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Topic: Hacking RC car to make a child happy - magic dust escaped from board. (Read 1 time) previous topic - next topic

DaveO

Hi all. Compliments of the New Year to all.

Position : sons 7th birthday 24 Dec. He wanted a specific RC car, which he got. Not overly expensive, but Made in China all the same.

Problem was the radio. First the trigger broke ( like only a 7 yr old can do ). Fixed that.
Next the antenna got snapped in half - still worked.
Then trigger broke again in a different place. Fixed that.
Antenna got snapped again - apparently you only need a 5mm antenna anyway ( ask my son )
Then it gave up the ghost completely, and trigger broke again.
Checked the transmitter board, and the pot (?) that the trigger connects to, is not registering anything, and with the broken trigger, is virtually unrepairable.

To cut a long story short :

We have another cheap RC car that got stood on ( same 7 yr old ) and busted wheels. So I got the transmitter and receiver board from that - also runs on 6v DC, same as the battery pack in the newer car.  Found the contacts on the receiver board and connected the 2 motors ( steering and drive ). They have only 2 wires to each motor, and the power over the wires was either +6V or -6V, depending on either left / right, or forwards / backwards.

It worked great, and his face lit up and we each had a turn. Unfortunately, after about 4 minutes, it stopped, and I could smell the magic dust escaping from the receiver board. To make matters worse, guess who was driving when it escaped - me.

So he doesn't want another birthday present, or another car ( and no more of this model available ), he wants THIS one.

My thinking was that the cheap receiver board could not handle the current drawn by the bigger motor, and it fried / died after a few minutes of continuous use.

I do have another cheap board, and was thinking that I should use that, but instead of connecting the board outputs to the motors, connect them via relays or transistors that can manage the motors load from the battery to the motor, instead of pulling the current thru the board.

Can anyone please help me with a simple wiring diagram that would take a +6v / -6v feed, and trigger the motor ?  In stock I have some 5v relays, transistors, diodes and resistors.

All help greatly appreciated.
Regards

oric_dan

You can do a search on "relay h-bridge", or take a look at the following ckt. It uses
one relay to switch motor direction and a MOSFET to turn the motr on/off, but that
could be replaced with a relay too. Pretty simple. You will probably need to use
transistor inverters to provide enough current drive the relay coils, and be sure to
wire reverse diodes across the relay coils to quench inductive spikes.

http://circuitbuilder.blogspot.com/2012/05/making-h-bridge-motor-driver.html

zoomkat

Quote
So he doesn't want another birthday present, or another car ( and no more of this model available ), he wants THIS one.


I suggest you let him play with the toy like it is. This could be a learning moment that he should take more care with his gifts.
Consider the daffodil. And while you're doing that, I'll be over here, looking through your stuff.   8)

DaveO

Normally I would, but I am with him on this one - the trigger was a krappy design, and the arial wasn't completely his fault.

zoomkat


Normally I would, but I am with him on this one - the trigger was a krappy design, and the arial wasn't completely his fault.

Problem was the radio. First the trigger broke ( like only a 7 yr old can do ). Fixed that.
Next the antenna got snapped in half - still worked.
Then trigger broke again in a different place. Fixed that.
Antenna got snapped again - apparently you only need a 5mm antenna anyway ( ask my son )
Then it gave up the ghost completely, and trigger broke again.

We have another cheap RC car that got stood on ( same 7 yr old ) and busted wheels.


Reality check!
Consider the daffodil. And while you're doing that, I'll be over here, looking through your stuff.   8)

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