Loading / Rapid de-loading of DC motor

[jim hardy]

The motor is switched off after the rotor arms accelerate.

No, the power supply is switched off.
I do not know whether the power supply output terminals then present an open circuit to the motor or a short circuit to the motor or somewhere in between.

That is an unknown that should be nailed down because the motor will regenerative brake into the power supply if the power supply will accept current from it.

Put one of these between the power supply and motor to eliminate that unknown.

If anything changes as a result then that challenges one of the basic assumptions, that the motor is 'switched off' by that power supply switch. It may instead see its supply gradually tapered off in which case the deloading is not so rapid.
If nothing changes then that basic assumption is probably okay.
But one needs to know from observation not assumption.

 

[chazemz]

Hi Jim, fitted switch, there is no change in the observations.
Regards Roger.

 

[Baluncore]

Thank you for your kind words.The sliding magnets are there for a reason. The clue is in the title of this thread.

Why not rationalise the design by placing the fixed body magnet inside the arc of the rotor like this.

 

[jim hardy]

Hi Jim, fitted switch, there is no change in the observations.

Good. That's answered.

 

[jim hardy]

If i understand the original question it is "Why doesn't the frame wobble more at the blade passing frequency?

What I am observing is that as the rotor arms accelerate and decelerate every quarter turn there is no counter rotation of the body.

Which for me is answered by watching it, i see wobble in the frame as the blades pass.

There is nothing magic about motors.
The whole of your system is the sum of its parts. Sum your momentums .

 

[chazemz]

If i understand the original question it is "Why doesn't the frame wobble more at the blade passing frequency?
Which for me is answered by watching it, i see wobble in the frame as the blades pass.

There is nothing magic about motors.
The whole of your system is the sum of its parts. Sum your momentums .

The original question is the same as now. How is the body able to move in the direction of the rotor arms when the power is switched off?
This fact is easy to see but difficult to understand. The visible angular momentum is out of balance in the system, this does not mean it IS, just we do not see it. Energy in MUST equal energy out, nature sets the rules. If nature is taken out of balance it will do what ever is necessary to restore energy balance. To many people a tornado spitting out golf ball sized hail stones may seem strange,but as you are well aware it is a frightening reality.
If you are saying that it is not the motor then we go back to the other system. Would I be correct in saying that as the rotor arms slow down and the torque reaction is countered by the body magnet that this energy is transferred to the magnetic fields of the colliding magnets. One of those magnets wants to turn and as the magnets are forced closer together this desire to turn grows very rapidly. Therefore at de loading a lot of potential energy ( or stored angular momentum ) is released as the magnets de torque ( maybe unconventional term ). Since this energy has doubled up, on release something has to give. The motor has to accelerate due to the applied voltage. As this has priority you may find that the body cannot counter rotate because conservation of angular momentum would then be violated .Same as Newtons cradle, two balls collide , two balls accelerate. If one ball moved after the collision KE would not balance. You cannot have it both ways here, I am of the opinion that conservation of angular momentum is the priority and force pairs must step aside so that balance ( not symmetry ) is maintained. I will think further on this and comment again, If anyone has any comments to make please feel free.

Regards Roger.

 

[jim hardy]

Most collisions fall somewhere between elastic and inelastic.
Momentum is conserved.
Kinetic energy divides between motion and work done on the bodies.

If you are saying that it is not the motor then we go back to the other system.

Probably your motor is key. Testing with the motor switch you added answered the question "Does regenerative braking returning power to the supply? ".

Next question - "What is the nature of torsional friction in that motor?"
My intuitive feel is the motor becomes an effective mechanical brake as soon as it's de-energized. That might be just friction in the gear train, or , since it's made to drive a leadscrew mechanism it would be logical for it to have an automatic mechanical brake to hold its garage door "where is" on power fail mid-travel.
Spin your motor by hand . You'll get a feel for its internal friction and inertia, and any mechanical brake will announce itself.

One of those magnets wants to turn and as the magnets are forced closer together this desire to turn grows very rapidly. Therefore at de loading a lot of potential energy ( or stored angular momentum ) is released as the magnets de torque ( maybe unconventional term ). Since this energy has doubled up, on release something has to give. The motor has to accelerate due to the applied voltage. As this has priority you may find that the body cannot counter rotate because conservation of angular momentum would then be violated

My advice is write the formulas and apply algebra...

“When you can measure what you are speaking about, and express it in numbers, you know something about it, when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind; it may be the beginning of knowledge, but you have scarely, in your thoughts advanced to the stage of science.”

― William Thomson, 1st Baron Kelvin

I think i'll bow out of this one, too many unknown details about the mechanism.

