Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

12 volt dc motor and PWM

  1. May 2, 2009 #1
    Hello all.
    First off, I am a total newbie and need some help in getting my "project" up and running.

    Here goes, I'm trying to get a dolly (weighing around 50lbs. or so) to move at a fairly slow constant speed.
    I'm thinking my best option is to find a 12 volt DC motor along w/a speed control (PWM) that is capable of achieving such awesomeness.

    I've done some research and I see there are millions of dc motors to choose from along w/ a handful of PWM's. How can I tell if the power supply (12 volt marine battery), motor, and PWM will all work? Is it possible to fry the motor or PWM due to the Amperage coming out of the battery? (is that a stupid question?) How big of motor would I need? I know speed isn't a issue but I need something w/ a lot of torque.

    Basically, I have an idea of what I need to do but am worried that if I get the wrong components I'll fry one thing or the other or myself. If you or someone you know has experience w/ this or a part list that'd be good for me I'd be grateful.

    Thanks so much for your help.

    -CD
     
  2. jcsd
  3. May 2, 2009 #2

    vk6kro

    User Avatar
    Science Advisor

    You probably need a geared motor controlled by a PWM.

    I had an idea though.

    Elderly folk drive around on little electric mobility scooters, "gophers".

    These have all the electronics and motors and wheels you would need.
    If you could pick up one of those cheaply and remount the bits, including the very nice battery these things use, you would have a chance of making this a practical project.

    New ones are probably expensive but second hand ones might go cheaply.
    I had a look on EBay but couldn't see any cheap ones.You'd need one in your area, though as shipping would be expensive.

    Or you could just buy up on the important parts.
     
  4. May 2, 2009 #3
    Hi there Vk,

    Thanks for the scooter suggestion. I did think of that as a solution and haven't totally ruled it out yet. The only problem is the price of those things. I think it'd be cheaper if I were to "part" it out and wire it all up that way.
     
  5. May 2, 2009 #4

    vk6kro

    User Avatar
    Science Advisor

    Yes. New ones cost $3000 or so.

    They are beautifully constructed though. They have motors in the back wheels and a great control box.
    I saw some for about $500 second hand. They would normally be sold when the owner moved into a nursing home so they might be looking for as much cash as possible.


    Anyway, if you got the model number of one you could ring up and ask how much a set of back wheels and motors would cost. I think they have two motors.
    That has to be a lot cheaper than a new one anyway.
     
  6. May 2, 2009 #5

    RonL

    User Avatar
    Gold Member

    Not sure just how much torque you need, but this might be close for a start. The 280 RPM will need to be geared down more, which can be done with pulleys and belts.

    Look under both electrical, and power transmission, there is a lot to chose from. I have ordered lots of things from these people, and have had no problems or disappointments.
    Ron

    https://www.surpluscenter.com/item.asp?UID=2009050210082290&catname=electric&item=5-1623
     
  7. May 2, 2009 #6
    That motor looks like it would probably work but I'm curious at what type of PWM I'd need.

    Do I have to match up the AMP's? Again I'm quite new to figuring out amps, volts etc. and don't want to mess anything up.
     
  8. May 2, 2009 #7
    A good mobility scooter comes with a) 24 volt battery b) motor and gearing c) a forward/reverse PWM speed control c) can move 250 pounds at 5 mph d) cost about $800
    go to
    http://www.spinlife.com/Pride-Go-Go-Ultra-X-3-Wheel-Travel-Scooter/spec.cfm?productID=79592
     
  9. May 2, 2009 #8
    Last edited by a moderator: Apr 24, 2017
  10. May 2, 2009 #9

    vk6kro

    User Avatar
    Science Advisor

    Would something like this work?

    http://cgi.ebay.com/DC-HIGH-TORQUE-G...DLVI%26ps%3D54 [Broken]

    Possibly not. That is a 24 volt 0.2A motor or about 4.8 watts.

    Apart from maybe not having enough power to work, you would need to know what happens to the gears when you stop the Dolly. If it is a worm gear and you try to stop a heavy load by cutting the power to the motor, the gears can be stripped of teeth after you do it a few times.

    The scooters probably have a slipping clutch arrangement to cope with these destructive forces.
     
    Last edited by a moderator: May 4, 2017
  11. May 3, 2009 #10
    Thanks Vk,
    I didn't even realize that the teeth could get stripped.
    Perhaps using the type of motor used in a scooter wired up to the PWM (if I can't find the entire scooter assembly).
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook