Some electrical questions
 

Hi guys. I would like to use some motors I pulled off an RC car with my vex controller, picture below:



The battery for the car was 6V. I'm assuming the motor would draw the most current when it's stalled, so I "stalled" the motor by holding the gear with a pair of pliers and the current was a little over 1amp.

Is it safe to use the two said motors? I don't want to let out the magic smoke :D


Thanks in advance,

Nathan

Re: Some electrical questions
 

The VEX controller outputs are PWM outputs, so you are gonna need a speed controller. You can buy those at hobby shops, and plug it in to the Vex controller.

Re: Some electrical questions
 

My grand plan was to take the speed controllers off two vex motor modules I have, and then wire a 6V battery to the speed controllers. I assumed this would work.

I found something interesting out. I just did my same "stall" test with a vex motor module and it drew almost 1.4A. I find that surprising since on the vex website it says "Current Draw (+) Power pin 5mA to about 1 Amp. at stall per Motor."


Nathan

Re: Some electrical questions
 

Unless the goal was just on/off/backward, in which case you could use a Digital output. I'm pretty sure there's some kind of power safety, like on the IFI RC, to prevent you from drawing too much current (i.e. imagine a short.)

Jacob

Re: Some electrical questions
 

Nope, I need fine control over the motor speed. PWM is the only way I know to do this, there's no such thing as an analog OUT is there? That would be kind of cool.


Nathan

Re: Some electrical questions
 

You could build one, using some resistors (wiki R2R ladder). Then you could have the resolution of 2 ^(how ever many digital outputs you could spare).

That isn't very viable though.

Speed controller sounds the best.

Jacob

Re: Some electrical questions
 

Well, I connected the signal wire (white) on the vex motor module to my vex controller, hooked up a 6V battery to the positive and negative connections and attached the motor in the above picture but the motor didn't turn and the speed controller got really hot.

Guess that plan is blown :)

Re: Some electrical questions
 

I just realized why this won't work. Forgive my stupidity, I'm not an electronics guy.

The motor's speed controller has three inputs, black, red and white. I was hooking up a battery to the black and red inputs and the PWM signal from the vex controller to the white. I now realize that this setup won't work because the PWM cable doesn't have it's reference to ground, is that correct?

Is there any way I can give an alternate source of power to the motor with just these three inputs?


Thanks for the help,

Nathan

Re: Some electrical questions
 

Alright, common grounded it and victory has been achieved. TY for the replies.

Re: Some electrical questions
 

Glad to hear it!!

Re: Some electrical questions
 

http://banebots.com/pc/ELECTRONICS/BB-0309

although i havnt used these before, thay should work for what you need.

Re: Some electrical questions
 

I realize I am reviving an old thread, but I was wondering exactly how to connect a vex motor module to a standard pwm off an rc receiver. It only has a output of up to 40ma so I definitely need to wire it up to the battery.

Re: Some electrical questions
 

probably what you just said. i havnt done it before, but i'd splice the motor cord, hook up the power, and then hook the ground and pwm wires to the corresponding ones on the radio reciever.

Re: Some electrical questions
 

Since pictures usually help me, here is what you need to do:

Attachment 6639

Also, for those of you that want a laugh.. MS Paint!

Re: Some electrical questions
 

Thank you. I will try that today.