How to power BIG DC motors, etc...

Discussion in 'The Projects Forum' started by titana, Mar 29, 2010.

  1. titana

    Thread Starter New Member

    Mar 29, 2010
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    Hi,
    I'm new here. My real name is George. I thank the admin for the good work. Nice forum and nice colours/graphics.
    I want to become a programmer and an electronic engineer so I can design and just make stuff like robots and program them. I love that job!

    I can already script quite complex stuff using a scripter called GlovePie. (Love it!). The reason that I wanted to register in this forum is that I need some support for my crazy ideas and hope that I'll find it here... Maybe they are not that crazy for you!

    For the moment I want to tool up my poor desk, and add things like electric motors, servo motors, controllers, and an Arduino board which will do almost for all my project ideas.

    Well! My "first" project will be a Segway. I don't purchase a real one because it's not the Segway that I want. I like to build and disassemble the whole thing and mount/unmount just anything... (because of the price too. hehe) The real inventor was really genius! I like the challenge.

    Well I've already made simple little projects like a camera mounted on 2 small servos (1.5kg*cm each) following an IR led, etc. I've never used high current projects or stuff which drain a lot of current... since now!

    For now, I just want to know how to power all the big motors? I want to use quite powerful motors like a 1000W total power. I hate batteries, and they are really expensive for such a power. Plus they have to be charged all the time... (definitely hate that!!!)

    Does anybody have an idea of how to power any motor from 24V-48V and more or less 10Amps each? I want to be able to use and power up anything with my wall plug if possible. The problem is that the wall plug current is in AC. (And could become very dangerous for me too! I know that!)

    This was mostly an intro. I'll try to describe exactly what I need from you now next time. Tomorow...
    Sorry for my bad English!

    Thank you in advance!
     
  2. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Assuming two motors: 350W, 24V @ 22A; 450W, 36V @ about 20A?? or a 450W, 24V @ 28A , for each motor. Rapid reversal might require electric brakes & heavy H bridges. Motors from All Electronics. Wish you luck.
    Wild thought: Motor with gear reduction having two contra rotating output shafts coupled to two magnetic particle clutches, which then drive a common gear[ or timing belt]coupled to one drive wheel = fast response, no H bridge, no motor reversal???
     
    Last edited: Mar 29, 2010
  3. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    117 VAC to 36 VDC @ 50 A- Ouch!! $$$. Maybe Pb-H2SO4 battery with 10 A charger would be cheaper.
     
  4. rjenkins

    AAC Fanatic!

    Nov 6, 2005
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    Hi,

    I'd start with a DC power supply, for two reasons:
    Tthe rest of the work can be done at low voltage (for safety), and once you get it working, you can swap straight to battery power when you take it out for a run!
    (And the power supply will become the battery charger).

    As far as the general design goes, have a look here - some guys at MIT have done this and published all the info:
    http://web.mit.edu/first/segway/
     
  5. titana

    Thread Starter New Member

    Mar 29, 2010
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    Thank you a lot...
    Now, at least I know there's people who I can trust!

    The main issue is the charging time / autonomy of a battery-powered project. It would be 1000 times easier to do it with batteries, but remember that I have loads of ideas and these ideas require a lot of experiments. That means that I'll have to cut the whole project for charging the battery pack... all the time. Unless I find a way of experimenting with smaller in scale stuff first.

    Anyway! I said that I would write more details today on the motor power...

    I need at least 2 motors with the following specs. (more or less)
    36V DC or AC with the apropriate driver working on PWM!
    8A - 10A
    and + or - 250W-350W each. Quite big difference, I know! I didn't really matter for the exact values yet. The motors can be in AC IF possible to operate them from the wall plug without any danger! Actually, is it possible to find a DC generator else than batteries? Like an alternator, a dynamo which uses circular speed to make power? In my physics course we learnt that it IS possible. I don't know if there is a factory made!

