Society of Robots - Robot Forum

Electronics => Electronics => Topic started by: Private Reid on March 24, 2008, 02:27:30 AM

Title: Motors? Servos?
Post by: Private Reid on March 24, 2008, 02:27:30 AM

Hey

I have a problem, see I am building my own robot and at the same time following the $50 robot tutorial but I wish to use DC motors instead of servos but as you can see on this page http://www.societyofrobots.com/step_by_step_robot_step3C.shtml (http://www.societyofrobots.com/step_by_step_robot_step3C.shtml) (about three quarters down) the servo has three wires coming from it while a motor only has two?

Is there anyway I can convert the motor to work?

 ???

Title: Re: Motors? Servos?
Post by: hazzer123 on March 24, 2008, 03:16:51 AM

To convert a DC motor into something that will work with the project, you would have to get gear the output shaft down a lot.
DC Motors have very little torque and very high speeds, so you need to use gears to produce the required torque.

Also, to have bidirectional control of a DC motor, you need to use H-bridges. These allow a microcontroller to reverse the voltage across the motor in order to change the direction of spin.

Here the SoR tutorial on H-Bridges - http://www.societyofrobots.com/schematics_h-bridgedes.shtml (http://www.societyofrobots.com/schematics_h-bridgedes.shtml)

If you made a geared down DC motor with H-Brdiges, however, you wouldn't be able to just slot it into the circuit and it would work.

You would need to learn how to output Pulse Width Modulated signals (PWM signals - also on the H-bridge tutorial)  from your microcontroller.

This would be quite hard for a beginner. Anyway, the gearing and H-bridge components would not be significantly cheaper than buying a standard HS311 servo.

I recommend just getting a couple of servos. They are greatly reusable and good value for money.

Title: Re: Motors? Servos?
Post by: Private Reid on March 24, 2008, 03:58:43 AM

Aha

yes H-Brdiges, possably not for me...
I think your right. buying a few servos will supplement my needs...

Title: Re: Motors? Servos?
Post by: Admin on March 24, 2008, 06:46:03 AM

http://www.societyofrobots.com/robot_faq.shtml#servo_motor

I recommend reading all of the FAQ ;D

Title: Re: Motors? Servos?
Post by: ed1380 on March 24, 2008, 03:49:29 PM

you could get a gearmotor and an ESC. an ESC is a type of h-bridge that converts servo signals for use by DC motors. just make sure its bidirectional.

Title: Re: Motors? Servos?
Post by: Private Reid on March 24, 2008, 05:21:01 PM

"But if you want to use a basic motor for a robot, you MUST purchase and wire up a motor driver separately."

This is said in the FAQ (found at the link admin provides). How would i wire it up separately? would i use a motor drive?

Title: Re: Motors? Servos?
Post by: Private Reid on March 24, 2008, 05:23:52 PM

lol... I posted that wrong. I mean how would i wire it up? using a motor drive.

Title: Re: Motors? Servos?
Post by: ed1380 on March 24, 2008, 05:56:23 PM

H-bridge
whether it be a smd, dip, or esc.
check the datasheets for details on use

Title: Re: Motors? Servos?
Post by: superchiku on March 25, 2008, 06:34:27 AM

wat are the ratings of ur motors see if it is L293d compatible otherwise use L298

Title: Re: Motors? Servos?
Post by: Admin on March 30, 2008, 02:32:07 PM

Just search this forum and google for motor driver, ESC, L298, motor controller, etc.