Need help for motorized running wheel project

Discussion in 'The Projects Forum' started by beaulieumar, Aug 10, 2015.

  1. beaulieumar

    Thread Starter New Member

    Aug 10, 2015
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    Hi,
    I am not so familar with motor project, so I need some help to more understand my needs.

    I need to motorized a running Wheel (for rats), for a project at the university. I have try with a stepper motor, but meet 2 problems:
    1) Since I need to go very slow (< 1 rpm), the Wheel was rotating by step (even if I was going at 1/16 steps). My motor has 200 steps.
    2) I was able to rotate the Wheel faster (or slower) than the speed specify with a little help of my hand (simulate a rat running in the Wheel).

    Because of the problem #1, I figure I need to use DC motor. Is is true?
    I think the problem #2 can be solve by using a bigger motor (more torque - the one I use is 177 oz-in). Is it true?

    Also, if I use a DC motor with a speed controller, can I use any PWM speed controller (using correct Amp. and Volt specs) even if I run at a very low speed (< 1 rpm)?

    I didn't have bought the DC motor and speed controller yet, but I looking for DC motor with less the 100 rpm and higher torque that the stepper motor that I have).

    Thanks for any help

    Marcel
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    To get that low a control with a DC motor open loop, then some kind of reduction would be best, If it is a wheel cage then quite a large ratio could be used.
    See Dryer drum method!.
    You can build a simple PWM controller they are also $5.00 on ebay.
    Max.
     
  3. beaulieumar

    Thread Starter New Member

    Aug 10, 2015
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    Thanks Max for your answer.

    If I understand correctly your answer, you suggest that I use a gearing system or strap/pulley system to have the motor rotate > 1 rpm. I thought at that, but I want to make the building part simpler is possible. But if needed I will do that.

    Dryer drum method: Do you mean strap/pulley system?

    Motor theory question: If I can stop the rotation of a motor shaft, does it mean that I use more torque force that the motor have?
    If yes, is it true for all kind of motor (stepper, DC, AC, etc)?
    I figure that is a mechanism to protect the motor to be broken.

    Thanks again,

    Marcel
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    A stepper motor can be stalled without damage, a DC or BLDC can be damaged (over current) if stalled by load etc and the voltage not controlled accordingly to be within the continuous current rating of the motor.
    Torque = Current, RPM = Voltage.
    Depending on the dia of the drum/wheel a belt similar to a large O ring and go around the drum and be driven by a small dia pulley on the motor, similar to the Dryer method.
    Max.
     
  5. BR-549

    Well-Known Member

    Sep 22, 2013
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    What is the length and weight of the rat?

    Have you a proposed diameter for the wheel? Have you played with rats before?

    One RPM has the rotational rate of a second hand on a clock. Are you really going to be using that or less as part of your speed range?

    Do you want a rat at rest, or a running rat, to effect the speed of the wheel?

    If the rat can not influence the speed, please be careful, high acceleration or deceleration rates can harm the rat.
     
  6. beaulieumar

    Thread Starter New Member

    Aug 10, 2015
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    Thanks Max, for the motor information.

    The rat weight will be 400-600 g (14-21 oz). The Wheel has a circumference of 1.44 m. And an ethic committee has accepted the experiment.
    We want the rat not to sleep for a certain amount of time, so we will be running the Wheel at 0.4 m/min. (0.28 rev/min).
    We want the Wheel rotation fixed at 0.28 rev/min ( the rat should not be able to run in the Wheel during the experiment), so there will not be high acceleration or deceleration at all.

    Thanks for the answer and welcome to any new suggestion.

    Marcel
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Another thing depends on how precise the rpm has to be maintained, if quite precise, the stepper motor may prove the cheapest route, but gearing or reduction of some kind is going to be needed, regardless, I would say, for that slow a rpm.
    Your stepper motor problem of seeing individual steps is because reduction is needed, and will apply to just about any motorized method, IMO.
    The problem with the DC motor etc, will be in precise control of rpm, where if needed feedback would be required or a governor of some kind
    Max.
     
  8. beaulieumar

    Thread Starter New Member

    Aug 10, 2015
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    You are right, Max, gearing with a stepper will solve the seeing individual steps problem, but so my second problem with the stepper (rat cannot modify the Wheel speed by himself) can be solved by using a bigger motor (more torque than 177 oz-in). Is it true?

    Marcel
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Remember when using geared reduction, the increase in torque is the ratio of reduction.
    e.g. 177 oz-in is 1770 oz-in at 10:1.
    Max.
     
  10. beaulieumar

    Thread Starter New Member

    Aug 10, 2015
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    Ok, that will help.

    I will try a gearing reduction with my actual stepper, I will see if it is working OK.

    You are been very helpful, Max.

    Regards,

    Marcel
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
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    For components and ideas a useful site I have found is Misumi, the huge catalogue they will ship to you is worth it in mechanical applications and formulae.
    Are you in N.A.?
    Max.
     
  12. beaulieumar

    Thread Starter New Member

    Aug 10, 2015
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    Thank you for the information. I will take a look at Misumi.

    Yes, I am from Montréal, Canada.

    Marcel
     
  13. BR-549

    Well-Known Member

    Sep 22, 2013
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    May we see a picture of the wheel and cradle?

    And I assume the rat will be confined to the wheel?

    So the wheel has inclosed sides on it?

    What is estimated weight of completed(walled in) wheel?

    Is there any excess shaft length? What size?

    Is it possible to use the circumference of wheel for rotation?

    Many questions remain.
     
  14. ISB123

    Well-Known Member

    May 21, 2014
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    Don't lie to us you are working on a Rat blender.
     
    Sensacell and shortbus like this.
  15. ian field

    Distinguished Member

    Oct 27, 2012
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    Gearing down a stepper may not be the best way to go, it might solve low speed "cogging" but torque tails off fairly quickly at high RPM.

    A DC motor geared down with pulleys would have little risk of stall current damage. A VCR capstan belt might be big enough, but there's probably better options.
     
  16. MaxHeadRoom

    Expert

    Jul 18, 2013
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    At .28rpm at 10:1 would still only be 2.8rpm?
    Max.
     
  17. ian field

    Distinguished Member

    Oct 27, 2012
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    A drive belt round a tread wheel for a rat, hooked over the motor spindle would give a reduction ratio of quite a lot.

    Might even be necessary to attach a pulley wheel somewhat smaller in diameter than the rat wheel.
     
  18. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The diameter of the drum is <18" so a .5" pulley would give ~a reduction of 28:1. = approx 8rpm on the motor.
    1600 pulses /min
    I would look at a variation of this route, personally.
    Max.
     
  19. ian field

    Distinguished Member

    Oct 27, 2012
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    Must be an awfully big motor to have a 1/2" spindle - and someone was worried about stalling it - must be an equally gigantic rat!!!

    This job could be done with literally a toy motor with a spindle diameter about 2 - 3mm.

    There are projects online for back emf sensing controllers that can be set for a desired speed relatively immune to loading.
     
  20. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    as Max alluded to in post # 4, contraption is a drum about 46 cm dia. turning at 1 revolution in 3 min & 34 sec. ( that is slow, rat will run up on side then take a nap & run up again.). Surplus houses have many options on geared motors, DC & AC.
    Just looked up 2 from Electronic Goldmine, 72 RPM, would need extra reduction of 257:1, G20726; or a humongous reduction of 7776:1, on 6Vgives 1 revolution in 4 min. Operates on 3V to 24V DC. # G20272
     
    Last edited: Aug 11, 2015
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