How do you combat the weight of 4 barrels/balls+a collection mechanism with a 6 bar? I think it would fall down lifting all that weight. Would you have to chain it with rubber bands?

So far, the best way we have found to combat the weight on a lift system is to use a relatively strong gear ratio with 393 engines and Latex tubing: http://http://www.vexrobotics.com/products/accessories/structure/275-1262.html
It works relatively well with our extended 4 bar.


OK thanks.

Yeah we just used bungee as a virtual counterweight, although you can make a shock-like mechanism which mat work better in your case.


Bungee? What do you mean?

Also, what is a shock like mechanism?

Sorry, I think you would call it “rubber bands”. The long black Nylon cords. These shocks I’m referring to are the shocks in your car that are used to absorb boups in your drive-train. You can make a device like this to turn the tension of the bungee and turn it into compression. This will help alleviate some of the force off the rotation point.


Is it a VEX part? The shocks I mean?

No, I think what he/she means is to use the tensional force of the latex tubing or rubber bands on the other side of the fulcrum of your arm, so it is pulled tight when the arm is down. This helps counteract the force of the arm’s weight on the lift motors.
However, on a robot with a huge arm, there may not be any other side of the fulcrum to attach the elastic to. In this case, find two points on any of the metal arm joints that are far apart when the arm is down, and come together when the arm is up. Tie the latex tight there. But with this method, the force vectors might not line up perpendicular to the fulcrum, so the total counteracted torque may be smaller.

Thank you for explaining that better. You guys are helping me a lot! Thanks :slight_smile:

My team always uses rubber bands because they’re cheaper and the latex tubing we had tended to break easily once it had been well-used.
To support the arm, I know a lot of teams like putting the rubber bands on the back of the arm, but I’ve never seen the advantage to that when you’re losing so much arm length. What we did instead was put the rubber bands between the 2 bars on the 4-bar (or 6-bar, as it would work the same way) such that when the arm was down, the rubber bands stretched from the top bar at the end close to the powered pivot to the bottom bar at the end close to the intake. This allowed fairly constant force and rubber bands that did not get in the way.

I am pretty sure we are going to use either rubber bands, and/or latex tubing. It would help stability.