Society of Robots - Robot Forum

Mechanics and Construction => Mechanics and Construction => Topic started by: kronin on March 21, 2009, 12:41:47 PM

Title: replace servos with DC motors?
Post by: kronin on March 21, 2009, 12:41:47 PM

Hi. I´m new to this robotic stuff, so i figured that i would start with the $50 robot, just to get some basics.
Unfortunately, where i live, the $50 robot is more like a $100 robot due to expensive parts - the cheapest servos i can find is around 20$ each, wich leaves very little money to get the rest of the stuff. :-[
however, I have a lot of small DC motors , so i was wondering if i could replace the servos with them? what modifications do I have to make to the schematics, if it´s possible to do?
I know the dc motors aren´t very strong, but just as a proof of concept, they´re strong enough to what I´m trying to accomplish..
I don´t know if this is the right board, but I dont want to double post, so i´m trying here first ;-)

Title: Re: replace servos with DC motors?
Post by: offy on March 21, 2009, 12:45:08 PM

For DC motors you need a motor controller. A dual one controls 2 DC motors, they vary from $50 to $200. Servos would be cheaper to start out with since they plug right into the board.

Title: Re: replace servos with DC motors?
Post by: Webbot on March 21, 2009, 01:04:10 PM

I have done a tutorial on creating DC motor controllers - so you can check that out. Do your motors have gearboxes? If not they may run VERY fast and have LITTLE torque - so as soon as you put the robot on the floor then the motors will stall.

Title: Re: replace servos with DC motors?
Post by: kronin on March 21, 2009, 01:51:09 PM

wow - you guys work fast :)
I guess you´re referring to http://www.societyofrobots.com/member_tutorials/node/163 (http://www.societyofrobots.com/member_tutorials/node/163) for the motor controller tutorial? I will have a look at my electronic stuff and see if i have the parts needed to build one
now, maybe i´m not quite ready for this, but how do i make the circuitry to include a motor controller in the $50? it uses 1 pin for a servo, but either i´m misunderstanding something, or a dc motor requires 2 pins (but witch??)
Yes, i have gears for the motors (stripped an old RC), so i think that part is easy to solve.

Title: Re: replace servos with DC motors?
Post by: want2learn on March 21, 2009, 04:16:07 PM

If you stripped an rc model, couldn't you use the servos from that? Very few rc models use only motors

Title: Re: replace servos with DC motors?
Post by: SmAsH on March 21, 2009, 05:02:58 PM

Quote from: want2learn on March 21, 2009, 04:16:07 PM

If you stripped an rc model, couldn't you use the servos from that? Very few rc models use only motors

i thought that was just the expensive ones? all the rc cars ive taken apart use dc motors?

Title: Re: replace servos with DC motors?
Post by: want2learn on March 22, 2009, 12:44:48 AM

I said model. ;) not toy

Title: Re: replace servos with DC motors?
Post by: SmAsH on March 22, 2009, 12:49:49 AM

ohhh sorry, my bad. yeah, i can imagine most of them would have servos. but why pay for the model when you can just buy servos? i can understand if you find a broken one but...

Title: Re: replace servos with DC motors?
Post by: Admin on March 22, 2009, 06:43:03 AM

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

You can get decent dual packaged motor drivers for as little as $20:
http://www.pololu.com/catalog/product/1110 (http://www.pololu.com/catalog/product/1110)

But depends on your current . . .

If you don't care about reverse, you can use a simple $1 MOSFET per motor.

But I personally recommend just buying the servo. Once you have it, you'll never have to buy it again.