Many teams have reached out to our team asking for how our suction mechanism works as we were one of the first few teams to think of it. This is a bit late but better late than never!
Instead of explaining the mech generally, I’ll discuss the problems we’ve faced throughout the design process and its key aspects.
The first thing that makes our mechanism unique is that we use a suction cup unlike many of the top teams. They use a suction pad. The suction pad is probably the better way to go, but at the time, the beginning of build season, we only knew the existence of suction cups.
Next, we needed a way to lift the suction cup and flip it out onto the platform. The first part seemed obvious: some sort of lift. But flipping it out was difficult. Looking at other teams now, 254’s piston method is clever. But, the method we came up with was somehow the solution to all our problems. It was to use a winch. We attached rope from our suction arm around a pulley on the carriage to a winch. That allowed several things:
- We had rope run so that it would reel the suction cup arm in. Once the suction cup was sucked, instead of reeling the suction arm in, it would reel the robot up. In addition, the winch motor was slightly behind the lift. That meant, as the rope kept on reeling in (as the rope shortens), the angle of the rope to the carriage increased over time and the direction of the pull force would go from
vertical --> slightly diagonal, which tilted our robot forward towards the platform.
That gave the benefit of:
- being pulled up towards the platform since robot tilting means --> lift also tilting
- slightly closer center of mass
It may not have been much, but the tilt helped. In fact we put a 90 degree rope so the robot wouldn’t tilt back instead. Without it, our winch motors failed.
- We had a ratchet on our winch motor so the suction cup arm wouldn’t pop out during the match. That replaced the need of running the rope both ways and made managing the rope alot easier. We still needed a force to pull the suction cup up and onto the platform. That was where the constant force spring came in. It actually provided a slam force that slammed the suction cup on to the platform and decreased our suction cup pumping time.
For others trying to attempt a possible suction design for the offseason, perhaps, there are a few things to keep mind of.
- The math regarding leverage: the suction mechanism requires a fulcrum. And if your fulcrum is too close to the suction cup/pad, it’ll multiply the weight of the robot and the suction cup/pad might not be able to handle it.
- The investment of a suction climber. We had to dedicate an entire lift and backside of our robot for it. And the bad placement of our lifts (our front lift all the way in the front, climber all the way in the back) cost us stable driving (it made us very wobbly as we went for rocket lvl 3, since we just became a huge lever). Next time, I’d put the climber more towards the center and closer with the front lift, like 254.
That’s about it. While it’s not too impressive, I hope it’s somewhat educational! If you have questions feel free to ask.