Identifing the type of a DC motor I cant visible see

[Jerran]

I hijacked an old RC car from my son for a robotics project. The motor Im trying to identify is used to stear the front wheels. Before taking it apart I assumed it would be a servo but after cracking the case open I think its probably a stepper. I cant get to the motor without melting the body apart so disassembling the chassis to get to it isnt an option.

The motor has 2 sets of wires running into it, one is a 4 wire ribbon and the other is a pigtailed pair of braided wires. I cant find the remote to test the voltage of the lines during its 3 phases( left, right, straight).

Any guesses to what type of motor it is and/or how I could test it to find out.

 

[Nigel Goodwin]

I hijacked an old RC car from my son for a robotics project. The motor Im trying to identify is used to stear the front wheels. Before taking it apart I assumed it would be a servo but after cracking the case open I think its probably a stepper. I cant get to the motor without melting the body apart so disassembling the chassis to get to it isnt an option.

The motor has 2 sets of wires running into it, one is a 4 wire ribbon and the other is a pigtailed pair of braided wires. I cant find the remote to test the voltage of the lines during its 3 phases( left, right, straight).

Any guesses to what type of motor it is and/or how I could test it to find out.

It's unlikely to be a stepper, that wouldn't be a very good choice for steering - also expensive for the manufacturer.

 

[Klaus]

It's unlikely to be a stepper, that wouldn't be a very good choice for steering - also expensive for the manufacturer.

But, the 4 wires would favour the stepper type, IMO. I've seen quite tiny stepper motors inside disk drives and CD players.
Anyway, to test this, short all 4 wires together and try to turn the motor by hand ( if that is possible). On a stepper motor you will feel noticable 'cogging' as the rotors magnetic forces resist the field generated by the shorted turns in the stator. Of course, if there is some kind of inaccessible worm gear reduction you can forget about this test :wink:
Klaus

 

[Jerran]

I found a second identical vehicle so I decide to melt one apart and see what I was dealing with. What I fould was a DC motor with a limit controlling circuit built into the shaft of it, actually built onto it be precise. The braided wire was the source and ground like I suspected. The 4 ribbon wire was actually 2 pots,2 copper traces with 2 wipers to maintain contact, with a common center tap and a shared leg. Kind of an odd design but basically it had 2 copper disks sandwiched together with a pot on each side, the shaft would rotate till a connection was made on one of the lines and would stop to hold that spot. Im guessing it would read the voltage on one side for force feedback to maintain the on/off connection on the other.