board... they use 2 of the transistors stacked....did u notice the ZZ se seems to have more forward power than reverse (it did in my friends at least). I really need to check my old electronics book on the transistor...it does amplify current in some way..that's why transistor radios were made instead of using germanium diodes, right?
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  #13  
Old 09-23-2003, 10:15 AM
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The switch from tubes, to germanium transistors, and and later silicone transistors is mainly due to cost effeciency, and mass production. Many audiophiles, and guitarist still prefer tubes for sound quality, though silicone transistors do pass a current more effeciently..

Anyways, I have to look for those stack transistors, replace those with some stacked FETs, and we're in business. Good find! I'll test that after work today.

I have no clue what the black box is, I could only guess.


****EDIT: There are no stacked transistors on the bottom of the board the only single transistor in that vicinity is part of the circuit going to the antenna. My wife snagged the camera, so I can't take a picture of what I'm seeing. Is there anyway you can take a picture of your PCB so I can where those stacked transistors are at? Also do you have the Savannah, or Enfini?

Also I just noticed what you said. Diodes just keep a signal going one way, like a valve. They perforn an entirely different function than a amplifying/switching device. Transitors replaced tubes, and were much smaller, hence all the kids in the 50s and 0s with their little transistor radios. They were initially made from germanium, but later switched to silicone because it's more readily available and cheaper. Transistors do amplify, but not in the sense that you are thinking. I don't know how to explain it other than how i already did.

They amplify by opening up the current from your power source. mosfets just allow more of that current to flow than a silicone transistor.

Last edited by crazydave; 09-23-2003 at 10:40 AM.
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  #14  
Old 09-23-2003, 11:04 AM
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Ya know the little black rectangles with three connections on the bottom (same side as the two circles of black epoxy that covers the two microchips...) They're the same size as the transistors on the MSpros but they have a different id number....There is one with the same number as the rest it's BKD i believe, (all on bottom are BKD or 3E), but it is raised up two times higher than the rest... It's the white RX7-- Savannah..... It has to be stacked, otherwise the part id number would be different vrai ou faux.....
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With mosfets for throttle and steering
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  #15  
Old 09-23-2003, 04:44 PM
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Every brand of car has different markings on the transistors. ZZs are different then MSs. I checked 3 different ZZ boards from each generation. In all the markings on the NPN transistors are 'S1A' with a sideways 25. There is a larger transistor on the back of the board labeled '3E' that is part of the reciever. On my SE the only transistor in the vicinity of the 3 contacts from the black box is also labeled '3E'.

If you follow it's leads on the circuit, you'll see it eventually leads to the antenna, and is part of the reciever.

Look at this picture of my PCB, and tell me if there is another transistor beside the one I described. The shaded area is where the black box is, the transistor is above that in the picture.

If yours does have an extra, you have got to get me a picture of that.
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