# Question on centrifugal brakes

1. Sep 15, 2007

### enkiduz190

hey guys, i was wondering if any of you know the general values for the friction coefficient as well as the mass of the brake shoes and the spring constant for the centrifugal brakes (i know there are probably all sort of values, but please just give me a general rough estimate)? The brake is gonna be incoporated in a weight lowering mechanism of about 1000kg.

i tried to search for it, but cant find anything, so if anyone has knowledge in this field, please give me a rough estimate on the values, really appreciate it.
THANKS ALOT!!!

Last edited: Sep 15, 2007
2. Sep 15, 2007

### Danger

Welcome to PF, Enkiduz.
I won't be able to help with any calculations, but I just want to clarify what you mean by 'centrifugal brakes'. I've never heard that term. Do you mean some sort of automatic system such as the 'flyball' governor on a steam engine that stops something when it goes too fast?
In any event, the sort of mechanical device involved would make a big difference to the numbers. While you mentioned how much weight is involved, we don't know what mechanism is doing the work. For example, is it hydraulic, or pulleys and cables, or...?

Last edited: Sep 15, 2007
3. Sep 15, 2007

### enkiduz190

http://science.howstuffworks.com/elevator5.htm
the braking system i am working on is very similar to the one they have in the diagram, except that instead of using a hook, the centrifugal brakes uses brake shoes and brake pads to stop the rope drum from rotating when it goes too fast.

the braking system i am working on works like this:
the rope drum have cable which connect the lowering platform, if the platform falls too fast, then the centrifugal force will force the brake shoe and the brake pad out, thus stopping the rope drum.
i hope this provides more information as to what i am looking for. thanks guys

4. Sep 15, 2007

### Danger

I know what you mean now. I've never seen that sort of elevator safety before; I'm more used to the ones that clamp onto the side-rails.
So your idea, it would seem, is to have the same governing system as the one depicted, but with less 'g-load' upon braking. That's a pretty cool idea, and I wish you the best with it. Unfortunately, that doesn't imply that I can help you.

5. Sep 17, 2007

### mgb_phys

It's a common system on things like mine cages - usually as an emergency system if the motor controlling the cable drum fails.
The problem with using it as the sole speed control is that the brakes heat up and so tend to expand, so putting in more braking force and so more heating - and so on until they seize on.
For lighter load systems like autodesceding abseiling lines you use a fan rotating in a housing and let air ( or oil ) resistance slow it down so it is easier to dump the waste heat.

6. Sep 23, 2007

### enkiduz190

Thx for the info, i will now modify the design accordingly.