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How Motor Torque Effects Weight Transfer

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  • davejr
    started a topic How Motor Torque Effects Weight Transfer

    How Motor Torque Effects Weight Transfer

    Fact or Fiction

    The torque created by an inline slot car motor under acceleration adds weigh to one rear wheel, and reduces the weight on the other rear wheel.

    A motor that makes 400 g/cm of torque will add about 200 grams of weight to one tire, ( 2cm from the center of armature to the inside edge of the tire tread ) and subtract about 200 grams from the opposite tire.

    This demonstration was performed with a piece of track suspended by two nylon strings. The strings are attached 1.2cm above the road surface, right at the center of gravity of the car.



    With the test chassis placed on the suspended track, the track becomes very unstable. It takes 3 to 7 grams of downward force at the inside edge of the tire tread, to tip the road surface to approximately a 20° angle.



    It takes about 36 grams to tip the track surface to approximately 45°



    The video demonstrates what happens when over 14 volts is applied to the motor. The motor will produce more than 450 g/cm Ts at this voltage.

    This would produce an amount of about 225 grams of weight at the inside edge of one tire, and the same amount of weight is removed from the opposite tire.

    [ame="http://s164.photobucket.com/albums/u20/davejr-photos/?action=view&current=WEIGHTTRANSFERVIDEO.flv"]WEIGHTTRANSFERVIDEO.flv - Video - Photobucket - Video and Image Hosting[/ame]

    This single frame from the video shows the track at it’s maximum deflection, about 20° .



    Dave
    Last edited by davejr; 04-01-2009, 01:29 PM.

  • bemoore
    replied
    Originally posted by RichD View Post
    In that case the torque effect would want to steer the car, but with Thunderjet type cars I have never noticed any difference in handling between right and left hand corners.
    The effect is there. Maybe not so noticeable with Tjets, but try it with no-mag AFX's running stock tires. The car is way overpowered in that trim, and will fishtale dramatically under acceleration, and will kick to one side under deceleration.

    Leave a comment:


  • davejr
    replied
    RichD

    I did a video demonstration of what happens with a sidewinder, to show the same forces created by the motor.

    http://slotcarillustrated.com/portal/forums/showthread.php?p=248301#post248301

    Dave

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  • Mark
    replied
    nevermind.......didn't refresh the thread. dave & Rich already covered.

    Pretty much, the gist is there's always going to be a force going in the opposite direction of the motor's rotational direction. Happens in all automobiles, slot cars, bikes, go-karts, whatever....if something rotates one way, there's always a reactive force.
    Last edited by Mark; 01-20-2009, 10:58 AM.

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  • davejr
    replied
    This video is just a hypothetical of “what if”

    The motor shaft is connected to a stationary drive shaft to demonstrate what would happen under the same circumstances if the torque of the motor could be applied as weight on the tire.

    Dave



    [ame="http://s164.photobucket.com/albums/u20/davejr-photos/?action=view&current=WHATWOULDHAPPEN.flv"]WHATWOULDHAPPEN.flv - Video - Photobucket - Video and Image Hosting[/ame]

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  • RichD
    replied
    This subject came up on another BB a few days ago when someone thought that a sidewinder car would do the same thing. I came to the same conclusion that davejr did, that the mass of the armature was a deciding factor and that only a car with an inline motor would exibit this side to side twist. A 1/32nd car has a small armature in comparison to the total mass of the car, so I did not expect the effect to be huge. In the case of an HO car the ratio of the mass of the armature and the car is much lower and the weight to horsepower ratio is a lot lower as well so I would expect the twisting effect to be greater. All that is mostly swamped out by the downforce created by the car's motor and traction magnets. I suppose that if one was running on an ovel and was a real fanatic that you would want to take advantage of the torque effect. Another thing to consider would be the effect on pancake style cars, especially those with little magnetic downforce. In that case the torque effect would want to steer the car, but with Thunderjet type cars I have never noticed any difference in handling between right and left hand corners.

    Leave a comment:


  • davejr
    replied
    In the first video the power wasn’t momentary, full power was applied to the slot car for over 5 second.

