Electric Motors - Torque Delivered

Discussion in 'Physics' started by Daniel - RoboNoob, May 22, 2009.

  1. Daniel - RoboNoob

    Thread Starter Member

    May 21, 2009
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    Hey all,

    I have 4 electric motors that I'll be attaching to gears and using to try to move a robot. The problem is, I'm not sure which parameters to look at to calculate how quickly my robot will move.

    I have the spec sheet of the motor, but I really just don't know how to use it.

    I'll apply the maximum voltage to the motor, causing it to output what torque? How does the load on the motor effect this? (What is the load on the motor...just the mass of the robot resting on top of it?)

    Finally, if I know the mass of my robot and the motor specs, how can I make the robot move a desired distance, x, in t seconds?

    Thanks everyone,
    Robo-Noob
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    Not enough data to help out - for one thing, there are 6 different motors listed in the PDF spec sheet.

    The motor torque is dependent on the loading. Max is the stall torque. The load the motor experiences is affected by friction in the drive train and the ratio in the transmission as well as the mass it is trying to move. It's better to gear it down and move slower than to have a hot, overloaded motor.

    The load on the motor will be affected by not only the robot's mass, but what kind of gear ratio and what sort of drive mechanism you use.

    As to distance traveled in a unit of time, see the above.
     
  3. Daniel - RoboNoob

    Thread Starter Member

    May 21, 2009
    11
    0
    Thanks for helping out BeenThere - the motor being used would be the 200142; as for the gear ratio...I'm really not sure what to do...I want to choose that such that I can move about 1.5 meters in a second (starting from rest)...my overall bot will have a mass of about kg.

    How do I take into account friction in the drive train?
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    Your mass did not come through.

    The motion is going to be a function of how many revolutions the drive wheel has to make in order to go 1.5 m. Then you have to think how many turns the motor will have to make to drive the wheel that many revolutions in one second. Plus a guess about how much less than no-load RPM the motor will be turning.

    Rule of thumb - if it has to scoot, make it as light as possible.
     
  5. PRS

    Well-Known Member

    Aug 24, 2008
    989
    35
    I'm not being funny here, Daniel, but my approach at first would be experimental. Then I would refine my knowledge so that I'd be able to compete. Put your motor and drivetrain together on a wheeled platform then load the platform with various weights. You should obtain a feel for it that way. No one starts out a rocket scientist and there's no school like that of experience.
     
  6. Daniel - RoboNoob

    Thread Starter Member

    May 21, 2009
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    Sorry about that, BeenThere - mass would be around 2 kg. Also, any advice on how to guess how much less than no load my motor will output?

    PRS - I would love to be able to experiment, but unfortunately my budget is tight enough that I'm scared to waste money on an too strong or too weak of a motor...I totally agree though, would love to be able to do it experimentally instead of theoretically.
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
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    Any of the motors can move 2 kg. But you get more scoot with larger motors, and can pull a better gear ratio.

    It's all a guess, as we have absolutely no idea of your robot's wheel/track arrangement.

    Have you searched surplus sites for less expensive motors? Some experimentation is going to be necessary, as you are not following a kit with established parameters. you will need some fudging to find a satisfactory final drive ratio.
     
  8. BillO

    Well-Known Member

    Nov 24, 2008
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    136
    The information you are seeking is there, but this a complex situation.

    Row 4 gives the torque load that will result in the rpm in row 5.

    Row 7 gives the torque at stall. This will be the torque exerted by the motor to get the robot moving and is the maximum torque the motor can exert.

    Row 2 gives the no load speed. At this speed the motor is only producing enough torque to overcome its own internal friction. in actual use in the robot, the maximum rpm will be different as you will have the friction in the drive system and the rolling friction of the robot to contend with.

    Begin by using a gear ratio that will give a reasonable speed for the rpm in row 5, build it then test it. If it is too fast, then limit the current to the motor, if it is too slow then re-gear it.

    Edit: These seem to be some form of AC motor, however the page shown does not describe the nature of the required driving voltage or desirable frequency range for the specs given. I would be tempted to use standard NEMA rated 4 phase stepping motors for this application as there is so much available for them off the shelf.
     
    Last edited: May 30, 2009
  9. Daniel - RoboNoob

    Thread Starter Member

    May 21, 2009
    11
    0
    Thanks a lot BillO and beenthere. It's good to know the motor will be able handle the load and BillO, your breakdown of the spec sheet was great.

    Just to let you know, its not an AC motor but rather a Brushless DC motor.

    I've done a bit of surplus searching, and have actually ordered a prototype motor! I don't have high hopes for it though, its torque output is just way too low.
     
  10. BillO

    Well-Known Member

    Nov 24, 2008
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    136
    Daniel, A brushless DC motor is a brushless AC motor with drive electronics. The EC45 models you show in the specsheet are not of the ones with integrated drive electronics. They will require an AC dirve signal of a specififc waveform, phase and frequency to operate.

    The compnay does offer several versions of the EC45 with integrated drive electronics at almost 3 times the cost. The part numbers of the untis with drive electronics are of the form 35XXXX.
     
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