My 8th grade students are doing a VEX Swept Away Classroom competition with the local high school. I have students who built a rack & pinion lift but the height seems to be causing issues. It goes up very smoothly at first but then the gears start slipping and they fall. I’m thinking this is just too high for a simple rack & pinion and they need to re-design but thought I’d check here first to see if anyone has suggestions for them. I’ve included an image. Thank you!
That is a super tall rack & pinion lift, but the gears shouldn’t start slipping at a certain height. Maybe add some more support to it. Also it would help a lot if you reduced the weight of the “bucket” thing that carries the balls, this would probably be the best thing to do
With that design, I wouldn’t think height (within realistic constraints) should ever be an issue. The motor only needs to supply the same torque regardless of height. Meanwhile, the triangulation should keep the rack fairly vertical. What gear are they using for the pinion? I like using the metal 12-tooth gears instead of the plastic ones. It looks like they went with more teeth, which means less mechanical advantage. (I know mechanical advantage is trickier to figure here, but it’s not non-existent as some claim.) But are they using a high-strength gear? Also, I can’t see how it’s attached well. A photo from the other side, focusing on the area around the pinion could be handy.
Hmm… Could it be not a height issue but a specific rack or transition issue? Maybe one of the racks is worn down? Maybe two racks don’t quite meet right? Either would mean when the pinion gets there (not to a specific height so much as to the problem area) it fails.
Thanks so much for the suggestions. They are using aluminum for their bucket and have it as light as possible for it to still hold the football without it falling out. Tried other designs but they didn’t work unfortunately, just this one. They are using a 36 tooth high strength gear. I recommended the 12 tooth metal gear but they didn’t want to do that. I explained the mechanical advantage but they didn’t think it would make enough of a difference. I agree with these suggestions though - thanks guys!
@RuizK1 is the team using bearings (Vex Bearing Flat 276-1209) for their axle and how long is the axle?
When bearings are not used there is enough play inside of the holes on the side plates where the axle passes through to allow the gears to skip. They will also skip if the axle is too long. It will bow under stress and the gear will hop.
Metal 12 tooth and you shouldn’t have a problem with this lift. I’m ashamed that I know that type of lift so well but I’ve had a couple of these under my belt. You shouldn’t have a problem. Just please. For the love of all that is good in the universe, don’t do what I did and make a two stage or more lift with this mechanism. It isn’t that effective and not at all appealling to deal with.
It appears that the two metal slides are only connected by the rack gear on the front. This makes me think that the slides are becoming misaligned and the leading edge of your plastic slider hits the second metal slide and inhibits the powered part from going any farther up.