balancing woes

[jacquesm]

Today we spent all day on balancing the machine, little bits of progress, but it still shakes very bad around 150 rpm.

There are whole slew of suspects here to address one by one:

blade imbalance

governor malfunction, one weight going 'earlier' than the rest

excentricity

tracking errors

play in the governor

weight imbalance in the governor

'tip' wobble in the governor

I just talked for a few hours on the IRC channel with the folks there and we came up with a plan of sorts to fix it step by step.

center the ip (that's a pretty nasty mod, but I can see it needs to be done)

lock down the governor

spin it up and check for imbalance, if any fix that

unlock the governor

repeat

possibly build a tarp around the machine in lowered state so we can check without the wind playing around with it

remove the back seal from the main shaft, flush the bearing to reduce friction during balancing

[Flux]

I once had a go at the wincharger type fly governor and had similar problems.

For a simple fixed pitch wooden prop static balance is good enough and as long as the blades are similar the aerodynamic forces seem to be no problem.

When you have heavy metal parts moving about, things are not so easy, they really need to be dynamically balanced. Even if you make them identical as far as possible it seems difficult to get everything to move exactly together and stay in balance.

I agree that the first step is to lock the governor and be sure all the blade pitches are the same and then check for balance.

If all is well try locking with the blades at a different angle, if still ok it would indicate that the blade pitches are not tracking when governing.

Make very sure that the control weights are identical in weight, radius and angle as close as you can get them, they are the most likely things to cause a couple when they move as they are the heaviest bits to have an effect.

If you are really in trouble it may be worth removing the blades and checking the hub for balance at various speeds by driving it from a motor and belt or something.

Flux

[DanB]

you said 'center the ip' (what is ip?)

is the the case that the governor is part of the alternator case?  In the future (or perhasp this time) perhaps it would be worth having the governor be a seperate part so that all that could be balanced off the alternatoer.

I could be wrong, but from my experience (judging from the metal you used in your laminates) I suspect the drag from the iron losses is greater than that from the bearings.  I wonder if you could pull the stator out just for balancing?

sounds tricky!... Im sure you'll get it soon though.  I cant wait to hear how it performs.

[jacquesm]

hehe, sorry Dan, I meant center the 'tip'

The governor base plate and the latnerator case are separate, but to complicate things the bolts that hold on the governor are under the shafts

This oversight will be corrected in later versions...

[Flux]

Perhaps the wording I used is a bit confusing in that post. When I said lock the hub and try for balance I meant dynamic balance or effectively check for vibration. You are not likely to see any change of static balance in any of these cases.

Dan, I didn't want to show my ignorance by asking what the ip was, feel hapier now I know what was intended.

A very small movement of the governor unit with respect to the shaft will make an enormous difference to the balance, but once done it ought not move.

Flux

[nack]

# blade imbalance

  If the blades were weight-matched before mounting and static balances after, they should be OK, but worth checking.

# governor malfunction, one weight going 'earlier' than the rest

  You might get better tweakablility if the weight struts were replaced with turnbuckle adjusters.

# excentricity

  Possible - from the pictures I've seen I suspect you of doing better layout work though.

# tracking errors

  ?

# play in the governor

  see eccentricity

# weight imbalance in the governor

  see eccentricity

# 'tip' wobble in the governor

  This is my suspicion.  I don't think I would trust allthread to be rigid.  Any radial deflection here will reflect on the governor weights, as well as contributing it's own offcenter mass to vibration.

If this is the deal, you might want to cut a nice fat pin on the lathe (with lot's of shoulder to keep it square).  The spring tension can be adjusted by shims to allow for a nice square shoulder on both ends.