I just received my stepper motor with an easy driver today and I have to say that I love them. I got it all to work and even wrote custom software to control it! But then it hit me how do you mount the stepper motor to something and then this idea hit me. Its not a huge motor with only 2.4kg of holding torque so a nice thick plastic adapter will work. I figure that a single plastic part can be cast with a flat face with holes for mounting stuff and a 5mm hole in the center that is 1.25 inches long to attach to the shaft. Since the torque isn’t high epoxy can be used and with more than .75 square inches of surface area on the 1.25 inches of shaft the epoxy will have more than enough surface area to bond to. Sparkfun already makes the laser mount for the slim laser module that they carry so why not throw this in!
In the end I tried to make it as simple as possible to install, no threading the motor shaft, drilling holes ect… You simple put epoxy inside the adapter and on the shaft then slip the adapter onto the motor shaft and wipe away the excess epoxy then you wait for the epoxy to fully harden and voila.
Here is a simple model that I made in about 10mins to show what I am thinking of.
Except for one small problem. Epoxy doesn’t really bond, or stick to anything, and requires mechanical keying to stay attached. Just try freezing something like this after the epoxy sets, and you will be able to break it loose quite easily (actually, it will have been broken loose already due to the forces created as a result of the temperature change). I made this mistake once, and I was dealing with far larger surface areas than you are considering.
That being said, you may find that silicone would work better, as it has pretty good surface peel strength, and enough flexibility to stay attached.
That’s assuming you put the epoxy through those rapid temperature changes. I have two small sheet metal parts glued together with epoxy and I tried every hand tool, pliers, a screw driver, a hammer, and even a combination of them with it clamped in a vice to try to split them. Today those two pieces of sheet metal are still glued together!
I am going to build a prototype of this adapter, I would have started it today but my hobbyshop was closed. Before I glue it onto the shaft I will get some silicone and epoxy and then test them to see which one is better.
It is not about the temperature changes, or the rate of change, as much as it is the bond geometry. Epoxy will shrink when cold, or expand when heated, by a large amount compared to steel, which can create large forces with only a small change in temperature. On a flat plate, this doesn’t matter much, as the epoxy doesn’t come under tension, though it will come under shear forces. But, in a cylinder, if the epoxy shrinks more than the surrounding plastic (and it may not), it will pull away from the plastic wall. At the very least, you would want a non-smooth surface for it to mechanically key to.
Yes the epoxy was mixed correctly, and the mix ratio was determined by weight, as per the manufacturer’s specifications. Check out www.westsystem.com for an excellent supply of epoxy, and for some good technical articles.
Its made from 1.5mm sheet styrene and 1/4in styrene tubing. I cut 5 disc out of the sheet and put them together with epoxy to form one 7.5mm thick disc. Then I inserted the tube right before the epoxy set and glued that in. It then dried for 30 minutes (this is 60 second epoxy) and I sanded the excess epoxy with a belt sander then smoothed all the plastic out with an orbital sander. After that I made sure it worked good and it did then I drilled holes and painted it with flat black paint.
The adapter is not epoxied to my motor and I don’t think I will do that because the fit between the shaft and the tube is very tight. If I put 1 layer of tape over the shaft that alone will give it a lot of holding power. Obviously it won’t hold up to high torque loads but this way its easy to remove. In the future I need to add a support between the top with the screws and tube like a cone don’t get me wrong it feels solid right now but that is a weak point.
I will make another video to show the adapter working but for now I have some pictures of it so enjoy!!!
In the future I will have videos featuring this motor and adapter like robots and my other projects that I do! So stay tuned, I am also thinking about making a tutorial for building your own!
