4 motor or 2 motor base drive

  1. last week

    Should we do 4 motor V5 motor base drive or 2 V5 motor base drive??

  2. 536Mentor

    May 16 Event Partner, V5 Beta Tester Appleton, WI 536

    To be honest, I think it is way too early to know.

  3. 2 motor 200 RPM or 4 motor 600 RPM. I would suggest 2 motor 200 rpm because it's the same torque as 4 motor speed and is plenty fast.

  4. callen

    May 16 Braintree, MA, USA

    @Harrison40500H I would suggest 2 motor 200 rpm because it's the same torque as 4 motor speed and is plenty fast.

    How are you getting that?

  5. 9065_Parker

    May 16 Platte City Missouri 9065C

    @callen How are you getting that?

    The numbers released by VEX and the technical specs all support those numbers.

  6. Rick TYler

    May 16 Teachers/Coaches, Event Partner, V5 Beta Moderator Redmond, Washington Founder of Exothermic Robotics

    I built an aluminum ITZ robot (without mobile goal lifter) using V5 and two drive motors running at 200 RPM with 3.25" wheels that worked fine, even geared up 5:3.

  7. callen

    May 16 Braintree, MA, USA

    @Harrison40500H I would suggest 2 motor 200 rpm because it's the same torque as 4 motor speed and is plenty fast.

    @9065_Parker The numbers released by VEX and the technical specs all support those numbers.

    No, they don't. Part of why I asked was to clarify what you meant by "speed," to clarify if that's the current middle-range 393s as oppose do a different number of rpm V5 motors. I'll just address both:

    Notes:

    1. Power = Angular speed * Torque.
    2. I'm not going to deal with frictional losses with different number of motors, chains, etc. I'm just going to make it ideal

    I think you meant the other, but just in case, 2x V5 at 200 rpm v. 4x V5 at 600 rpm:
    Let's set the 2x V5 at 200 rpm as power P with torque T2: P=200*T2
    Then 4x V5 at 600 rpm gives 2P=600*T4, or T4=(2/3)*T2.
    So the torques are not the same.

    I think you meant 2x V5 at 200 rpm v. 4x 393 at 160 rpm:
    A little trickier due to different values.
    Non-stalling first. The 393 is listed between 2.70 W (continuous) and 3.93 W (peak). Let's use 3.3 W as an average, figuring you're probably not truly running continuously but also can't stay at peak for too long. I'll use Ta for the 393 and Tb for V5.
    2*11=200*Tb, and 4*3.3=160*Ta. So Tb/Ta=1.33=/=1.
    Even if we try to skew things as favorably as possible for the 393, assuming it can run peak power whenever it wants for as long as it wants,
    2*11=200*Tb, and 4*3.93=160*Ta. So Tb/Ta=1.12=/=1.
    And now let's look at stalling. That's 2.1 N*m for the V5 and 1.67 N*m for the 393. To be consistent we assume the same size wheels and external gearing. So for 2x V5, that's 4.2 N*m. For 4x 393, that's 6.68 N*m. Normalizing for the different speeds, that gives us Tb/Ta=0.5=/=1.
    So we can see that the torque really aren't the same. 2x V5 at 200 rpm are easier to stall, but avoiding that they can provide noticeably more torque than 4x 393 at 160 rpm.

  8. 9065_Parker

    May 16 Platte City Missouri 9065C

    @callen I was refering to the 2m V5 200rpm vs 4m 393 at 100rpm. Also the V5 motors dont "stall" in the same way that 393s do, they limit their power so they cannot, so you can push them harder than you could a 393.

  9. callen

    May 16 Braintree, MA, USA

    VEX refers to 100 rpm 393s as "torque," not "speed."

    4x 393 at 100 rpm easily beat out 2x V5 at 200 rpm for torque. Of course, the V5s are driving twice as fast and are not nearly so weak as half the torque in this comparison.

  10. If you were to do a four motor 600 rpm v5 base, then you're gonna have to also gear it for torque, but I don't it'll be that much. I'd do the math, but I'm at school right now writing this on my phone. I'm thinking a 3:1 is fine, max 5:1

  11. callen

    May 16 Braintree, MA, USA

    @Inventor Inventor If you were to do a four motor 600 rpm v5 base, then you're gonna have to also gear it for torque, but I don't it'll be that much. I'd do the math, but I'm at school right now writing this on my phone. I'm thinking a 3:1 is fine, max 5:1

    As a general rule of thumb, never use V5 at 600 rpm externally geared to increase torque at 3:1. That would have the V5 going at 200 rpm. You could cut down on friction by just running the V5 at 200 rpm internally instead of swapping out to 600 rpm to just externally gear it back. I can imagine some limited cases where it might be useful, but even then only possibly and likely still not.

  12. callen

    May 16 Braintree, MA, USA

    @9065_Parker Also the V5 motors dont "stall" in the same way that 393s do, they limit their power so they cannot, so you can push them harder than you could a 393.

