Author Topic: How to do a "brake" for an axis?  (Read 1976 times)

Offline CrazyModder

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How to do a "brake" for an axis?
« on: August 01, 2016, 07:10:19 PM »
Hello,

I have a lever which controls an analog axis in a DIY HOTAS project (like the throttle of an aircraft). So far so well, everything works just fine. I just have trouble getting it to not flop around too much. You see, I'm good at making axes rotate easily, not in artificially making them resist movement. :)

To put it in more technical/mechanical terms: there is a 8mm axis, supported in ball bearings, that is turning quite easily right now. I want to somehow brake it so it still runs smoothly, but needs a noticeable force to turn at all. It should stay where I put it (even with its own considerable weight plus that of my hand resting on it), and when I turn it, it should have as little stick-slip https://en.wikipedia.org/wiki/Stick-slip_phenomenon as possible. It should turn buttery smooth, just with resistance.

My current solution is to clamp it between two pieces of material with some bits of jeans fabric glued on. This ... kind of works, just not very well. Hard to adjust, and seems to get less tight over (not too much) time.

Is there an "official" and/or more intelligent way to do something like this?

As for space constraints: there are a few free cm in every directon around the axis, not too much, but not too tight either.

Thanks for any hints!

Offline sparky961

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Re: How to do a "brake" for an axis?
« Reply #1 on: August 01, 2016, 10:33:29 PM »
Can't quite picture what you're doing but two ideas for controlled friction are some sort of heavy/sticky grease between plates, or a tight fitting UHMW plastic sleeve, maybe with adjustable tension.

Pictures would certainly help.

Offline David Jupp

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Re: How to do a "brake" for an axis?
« Reply #2 on: August 02, 2016, 03:02:01 AM »
Maybe add springs to your current clamp arrangement, to allow some take up for wear or thermal expansion.  Friction dampers like this used to be used on cars before hydraulic dampers became the norm - a bit like a disc brake, but set to 'drag' all the time.

Offline CrazyModder

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Re: How to do a "brake" for an axis?
« Reply #3 on: August 02, 2016, 03:21:22 AM »
a bit like a disc brake, but set to 'drag' all the time.

Yeah, like that. I actually thought of making a miniature disk brake (with a disk), but am nowhere near able to achieve the necessary precision, and the whole setup would be real engineering overkill.

Springs sound good. Also, overnight I had the idea to replace the current plates with a simple slotted slightly oversize 8mm hole which is cloth-fitted all around; with some hefty springs that should be promising. I'll see what I can come up with.

sparky, thanks for the input; I'll also see if I can find some slippery but tough plastic peace lying around (in fact, I may have some of these self-lubricating sleeves somewhere that are used instead of ball bearings for low loads/speed), it should take the hassle out of glueing fabric into holes ;). Regarding photos - just picture an 8mm steel rod turning very slowly, there isn't much more to it.

Offline Joules

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Re: How to do a "brake" for an axis?
« Reply #4 on: August 02, 2016, 03:52:27 AM »
Or maybe

http://madmodder.net/index.php/topic,11577.0.html

It could just as easily be spring loaded pads.
Just get doing and make swarf, you can decide what its going to be later.   :thumbup:

Offline mcostello

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Re: How to do a "brake" for an axis?
« Reply #5 on: August 02, 2016, 09:45:52 AM »
Belleville washer or 2 should solve the problem or a cork facing.
High Speed steel in a Carbide world.

Offline Manxmodder

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Re: How to do a "brake" for an axis?
« Reply #6 on: August 02, 2016, 11:25:39 AM »
Helixes aren't always downward spirals,sometimes they're screwed up

Offline tom osselton

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Re: How to do a "brake" for an axis?
« Reply #7 on: August 02, 2016, 02:35:57 PM »
I would think some cork that is spring loaded it worked fine in the old motorcycle clutches.

Offline chipenter

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Re: How to do a "brake" for an axis?
« Reply #8 on: August 02, 2016, 02:41:16 PM »
Add a gland and fill it with PTFE plumbers tape self lubericating last well on my steem loco .
Jeff

Offline Noitoen

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Re: How to do a "brake" for an axis?
« Reply #9 on: August 02, 2016, 03:14:29 PM »
Make a disk out of copper 1,5 mm thick and use a pair of hard disk magnets just like it was a disk brake caliper as close to the copper as possible. you will bee amazed with the drag it creates. I think some "vent" holes around the disk also changes the amount of drag. This is caused by eddy currents generated with in the copper when it moves in the magnetic field.

Offline CrazyModder

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Re: How to do a "brake" for an axis?
« Reply #10 on: August 02, 2016, 03:46:40 PM »
Thanks for all the hints, guys! Keep them coming, although you spam them way faster than I could ever try to test them. *need more man-cave time*

Make a disk out of copper 1,5 mm thick and use a pair of hard disk magnets just like it was a disk brake caliper as close to the copper as possible. you will bee amazed with the drag it creates. I think some "vent" holes around the disk also changes the amount of drag. This is caused by eddy currents generated with in the copper when it moves in the magnetic field.

Sounds like a fun project, I guess I will have to start to actually dismantle the last few of my old HDDs (no magnets inside SDDs that tend to fill my PCs these days :) ). Bbut I guess that when the axis it's not rotating it will provide no "holding power".