I'm not sure if this is off topic, but I have an arduino 2009 controlling a small 12V 1.1A electric motor that has a 3.0mm shaft. Does anyone know how I can attach a wheel/tyre to it to turn a lazy susan? The shaft seems perfectly round... Would soldering help at all?
You can get couplings for that, basically a tube with a 3mm ID and two grub screws. One end screws onto your motor shaft and the other to whatever you want to turn.
Have a look here
These are way too much for what you need but will give you the idea. I reckon any model shop would have something suitable.
For this sort of thing, it is also worth seaching the web for suppliers to robotics hobbyists.
You can get hubs like below. If you are a DIY type, you might make a hub from a piece of flat wood with thickness ~the length of the shaft. Drill a perfectly verticle 3mm (or a little smaller for a press fit if the wood is soft) hole in the wood for the shaft to fit into. Put a little glue in the hole then cerefully place the wood on the shaft. I've done this for quick testing of various setups to connect to round shafts (make sure no oil or grease on motor shaft). I try to use glue that will hold, but still can be removed if required. It is important to drill the hole straight to minimize wobble.
Does anyone know how I can attach a wheel/tyre to it to turn a lazy susan? The shaft seems perfectly round... Would soldering help at all?
Soldering probably wouldn't work unless you used a torch; you couldn't get enough heat to melt the solder otherwise, and using a torch would likely ruin the motor in some manner (demagnetize the rotor some, probably, depending on how much heat was applied for how long).
Your best bet is to find a plastic (nylon) or metal bushing that has an inside diameter equal to (or near) the diameter of the shaft; if you can find one somewhere in the range of 2.9-3.1mm, that would be perfect; undersized is better. Alternatively, get something close in size and drill it out to size (use a drill press with a vice to hold the piece).
After you have it fitting the shaft, drill and tap a hole perpendicular to the axis of the shaft thru the bushing. The tap will be to hold a setscrew or a small machine screw. You then want to figure out a way to attach this bushing to the wheel or whatnot; strong two-part epoxy (I prefer JB Weld, personally) is your best bet, but you might try other methods (drill and tap the end of the bushing for a screw, apply loctite?).
Then, use a file on the shaft to flatten one side of it. Once that is done, slip the bushing (and whatever is attached to it) over the shaft, and tighten down the setscrew against the flattened area to prevent rotation.
Thanks for the help. Right now I think I've sorted it out -- I'm going to try a piece of rubber tubing for now and see if that works. I'll keep you posted.