    Really? VEX lists "stall torque" for it. Also, are you saying that no matter how much load I put on these V5's, they can avoid getting stopped by it? That's certainly untrue. Or are you misunderstanding what the "stall" part of "stall torque" means? It doesn't mean the motor cuts out like the PTC's will do to it. It means zero rotational velocity, so stall torque is generally the maximum torque provided while static, which means it's forced to overcome this much or more to get moving it just can't get moving at all.

    So... I'm wondering something related. The info VEX provides is sadly lacking in an important spot. We (not VEX) can only reasonably measure torques at the shaft as far as ratings for a motor. But is the stall torque listed for the V5 for 200 rpm, as that's base model, as opposed to 100 rpm for the 393? If that is the case, my final calculation for stall torques would be Tb/Ta=1 (just barely over).

  13. Riptide

    May 17 Canton, Michigan 21636A

    @callen Really? VEX lists "stall torque" for it. Also, are you saying that no matter how much load I put on these V5's, they can avoid getting stopped by it? That's certainly untrue. Or are you misunderstanding what the "stall" part of "stall torque" means? It doesn't mean the motor cuts out like the PTC's will do to it. It means zero rotational velocity, so stall torque is generally the maximum torque provided while static, which means it's forced to overcome this much or more to get moving it just can't get moving at all.

    So... I'm wondering something related. The info VEX provides is sadly lacking in an important spot. We (not VEX) can only reasonably measure torques at the shaft as far as ratings for a motor. But is the stall torque listed for the V5 for 200 rpm, as that's base model, as opposed to 100 rpm for the 393? If that is the case, my final calculation for stall torques would be Tb/Ta=1 (just barely over).

    The motors have an program that cuts out power at 55C .

  14. nenik

    May 17 V5 Beta Tester

    @Riptide The motors have an program that cuts out power at 55C .

    Though it is the actual motor temperature (or rather the temperature of the built-in electronics), which is very different from the PTC behavior. The 393s could have been pretty cold when the PTC tripped in a stall and vice versa.

  15. callen

    May 17 Braintree, MA, USA

    @Riptide The motors have an program that cuts out power at 55C .

    Sure, but that's pretty different than what stall torque is. Power cutting out at a temperature is not the "stall" in "stall torque."

  16. 9065_Parker

    May 17 Platte City Missouri 9065C

    No, if you say a motor stalled with a 393, you know exactly what i meant, the ptc tripped and the motor no longer runs. In an ordinary match, unless your running into the wall most of the time, getting that high of a temperature shouldn't happen.

  17. meng

    May 17 Singapore 8059

    @9065_Parker No, if you say a motor stalled with a 393, you know exactly what i meant, the ptc tripped and the motor no longer runs. In an ordinary match, unless your running into the wall most of the time, getting that high of a temperature shouldn't happen.

    What @callen is trying to explain is this....

    By definition, stall torque is the maximum torque output when the motor speed has decrease to zero.
    In application, this happens when the load torque required is greater than the motor torque, and hence, the motor stop turning (or stalled). And the torque is the stall torque.

    As for ptc, it trips or cut the current supply to the motor once it reaches certain temperature. And normally, this happens even before the motor reaches stall torque.
    Basically, ptc stop the motor from turning by cutting the current supply, which is different from the motor not turning due to the load being greater than the max torque that the motor can supply.

    So in that sense, in vex, when we say the motor stall... most of the time we are just saying that the ptc tripped. But of course, there are also times that the robot hits the brick wall and the load torque required is greater than the max torque and the motor really stalls.

  18. 9065_Parker

    May 17 Platte City Missouri 9065C

    @meng What @callen is trying to explain is this....

    By definition, stall torque is the maximum torque output when the motor speed has decrease to zero.
    In application, this happens when the load torque required is greater than the motor torque, and hence, the motor stop turning (or stalled). And the torque is the stall torque.

    As for ptc, it trips or cut the current supply to the motor once it reaches certain temperature. And normally, this happens even before the motor reaches stall torque.
    Basically, ptc stop the motor from turning by cutting the current supply, which is different from the motor not turning due to the load being greater than the max torque that the motor can supply.

    So in that sense, in vex, when we say the motor stall... most of the time we are just saying that the ptc tripped. But of course, there are also times that the robot hits the brick wall and the load torque required is greater than the max torque and the motor really stalls.

    Yeah I unserstand, i was just trying to explain why the terminology wasnt clear.

  19. callen

    May 17 Braintree, MA, USA

    @9065_Parker Yeah I unserstand, i was just trying to explain why the terminology wasnt clear.

    If it's not clear, don't use "stall" for ptc's tripping. "Stall torque" is common terminology. Using VEX stuff, we should care more about VEX's terminology, and VEX uses "stall torque" as well. Basically, saying "stall" when you're talking about ptc's tripping is needlessly making things confusing, especially when what you're responding to was very specifically talking about "stall torque."

 

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