Can't get this RC car to work

Søren

Joined Sep 2, 2006
472
[...] My intentions are to finish this and to make it good.
That's the spirit :)


Indeed i did took a 22AWG wire and solded into the case of the motor and then connected to the ground of the battery, by fat and short i think you mean a wire with a bigger diameter, right ? WOAH, i forgot to mention, i changed the battery of the transmitter to 9v and improved considerably the signal, it took away a lot of capacitors from the receiver, and i got a result that was so nice, when i pressed the button the motor instantly answered my call, and instantly stopped when i released the button, the system stopped working before i could try with the correct wire length, i was using 15cm.
Yes, a heavier gauge wire and not any longer than required to reach.
Great and with the right length of antenna, it should get an even farther range.
For the transmitter, use a half wave length antenna, even if you use a quarter wave length for the receiver.


Also the shield you meant, it goes around the motor wires and then connected to the ground ? Can you link me an image so i could see that in action ? Another thing, i was thinking of putting some case around the motors to minimize the noise that is deafening the receiver, is that viable ?
You can see a screening braid here: https://www.wirecare.com/product.asp?pn=WC00589578

The cheapest would probably be to get a length of RG-8/U coax cable, as used for communication radios - they're about 1cm in diameter - strip the outmost layer of isolation without harming the shield and then push the end of the shield from one end towards the other end. This will loosen the shield braid by increasing the diameter a bit and you can then work the shield off little by little.
I haven't got a picture of a shield set-up as this, but it's pretty easy. Stuff the wires through the braid. untangle around 1..2cm of one end, twist it and solder it to the battery 0V/ground - leave the other end open.

A box around the motors may help, but it's hard to make it really "tight" all the way around and the wires should go through minimal holes.
If you had a source for mu-metal or even better Metglass (a metal despite "glass"-part of the name), that would be extremely good for all sorts of screening, but both are very expensive.

If you can install a thin sheet of mild steel between the motors and the rest and ground it properly (at the battery 0V), it will help as well and totally wrapping the motors sound a bit like overkill to me, as the only place they aren't already shielded is the terminal end and vent holes (if they exists).

Just getting the noise out of the supply wires will really help, as I'm sure that's what's causing the problem.

I realize that you might not be aware of what a common mode transformer is (lots of DC brushed motors in pro equipment have them):
Here's a drawing of one - notice how the wires are wound in opposite directions, to cancel common mode signals (the noise, orange arrows), while passing differential mode signals (the power to the motors).

You can make one yourself (a ring core from an old PC psu or similar would do) and place it close to a motor with eg. a 100nF cap on each side.
The more windings the better. Remember to wind them opposite of each other.


I forgot to mention that i reduced the platform, now its smaller and its lighter. And i have only one front wheel and it's made from silicon, that problem of messing with the direction no longer exists.
Silicon? Silicium or the rubbery compound?
I'd think that the former is far too brittle, while the latter would probably have too much friction.
As the sole purpose of the front wheel is to support the platform from tipping to the ground, I'd go for a hard nylon wheel with a rounded profile if possible, to keep friction low, but as long as what you've got works for you, no need to change it :)


If the maker stands by my side, the project will run smooth now.
Oh well, you're the maker on this project :)


EDIT: I dismounted the controller and took the transmitter off. Then i tested it on two protoboards with a LED being the load i'm trying to change the state, and it WORKED, i really don't know what happened before, but it's all good, back to testing. I am awaiting your answers about the shielding thing.
Great! :)

Hard to say what caused it - could be a simple latch up or a short somewhere, but now that you've taken it apart, it's impossible to tell - just make sure that your transmitter is really made for a 12V supply! If you post a link, I'll check them out for you.

It's always good to have a spare, of stuff that takes a long time to reach you - last time I bought such modules I bought 5 pairs and one receiver is permanently wired up for checking correct behavior (and for hacking the protocols) of other 433MHz equipment.
 

Thread Starter

André Ferrato

Joined Apr 5, 2015
215
I am always excited to read your answers, they're pretty awesome. My tests at the university are starting tomorrow, two entire weeks of evaluations, so it may take a lot of time for me to do something again in this project, bad timing for these tests, but after that, my vacations start and i intend to do many projects as possible in the couple months period. So a heavier wire gauge for the motor wire, a shield for it and common mode transformer for the motor, i got it, but first i should read and research about this common mode. About the platform of the RC car i calculated the momentum of each weight force and used an approximation for the tangential force of the motors and got a really got balance, between weight and all momentum. I course M.E. (Mechanical Engineering), i'm at my first year and have a calculus test tomorrow, need to study a lot :(

Also this is the wheel i'm using now: http://www.leroymerlin.com.br/rodizio-35mm-giratorio-gel-transparente-italy-line_88525101
Transmitter is designed to work at 12v and has a 13.3v stress rating, i'll make it work in the edge using the correct antenna lengths. And about the spare pair thing, i thought about it initially, but i didnt had a lot of money to spend, but now i have :), so i'll buy many things. A workshop is being created at my house ahaha.
 

Søren

Joined Sep 2, 2006
472
Hi André,

[...] My tests at the university are starting tomorrow, two entire weeks of evaluations, so it may take a lot of time for me to do something again in this project, [...]
Study and sleep a lot :)
Don't spend time here for the next two weeks, your education is far more important than your hobby presently.
Go be all that you can!

Wish you the best (not luck, but hard work ;))
 
Even I have the same problem, motor doesn't stop even after the switch is offed.but when I checked it with led's I works perfectly, so please give a solution to it soon!
 

Thread Starter

André Ferrato

Joined Apr 5, 2015
215
Hello @manjugiddu , i stop posting here because i solved the problem and forgot about that project. The solution was to put a ferrite in the cables that leaded to l293d, i believe it worked as a low pass filter, something like that, you should try it, those motors that i was using were really noisy.
 
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