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Replace servos with DC motors? — Parallax Forums

Replace servos with DC motors?

RobocopRobocop Posts: 9
edited 2007-03-04 04:38 in Robotics
I'm looking into replacing the servos that came with the Boe Bot with DC motors. Is this possible? Am I going to need any extra hardware?

Thx! smile.gif

Comments

  • allanlane5allanlane5 Posts: 3,815
    edited 2007-02-27 15:04
    The nice thing about the "Modified Servo" is that it provides a DC motor, some gearing, speed control, direction control, all with a single PULSOUT control signal.· And that control signal only has to be repeated every 20 mSec, so it gives you time to do something else.

    If you replace that with a 'plain' DC motor, you'll need to add an H-Bridge circuit to give you direction control, and perhaps an additional processor to handle PWM for speed control.

    Parallax sells three solutions for this.· The HB-25 is the high end, at $50 per motor.· The Motor Mind B is the mid-end, at $28 per motor.· And the Pololu Motor Controller is the bottom, at $23 for two small motors.· They also sell the PWMPAL, which will handle the "continuous PWM" signal part of the problem, if you want to make your own H-Bridge circuit.

    Now, each HB-25 module will support one DC motor, and uses the same 'Servo' control signal, so that might do it all for you.· To control two motors, you'll need two HB-25's, but they do have a 'feed-through' mode which lets you control two motors with a single I/O pin.

    They're around $50 each, so this increases the cost a bit.· However, they DO have the on-board processor and H-Bridge, and can be plug-compatible with a servo motor.

    At the low end, the Pololu Motor controller costs $23, can control TWO motors (up to 1 amp each), and again has the on-board processor and h-bridge.· This may be more what you want, if you're using small Servo type motors (1.9 to 9 Volts, up to 1000 mA each).· The HB-25's will support much larger motors, but may be overkill depending on what you're trying to do.





    Post Edited (allanlane5) : 2/27/2007 3:12:48 PM GMT
  • slamerslamer Posts: 52
    edited 2007-02-27 16:16
    Ahh a Hot Rod Boe Bot. Ya it's totally posible to build a more powerful Boe Bot based drive train. You can add bigger motors or even over volt the servos with some more modifacations and adding a duel motor speed controler. Iv'e actually juiced up standard servos with modifacations·up to as much as 16 VDC. In reality 12 VDC is a lot, so I'd keep the voltage between 9.6-12 VDC. Using heavy duty servos with metal gears instead of plastic is a good idea to prevent stripping out the gear boxes. Heres a wepage on how I've run servos in TURBO overvolted mode. Of course this definately voids all warrentys...

    Over-volting Servos (Team K.I.S.S style)
    http://www.teamkiss.com/antweight.html

    www.teamkiss.com

    Small 5-6 amp duel motor speed controllers compatible with the Basic Stamp2 Pulsout Commands.

    http://www.robotcombat.com/marketplace_scorpion.html

    http://www.robotcombat.com/marketplace_soz.html

    If you want even more carpet tearing power you can also use a BS2, a duel motor speed controller and lots of other battle proven motors..

    http://www.robotcombat.com/marketplace_ant_motors.html

    One of the many cool things about the Basic stamp2 is it's signals can talk to most of the normally·Radio Controled speed controllers we use in combat robots. Hmm imagine a Super·Boe Bot with 30 Horsepower weighing 340 lbs. Now that's just scarry! Sounds like fun to me....

    Build Safe, Build Mean, Build Strong....







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    Post Edited (slamer) : 2/27/2007 10:22:08 PM GMT
  • RobocopRobocop Posts: 9
    edited 2007-03-04 04:38
    Thx for the info!
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