Drivetrain, High or Low?

You don’t need a heavy torque ratio, though. Our Gateway robot (4 high-torque motors, geared 1:1) pushed 10 sacks with ease. If you can push an opposing robot, sacks will give you very little trouble.

We built a base with 4 high strength motors at a 1:1 ratio and found out that after about 7 sacks our robot was struggling to push the pile. If you plan to push around more than that you need to have more torque on your drive.

How heavy was this base? We have found that weight plays a huge role in a robot’s ability to push things. Our Gateway robot weighed 25lbs, so pushing many sacks was really easy.

Ours was about 15 to 20. Did you test it on the field tiles?

Yes, I did test on field tiles. I tried pushing sacks in rows (both parallel and perpendicular to the robot’s motion), piles, clumps, stacks, and walls. Our robot pushed them all easily.

Were your 393 motors set for internal torque, or speed? Ours were set for torque.

We had ours set for torque, and the robot weighs 17lbs. I just tested it again 30 minutes ago with 7 sacks and got the same results. Is there anything else on your robot that is noteworthy that we don’t have?

Our robot has 6 wheel drive, with 4" wheels (4 omnis, 2 regular), but I don’t see how much of a difference that could make. Yours being 17lbs, ours is significantly heavier than yours. What kind(s) of wheels do you have, and how big are they?

We have two 4" omnis and two high-traction

Omnis tend to have more traction than High Traction, so our greater number of omnis and our greater weight are probably the factors that allowed us to push the sacks so easily.

Ok, that would make sense. This year I plan to replace the wheels with mecanum, which have more traction(?). I also need to finish the actual mechanism and put it on the base, which will definitely increase the weight. But going back to the topic, what is everyone else’s idea for a base?

As of now, I am using mecanums for strafe, with a central omni wheel for support and encoding. I think most teams will run 1:1 this year, which would be lower than the average last year, as most teams that I talk to were running 1:1.6 for speed.

Wait, so your omni is not powered and only helps with navigation?

Yep, It is so I can know exactly how far forward my robot has moved without needing to worry about my drive wheels slipping or coming off the ground. It doesn’t encode strafe though, so I will need to encode my mecanums for that (unless I put in a sideways encoding wheel too (not on my to do list :p)

We’re building a new chassis with a protective skirt around the wheels, so the sacks don’t get caught. We could leave a gap in the middle of the bottom of the chassis (where there are no wheels), so we can still drive over sacks if need be. However, I think it’s better to be able to push sacks than it is to drive over them, so we can score extra sacks on the floor goals when we need to.

Our opponents’ floor goals also provide a good opportunity for SPs, if we’re against weaker teams. Plop a bunch on their floor goals, and then plop an equal amount in your trough. It’s not very risky, and SPs are worth it.

The SP wouldn’t be worth the effort it would take to push them, you would be better off picking up sacks and doing a 2/3:1/3 split, you would get more score, and more SP. I’m also experimenting with low edges around the wheels because I think driving over the sacks will screw up my intake, every design I have seen this year has required keeping the intake low to the ground, and driving up on sacks wont help this.

I just think any kind of low edge has too much potential to catch on top of sacks, causing the wheel to come off the ground. It is very difficult for the sacks to “slide” across the foam tiles. In the extremely off chance that a sack gets caught under every single low edge, you wouldn’t be able to drive at all :p.

I think that the only situation where you would want to drive over/through sacks is when going to score in a goal, which means that the height of the intake relative to the ground shouldn’t matter.

As an aside, I currently have a robot that is driving over sacks perfectly with mecanum wheels without any jamming issues. I’m just using narrow C-channel with the wheels mounted through the centre holes, so nothing special with the height of the chassis. Also, I’m finding that mecanum wheels are performing much better on a 1:1 drive ratio than the 1.6:1 that my team was using last year. I’m still not confident they are the absolute best choice for this game, but I will definitely be using them for at least the start of the season.

The edge on our robot is ~1/16" off the ground and hasn’t ever gotten a sack stuck under it. The only way it could possibly happen is if another robot lifts a side off the ground and pushes a sack under us.

If your robot were to get heavier than it is now, per se like when holding sacks, wouldn’t you be at risk of dragging on the ground.

Yeah but if it becomes a problem we can simply shave down the angle pieces we are using as a skirt.

And it actually pushes the sacks along? Still sounds unnecessarily risky to me, but hey, if it works then cool.