The problem with the linear motion kits and parts are that since it is just plastic rubbing against metal, excess friction, and binding can and will occur. (very well know problem with vex linear motion).
I know there are many ways to use bearings and/or wheels to reduce friction including systems in drawers. I’m wondering how plausible it could be to have a part similar to the green slider in kits today, but with a bearing cage on the outside to reduce friction. it might also be nice to be a little bit longer. would it be too expensive, heavy. the bearings would be unable to get out of the cage but be sticking out enough to roll against the inside of the same or similar steel slides. you could then attach everything the same way as if using the old kit.
is it not reasonable?
too complex?
more problems?
do any official personnel have anything to say? I would love your input!
I am really interested in this idea and want to get as much feedback as I can about it!
Green Egg built something along the lines of what you suggesting during gateway with their expanding bot. They used the nylon bushings as rollers and 5 wide c channel with some bracketing to get it to work.
I like the idea of some sort of change/modification to the linear motion kit. Personally I would have preferred that they left the slides alone…the older set seems to be more useful.
I do see the goal they had in mind with the newer plastic truck style sliders, but it seems they have proved to not be very high quality for two reasons.
1.) Friction, friction, friction. I thought the metal on metal sliders were loaded with friction. But if the plastic truck has ANY force acting on it that isn’t perfectly linear…FRICTION.
2.) I don’t like the self tapping plastic holes. Students are way to likely to strip them out, making the trucks completely useless in most cases (and of course you can’t buy just the trucks).
In the end I’m not sure if I want VEX to dedicate their time to designing a linear motion kit…or if students should design their own creative ideas (like green egg robotics).
Here is an idea for linear roller system:
For a track, imagine a 1x2 C channel, crimped from U shape to C shape: insert a 0.4x0.9" iron mandrel and crimp the edge uniformly over the whole length.
For a roller, imagine the tank-bogie wheelset or the winch pulley riding on the crimped edge.
Since the v-notches every 5 spaces on the C channel are now dents in your rolling surface, cut uniform v-notches all along the edge (like rack teeth) and notch the rollers into gear teeth to match them, and make the axle hole square. Now the rollers can be connected with an axle to keep both sides rolling together at the same time, like a herman-miller-brand office shelf flipper lid.
Left drawing shows top view of nested vertical slides (ala jpearman cascade linear lift), only top front roller shown. Brown C are stage2.
Use 2 pair of rollers for each stage, one pair rolling on each edge of C, to provide the ‘length’ of the slider that keeps the moving part from rotating away from the track.
Right drawing shows that each roller only rolls on one edge of C. Upper stages of sliders are tilting forward, held from flopping forward only by the moment arm of the distance between these two pair of axles. The edges of the two rollers can touch and roll against each other, since the front/back rollers rotate in opposite directions. https://vexforum.com/gallery/files/1/5/6/8/_182541.jpg
Need some care to allow rollers to pass by screwheads inside the track that attach to the next level of slider. Without the C crimp, its hard to avoid these obstructions, and hard to keep the rollers contained.
C-channel (without V notches) is generic and multi-purpose, but would be confusing to stock compared to the U shaped ‘c-channel’ available now.
Smooth rollers with setscrews/locking-clamps are generic and can also be used as rope pulleys or axle spacers or other motion hw.
There are commercially available linear bearings out there with brass nuts embedded in them. This fits in a track that is a C versus a folded angle like vex sells
There are other styles out there with roller bearings in tracks. So maybe a new part that was the truck with inner or outer roller bearings as one product and another being the plastic slide with brass nuts embedded in it.
The track is one element while an expanded choice of slide trucks would expand the design opportunities.
I like this idea. The metal part of the linear motion kit is fine. Maybe VEX could just design some additional trucks made of different material. This seems like an affordable modification to an existing part that would not be overly difficult for VEX to implement.
The metal rails are fine, but could be better. For one, they are heavy because they are steal, but it might be difficult to make them much lighter as aluminum would be difficult to use for this. Also, the slides do pop out of the rails when under a very large amount of force, so more of a closed shape like Team80_Giraffes posted can be useful.
Igus gives away parts to robot teams.
For an off-season non-compete project, you could get a bunch of Igus linear slides, and see if they work any better. Any BEST Robotics team or Hub might have extras to give away as well.
exactly what I was thinking.
this would work better and be easily implemented. I think they at least have to put brass nuts imbedded in the sliders instead like the rack gears do.
Your manufacturing goes from one hole straight through to a precise drill part way down (maybe it’s in the mold of the plastic truck).
The brass part adds a bit of cost to the part too. Hopefully those are not that expensive. So anywhere from a few cents to a few dollars more per part.
Soooooooo…
With all this talk about any commercially available nut being legal, could you get those brass nuts and drill out some green slider tracks yourself? I think so! It’s an 8-32 thread.
You will notice the flange on the end of these. That holds on to the plastic from the bottom and the surface area of the flange against the plastic keeps it in place. You “counterbore” it or “spotface” it so the flange gives you some room to hold the fitting in place. (a countersink is apparently at an angle) The main force it will help with is the tension force of the screw tightened into the nut. It’s kind of like the head of a screw against the piece you attach it to. That surface area is pushing against the material helping hold it in place. In this case you went into the material to get that surface area.
See this document for more details about screws and how they hold
Pages 9-10 show the counterboring.
Page 15 of this document talks about the clamping force on the screw. It’s pretty good overview of screws and the forces you get on them.
I doubt it. Based on what Karthik said these would not be legal at all. He restated the “ANY commercially available nut” rule to basically being any nut that is a common replacement of a standard VEX part.
I’m not particularly happy about how the rule is now basically irrelevant, because it is no longer true that “ANY commercially available nut” is legal. I hope they fix this for next year.
This cost us a Skyrise tournament final final match… although we would have lost anyway. Elevators in Skyrise demonstrated this very well. Linear slides just pop out.
