any advice for the rubber bands on a scissor lift? where to place them?
I have learnt to place them far apart on the x so they give more even pull as it lifts.
Also, should I have them equally distributed on all of my four x-s?
It seems as though the (Planetary geared) scissor lift approaches a point, really close to the bottom, where the motors are loaded alot. At this point exactly, I have observed, is when the top x is just barely affected by the bottom x. (due to the slack in the lift) (Like, before, the motors are ‘compressing’ only the bottom 3 x-s because of the slack in the system) Since all the x-s are suddenly engaged at this point, the torque required at that instant is very high.
Any advice to minimize this with elastics?
The “slack” you mentioned was fixed on my bot by using 2-4 bearing blocks at every connection on the lift. Also for tension with rubber bands or elastic, i doubled the rubber bands (or had elastic tubing so it has no stretch when fully lifted) and put them at the top/bottom of the X’s so they are a maximum distance apart. As for equally spacing the elastics: it can help. it wont fix all of your problems, but it should help with some of the slack issue.
Hope this helped! if anything is unclear, just ask or message me.
Yes, you are correct and it is normal that slack will build up in the sections, especially at the beginning of moving. This is mostly because the most force is needed when the lift is all the way down.
Elastics/Latex Tubing will help a lot, especially if it spread out. You want them to pull on each stage, so it evens out more. Another thing that can help is spreading out the stages your motors are on, placing them higher up or on multiple ones.
And, if you have the height lift well below 18", make it so the stages don’t go down all the way, this will help you a lot, especially as you need less motor power at the start.
I think by 2-4 he meant to stack 2 bearings in top of each other, but I would not recommend that because it will be very hard to align them, and the increased friction from misaligned bearings will outweigh any small advantage.
Keeping it stretched is one key element. Keeping a good long stretch throughout the lift can be tricky as it rises. Search on the forums for some force curves on the rubber band and see that they have good pull force at a certain distance and practically nothing below that. Some cal tech class was the link. So placement is key and it may not be what you think. Doubling up/folding over the rubber bands to keep a stretch distance throughout the motion can help.
Having rubber bands on both the inside and outside of the scissor will help prevent the bands from bowing the scissor and causing stresses in that plane.
Rubber bands at multiple levels will make the difference in growth among levels less.
Try and not place the rubber bands on the joint axles/bolts. You will only cause a bending stress on them and hurt yourself in the long run. Using the first tip may make you move the bands from there anyway.