I’m curious if any teams have implement a design element to help prevent them from being pushed around when trying to shoot this season. Our team has a pretty reliable ability to hit the upper goal and did pretty well at our last District event… We did sometimes have teams that tried to play defense and push us while we were lining up to shoot.
As we are prepping for our next event I’m brainstorming for a counter to keep us firmly planted while we shoot. We have a kit of parts chassis and standard 6" drive wheels in a differential drivetrain with four Falcons and a 10.71:1 gear reduction ratio… I may be imagining things, but I seem to remember posts where some teams with mecanum drives would use foot pedestals (powered by pneumatics or motors) to firmly plant themselves against being pushed while shooting and etc…
Has anyone tried this? Is it even legal? Has anyone tried anything remotely similar when another bot is throwing its weight around?
Or is there a software solution? Maybe locking each wheel in some sort of PID setpoint when we go and shoot and then releasing it when we are done shooting?
I believe this would be allowed as long as you don’t entangle yourself with the field or bring your bumpers out of the bumper zone.
Another option is to shoot from a more protected spot such as against the fender or the protected zone. These were two shots 4607 wanted to be able to make when designing our new double flywheel for GNR.
Thanks! Have you ever done it with motors instead of pneumatics? We haven’t had to pneumatics on our bot this season yet, and so I’m wondering how difficult it’d be to convert the concept to be driven by motors so that we can save on the weight of the compressor, tanks, and etc.
You could make a motor driven system, but it might be more complicated than adding pneumatics. The neat thing about pneumatics is that one little motor (in the compressor) can power lots of things all over the robot. But since it’s only one little motor, those things won’t be able to do much work. I expect you could have a shaft go across the robot somewhere, and have some cam shaped “wheels” on it with tread on them, and have a motor make it rotate part of a turn, to push them below the level of the wheels. Having two of these assemblies could get the robot totally off it’s wheels.
Perhaps someone has done this already…I haven’t noticed any, but I don’t look at all the robots or robot designs.
We have never used it with motors, but there are many ways to make them work. Consider how you can spring-load the brakes to return if there is a failure. This is a big plus of pneumatics with spring-return cylinders.
Methinks I heard someone also use PID on the drivetrain to hold position. Essentially responding with a push back to any perturbation. May be a lot quicker to do the 95 method though.
This is what I would recommend @ op. We were at your district event if you might recall, and shooting against the fender is very hard to defend against for the average team. Also I didn’t see any teams taking advantage of the rule-protected zones. I liked your guys’ robot though, excited to see what you guys do for your next comp and (hopefully) states!
Yup. On 1114 we called this “base lock” and started implementing it back in 2006. It was pretty revolutionary back then, but now it’d be pretty basic for any team using closed loop control to implement. There’s a decent overview of an older implementation in this thread.
Some kind of traction plate to hold position is certainly doable, but has its own challenges with packaging, the forces it has to withstand, etc. so it takes some effort.
You can do different things to mitigate pushing depending on the type of displacement you’re trying to avoid. If your problem is that you are being spun, you can drop traction pads or wheels on one end of the robot so that only your back wheels touch - this lengthens your wheelbase which can help avoid that. (Fun fact: In 2010-2014? some teams designed their entire drivetrains in part to allow for a traction wheel drop to prevent spinning, and that traction wheel would be driven to still allow for powered movement. Not really an option this late in the game but something to think about for a future project perhaps)
If your problem is being pushed in the direction of your wheel travel, you could consider a brake mechanism of some sort. Due to mechanical complexity it is really something you would design in the drivetrain from the start though, so maybe the software solution is the quicker fix here.
@Anthony_Galea Thanks!!! Rochester was a fun event!! We wish you guys the best as well!
Our next competition will be at MCC… Our plan in the next three weeks is also to give our shooter a little more oomph to shoot from the rule protected zones and to dial in the different closed position velocity loops to be more granular and get more “sweet spots” deeper in the field.
We want to be that robot that can hit the high goal from just about anywhere and can match up other teams in climbing.
@Karthik Thanks! So a closed loop position control PID on each of the four drivetrain TalonFX’s is along the lines of what I was thinking of testing…
Maybe sense the current position of the encoder when we go to shoot… Make the current position of each encoder a setpoint while shooting, and then releasing those setpoints when the shooting command ends.
Have you considered finding ways to reduce the time needed to line up and shoot? If your robot get hit after the ball is already on it’s way, it should still score.
Rochester was a fun event!! We wish you guys the best as well!