My Advanced Mechanics & Motion Kit just showed up today, and I thought I’d post a few details and my initial impressions for folks that don’t have them yet.
These have set screws on both ends, which are needed for stability of the joint. They appear to be good up to about 45° off-axis. They seem fairly strong, though they do have a bit of play. If you need to transfer power through a variable-angle joint, these are the way to go. Even for fixed-angle joints, these will be simpler and possibly lighter than using bevel gears.
Each segment is about 1.175" long with 6 turns. That makes the pitch about 0.196"; about 0.2" of travel per turn. At this pitch, it appears to be very hard to back-drive, so holding a position under load might not need an active control loop.
You loose one turn in the nut, so the maximum travel will be about 1.175" x segments - 0.196". The kit comes with four segments and one nut, which is enough to make a 4.5" linear actuator.
They have surprising little play given how smooth their operation is. Friction is very low even with significant axial load (pressure in-line with motion). Torsional load (twisting the nut off-axis) will make the friction go up noticeably, so make sure the structure being moved is constrained to the axis of the lead screw (e.g., use the Linear Motion Kit). Operation seems very smooth even across the segment joints - I wasn’t able to feel where the joint was when moving the nut by hand.
These are pretty much what they look like. The handle is offset from the axle by 1.5". The whole thing is molded as a single piece of plastic, so the handle does not free-spin. Neither the handle nor its central hole is a standard Vex diameter, so there aren’y many attachment options other than elastics. I think you could tap-drive a 6-32 motor screw into the handle if you tried, though. Could be fun to use these with the worm drives above to make a model milling machine.
16t & 32t Bevel Gears
These are similar in design and construction to the 24t bevel gear used with the differential. All these bevel gears seem to mesh reasonably well with each other, which means they can provide power transfer across a variety of angles. The pitch angle between the new 16t & 32t gears appears to be close to 22.5°, whereas the 24t bevel gear’s pitch angle is 45°. This should allow combinations at 135°, 112.5°, 90°, 67.5°, and 45°. I’m not sure how practically useful all these combinations are, but it does open up some interesting options.
Cams and Followers
The cam followers offer about 2.9" of travel, and have the same type of self-tapping holes that the new linear motion trucks have. There is no clearance between the follower and its mount for nuts, so you have to use screws that don’t protrude out the back, or travel will be limited. It seems like these could be used as a light-weight linear slide for short travel (perhaps in conjunction with the worm drive?).
The cams themselves are pretty much what they appear to be in the picture. It would be nice if Vex posted a function or graph showing the cam’s shape (hight-vs-angle), since it isn’t exactly linear. It seems to flatten out near 0° (the drop off) and 180°. One potentially useful result of these flat-ish spots is that you can mount the two cams back-to-back and the resulting union of the two profiles looks much like a pear cam or an eccentric cam.
Each cam has two of the axle inserts that the high-strength gears use. They can be removed if you need more inserts for your gears (or if you want to fit the cam to a 1/4" square shaft for some reason).
High-Strength Worm Wheels
What can I say - it is great to have these in-hand now!