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RC Car Motor Problem

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Chet T16:
I bought a cheap rc car for messing about with, i opened it up and inside it had an RX-2-G chip with the outputs connected to 2-H bridges controlling 2 motors, one for steering and the other for moving. I wasn't going to use the original controller so i removed the RX-2-G IC and connected an arduino+bluetooth module to where the outputs were - setting the relevant arduino pin high turns the  motor on in whichever direction.

Firstly, i know its not ideal but the arduino is powered from the existing three AA's in the car. When i tried to turn one of the motors on the voltage dropped enough for the bluetooth module to reset. I put a 1000uF cap across the batteries and that seemed to solve it. The motor for turning the wheels works fine but the motor for the driven wheels will not work, they will 'click' a little like they are trying to turn but it's like the arduino is resetting and it repeatedly clicks. I tried adding more caps in parallel (three in total) but it made no difference. If i remove the batteries and power the car from my bench supply set to 4.5V is works fine and also if i power it solely from the usb on the arduino it works fine.

Do i just need a bigger cap across the batteries? I would've thought the batteries would be able to recover quicker than the bench power supply but i guess not?

Also i'm not sure why the wiring for the motor is setup as in the picture, can someone explain it? (both motor connections are coiled around, hard to tell from the pic)

You might try adding a shottky diode in series with the power feed to the micro, to decouple the transient from it. Add another 1000uF capacitor at the micro input along with the one on the battery.

The motor wiring is done for RF noise suppression, the choke reduces the noise fed back to the board from the motor brushes.

yes sounds like the power rail is highly unstable. the above suggestion is a good one. will the arduino work on 3.3V providing you account for that in your program and circuit ? I mean how much can the arduino tolerate ?

Chet T16:
It's a 5v nano board with 16MHz crystal and i believe you can't run them at 3.3v and 16MHz.

I don't have any shottkys but i'll pick some up, in the mean time i'll add the other cap and see if it helps. I'll also so if i can get the scope to trigger and compare the differences with the battery v's the power supply.

Thanks for the replies

As first attempt I'd feed the Arduino and Bluetooth module from a separate source. If it then starts to work reliable you can attempt to get them to work together. But I doubt it will work, the main motor is probably too powerful for the 3 AAs already and draws too much power to allow the Arduino to survive on the same power source. I don't think some capacitors will be enough to help, maybe if you use one of those 10 farad caps sold to car stereo freaks. But those are way bigger and heavier than three additional AAs or AAAs.


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