Loading / Rapid de loading of dc motor

Thread Starter

chazemz

Joined Mar 8, 2017
8
Hi, I am as the title says loading and de loading a dc motor every quarter rotation. I am finding that in the acceleration phase the motor is applying a very small amount of torque reaction. This is puzzling me? Could it be to do with change in flux density?, inductive kickback?, or anything else?I am not an expert so try to keep any answers on the simplistic side.
 

Papabravo

Joined Feb 24, 2006
13,002
It might help if we understood what you mean by loading and deloading a dc motor. AFAIK this is not exactly standard terminology.
 

Thread Starter

chazemz

Joined Mar 8, 2017
8
Sorry, I am rotating a magnet into the repelling magnetic field of another magnet and then rapidly taking away one of the magnets. The motor decelerates and accelerates every quarter turn ( the rotating magnets are enclosed within four rotor arms ). Hope this helps. Power is supplied to the motor at all times as it rotates.
 

MaxHeadRoom

Joined Jul 18, 2013
20,087
If this is a DC motor, the strength of the field decides the available torque (current).
The max rpm is also based on the field strength, the lower the field, the higher the rpm for a given voltage applied.
It sounds as though you are varying the field as the motor rotates?
Max.
 

Thread Starter

chazemz

Joined Mar 8, 2017
8
Thank you for the reply. So is it possible under these circumstances for the rotor arms to accelerate ( under no load conditions ) and apply very little torque in the opposite direction to the rotor arms?
 

Papabravo

Joined Feb 24, 2006
13,002
Sorry, I am rotating a magnet into the repelling magnetic field of another magnet and then rapidly taking away one of the magnets. The motor decelerates and accelerates every quarter turn ( the rotating magnets are enclosed within four rotor arms ). Hope this helps. Power is supplied to the motor at all times as it rotates.
Verbal descriptions are almost useless (at least to me) in understanding mechanical relationships. Other people's mileage may vary
 

Thread Starter

chazemz

Joined Mar 8, 2017
8
I have put a video on YouTube. Please watch it to the end - it is only 62 seconds long. At the end the body is stationary and in rest position when rotor arms accelerate. Power is switched off. Momentum transferred from rotor arms to body, body moves in the direction of rotor arms. This is very puzzling?


Any comments or questions most welcome.
 

MaxHeadRoom

Joined Jul 18, 2013
20,087
Tricky to fully understand what is happening, I would have preferred to see what would happen if both systems were mechanically separate, IOW allowed to rotate on their own at will without as much Mechanical connection to the other, at least as much as possible.
I assume those are magnets on the end of each arm and one on the L shaped arm?
Max.
 

Thread Starter

chazemz

Joined Mar 8, 2017
8
Yes the rotor arm magnets are in tubes, so when they are facing the body magnet they they are propelled rapidly down them. I am trying to discover why there is so much energy in the rotor arms at point of transfer than in the body. This simply does not make sense the way I understand things. Therefore I am looking at what I do not fully understand , the inner workings of the motor under these conditions Correct me if I am wrong but I was thinking that there will be a partial inductive kickback ( power not switched off ) and this would impede the supply voltage. If so what would be the effect?
 

djsfantasi

Joined Apr 11, 2010
6,200
Yah! I mean, really. I've read through your descriptions several times and watched the video several times as well. I still can't figure out what you're asking, let alone what you're doing. I assume that English is not your native language...
 

djsfantasi

Joined Apr 11, 2010
6,200
There is some force on the L in the opposite direction apparently. You can see it the early portions of the video as the L starts to return after being pushed forward. Per you description. The magnets are placed on the arms so they repel the magnets on the L. Hence, once the L is pushed forward, the arm passes and pushes the L back a little. So, for each motion forward, it is pushed back as well and the forward motion vector minus the backward vector leaves a small forward vector. This may be due to the magnitude of the forward momentum and hence the additional force needed to change direction. The spacing of the arms may allow this difference to dissipate. Again, I cannot be sure.

When power is removed, I don't have an explanation. If the magnets were to recede in their tubes, there would be less oppositional force and the reverse momentum would take over.

Just totally making a guess here, because as in my last post, "I don't even know what I talking about!" (Abbott&Costello)
 

Thread Starter

chazemz

Joined Mar 8, 2017
8
There is some force on the L in the opposite direction apparently. You can see it the early portions of the video as the L starts to return after being pushed forward. Per you description. The magnets are placed on the arms so they repel the magnets on the L. Hence, once the L is pushed forward, the arm passes and pushes the L back a little. So, for each motion forward, it is pushed back as well and the forward motion vector minus the backward vector leaves a small forward vector. This may be due to the magnitude of the forward momentum and hence the additional force needed to change direction. The spacing of the arms may allow this difference to dissipate. Again, I cannot be sure.

When power is removed, I don't have an explanation. If the magnets were to recede in their tubes, there would be less oppositional force and the reverse momentum would take over.

Just totally making a guess here, because as in my last post, "I don't even know what I talking about!" (Abbott&Costello)
Hope this sketch helps?

If I go through the sequence. Power is switched on, so torque is high and body starts to counter rotate.Torque reaction drops and the restoring force of the string and wires act on the device causing it to swing backwards and forwards a couple of times. Device then settles in rest position. All the time the rotor arms are accelerating and decelerating. As the rotor arms begin to accelerate ( after a tube magnet travels down the tube ) the power is switched off. The following rotor arm magnet collides with the body magnet imparting the rotors momentum onto the body. The body then moves in the direction of the rotor arms. As the rotor arms accelerate force pairing would indicate that the body should counter rotate at the same time. So when the power is switched off these two forces should cancel each other. This does not happen since the body rotates quite clearly at the end of the video against the restoring force?
 

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