Best Claw Design for Back Dumpers?

Given that the metagame is claws right now, I’ve been wondering what other teams have had the best success with? Right now we are using,

Gearbox: 60t (driven) 12t (driving) 36t (idler) 36t (idler) 36t (idler) 36t (idler) 12t (driving) 60t (driven) for gearbox, 2 motor 5:1 torque ratio
Pincers: 1x2x1x25 L-channel on top of the 60t gears, gusseted onto a 1x2x1x10 L-channel, with elastic assistance to hold the claw closed. The pincers are about 4 inches off the ground. We previously had deployable standoffs under it, but it was too hard to drive around with them.

Have you considered taking out the idler gears? It allows for your claw to grab more stars at a time because each side of the claw can stop in a different position.

My robot has a gear box of 72:12:36:36:12:72 with the driving gears being the 12t ones and the pincers being attached to the 72t gear. We have elastics also. We also don’t have any scoop underneath it. The pincers are L-channels and tilted slightly towards the ground. This claw can hold ten stars without burning out, but they have to be arranged in a specific arrangement. It can pick up up to 6 stars reliably without shifting them around too much.

Gross gross gross. Nearly every team I’ve seen with sides that aren’t mechanically attached are much worse off for it. They drop EVERYTHING. They say, “Oh, we have PID on the sides.” Sure, but you also don’t get the extra strength if one side is struggling with more objects. Usually these claws end up floppy and bad.

We’ve never had problems with dropping stars, but I guess we are using a fork/ claw hybrid.

Yeah, mechanically linking the two sides together is only really necessary if you do not run prongs. Otherwise I think the idler gears just add weight.

I still think that idler gears would be helpful in a pronged setup, because it distributes the power of the motors to the side of the claw that needs it most. Also it helps when mechanical issues occur like if a wire gets unplugged or the axle of one of the claw arms comes out.

Eh, we’ve never faced any issues where one side doesn’t get enough power. I’m also assuming good enough build quality where shafts don’t fall out of motors or get unplugged.

Here is a claw that is not mechanically linked without forks throwing 2 cubes to the far zone, but maybe they should just skip it and add the weight of mechanically linking the two sides so that if one fork gets hit really hard and skips some gear teeth they will remain out of sync for the entire match. This idea of using programming can never work.

https://kidsinc1.box.com/s/069b8ro6876fp226jpba3jv4dl34osyn

I’m sensing sarcasm. :wink:

So it can grab two cubes lined up perfectly, but how does it deal with stars on one side of its claw with none on the other? That’s where it has a disadvantage. It has half the power.

I don’t know how you could hit the claw do hard that the gears skip. Never happened to me.

anyone ever considered linking the arms mechanically without gears or sprockets? :wink:

We may have to make some more videos and post them later this week. The team is getting ready for a skill tournament this weekend. I will see what I can do for video.

So far, it has done well with cubes and stars together. I know it handles 2 stars and a cube to the high zone easily, but will have to have them show me 3 stars and a cube.

You do not get any more power from mechanically linking the claw. You only get more friction. Friction may help you hold things but if there is enough friction to make that much of a difference, then it will also be noticeably slower.

I am not saying that it is bad to mechanically link the two sides of the claw. I am just saying that the claw design our A team used when it was mechanically linked had a lot more problems than the design it uses now. There is the added benefit of it being lighter this was as well. They have a robot that is about 10 pounds with both batteries.

How many holes apart do you guys think the pincer gears should be to best grip 5-6 stars or a cube+2 stars or a cube+3 stars? We’ve had issues with stuff just falling out of our claw at capacities higher than 3 stars or a cube.

You do not get any more speed, but you get double the torque, if only one claw arm is moving the objects.

Ya I agree with @mwang17 there is no reason to have mechanically claws if you have the prongs. If you have build quality that is up to par and you have the correct gear ratio, I believe that a claw that is not mech. connected is better, more efficient and lighter. If you want mechanically connected claws you can do it in the code saving a tone of weight.

Let’s say you have a 1:7 claw. One way to mechanically link these is to do the gearing 84:12:36:36:12:84. So you add 2 axles (we’ll say 3 inches) and 2 HS 36 tooth gears (lighter if you do LS). Each 36t gear is .012 lbs, and each 3 in axle is .013 lbs, coming to a grand total of .05 pounds saved. That’s not very much.

If all the objects are centered, there isn’t a big problem with no mechanical attachment. If objects are to the side, though, you want mechanical attachment. If you have mechanical attachment and only one side of the claw is actually touching objects to line them up, you have double the power you would otherwise.

I don’t doubt that capacity of non-linked claws is the same in ideal circumstances, but I don’t see a big problem with linking them. You guarantee alignment and high power, and as @puzzler7 mentioned, the weight gain is negligible.

Personally I think having a non mechanically linked claw grabs objects better because you can grab it when it isn’t centered. The other claw arm will swing in to grab the objects if the other claw cannot move the stars central.

But a mechanically linked claw will just move the objects to the center without any objection. And that requires much less tuning, and you will lift more evenly, and objects will be right over your standoffs.

A mechanical linking also means that you won’t be completely screwed over if a single sensor wire comes unplugged. Obviously a good team should be running through a checklist, checking all their wires, etc. but it still happens.