    Could you tell me more on these electric brakes, Bernard? I mean how to mount them. Is there a specific way to mount them? Can they be mounted on any motor? Thanks. How do they work? Need too expensive parts?
    I've already heard of that H-bridge but don't know what it really is. I'll google that with the brakes.

    If I use batteries, does anybody know where to get them for less $$$? I'll google that too! But if someone already knows a site... feel free to post it here!

    Thanks a lot Bernard and rjenkins! I'm back in evening/.
     
  6. rjenkins

    AAC Fanatic!

    Nov 6, 2005
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    For your Segway application, you need high torque and good speed response.

    This is easy with DC motors and difficult/complex with AC.

    24V or 36V are reasonable voltages to work with and both new & surplus electric scooter or wheelchair motors are readily available.

    The current range at about 20A max per motor is practical for DIY construction.
    Using a full bridge (aka 'H' Bridge) for each motor will allow speed and direction control.

    You will need to study the design of servo amplifiers.
    In brief, they have two feedback controlled 'loops':

    The Current loop drives the motor (via PWM). The input to that represents from zero to plus/minus the maximum motor current, with feedback from a current sensor (eg. hall effect).

    The Speed loop takes the command from the control system (from zero to plus/minus maximum speed) and compares it to the actual motor speed, measured by a tachometer on the motor or taken from the motor armature voltage via some filtering (ie. the back EMF of the motor).

    The output of the speed loop controls the current loop.

    The two 'loop' stages could be two opamps, or it could all be emulated in software in the PIC (or whatever) that generates the PWM signals.
     
    Last edited: Mar 30, 2010
  7. titana

    Thread Starter New Member

    Mar 29, 2010
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    Hey, thank you Robert!
    I was looking for batteries now... Are the lead batteries any good? I think that finally I'll power anything with batteries!
    Thanks for the extra info!

    See you later
     
  8. titana

    Thread Starter New Member

    Mar 29, 2010
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    I already know how the servos are made. (I am an RC-modeler too. I use these servos all the time and know how they work.)
    I never thought that it was possible to use a similar system of "loops" for continuous rotation motors... Cool idea! Then it will rotate more "tight", and more precisely.

    So do I need actually 20A per motor @ 24V? that means a power of 480W per motor... Do you think that the "segway" will work precisely enough? Actually I thought to power each motor with something like 250W at the begining, but in the other hand it did look too few for me!
    The problem now is the money...

    Thanks again.
     
  9. titana

    Thread Starter New Member

    Mar 29, 2010
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    Hey guys!?!..!
    I've found an idea!!!
    What if I used an old PC power supply for it??? I found an old one with a power of 500W I think in my attic!!!

    Could I try something with it?
     
  10. titana

    Thread Starter New Member

    Mar 29, 2010
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    Actually, the supply is 380W.
    I have one output of 12V@17A. The only one that has 12V and could be used. I guess this is not enough.
    Can I use 12V motors?
    thnx
     
  11. rjenkins

    AAC Fanatic!

    Nov 6, 2005
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    If you half the voltage, you double the current and the wiring & transistor switching losses all go up.

    A simple transformer-rectifier should work if can find a transformer with the appropriate voltage.

    Anything designed to work with 24V from batteries must cope with around 20V to 30V range, so you don't need much in the way of regulation for the high current supply.
     
  12. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Electric wheelchair with dual 250 W, 22V DC @ 11.5 A motors ran quite well on 12 V @ about 8 A. A junked UPS yielded a nice transformer giving 23 VDC @ 20 A PS.
     
  13. titana

    Thread Starter New Member

    Mar 29, 2010
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    thanx guys!!!
     
  14. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Look at Placid Industries Inc. for clutch & brake inf.
     
  15. titana

    Thread Starter New Member

    Mar 29, 2010
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    I think to buy the Arduino Mega right now... to start controlling my small dc motors...
    after I've "burnt" some of them, I'll try to get biggers! and then clutches, brakes, tachometers...
    thanks a lot for your interest guys!
     
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