I’ve been wondering how much help bearings provide in reducing friction in lift systems.
A bearing usually requires a spacer (one of the small black ones or the nylon spacer) to make way for screw heads on each pieces of metal.
Without bearings, all that is necessary is a single teflon spacer to make sure metal doesn’t rub against metal.
What I am afraid of is that the extra space required between joints for bearings might make it easier to either bend screws or put a lot of stress on the joint, causing the bearing to be less effective. Also, bearings add a lot of weight (I had over 200 screws (plus 200 nuts) and 100 bearings for my scissor lift).
Many successful robots (400x this season, 9090c and 26 in toss up) have had lifts without bearings (especially those with scissor lifts) in past years. To those who have experimented with both, what do you think?
Although I wish I knew the answer to this question, I dont.
We tried using bearings on our scissor lift at the beginning of this year, but as you mentioned, I didn’t like having to use spacers at every joint and I ended up losing a 1/2 pound in screws when I pulled them all off.
That being said, I plan on going back to bearings to see if I can reduce some of the friction and slop in our lift. I feel like the extra weight can be accounted for in elastics and as long as you use white spacers instead of the black ones (Larger diameter, more surface area against the metal) you’ll be fine.
In my own opinion, I think it’s a trade-off. Bearings force you to use spacers and add weight, but they reduce slop and friction at the same time.
I haven’t used Shoulder screws in years, but I vaguely remember being unimpressed… I’d have to revisit that before I pick a side:confused:
Well in my opinion, I would definitely use bearings!!! First of all, using them reduces friction on motors. You definitely don’t want to burn them out. Also you don’t have to put in a screw on both sides of the bearing, just put one screw in one side, it works just as well to hold it in, but loses some weight as well. Plus, by going metal to metal it will eventually wear out the metal pieces the axle is sitting in, making the axle able to move around with some freedom. I think it is worth the little bit of weight to make sure everything is smooth, and frictionless. Plus, how is a half a pound going to make a difference?
With the 2 stage scissor lift we had in Toss Up, we were perfectly fine just sticking a screw into each joint–there was definitely slop originating from each joint, but there were so few of these and the lift was short enough that this wasn’t an issue.
With 3 and 4 stage scissor lifts, I find that the formerly inconsequential amount of slop is magnified greatly by the sheer height of a 6 ft lift and the increased quantity of joints. I would recommend (this season at least) that some sort of slop reducing measure is taken on these joints…
My current lift, a 4 stage scissor lift (surprising I know) uses piles of bearings. (First competition this Saturday, maybe a teaser soon ish?)
Although, don’t let this stop you from using shoulder screws–my decision was simplified by the fact that we didn’t have enough shoulder screws on hand. We’ve tried them several times, I think shoulder screws can also work quite well if you “do it right”.
Shoulder screws may be a bit tight in the square hole and not allow as much turning as a bolt or square shaft.
The shoulder is metal against metal. That has a higher coefficient of friction than plastic. Nylon and teflon washers are the ones with the lowest coefficients of friction.
Using Nylock nuts on bolts can make for a semi-loose axle where if you don;t tighten it down completely the screw based axle will turn nicely.
Without the bearing block you gave more wiggle room. As was stated, that makes the lift have additive error as you get higher up. 5 feet at a few degrees is a pretty far offset/error versus at 2 feet high.
Keep it tight, but keep the friction low. Have fun with that!
(3 months was the build and optimization time for 80N back in Gateway for a 72" scissor so don’t despair after a few weeks)
We have bearings on each single joints of our scissor. So far they do seem to help a lot. Because we have extensive amount of elastics, the joints are held particularly tight and we are now satisfied with the low friction.
However, we do have a pretty different scissor design, much like team 8192 in gateway. The design has nice stability, so we are satisfied with the small black spacers so far. White spacers are great but so expensive…
This year, because the lifts are so high, we are using bearings on our lift to increase the stability. For us, the screws used in the joints on our lift can move around, which, when existent on every joint on our lift, renders it extremely unstable, so bearing flats help a lot.
My team uses bearing where ever there is an axle. we use two or more per axle depending on how many supports we have for that axle. for your weight problem of using screws with nuts try using the plastic pop rivets instead they are lighter and easier to put on then screws.
