Presenting team 99999v’s second robot of the season!
One of the biggest problems our first robot this year had was the drive speed. It was only 200rpm on 3.25" wheels, which is very slow and was one of the factors that caused our robot to lose the competitive edge we had early in the season. We wanted this robot to be much faster, be more compact, and have better traction. The way we acheived these things is somewhat unusual though.
First thing you might notice (and have probably seen already) are the angled motor mounts.
These are made from bent and drilled HS shafts, which we chose to use over something like polycarbonate for strength and rigidity. Machining these was very painful, but it was definitely worth it to be able to fit all the drive motors so compactly.
We also wanted to have much more traction, because 3.25" omni wheels aren’t quite as grippy as 4" or 2.75" wheels, but we were pretty set on using 3.25". And because 3.25" traction wheels aren’t all that great (the non-constant diameter isn’t very good) we decided to make custom traction wheels by cutting up flex wheels and wrapping them around a complicated assembly made by lathing a slot into 60t gears, running a ring of chain through that slot, bolting the chain to the gears, and then zip-tying the custom tires to that chain.
again, not necessary, and fairly difficult, but worth the effort. I’m very happy with how these custom traction wheels work, the grip they have on the platform is phenomenal, and the pushing resistance is a very nice bonus.
This isn’t anything that special about the lift. We chose to go with a 6 bar over a 4 bar simply because that meant we could mount the HS shafts on the 12t gears and 80t gears down near the bottom of the towers, out of the way of the conveyor. The top shaft was placed inside the conveyor.
The lift was designed to be decently light and compact, while still achieving plenty of height and reach, and I’m happy with that it works. It’s not the fastest lift there is, but as I expected, I didn’t find myself using the lift very often in matches at Kalahari, parking was a central strategy to this robot and we almost always did that instead of lifting goals.
This is the part of the robot that was the hardest to get right. Rings behave in strange and often confusing ways that make them difficult to consistently and quickly handle and score. The two major problematic points of the system are the bottom where the rings are sucked in and funneled up the tray, and the depositing area where the rings need to be redirected and dropped onto the goal post.
The things we discovered for the intaking section of the conveyor was that it’s better to have a single roller which rings are passively funneled into (by a funnel-shaped opening on the front of the robot) than it is to have a wider intake which actively funnels the rings. This is because a wider intake has the tendency to jam up, especially with multiple rings, and a single roller doesn’t have this issue. This doesn’t really seem to sacrifice any fielding speed or range either, because the rings will passively funnel into the intake as long as you drive into them. We had problems with rings jamming or getting spat back out, but we solved these with large polycarb walls and guards which contain the rings inside the conveyor as they funnel in and up.
As for the depositing portion of the conveyor, we found that the most important factor in the reliability of ring deposit was actually the compliance of the tray. When we had our tray rigidly affixed to the towers, rings would often jam and spit out in unpredictable and erratic ways, never being able to get the accuracy higher than around 50-60%. When we simply removed the supports for the upper half of the tray, the consistency increased by a whole lot. The upper half is free to flex and bend all it wants, the lower half is completely rigid. This seems to give the rings the freedom to do what they need to do in order to get where you want them, and if you’re struggling with consistant ring deposits, I think compliance is the answer.
We also use rubber standoff links for the hood of the conveyor, which help cushion the rings as they impact and reduce the amount that they ricochet backwards, which also helps in getting them to consistently drop down onto the post.
We designed our intake to run in the opposite direction compared to our previous robot, where it intakes rings at the front of the robot and spits them out at the back. The main reason for this is that it allows us to hold a goal in the lift on the front of the bot, while scoring rings on the back. The ability to lift the same goal we scored rings on was really useful early in the season when goal capacity wasn’t so important, but now two goal capacity is extremely important, and lifting goals is not, so this was definitely one of the biggest improvements over the previous design, and there’s a reason that this general layout of lift in the front, rings on the back, has become the meta (in terms of design strategy, the actual execution of this design strategy varies wildly from robot to robot, so I still think it’s hard to call this the meta, at least not in the traditional sense)
The front clamp is also pretty unique on our robot, though I can’t claim the idea of a locking clamp. @Ben was running with one at Kalahari, and it worked very well so I basically used that idea of a over-center lock but with different geometry. This allows a single pneumatic cylinder to power the clamp at very low pressure, while still retaining more grip than any non-locking clamp ever could. The way this works is that when the latching arm of the 4 bar is pressed upwards, the two other bars will try to invert themselves and thus seize up, preventing the latch from opening. But the 4 bar is driven by the top bar, which is free to move, allowing the clamp to still open and close as I please, but not allowing it to be opened by external forces like an opponent’s robot pulling on a goal.
Here’s a video that might show it a little better in action:
Locking Clamp - YouTube
I would highly recommend using a clamp like this, it’s objectively better than a non-locking clamp and there are many ways you can achieve this locking functionality with simple 4 bar linkages.
Rear Clamp + Tilter
The rear goal mech is split into two subsystems, the clamp and the tilter. For the clamp, we basically just re-used the design we made for our clamp on our last robot, because it worked very well, had excellent leverage keeping the goal secure, and didn’t take up space above the goal where the rings need to have room to fall. It worked on the last robot, and it works on this one. Wouldn’t recommend it for a front clamp where you want more reach and ideally locking capabilities, but for a rear one it’s just fine.
And for the tilting part, it’s just a single pneumatic cylinder that pulls on the whole clamp, which is mounted to the base on hinges. Very simple, but works well.
We wanted the goal to be tilted so that it would be very difficult for an opponent to latch on to, and because that seemed easier and more compact that a larger 4 bar that brings the goal into the bot, or a deploying ring mech that sticks out to hang over a level goal.
And we chose to use a tilting clamp instead of a forklift because it holds the goals much more securely, and it doesn’t involve unwieldy forks sticking out the back of the robot.
Performance So Far
This robot has so far been used at one competition, the Kalahari Classic Signature event. This was such an amazing experience, and I’m very happy with how the robot performed. We executed some very good matches, including the high score of the event with 2145z (great alliance partner), 274 points (almost 294, but I dropped a neutral goal off the platform on accident.)
Feel free to ask any questions, I’ll be happy to answer them.
This has been such an amazing season so far, and I’m so excited to see how the rest of it plays out. Good luck to everyone, and hopefully I’ll see some of you at worlds!