I would like to mount the 37D motors at a 90 degee angle from the weels they are driving (one motor per wheel.)
It seems that miter gears with 6mm diameter and set screw would be the right thing to use.
However, I can only find really expensive gears (no doubt very nice) from high-end machine part shops.
Do you know of any other source for miter gears that fit your gear motors? Or some other solution to make a 60-90 degree elbow? Perhaps you’d like to carry some as parts yourself? 
Hello.
Parts like that are something that we would like to eventually carry, but we don’t currently have any plans for getting them. McMaster-Carr, Quality Transmission Components or SDP/SI might have something that will work for you application. One of the big factors in the cost of the miter gears is the material, so you might look into nylon gears as they tend to be cheaper. You could also look into the bevel gears they use for RC car differentials. They might require some modifications, but they are generally more affordable.
Please let us know if you find any interesting solutions.
Grant
Thanks, Grant. I’ve looked at McMaster, which only has imperial sizes, and SDP/SI, which has bevel gears with 2:1 or worse ratios in plastic, but no suitable size miter gears in 1:1 ratio. Which means I’d have to go brass or steel, which means $25+ per individual gear.
I also looked at RC car gearboxes, but they generally use 3mm bore, with not enough clearance for the 6mm I need (and getting 6mm press fit out of injection molded RC gears would be… challenging.)
If this was the kind of thing that the world needed 10,000+ of, then doing a mid-size run for them would bring down the price significantly, but it seems the start-up cost for each individual size is significant… And I can’t find an affordable manual gear hobbing machine on eBay, either
I had looked at quality transmission before, and they have one gear that comes close, but it’s not set screw based, which makes fitting it on the D-shaped drive shaft harder. (But “harder” is better than “impossible” 
I am not sure if this would fit your application (it sounds like you are looking for a 1:1 ratio), but I have one of these hpi racing bevel gear sets. They don’t provide very much information for them on their website or where I bought them (Amazon). However, I measured them and found that the larger gear has a 6mm hole, and the smaller gear has a 4mm hole. I don’t know of a good way to fix them to a shaft, but they might be able to be fixed using epoxy. They are made of metal, but I am not sure what kind of metal they are made of.
- Grant
Interesting; thanks for the note! I had looked at them on Amazon but because there were no measurements, I didn’t want to try them unseen. I’m a bit bewildered by all the RC parts that just say "fits on " without any real dimensions…