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Old Mar 28, 2004, 07:24 PM
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Joined Mar 2004
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Question
Proportionaly switching to a higher current?

Hello, I am trying to figure out how to use a micro infrared controlled car circuit board for driving a large motor and servo.
It needs to somehow switch through a transistor or something, but it has to be DPDT and remain proportional!
Anyone got any idea's?
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Old Mar 29, 2004, 12:39 PM
Oxford Panic
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United Kingdom, Oxford
Joined Feb 2003
3,658 Posts
You could try pulsing the signal from the transmitter, have a look at...

http://www.rcgroups.com/forums/showt...96#post797696.

Andy.
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Old Mar 29, 2004, 01:21 PM
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I am talking about the receiver board in the car
and how to make it control a stock RC car motor.
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Old Mar 29, 2004, 08:16 PM
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Canada, NB, Fredericton
Joined May 2002
927 Posts
You can drive a larger motor by using a FET (Field effect transistor). You can either replace the output transistor on the circuit board, or use the existing motor outputs to power the FET.
Key things are:
1. Get the right type of FET, there are N-channel and P-channel FETs. One turns on a negative supply with a positive signal, the other turns on a positive supply with a negative signal. (simplified, there are others)
2. A FET which can handle the current you want.
3. Low Rds, this is the resistance across the drain and source (Rds) of the FET (extra resistance just gives you less voltage and more wasted heat).
4. Low enough Vg, make sure the required signal voltage is low enough to be provided by the signal you'll be feeding it. This is the voltage required at the gate (Vg)

Without knowing what the infrared system is like, it's hard to speculate on how you could connect a servo. If it's anything like the toy cars I've seen, you're probably out of luck. Sure, you could probably rig up something using a microcontroller, but you'd be better off building an IR system from scratch (see the DIY-IR threads).
If the circuit isn't proportional to start with, it's not too likely that you can add it on...sorry.

Your best bet for trying to use it for anything may be a FET to increase motor power, and a simple "bang-bang" actuator coil (see bitcharger threads for more details)

D.
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Old Mar 29, 2004, 08:29 PM
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The car in question says it is proprtional, see this link.
http://www.tisinc99.com/irrcmeracsil.html

Also it uses servo steering!
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Old Mar 30, 2004, 06:35 AM
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Canada, NB, Fredericton
Joined May 2002
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Cute.

The throttle shouldn't be any problem.

The steering may be trickier. I wouldn't think it would be outputting a classic RC servo signal. It might have the servo circuitry built into the controller board, and have leads for the servo motor and a feedback device (resistor pot).

Have to buy one to find out, I guess.

D.
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Old Mar 30, 2004, 11:50 AM
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Joined Mar 2004
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My problem is how to wire it up so that the motor can go in reverse. I don't know exactly how FET's work but it is not simple with a PNP transistor.

Does anyone know how much current micro car receivers can handle through the motor and steering leads?
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Old Mar 30, 2004, 08:56 PM
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Canada, NB, Fredericton
Joined May 2002
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H-bridge. It will give you full forward and backward, but it requires 4 FETS (2 of each type). Note that you can get dual FETS, which bundle a P-channel and N-channel FET together, so you'd only need two dual FETs (e.g. NDC7001)

Google search for it, or check out:
http://www.dprg.org/tutorials/1998-04a/
http://www.4qdtec.com/bridge.html
etc.

D.
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