Reverse double 4 bar

We have a RD4B lift that works pretty well. We have 6 motors on the lift running a 7:1 ratio. It has power to run the lift up but it still seems to strain a bit when lifting. Could use a little bit more power. But with 6 motors it seems it should have plenty. The motors are running at full power. We have seen other RD4B lifts with a 7:1 that run 4 motors that seem to have plenty of power?? Here are a few pics for you to see.

It’s hard to tell but it looks like you need a lot more rubber bands. There should be as many as possible as long as the lift stays down on its own. If you take the shafts out of the motors you should be able to raise the lift with one finger.

Check to make sure you don’t have unnecessary friction. Take off the motors or pull out the shafts a bit so they spin freely. You should then be able to move the lift easily by hand.

It appears to me that your arm bars are not screwed to the green gears but are instead somehow locked on the large shafts. If that’s true, is it possible your connection between the large shafts and the arm bars is slipping?

When building more conventional 6 or 8 bar linkages I have found that they work much better when both linkages are directly powered or driven by a gear. Instead of driving say the bottom linkage and expecting the top linkage to follow.

In looking at this design the top bar of the bottom 4 bar and the bottom bar of the upper 4 bar are being directly driven while the others are following. Could that be the issue?

Not to insult your intelligence, but do make absolutely sure all of your motors are actually turning in the direction you think they should be turning in - and that none of them are just slacking off and doing nothing but creating friction.

Oh I understand… but yes, all the motors are pulling their weight.

As many elastics as you can, until the arm is slightly popping up from them. These will do much more than crazy gear ratios and many motors.

As most other people have said, you are going to need more rubber bands than what you currently have on your lift. Many teams have a huge amount so that the lift only just stays down within the 18" height limit, and one I saw at a competition last weekend had to use pneumatics to lock the lift in place so it stayed in size, just because of the size of the assist the robot had.
Also as pointed out the bolting of the lifting bars not directly to the 84T High strength gears (or Ultra High Strength in this case?) is slightly concerning, But if it works well for you they there is probably no need to change it.

That’s funny, we use a pneumatic lock on our lift too.