mechanical

[bj]

   Second try, 'cause I messed up on the first

   I have been following Chris's thread on brakes, as I too believe it is something I will eventually need.  Not for speed control, just for the time when it has to be stopped.

   The idea I was playing with was a band type brake.  They are self-energizing to some extent, so apply force needed is less.

   I am already going to a through type shaft for other reasons, so adding a brake on the end is no big deal.

   Toying with air activation, as a small leak would matter less.

   I know that friction material wear might be an issue, but if I have to use it, I am probably going to be doing some serious maintenance anyway so it will be easy to replace.

   This will be going on a Dan's ten footer.

   So, what do you folks think?  Please feel free to tear it apart.

   Thanks in advance

   BJ

[windy]

bj

 I am building a 17 footer and am planning on using a band brake. I am going to weld an 8" stainless steel ring (1.25"wide) behind the back rotor and wrap the band around it. Not sure how I will engage it, but I am thinking of using a 12 volt linear actuator.

windy

[bj]

   I think the bands are the simple answer, but I have been wrong many, many times before.

   I thought of air, for one reason, because I have the parts, for another,I made up a quick test rig with a band on the outside of a brake drum.  Spun it way up and applied.  It stopped the drum with scary speed.  A simple drum has very small mass, so I don't think it will be that way with blades etc. but I think it has a chance of working.

[windy]

 The band brake is used in a lot of go-carts and they are only 4" in diameter. So the band brake should work on a windmill. Not sure what kind of torque is generated on a 17 footer in runaway conditions.

windy

[Airstream]

Continuous duty - its hard to wrap ones' mind around. 24/7/365. Even Baja or Lemans or 24 hours of Daytona Racing are not continuous duty. I mean a go-kart will overcome the neutral drag on a band brake and it will work right up until it burns out but that is still only a few minutes out of a year, not left unattended and possibly rusting or otherwise contaminated for months then called upon for fail-safe duty...

Placing the band brake in a sealed capsule and ensuring it will not contact the drum until needed - and return to a purely neutral park when released is an interesting challenge. Getting enough leverage to exert clamping force to snub the fly wheel effect of all the moving parts is an interesting challenge, I mean even with force multiplication of levers & rods from the go-kart brake system there is still input potential of a couple of hundred pounds force of the driver stomping on the pedal (why'd that cop pull in front of me?) that needs to be duplicated...

[ghurd]

Two thoughts.

What about...

An "anti-converted" motor?

Maybe a 120V 4 pole single phase.

Turn the rotor down a bit and add a really thick piece of pipe, as long as the can will hold.

Turn the pipe down so it fits back inside the motor.

Connect it to the rear shaft.

Only use the run windings.

Apply DC to stop.

Could even apply AC directly from the PMA.  Braking force would be related to the PMA voltage.  In my mind, I think it would be safer than direct shorting.

It would not hold it at a dead stop, but it sure would slow it down.

Possibly an automotive A/C clutch between the band brake and shaft?

I don't know anything about them but always figured they'd be good for something!

Something to keep in mind for air is there can be issues with ice.

G-

[REdiculous]

I've been wondering if you couldn't slow or stop a windmill with some properly placed aluminum and (electro)magnets?

I really need to ketchup, mustard.

[DanB]

Im sure it could work fine.

I kind of like the idea of folding the tail  - or - as DaveB has done, a brake pad.  I would worry that a brake involving a band would stop it Really fast which could be bad.  But done right... just about anything can work!

[fabricator]

Something to remember is these things will likely spend 99.9% of the time not in use, if I build something it will be with the idea in mind of simply using it to shut it down if the weather gets ugly, say the weather man is calling for possible storms in the area today or tonight, I'd simply shut the mill down for the day or night, the possible damage to the investment FAR, FAR outweighs any possible gain from the electricity harvested in any given period.

[bj]

   Agreed Dan--after my little test.  Another reason I was toying with air apply.  I can use a small orifice, and slowly build pressure.  I am sure an almost instantaneous stop would do as much damage as whatever impending doom was coming.

[bj]

  Agreed Fabricator.  I think I would rather leave some lights etc off overnight and not have to build another stator.

[bj]

  Hadn't even considered either idea.  I really like the AC clutch.  That way I could preset the brake for the right drag, and then flip a switch.  No issues of drag either.  Added bonus is that I have about a half a drum of them, used, but usable.

   Once again, Ghurd, thanks for clearing a bit of fog for me.

[ChrisOlson]

I would think that a band brake would work fine.  Just that whatever you use for an actuator must be able to sit up for there for months unused, and still work on the day you need it.

I got to try my eddy brake in a real wind yesterday.  The turbine was putting out a little over 400 watts in a 15-20 mph wind.  I pulled the fuses on the rectifiers to unload it and let it free-spin, then threw the brake switch.  It stalled the blades in less than 2 seconds, then throwing the stator shorting switch brought it to a crawl.  So I've found the faster my eddy brake spins, the more effective it is.

The bad part about my brake is that it won't hold the turbine stopped after it's applied.  A band brake would be able to do that.

But how are you going to hold the band off the drum when it's not in use?  I would think that with vibration and wind the flexible band might move around a bit and touch the drum, creating drag you don't want.

--

Chris

[RP]

A couple thoughts on band brakes:

1.  Consider a large V-belt and pulley as the band and drum.  Self locating, designed for friction, already designed as a controllable, fairly reliable clutch system in riding lawnmowers, etc.

I think if you kept it out of the sun the belt should be good for 5-10 years in standby service.  I get 10 years out of them in my lawn equipment using them all summer.

2.  The way to keep the band out the way when not in use is to provide a female outer shell around the outside of the band and apply a slight pressure to keep it "pushed" out against the outer shell when it's not being pulled around the drum.

This is actually done in v-belt clutches to keep them from dragging when disengaged.

Hope this is clear

[windy]

RP,

Good idea! I have some C belt pulleys laying around. I'll have to look into this.

windy

[don1]

R P

  The V belt may seem like a good idea. When you talk about how long they last on your mower.  The difference will be that your mower belt is not always under friction. It cools as it travels between the pulleys. If my memory serve me write the horsepower rating on any given size belt goes up as the length of the belt increases because there  will be a longer distance between pulleys. To use a V belt locked in one position around a pulley as a break the belt may heat up very fast with no way of cooling. If your break is powerful enough to stop the mill quickly then it may last.

 I did use a v belt and pulley break on a cart as a kid and I soon opted for the drum break offered by Sears.

  Thats just my two cents worth and that an't worth much. have fun with it. Don