We are having trouble with our double reverse four bar. For some reason, when it goes up, the top of the lift will retract and end up in the back of the robot. We have seen teams where their double reverse four bar goes up completely straight. Does anyone know why that is?
Thanks in advance
Could you please please * please * post pictures?
what do you mean the top bar retracts and ends up in the back? if you mean what think you mean, its that the 4 bars aren’t at perpendicular angles. you need the x motion of the second stage to cancel out the first stage, so you’re left with strait, up and down linear movement.
Lol send pics
I can do you one better: a video of the problem (I hope this helps).
https://drive.google.com/open?id=1JxHJ2wPHSEnJhcuGZ67bgzo-odEF-cC-
How a double reverse 4 bar works, is that the two bars need to be the exact same length. If you have 17.5" on one side, and 12" on the other, then the lift won’t move parallel. Find the lengths from axle to axle on the bottom 4 bar, and then on the top 4 bar you want the posts to be exactly that distance apart as well. Then you can build forwards using anything parallel to the ground. I’ll attach drawings if you don’t understand
I’m pretty sure you also need to the the two sections aligned so when the bottom section is horizontal, the top section is also horizontal (e.g. the angle of the top bar is the same as the angle of the bottom bars (just opposite))
If you think about it, the movement of the top bar forward is going to cancel out the movement of the bottom bar backwards, so the linear motion will be straight up from the axles on the bottom towers. Anything forward from there is not going to have anything to cancel out it’s motion. If you built a triple reverse four bar, then you could get linear motion with stages the same length as on the bottom.
It works now. We ended up sacrificing some height on our lift to make it go up straight. Not sure why it works, but it works, so…
That’s great! maybe you did some magic gearing?