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2) all the axles use differentials, so one motor per axle, not four independent motors, which makes the motor encoders not know which wheel is slipping
If that's your only worries about diffs, just use wheel encoders
I looked into that, but it has several draw-backs that don't work for me.1) A differential means that if one wheel slips, the axle doesn't drive. If the robot has the left side on a slippy thing (or hanging in the air while the bottom is grounded,) then the right side won't drive at all. Not good.
2) I have not found any wheel encoders that are sealed and would fit in the kinds of wheels I am using. I have found some very expensive hardware, and I have found some affordable, but non-sealed and non-robust hardware. This robot will run on soggy, dirty, lawns and probably romp over flower beds (entirely unintentionally of course) so, for example, the Parallax wheel encoders aren't quite enough.
So, given that I have some parts already, and would like to learn the mechanics of suspensions a little better than "I know next to nothing," are there any mechanics-like ideas that come to mind?
One very rugged method is, to use a (steel) spur wheel and a Hall switch and the only way that would give is, if you were running it over endless amounts of iron dust.
Study the wheel suspension on older race cars where the wheels are a bit outside the main body, hanging in two "A-frames" for ideas.
One way to make sure things will fit is to turn the axle yourself, but that's dependent on access to a lathe. You did say you wanted to build every part if you could, right?
I ordered some .125 steel rod and some 1/8" inner diameter flange ball bearings. However, the bearings don't fit on the rod. Measuring with calipers, I get the rod at .125 spot on but the bearings at .115" inner diameter. (Calipers are not great for this measurement, but this was as good as i could get)Is this an expected result?
Given a little roughness, you may need to cool the axle a couple of hours in a freezer, while heating the bearinga bit - say to ~45°C - don't go much higher, or you'll damage the lubricant.