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Electric hand throttles

  1. Oct 15, 2011 #1
    Hey everyone, I am building an electric bike and I was wondering if you can take a typical hall effect hand throttle and connect it to two controllers, so it can control 2 identical motors with separate power supplies giving each motor = amounts of voltage to run the motors at around the same rate. Attached is a simple wiring guide for how I am setting it up.
     

    Attached Files:

  2. jcsd
  3. Oct 15, 2011 #2

    Danger

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    This might sound incredibly ignorant on my part, but why would you even bother? Just run the motors in series/parallel through a rheostatic throttle. Why would you drag Mr. Hall out of his grave for something so simple?
    Incidentally, why would you need 2 motors for a bike? One larger one would be a lot more practical.
     
  4. Oct 15, 2011 #3
    I'm trying to do this at low cost with high power and controllers that can handle more that 2000 watts and more than 50 amps are expensive so I'm trying this idea
     
  5. Oct 15, 2011 #4

    Danger

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    2,000 Watts?! How the hell fast to you want this thing to go?
    I can see this being a cool experiment, but for practical use you'd be a lot better off from both a financial and an engineering standpoint by bolting on a 3.5 hp horizontal shaft Briggs and Stratton.
     
  6. Oct 15, 2011 #5
    High quality off road electric bikes typically use 2000 to 3000 watts easily check out stealthelectricbike.com I'm trying to make a cheaper prototype with similar results.
     
  7. Oct 15, 2011 #6

    Danger

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    Okay, two things strike me about that. The first is that I clicked on one of the bikes in your link and it specified two hundred watts, not two thousand.
    Secondly, I had no idea that you are trying to become a motocross champion. The only reason that anyone in my country has an electric bicycle is to eliminate a bit of effort on an inner-city commute. That's about 20 km/h max and half an hour of travel time.
    You obviously live in a vastly different environment, so I will bow out and leave this discussion to others in a similar demographic.
     
  8. Oct 20, 2011 #7
    1 HP = 746 watts
    2.68 HP = 2000 watts
    3.5 HP = 2610 watts
    That's not a lot of power.
     
  9. Oct 21, 2011 #8
    For an electric bicycle it is
     
  10. Oct 21, 2011 #9

    cmb

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    Watts wrong with a regular carbon pot (use two for redundancy)? I just bought some, bulk, @ 50 for £1! If 10 pence is too expensive for the application then you've got problems realising your ambition!
     
  11. Oct 21, 2011 #10

    mheslep

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    That depends what you mean by "at around the same rate". It is possible to have your one throttle control both controllers with (at most) some glue circuitry, but unless both the controllers are capable of being synchronized somehow the motors (DC?) will likely run at significantly different RPM and torque which I doubt you can tolerate.
     
  12. Oct 21, 2011 #11

    mheslep

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    3.5HP is 2.6KW.
     
  13. Oct 21, 2011 #12

    mheslep

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    They show $7900. Can you buy the bike, motors, batteries, and controllers for that?
     
  14. Oct 21, 2011 #13
    What I'm making would retail for 1000 or 1200 I'm putting finishing touches on it now and it has all the same specifications as the high end electric bikes on that website
     
  15. Oct 21, 2011 #14
    If you want there are a few pictures on craigslist look up electric bikes and you will see my ad
     
  16. Oct 21, 2011 #15

    cmb

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    So, what was this thread about. Looks like you are just using the forum for advertising, or did you really want an answer to your question?
     
  17. Oct 21, 2011 #16
    The original question is can you use a single throttle control with two different controllers to control the speed of 2 identical motors.
     
  18. Oct 21, 2011 #17

    cmb

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    The answer to that is:

    1) If the two motors are locked together (that is, their speeds are a function of each other, either by being on the same shaft or both in contact with the road by fixed gears) then;
    a) you can only run them from one control if the motors are torque controlled. That way, you simply get the sum total of the torque and small differences are unnoticed, and when you back off the throttle, or set it higher, you would do so until you sense the sum torque (viz. acceleration) is as you want it.
    b) you cannot run them as speed control because it is unlikely to be exactly the same speed, so they can fight each other with one trying to slow the other down (one applies a -ve torque while the other a +ve torque as they both fight to get to their 'set speed').

    2) If the two motors are summed on to a final output (that is, their outputs are put through some differential device that adds their respective speeds and torques) then they should be controlled for speed, because if controlled for torque then one can slow down to nothing whilst the other is running fast, yet both can put out the same torque and acheive whatever is the speed required.

    Are your motors torque or speed controlled, and how are they connected?
     
  19. Oct 21, 2011 #18
    I suspect the "control" is just some type of PWM that responds to the throttle with no motor feedback, so combining two controllers and two motors likely has no issue. Using a single throttle with two controllers, likewise no big deal, it will either work splitting the wires or with a simple buffer circuit.

    Trouble I think is more likely from how the two systems behave when one of the battery packs goes dead first, and generally from the use of two light duty systems for a heavy duty application.
     
  20. Oct 21, 2011 #19

    cmb

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    That would be a function of the details of the system and the motor type, to determine that. If they were permanent magnet AC ('DC pulsed') synchronous motors (as they would surely be, for weight efficiency) and were locked together and one PWM controller ran slightly faster than the other, then one would open its gates up and sink torque reaction back to the bus. Or are we talking about a motor/controller that has no regenerative braking - missing one of the benefits of having a motor/battery!?

    Whilst the other motor's PWM circuits are desparately trying to dump current from the bus into the motor to accelerate the shaft to its PWM speed, the slower one is sinking current back again as if it were 'regenerating' because it is running faster than its set speed.

    If the motors are locked on the same shaft, what you need to be 'simple' is one controller to operate two sets of drive bridges. Then you have to make sure the phases of the motor are mechanically set the same, too.

    Multiple traction motor control is not as trivial as you might first imagine.
     
  21. Oct 21, 2011 #20
    Devil is always in the details, for all we know the motors are not on the same wheel or perhaps one is a hub motor and the other driving via chain or belt.

    Where I have confidence is that use of a single control voltage won't be a big issue.
     
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