    Full stall torque is achieve the moment the power is applied and dissipates as the motor increases in rpm.

    The only added weight to the rear tire is from the inertia created by the acceleration of the motor's armature the instant power is applied. After that the track goes back to level.

    When the power is turned off after 5 seconds the car rotates in the opposite direction because of the sudden stopping of the motor from over 10,000 rpm.

    The track itself only weighs 12 grams, I don’t believe that this would absorb the over 250 grams of force that is created the instant the power is applied.

    I believe this demonstration shows that the only weight applied to the rear tires is from the inertia created by accelerating the armature and not the torque created by the motor.

    This small amount of force is only created when the car is at a full stop and the power is applied instantaneously as in drag racing.

    The videos demonstrate the car is level while the motor is spinning the tires at 10,000 rpm under full load, and the motor is still making over 300 g/cm of torque.

    The slot in the test track is tapered and stops the car under full power before the end.

    This video demonstrates what the test looks like from a different angle.

    [ame="http://s164.photobucket.com/albums/u20/davejr-photos/?action=view&current=TESTDEMOVIDEO.flv"]TESTDEMOVIDEO.flv - Video - Photobucket - Video and Image Hosting[/ame]

    Dave
    Last edited by davejr; 04-01-2009, 01:33 PM.

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  • Wet Coast Racer
    replied
    But it's accelerating in a different plane.

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  • ElSecundo
    replied
    Originally posted by DaveKennedy View Post
    Shouldn't the car be fixed in place to determine torque in any case? Because the car is accelerating as well as twisting from the torque... too many variables are in play here.
    Bingo.

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  • DaveKennedy
    replied
    Shouldn't the car be fixed in place to determine torque in any case? Because the car is accelerating as well as twisting from the torque... too many variables are in play here.

    Leave a comment:


  • Mark
    replied
    So this means........use this weight transfer as an advantage on certain parts of the track.....that's what I do with my Inlines.(right turns)

    I feel the difference......either that or my cars are horrible and can't turn left, LOL.

    Leave a comment:


  • bemoore
    replied
    I think one more tidbit of info needs to be added. This effect will occur only when the motor is accelerating or decelerating. At a constant speed, no wheel loading will occur. AND, I'm sure most of you understand this already, but under deceleration, the loading will be on the opposite wheel.

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  • Robert Livingston
    replied
    A momentary impulse will not be accurately measured by a typical gram scale, but this experiment gets around that limitation by correlating angle of tilt with grams of force.

    But there is the further limitation that the chassis and tilting roadway have their own inertia, which absorbs (some of) the grams of force exerted by the motor, which limits the tilt.

    The torque exerted by the motor is determined by the load on the motor. The motor is never at full stall, and never exerts full stall torque. It only exerts enough torque to pop the car forward. I would guess that is only a fraction of the torque the motor could develop at full, rotor-locked stall. The test does substantiate the theory that the chassis will try to twist under acceleration; it also shows that the torque is nowhere near as much as the full stall torque of the motor. Given the absorption of twisting force by the inertia of the tilting track's mass, the 3 to 7 grams implied by the static measurement of tilt per grams of force, is a low estimate of the actual loading of the left side tire during the burst of acceleration.

    I have to add that this is a very interesting demonstration, and that Davejr has suceeded (at least) in demonstrating the twist exists, as some of us predicted. Thank you, Dave.
    Last edited by Robert Livingston; 01-19-2009, 09:48 AM.

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  • davejr
    replied
    That is the point of this demonstration. Some people believe the torque created by the motor adds weight to one rear wheel and removes weight from the other. The video shows that only few grams of weight are created by inertia.

    Dave

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  • ElSecundo
    replied
    Originally posted by John Schoen View Post
    Aren't you confusing torque with inertia here? I would think that torque is transmitted through the rear wheels and inertia causes the rolling movement of the chassis.
    Yep, and angular momentum makes the deflection angle a useless measurement. Once the system starts to rotate, it will continue to rotate in the same direction, even after power is removed from the motor.

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