Help with rubberbanding my DR4B

I could use some help or some advice on how to place rubberbands on my double reverse 4 bar. I just cant seem to figure it out

Can we get a pic of how you’re doing it now?

15641665577633317720529883200941 15641666328186157605344737898733
So i have a few alignments i need to make but i have been trying and i just cant seem to figure out how to get these rubberbands on right

I also have alot of play on the upper section and i also could use some suggestions on how to fix that… Thanks!

The play can probably be fixed by properly bracing the two c channels that are around the gears together, not just having it held together by the collars on the axles. maybe secure them in a fixed position with another c channel going across or some standoffs.

Ok ill definitely try that… Any suggestions on how to put rubberbands on it? I just cant seem to do it right

Your pulleys are correctly placed, the only reason you might have issues with banding would be their ability to rotate freely. You’ll need to put quite a few on because the lift uses some steel. Consider using the aluminum from the bottom tower on the lift to reduce weight (unless you aren’t allowed to/can’t cut it)

1 Like

Ok… I just checked and sure enough i cant even rotate the pulleys… Thanks for the help and well see if that works. Thanks!

While pulleys being able to rotate is a good idea, the current placement of those pulleys isn’t correct. Here’s a quick drawing I made to illustrate how you generally place rubber bands on an rd4b lift.
rd4b
The black pieces are the towers, the red pieces are the arms of the lift, the blue pieces represent pulleys and yellow represents rubber bands going between pulleys.

The pulley placement isn’t optimized but it gets the general idea across. The main idea behind putting rubber bands on a lift is that when the lift is all the way down the rubber bands should be stretching the most and thus pulling their hardest which makes sense because when the lift is down all the way the motors are having to exert more force to pull the lift up than at any other point during lifting (usually, at least). Then as the lift goes up the rubber bands should be stretched less and less, the idea being that the rubber bands exert the least force on the lift (pulling it up) when the lift is at the top of its motion which also makes sense given that the only place for the lift to go after it reaches the top is down (unless it breaks :stuck_out_tongue:).

Hope this give you a (very) general understanding of how rubber bands are supposed to work and why. Good luck @churchy475!

edit: sorry about all the wasted space in the drawing. It’s been a while since I’ve used paint lol.

4 Likes

Thank you so much!!! I definitely have a better understanding of how it works now. This was a huge help! Thanks and good luck this year

If you still want some rubber banding ideas I’ve found that this rubber band calculator made by antichamber works very well.

https://scratch.mit.edu/projects/235244490/#player

3 Likes

Ok thank you! I will definitely try this…

I don’t do triangle banding on my lifts, so I guess I glossed over the position of the third pulley. Good explanation btw, I know I was confused about banding when I started building so something like that would have been helpful

I feel like this is your first time building this lift. While your rubberbanding placements are generally right i would advise you to widen your dr4b gear box and physically screw the gears on to the lift channels. Having the channels connected to your gears only through shaft (even worse since you are using normal shafts and not high strength) itll only lead to major problems. (Major slop due to the twisting of the axles.) After those fixes it just tuning. Good Luck

1 Like

It is our first time… Thanks for the suggestions and i will definitely make some changes to the current design