 

[CWatters]

It's not clear to me why the body doesn't spin in the opposite direction to the rotor all the time the rotor is turning (eg due to air resistance). There must be something preventing it. That something can be storing energy that causes the thing to rotate in the same direction as the rotor when it's switched off.

Edit: Even if that's not the cause its potential to be the cause needs to be eliminated. You can mount the body on two ball races and use them to carry the current from the power supply to the motor.

 

[chazemz]

Hi, Thanks for your comments. I am really busy at the moment, I have to take my younger daughter to York medical school tomorrow for a offer holders day and on Sunday I am picking up my elder daughter from university as it is Easter break. I will be in a better position to reply to your comments on Monday or maybe Tuesday. Have a good weekend.
Regards Roger.

 

[jim hardy]

It's not clear to me why the body doesn't spin in the opposite direction to the rotor all the time the rotor is turning (eg due to air resistance). There must be something preventing it. That something can be storing energy that causes the thing to rotate in the same direction as the rotor when it's switched off.

The wires?

When power is applied it swings through about 3/4 turn , looks like it's hunting about an equilibrium position .
I estimated period at around fourteen seconds, 1/14 hz.

Pick a name for starting position -
i call initial at t=0 6 o'clock because the flat vertical face points away from the wall behind
When motor starts it swings CCW to perhaps 2 o'clock,
then CW to perhaps 11 o'clock
then CCW to 3 o'clock
then CW to 9 o'clock
then CCW to 4 o'clock
then CW to 7 or 8 o'clock
then CCW to 5 o'clock
then CW to about 6:30 o'clock and gets switched off.
Where would it settle?

Wobble at vane frequency maybe (4hz?) is evident.

How it comes to be called 'reactionless' i do not see.

 

[chazemz]

It's not clear to me why the body doesn't spin in the opposite direction to the rotor all the time the rotor is turning (eg due to air resistance). There must be something preventing it. That something can be storing energy that causes the thing to rotate in the same direction as the rotor when it's switched off.

Edit: Even if that's not the cause its potential to be the cause needs to be eliminated. You can mount the body on two ball races and use them to carry the current from the power supply to the motor.

In the collision phase the repelling magnetic fields will stop the body from counter rotating. After the collision when the rotor arms accelerate I believe it is unclear to everyone why the body does not counter rotate. Some people do not like the term ' I do not know'; it takes them out of their comfort zone. The term 'I do not know' for me means there is something to learn and that is what I am trying to do. I am no magician and what you are observing is not magic. All I am at the moment is the boy in the crowd shouting “the king is wearing no clothes!”. The amount of energy in the rotor arms at exchange is clear to see . The lack of counter rotation is equally clear. In reply to your comments on the bearings, it may be a good idea for you to view the video of a device called dean drive. This device would not work when suspended from a string but appeared to work when in contact with the ground. Therefore any contact with the ground is a big no no. I have said that I have placed the device on a thrust bearing to observe the device with no restoring force. The end result is the same the body moves in the same direction as the rotor arms. At the moment I am looking whether there is any time lag in the magnetic fields of the motor. All options remain open for now.

 

[chazemz]

The wires?
View attachment 114675

When power is applied it swings through about 3/4 turn , looks like it's hunting about an equilibrium position .
I estimated period at around fourteen seconds, 1/14 hz.

Pick a name for starting position -
i call initial at t=0 6 o'clock because the flat vertical face points away from the wall behind
When motor starts it swings CCW to perhaps 2 o'clock,
then CW to perhaps 11 o'clock
then CCW to 3 o'clock
then CW to 9 o'clock
then CCW to 4 o'clock
then CW to 7 or 8 o'clock
then CCW to 5 o'clock
then CW to about 6:30 o'clock and gets switched off.
Where would it settle?

Wobble at vane frequency maybe (4hz?) is evident.

How it comes to be called 'reactionless' i do not see.

The wires exert a restoring force in either direction.

I have no idea what you are describing with the clock analogy. Please clarify.

The term 'reactionless' means without reaction. An object without weight is said to be weightless. Since the action is the acceleration of the rotor arms and there is no reaction (i.e. counter-rotation of the body) then is reasonable to use the term reactionless. You seem to like formula, so therefore
F + -F > 0

 

[jim hardy]

"Dean drive" sounds like crackpottery to me,

https://en.wikipedia.org/wiki/Dean_drive

as does the label "reactionless" for this thing.

That's my opinion.

old jim

 

[jim hardy]

I have no idea what you are describing with the clock analogy. Please clarify.

angular displacement from rest in units of hour markings on a clock face rather than degrees

 

[berkeman]

"Dean drive" sounds like crackpottery to me,

https://en.wikipedia.org/wiki/Dean_drive

as does the label "reactionless" for this thing.

This thread is done.