Does anyone know where we can buy a 1/2" hex shaft coupling that can accommodate slight misalignment?
Something like this Lovejoy coupling, but with a hex bore instead of a keyed round bore.
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Hex is rarely used in industry, so unless a FRC supplier sells it, you’re likely going to need to machine it yourself (e.g. by broaching).
Whats the use case for this?
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Define slight; a lovejoy coupling is for dealing with things we simply don’t deal with in FRC. Get a hammer, make the bearing hole oval, or machine a new part.
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Machine hex shaft to round. Add keyway if necessary. Use a round shaft coupling to make the connection.
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We’re connecting two hex shafts on opposite sides of our robot. Of course we’ll try building them as square as possible but in the real world there’s always some misalignment. The best way to accommodate that is with a flexible coupling. Otherwise you can get binding and wasted energy.
Andymark sell 1/2 female hex spacer stock. It is a pretty loose fit. That will allow for a small amount of misalignment. It will only work if you can tolerate the lost motion that comes with the loose fit.
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If you absolutely have to connect two separate independent shafts mechanically, this is absolutely correct - you shouldn’t try to support a pair of shafts in several different places and expect excellent results, and a flex coupling is one of the only ways to go. As others have said, the bad news is that this is largely not seen in industrial uses and you’ll have to modify existing parts.
Ideally I would… not do whatever you’re trying to do. If you actually must do so, then maybe buy a hex broach and add a hex hole yourself to an existing COTS product. If that amount of manufacturing is too much for you, this task just may be too complex for what you are trying to accomplish.
Are there other, more novel ways to transfer power to two mechanisms on opposite sides of your robot? For example - let’s just say you’re trying to retract two telescoping arms in order to climb (this is just the only relevant thing I can think of). Instead of linking two hex shafts together to drive two pulleys, could you route your cabling in such a way as for both cables to connect to a common drum?
That’s a good suggestion, but not practical for our specific application.
Unfortunately our expert machinist mentor dropped out his year, so we’re trying to keep our designs simple. However we do have a few parts (like a broached coupling) that will require skills beyond our capability. I think we’ll be able to find a machinist volunteer for those few parts.
This is a pretty good “hacky solution” that in the lifespan of a FRC robot is probably sufficient. I like it
Every robot I’ve made in the last few years has had a hex shaft going from one side of the robot to the other. Unless the two ends are grossly misaligned, the flex in the hex alone will be sufficient.
The suggestions to use the andymark hex spacer tube are also good.
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In my experience, hex shaft is pretty forgiving.
If you have to bend it slightly, it will probably be okay. You could open up the bearing holes slightly (with a deburr tool or a step drill) and have the bearings slightly angled.
I know how tough it is to get hex shaft across an entire robot. A rubber mallet is your friend sometimes
Also- could you create 2 new supports on either side and put the hex shaft in first, then bolt / rivet it down?
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Thanks for all the clever suggestions. I think the AndyMark 1/2" internal hex spacer stock will work fine for our needs.
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The sneaky way is to assemble the shaft with the mounting bolts LOOSE so that you generate the alignment you need, then tighten.
For hacky solutions, buy some fiber reinforced rubber hose. Bevel your hex shaft ends, shove it onto your hex and clamp with a couple of hose clamps. Instant flex coupling! Somewhat limited torque capability and some level of wind up/torsional softness.
With a better idea of what things look like, you might get some better suggestions. In our robot shown below, we have 7 shafts spanning the width of our ball handler - about 12” side to side. (And before people jump on me - we haven’t gotten to adding the chain guards yet!)
I was far more concerned by the plastic’s protective paper being left on but 
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It’s been peeled where it needs to be peeled at this point. It’s called “protective paper” for a reason - it’s still protecting the finish of the polycarbonate while we finish up the work 
And here I was hoping you were actually testing with cardboard!
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Is there a reason it cant be a. Single hex shaft instead of two
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