just got a couple questions about how much caution i should take in having a 20 inch arm going 180 degrees with almost a 20-25 pound endeffector on the end of the arm. i know this is quite a long cantilever but i believe the whole arm system could potentially get lighter. the arm rotates on the carriage of the elevator similar to the Quokkas design currently but not as balanced.
i’ve done some inputting on re calc and it seems to be do-able but if people have experience with this scenario, should i be worried or about how long this cantilever is or will it be ok
A 20" arm is on the long end, but the mass is the bigger problem. Lighten up the end effector and move as much mass towards the pivot point as possible. Don’t raise the elevator unless you’re in a protected zone.
Here’s 2102’s arm from 2019. Probably about the size you’re looking at, but all the powered components are at the pivot and everything sticking out is polycarb.
An end effector on an elevator is mass that REALLY matters. You ultimately care about how much the moment of inertia is about the pivot, or in other words minimizing the torque to swing it around.
When reducing overall mass you improve robot stability and elevator performance.
It’s really not about the total weight, it’s about where the weight is on the mechanism. If you have a kraken out on the very end of a 18in long grabber, that’s incredibly bad. If you have 2 krakens, but they’re at the pivot point, that’s fine. If you have 4 krakens, but they’re inside the carriage, you’re fine.
The further away from the carriage and the pivot point you go, the more the mass will be detrimental.
the issue im having is that the endeffector is trying to be a full width intake and outake similar to 3467 2024 but motors are not the main weight, its the compliant wheels because of the nature of the solid pvc pipe
heres my current design, obsviously its only been 2 days of prototyping so leaving any options of removing rollers open,
hopefully this can help clear up confusion
another similar design ive seen was the 840 dunk tank submission from this year and i saw how they had an almost full width intake (although its much simpler than this)
Try moving the coral wheels further apart (therefore decreasing number) and decreasing the ctc distance on the coral wheel shafts. Allow the complient wheels to bend sideways. The type of wheels may matter here… TTB squish wheels may bend sideways better, or stars may be what you need.
Think in 3D
The bottom wheel for the Algae is also likely unnecessary and can just be a bar.
I would do some testing but you likely dont need 2 sets of wheels to hold the coral. it’s rigid enough I suspect 1 set top bottom will be plenty. if the goal is a intake a funnel of plexi or 3D print might be better than a whole width compliant setup. Would help center better as well.
Our team is doing a very similar design but had not had the chance to test it as we are still on winter break. Really interested in seeing how well this works and what the results of your tests are.
I saw something at a competition last year that piqued my interest that I think would be useful here. I saw a team that used pool noodles instead of compliant wheels along a wide intake. You could use chunks of pool noodle to replace some of the compliant wheels while leaving some there for the defined squish. Maybe put compliant wheels in the center and pool noodles to the sides, or something.
I wanted to also ask if there’s a real reason why the coral intake is full width. The chute has ridges, and if you could line up with one of them consistently (using some form of april tag localization or something), you could cut down the intake to be much narrower, and have less compliant wheels taking up the weight.
well it’s not exactly full width, but 14-16 inches wide. haven’t seen too many teams go for a full width so you might be right about not needing it. we just wanted to optimize time at the hp station
Another quokka, the arm was just over 900mm total (3ish ft), but super well balanced, only half that on each side, so each side would be a bit shorter than the proposal.
