mecanum wheel Ball Intake : directing the ball? having troubles. Have two right VEX 4" mecanum wheels and two left 4" mecanum wheels on the out side of our 2020 ball intake and cant get them to roll the ball towards the center. 2" inch compression and a rather slow intake rpm (andy Mark intake roller kit) what do I need to do to get the balls to redirect towards the center of the intake?
2" compression is way too much. 1/4" - 1/2" or less is a good amount.
For whatever reason we had poor results also with 4" mechanisms from Vex no matter what we tried, we 3d printed some of our own 2" wheels based on Thrifty-bot’s and they work amazing. Best I can figure is that because the 2" are mounted at the ends there’s less torque pinching the roller-hub interface and thus less resistance, whatever reason they work great.
We also are currently using 0.5" compression, but we haven’t tested the different configurations extensively.
The compression against the ball from the roller to the floor and the compression from the roller to the bumpers has a big effect on wether or not they work for moving to the center. Play around with both distances to get the desired effect.
We prototyped the 6’ mecanum ball intake, but it did not work as planned, it would be more efficient to build a funnel type mecahnism after the intake to make sure no ball gets stuck. We have 4’ coming in soon, so I will come back and tell you how that works compared to the 6’
Funnels are jammy places of unhappiness with Power Cells–they just don’t work to get balls into single-file.
There is a way to use vectored intake wheels to center a ball, similar to the “ball magnet” from 2010–with the wheels about 2/3 up the ball and a wall (perhaps your bumper, or an idler bar right at mid-height, pictured) behind them. They’ll keep the ball against the wall/bumper/idler bar with backspin, and center it in the process–of course, in the middle you need something a little different to actually draw the ball into the robot.
We spent a lot of time prototyping different configurations of this concept. If you get the geometry right, it does work to center the balls before intaking them. The problem comes when you try to intake more than one ball at once. Since the balls are rolling on the floor (along the horizontal axis in your drawing), when two come into contact they want to rub on each other and the whole system locks up. There are ways to solve this problem, but there are also other styles of intakes that might work better.
Yeah, maybe. These balls like to jam a lot–at least jamming at that point gives you the opportunity to spit them out quick and reacquire if necessary. Maybe not ideal, but every design is a trade-off…
It’s not ever going to be as simple as “take intake, put mecanums on, now it’s better”. Things such as the compression and the spacing between the wheel and the bumper / reaction surface / etc are all critical for the mecanums to do their job correctly. Play with the geometry extensively in prototyping until you find what works.
The multi-ball jam issue is a real one with the Baby Yoda mecanums. There are ideas we have on 1720 - maybe running each side independently so one side could be paused while the other one clears, or run them all the way to one side of the robot. Lots of ways you can deal with this issue. Also don’t forget your robot will probably be driving while doing this! So try and simulate that in your tests if possible too.
Where can I find the stl files for the mecanum wheels you printed?
If you want to reverse engineer them yourself then I do feel comfortable saying that all I did was first download the STEP files off the Thrifty Store. To get the body I cut away the top half, cut away the roller(leaving the center nub that the roller rolls on), and adjusted the three holes on the center (a clearance hole for #6 bolt, a hole the correct tap size, and the 1/2" hex, each of which I oversized slightly because my printer likes to undersize holes by ~0.25mm). The roller I just made from scratch based on the dimensions from the original file, it’s a chambered hollow cylinder so nothing complicated. For the other side wheels my slicer has a mirror feature so I just used that. Print 2 body halves and 6 rollers and you’re off to the races.
After printing I cleaned up the roller holes with a drill to get a nice surface and tapped the to-be threaded hole in the hub. But other than that very minimal post-processing, didn’t need any support material which is always nice.
I printed mine in PLA so we’re going to try and get the ones from ThriftyBot’s store for the competition bot because he uses better plastic. It is nice being able to get them in the team colors though…
I got permission so I sent you a message with the files that I am printing. Anyone else that wants the files just PM me.