And so, a couple months ago I came down with a (tiny) fit of organizing fever and cleared up a small portion of a pathway in (one of) my massively parallel parts storage areas. I found some crappy motors I had gotten (cheap) from a surplus place that I had attempted to make into a 2-d swinging robot arm, to make even some small progress on the big proposal.
They didn't work worth a damn:
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| picture of crappy motors |
But, out of curiosity, I found a sketch of my intentions in an old notebook from 2014 (where you can clearly see why I do not practice drawing and painting as a profession):
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| picture of robot arm crappy drawing |
I got to thinking that maybe I could re-start the whole project by actually spending money to get motors and components that might work. (Over this course I realized that I could spend $200 on oysters and gin and have a fine time with friends for an evening, or I could spend -- well, more, but in the ballpark -- on motors and gears, and get in a week or two of mostly enjoyable fiddling around before discovering that things weren't going to work; so, bang for buck over hours this is a way more economically efficient alternative.)
There ensued a couple weeks of web surfing trying to figure out what "hobby servo" motors to get, even though I already have about 50 random ones.
There are a number of vendors.
Each has around 100 choices.
The choices are mostly incommensurate.
Comparing across the sources, and sometimes within a single source, is problematic. Plus there are around 10 different output shaft "spline" configurations, that are often not even specified in the literature. I finally realized that I had to stick to one source (servocity.com, the high price spread, but has reasonably complete spec sheets). And this lead me to realize that I had only two choices of splines because they were the only two that had available matching gears to be attached. So I got an assortment of the highest power motors with the same matching splines, and a buncha gears:
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| servo boxes |
Then, waiting on UPS Ground cheap(er) shipping, I thought I would just go ahead and design the mounting brackets and all. Thus I found that not even the motor manufacturer has mechanical drawings of their products (I did find one 3d rendering of one that I could rotate around in virtual space, which was kinda fun). Of course, one of the main things one wants to know when designing mounting plates for geared mechanisms is: How far is the output shaft from the mounting holes?
So. After the motors arrived I managed to measure and estimate the necessary and the gears seem to mesh OK. Just in case, here is my DXF drawing of the Hitek HS-225, HS-645, HS-755, and HS-805 motor mounts from which you may be able to extract relevant measurements. These are laid out to mesh two 32 pitch gears:
- 40 Tooth 1.250" Pitch diameter C1 Spline mount on the motor
- 20 Tooth 0.625" Pitch diameter plain bore on the mating arm
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| image of DXF for scale |
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