694's Suction Cup Mechanism

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:
  1. being pulled up towards the platform since robot tilting means --> lift also tilting
  2. 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.

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Here are some of our prototypes as well:

https://drive.google.com/a/stuypulse.com/file/d/10n2-FZ49RHxpXCd9WMuyiNCGsQirwJK2/view?usp=sharing

https://drive.google.com/a/stuypulse.com/file/d/1ZeeEI76nZRbXK6Exrt413jSfHJhfnYK2/view?usp=sharing

https://drive.google.com/a/stuypulse.com/file/d/1Q2ke2WfCZXyOQpQJTP50pK5v53r4vKeb/view?usp=sharing

We tried many different suction cups, but this worked the best on the HDPE: https://www.wpg.com/catalog/hand-held-vacuum-cups?material_weight_hand_cups=46

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Great Design! Thanks for sharing! Just out of curiosity, when you did your suction prototypes, did you ever think of using a different motor as a pump? For example could you use a slower motor like a Mini CIM, or does it have to be a motor with a faster RPM to increase the suction on the platform to lift your robot up? Thanks again!

We didn’t use a pump to create our vacuum. Rather, when we ran the lift up, the cup would slam down onto the HAB to create a partial vacuum. We would then fire a piston, which had a 3D printed piece that would interface with the handle on the suction cup. So, when we fire the piston, it pumps more air out of the cup, giving us a stronger grip on the platform. Over the course of the season, though, we did experiment a bit with the gearing on the winch. Initially, we had it at 28:1, but switched to 35:1 either during or after our second event for a bit more torque. Hope that helps.

That is interesting, didn’t see that. Thanks for clarifying!

What was your timeline for developing this mechanism?

We usually spend the first week of our build season researching and prototyping. We spent our
first two days searching for suction cups and the material FRC uses for the hab so we can know if the suction cup will even work. While waiting on those to deliver, we sketched a few mechanisms. After fully testing the suction cup, we started working on prototyping. By this time, we were fairly late compared to everyone else. It was week 2 already, and we were still prototyping. But, we had no past FRC game to base our mechanism on (it was also my first project) so we definitely spent a lot of time figuring out the most efficient build, how forces were being transferred, what part would be taking the most force, and etc. By the time we finalized a design it was the end of week 2 and we had just begun cadding, while the rest of the CAD was finished. We were fairly late but it was worth it as it became the most durable mechanism on our robot.

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And thank you guys so much for finding a suction cup that worked for this application. We were planning on a grab and flip mechanism and set it aside to work on the rest of the robot. When we circled back around and started developing we realized that we were going to be out of allowed extension rules to make it work.

Instead, we replaced out grab arm with your suction cup, and (we are the blue robot at the right climbing on the 3rd level of the hab):

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For any of those interested, I have several close-up photos taken that I will upload if anyone wants to see.