Dampers


Using Dampers to Reduce Resonance

Stepper motors are affected by resonance. The resonance can become so severe that the stepper will stall and lose position. Stalling can also damage the stepper.

Resonance sounds like a grinding or rattling noise. This is usually followed by a high pitched whine as the stepper stalls while still receiving step signals.

Resonance is caused by parts vibrating in concert with each other. It can be lessened by altering a variety of factors including micro-stepping, acceleration rates, speed, looser or tighter mounting hardware, thicker or thinner stepper mounts, longer or shorter mounting bolts, and a myriad of other variables.

A damper attached to the stepper's shaft can reduce resonance. It is essentially a mass that turns with the stepper; however, it is not simply a flywheel.

Caster Damper
Damper on back of stepper.

The damper reduces resonance by remaining slightly out of sync with the stepper. The out of sync vibrations help to counter the stepper's harmonics, which otherwise would crescendo and cause the stepper to stall.
 
This damper is straightforward, and all of its parts are from Lowes. It is made from a 2-1/2 inch caster, which performs better than a 1-3/4 inch caster.

The caster has a 5/16 inch bore. An axle is made by drilling a 1/4 inch hole in the head end of a 5/16 inch bolt. This hole accepts the stepper's shaft.

A hole is drilled and tapped for a #8-32 or similar set screw in the side of the bolt head.
The hole in the bolt for the stepper shaft can be drilled by tightening the bolt in a power drill's chuck, and clamping the drill bit in a vise.
A small bit is used to drill a centered pilot hole. The hole is incrementally enlarged with larger bits.
A drill press makes this easier, but the hole can be drilled with a hand held drill with Vise Grips holding the bit.
Two short screws with nuts are tightened into holes in a fender washer. The fender washer is epoxied or soldered against the bolt head.

The caster is sandwiched between a spring and washer. A lock-nut adjusts the spring's tension against the caster. This is a trial and error adjustment.

Damper parts
Damper parts.

The caster does not easily freewheel, but it will turn on the axle bolt.

The caster can also be used as a knob to turn the stepper by pressing it against the two short machine screws in the fender washer. The screw shafts will dig into the caster and keep it from freewheeling.
 
The difference in performance was impressive, especially with the Xylotex 425 oz.in. steppers.
An 18 turn per inch All Thread leadscrew driven by a Xylotex 425 doubled its top speed when the damper was used.
The rapid with the low cost leadscrew increased from 25 ipm to 60 ipm. The stepper's top speed increased well beyond the initial 450 rpm.