Understanding my Dynamic balancer
Understanding my Dynamic balancer
(OP)
I've used several dynamic balancers (Chadwick, DSS and others) on my two-bladed helicopter.
They all provide a velocity reading (ips) at a phase angle (zero to 359 degrees), relative to a opto-electronic trigger that starts (and presumably stops) the acquisition cycle when the "master" blade is directly "out front".
This reading is then manually plotted on a polar chart to find the corrective action.
A typical reading would be "0.5ips at 24 degrees".
Guys I've talked to that balance machinery for a living don't understand what the "24 degrees" refers to. They say that pure imbalances generate sine waves, and that maximum velocity always occur at 0 degrees and 180 degrees.
My question: If this is true, what does the 24 degrees in a typical readout "specifically" refer to? Is it the zero crossing "lag or lead" of the raw acceleration waveform?
They all provide a velocity reading (ips) at a phase angle (zero to 359 degrees), relative to a opto-electronic trigger that starts (and presumably stops) the acquisition cycle when the "master" blade is directly "out front".
This reading is then manually plotted on a polar chart to find the corrective action.
A typical reading would be "0.5ips at 24 degrees".
Guys I've talked to that balance machinery for a living don't understand what the "24 degrees" refers to. They say that pure imbalances generate sine waves, and that maximum velocity always occur at 0 degrees and 180 degrees.
My question: If this is true, what does the 24 degrees in a typical readout "specifically" refer to? Is it the zero crossing "lag or lead" of the raw acceleration waveform?





RE: Understanding my Dynamic balancer
The angle is the phase lag, ie the location of the positive-going zero-crossing of the sinusoid of the velocity.
If in the example above you were to move the trigger further round by 24 degrees, then the readout would be 0.5 ips at 0 degrees.
Be very careful, acceleration, velocity and displacement sinusoids are at 90 degrees increment of phase lag.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Understanding my Dynamic balancer
So then it wouldn't be possible to determine this phase relationship by capturing data only between the start and stop signals?
Sounds like a circular buffer would need to be employed to capture data prior to the trigger. Any suggestions as to where I might find a flow chart or psuedo code of this process?
RE: Understanding my Dynamic balancer
I know how to build an expensive (FFT based) balancing rig, I don't know how to build a cheap one.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Understanding my Dynamic balancer
"I know how to build an expensive (FFT based) balancing rig, I don't know how to build a cheap one"
I know of a balancing rig that has nothing more than a PIC microprocessor (possibly a DsPIC) and a 2-line LCD in it. The remote accelerometer, a MEMS type I suspect, and the photo-sensor connect directly to the A/D pin and digital input pin on the PIC. No signal conditioning at all!
It works pretty well, although I think it could benefit from some signal amplification, as the accelerometer signal diminishes as the balance become better.
It's not cheap either at $2200, considering the parts total up to less than $100.
Know of anyone I can commision to help me develope a similar unit?
RE: Understanding my Dynamic balancer
RE: Understanding my Dynamic balancer