Making Harmonic Dampers - Flywheel for Motors?

[AlanD]

Briefly (in responce to a request in another thread) - according to my understanding:

Basically a Harmonic Damper (a sort of rotational shock-absorber) is just an overhung (balanced) compliant-damped-flywheel which is coupled (attached) to the motor shaft with a collet or shaft-clamp through a central boss.

Think of a damper as a phenumatic-wheel with lead replacing the air.

The 'cogging' effects inherent in stepper motors leads them to become 'excited' at certain rotational frequency - this is commonly referreed to as mid-band-resonance and this is what a damper minimises by smoothing out the steps - it does this by adding a critical mass to dampen the 'cogging' - it may have disadvantages regarding acceleration/decelleration of the motor.

This one (below) appears to be a plastic moulded housing into which 'mass' has been added to give the inertia/loading.

Mass: 281gms
OD: 2.5"
Width: 0.75" (excluding the boss)
Inertia: xx?
Other features: it has a 'flag' for an interruptor/counter
Application: Fitted to a 100ozin NEMA 23 motor (as shown)

[Tim Tanner]

Hi Alan,

I think there is more to these dampers than just an attached mass. An additional mass would only change the system inertia and lower the primary resonance frequency. This may or may not help depending on your application.

The dampers I am familiar with have an inertial ring suspended in a viscous fluid. The fluid acts to absorb the resonant energy.

Regards,

Tim.

[Willbird]

Automotive harmonic balancers have an outer ring joined by rubber to an inner ring.

Bill

[Konstantin]

I have this 5phase steppers that have this harmonic drive, or something else since it is not a simple weight mounted on the shaft but it has a magnet also.
In the picture you can see the large disk but in it there is a smaller magnet disk.


Konstantin

[AlanD]

Hello Tim (and others) - you are quite correct to mention the other/proper kinds of dampers - I did actually mention rubber internediate-media in a earlier post to the original thread - I was trying to keep it simple but you highlight the need for a more detailed explanation and wider examples - (I don't have a rubber example at hand today)perhaps you can attach a picture?

While the compliant/conformant media versions are less within the means of most folks here (as is the mathematics?) - the underlying principles are important BECAUSE proper 'damping' avoids the problems of just adding flywheel INERTIA which can even distract the motor from starting (acelleration/decelleration):

This point of Tim's is important in considering the responces of home-made flwheel/dampers. However, it is NOT the fluid that absorbes the resonent energy - the fluid is just a coupling (damping) media.

My pheumatic-tyre (lead-filled) analogy gives the notion of rubber coupling between the flywheel and the motor shaft - including 'wheel-spin' as the analog of viscous-coupling - this slightly springy-spongy-flywheel analogy deserves some expansion?

Attaching 'mass' within suspensions of rubber or viscous fluids just modifies the responce and these are truer-dampers because of the delayed responce (because they perform a delay instead of the instant inertia of the rigid attachement of a simple flywheel). There is no doubt in my mind that, in a gven situation, they will be superior to rigid flywheels. The compliance of the rubber and/or viscosity of the fluid can vary the coupling of the damper and achieve results that do not have the compromises of a pure-flywheel.

This leads me to the warning - attach the dampers/flywheels with collet/clamping - NOT with grub-screws.

The whole physics of this subject and all the interelationships etc. are too much for 1 short DYI primmer Hopefully others who try DYI will learn to tune their systems and report with their findings and some practical details?

Originally Posted by Tim Tanner Hi Alan, I think there is more to these dampers than just an attached mass. An additional mass would only change the system inertia and lower the primary resonance frequency. This may or may not help depending on your application. The dampers I am familiar with have an inertial ring suspended in a viscous fluid. The fluid acts to absorb the resonant energy. Regards, Tim.

[pastera]

I have a stepper system at work that has dampers installed. They are simply a flat steel disc attached to the shaft, a disc magnet riding on a bushing on the shaft and some friction material between the magnet and disc.

Aaron

[AlanD]

Sounds very strange and curious to me - but it may be a damper of soughts. How about a few pictures Aaron?

Originally Posted by pastera I have a stepper system at work that has dampers installed. They are simply a flat steel disc attached to the shaft, a disc magnet riding on a bushing on the shaft and some friction material between the magnet and disc. Aaron