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Question about RC car mod

Question about RC car mod

Old 11-28-2019, 01:36 PM
  #1  
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Default Question about RC car mod

I am looking for advice on how to make a relatively simple mod of a standard toy RC car, which currently has forward/backward and left/right steering controls activated via a 2.4GHz wireless pistol transmitter.

I believe the car battery voltage (~10V when fully charged) is transferred directly to the motor & steering inputs, hence the car only runs at *full* speed (FWD/REV) or makes *full* turns (L/R steering)


Question is: how can I modify the circuit to enable proportional (to voltage) motor speeds and steering? I would like to be able to try both of the below options (both transmitting wirelessly at 2.4GHz), preferably using the existing motor driver (MX1919):

Option 1) Control the speed and steering via an app that talks to an on-board NodeMCU/ESP8266

Option 2) Control speed/steering using my Turnigy 9X transmitter and its on-board PWM receiver (which outputs PWM from 5 to 10% duty cycle range at 5V full rail)


It appears (from testing of the control board), that if I place a variable voltage between 5 to 10V directly from battery power to the motor & steering input terminals, I am able to achieve proportional control. I have an Arduino Uno and other components - transistors, caps, resistors, relays, etc. that I can use for either option above if required. Of course, minimizing the no.of these additional components is preferred, in order to maintain the compactness of the car design.


A schematic or fritzing circuit for the 2 options would be most helpful and appreciated. I can probably figure out the coding/SW part, but any relevant links there would be helpful too.


Thanks!

Sam
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Old 11-28-2019, 08:59 PM
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The receiver in the car outputs a pwm or pps? I think its a data telegram that encodes position (servo) and current (speed control). The motors certainly get raw pwm but the servo and esc conventionally converts pps to pwm. Roelof will probably chime in with the format of the telegrams or point you to something. But you may have to overcome the initial response of how practical is this. If its educational its one thing. however you may learn more from buying something and taking it apart and telling us what it does. Once you get to the PWM at the motor you will see its pretty simple. 50% pwm duty is 50% current/voltage or something comparable to half speed. If you want to program something and learn this stuff by reverse engineering some cheap servo and esc you might be able to take what is already there and improve it by creating actual velocity control instead of raw current control. You can get used stuff for nothing and you will wear out the fundamental learning part of this quickly.

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Old 11-28-2019, 11:24 PM
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It is all a switched system. Most simple thing is to get a cheap ESC, receiver (with transmitter?) and probably you do need a new servo too.

It the car worth the costs? For 100 bucks you can have an ARTR car with a proportional control.
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Old 11-30-2019, 10:44 PM
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Correct, the purpose of the RC car mod was to indeed help my kids learn a bit about proportional control using parts I already have lying around the house, like re-using the Tx & Rx from a quadcopter we had built a few years ago. Guess I could use the ESCs and other parts as well from the quad we no longer use. Or just buy the few parts required to convert it to a proportional-control RTR car. Let's see.

Thanks all.
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