Steering with 12v motor

[soninja8]

Its been such a long time since I have posted on here...anyways, I have this 12v electric motor that I took from an electric scooter, and I was wondering how I can use a regular servo to control the steering of the motor. I will be using a 12v lead acid battery to actually power the motor (I'm not stupid enough to use the 6v servo power LOL), but how would I limit the volts going to the motor so it can actually steer instead of going full to the right or left? If this question is too confusing please let me know! 

*Project info*
I am making a gas powered "tank" that runs off of a 30cc engine, and is steered by a regular 12v motor. All this will be controlled by a regular rc servo controller (one servo controlling the throttle, one controlling the steering).

[Tommy]

can actually steer instead of going full to the right or left

soninja8,  Google "sabertooth motor controller"

Tommy

[soninja8]

Thanks Tommy, since you suggested the sabertooth controller I have been trying to find similar ones at a cheaper price, but to no luck. Do you know of any dc controllers that can supply around 5-10amps under $30? Thanks!

[jwatte]

Its been such a long time since I have posted on here...anyways, I have this 12v electric motor that I took from an electric scooter, and I was wondering how I can use a regular servo to control the steering of the motor.

It sounds like you want to drive the steering rods using this motor as a servo.

A motor doesn't normally steer. For a motor to steer, you need to know where it is, and where you want it to be. (Servos you buy contain this system built-in.)
This means you'll need an encoder for the motor you use for steering, and a microcontroller that reads the sensor and drives the H-bridge to keep the motor turning to the place you want.
The Sabretooth controller does not have the necessary feedback to do what you need.

Do you know of any dc controllers that can supply around 5-10amps under $30?

Assuming you can find a suitable encoder for motor position, you may be able to use a "simple motor controller" from Pololu to get where you need to go: http://www.pololu.com/catalog/product/1372
It's $34. I don't think it does the encoder feedback part without you adding a small microcontroller of some sort (Arduino, ATmega, or whatever.)

[soninja8]

Your link does not work 

And I'm just looking for a cheap dc controller that turns a motor forward and backward so I can steer, since it won't be anything fancy

Thanks!

[jwatte]

I fixed the link. The thing I linked to will do what you want, for cheaper than the Sabretooth. (Assuming you only need up to 7 amps continuous power.)

I still don't understand how "turning the motor forwards and backwards" will actually make you steer correctly. What is the mechanical hook-up of this motor? What do you do to make your robot go straight ahead?

If *all* you want to do is go backwards, or forwards, or don't go at all, then a simple H-bridge motor controller is even cheaper.
This one is $28 and does up to 9A continuous:
http://www.pololu.com/catalog/product/705

[soninja8]

Thanks, I'm most likely going to get the 18v15 for future proofing.

And to explain what I'm doing: A 30cc engine will be powering the back wheels with a clutch and the throttle will be controller by one servo. For my steering I am using one electric motor controlled by a motor driver to move two bars that are connected to the front two wheels.

[jwatte]

For my steering I am using one electric motor controlled by a motor driver to move two bars that are connected to the front two wheels

Do you have any feedback there? If not, how will you be able to center the steering to go straight ahead?

[soninja8]

I see what you're saying, but I will not need them to return to forward position, as the vehicle itself will not be going very fast and I will always have my finger on the control.

[Tommy]

For my steering I am using one electric motor controlled by a motor driver to move two bars that are connected to the front two wheels.

soninja8, have you considered spring loading the steering axle to a center position(straight), gear the one electric motor
in a way that it can overcome the spring force yet spring back to center when motor power is removed.

Tommy   

[Mastermime]

So you're trying to use Ackermann's steering, not tank style steering?  Or did I read that incorrectly?

[soninja8]

For my steering I am using one electric motor controlled by a motor driver to move two bars that are connected to the front two wheels.

soninja8, have you considered spring loading the steering axle to a center position(straight), gear the one electric motor
in a way that it can overcome the spring force yet spring back to center when motor power is removed.

Tommy   

That's exactly what I'm thinking of doing, although I will have to either get a more powerful motor or gear it up. Also, I'm wondering how I could go in reverse since I am using an engine with a clutch.

[Tommy]

I'm wondering how I could go in reverse since I am using an engine with a clutch.

http://www.google.com/#q=go+kart+reverse+gear&hl=en&tbo=u&source=univ&tbm=shop&sa=X&ei=_E_1UK7bJcfX2QWOwoDwDw&ved=0CEYQsxg&bav=on.2,or.r_gc.r_pw.r_qf.&fp=260534c26339dbc2&biw=1356&bih=631


Tommy

[soninja8]

I'm wondering how I could go in reverse since I am using an engine with a clutch.

http://www.google.com/#q=go+kart+reverse+gear&hl=en&tbo=u&source=univ&tbm=shop&sa=X&ei=_E_1UK7bJcfX2QWOwoDwDw&ved=0CEYQsxg&bav=on.2,or.r_gc.r_pw.r_qf.&fp=260534c26339dbc2&biw=1356&bih=631


Tommy

I did some further research on clutches with reverse functionality, but all require 80cc+...

[Tommy]

That's exactly what I'm thinking of doing

soninja8, just keep in mind, if the motor is spun by the springs it then becomes a generator
and may harm motor drive circuits.

I am making a gas powered "tank" that runs off of a 30cc engine

IMO the simplest way to implement this type of task would be to use the ICE to turn a generator
supplying power too electric motors(two, one for each track).   

Tommy