I’ve search the forum and I haven’t found anyone who has done this. We can’t be the first!
We have 4 Toughbox Mini transmissions that came with AM14U frames. They take two CIMs each, but if we put only 1 Cim on each one, can we use them for mecanum, given the gear ratios and all?
We are on a limited budget but we might be able to do it this way.
Not a horrible way to go depending on your wheel size. Just make sure that you calculate out your FPS with our desired wheel size to make sure you have the output to your teams liking.
Not exactly what you are looking for - but we did run 4 toughbox nano’s last year with mecanum’s on the AM14U. We used 8 inch mecanum wheels.
It looks like the gear ratios for the nano and mini are about the same so you should be fine there, and we ran one CIM per corner like it sounds like you want to do.
We had to add some gearbox mounting holes and bearing holes in the chassis at one end, because we cut ours to a non-standard length.
We understand the limited budget 
We are trying to find 6 inch mecanum wheels for the project as our simple test shows that 4 inch wheels are going to hang because of the length of our chassis when going over the scoring platform.
I’m the poor coder who is just going to make this work! The builders intend on covering up one motor mount with duct tape or something like that.
If this works I am going to endorse this method to small teams who are considering, but out of reach of, the 750 dollar upgrade kit.
It can definitely work. There are three ratios I would consider, 8.46:1 (included), 10.71:1, and 12.76:1. Depending on your strategy, that is your choice to make.
8.46:1
10.71:1
12.76:1
Hey Doug! Just for future reference, it’s spelled mecanum. It’s an easy mistake to make. How did the custom bearing holes work out? Did you have to switch to chain due to the difference center to center?
Our team did AM14U with Touhgbox Nanos last year. We did have some difficulties with poor tolerances in andymark machining and the lack of a tapped encoder mount, which, because of the poor machining, we were unable to easily remove and tap to add the encoder. It was a mess and very difficult to assemble, although it does, in theory, work. I would not recommend doing it. I’d recommend finding some other gearboxes or make your own.
has anyone attempted to use the vexpro single reduction clamping gear box? could you get away with this set up. http://www.vexrobotics.com/vexpro/motion/gearboxes/217-4156.html
11:72 set up? with 8" wheels
11:72 with 6" wheels is a free speed of 21fps. Way, way too fast. Don’t even try 8" wheels there.
11:84 with 6" wheels is good, but if you want to use the clamping gearbox you’ll need two stages of reduction. Going 12:72, and then 16:22 via some sprockets to a versablock will net a free speed of 16.8fps, perfect for a 4-cim drivetrain. I don’t know how mecanums will affect efficiency or handling at that speed though. You can go to 11:72 for the first stage to back down to 15.3fps if you want.
This is still way too fast for a mecanum drive in this game. There’s no need to go 15 feet per second when your biggest sprints are 1/4 length of the field… you’re just wasting current. Mecanum drives do not work as well at very high speeds as west coast tank drives do.
I think for even 6" wheels, to use the clamp on gearboxes you really have to use the second reduction add-on to have good performance. Unless you’re racing for the middle bins (and even then…) I would shoot for the 8-11 FPS range this year, but that’s just me.
What do you define as a “very high speed” for mecanum? For me, high speed WCD is 18fps+ on 6 cims. For 4 cims, 17fps. Is mecanum actually that limited in terms of speed? I thought I read that they could go at least 15fps.
I don’t think acceleration is a problem. A 15fps bot’s time-to-distance is as good as or better than a 10fps bot for anything more than several inches. So you’re not wasting current by running at a higher speed- it’s very well used current.
EDIT: See here: https://www.youtube.com/watch?v=YbluSr2Mf5Q That’s a 15.4fps mecanum bot.
DOUBLEEDIT: I would test both speeds actually. I have never seen anybody even try a mecanum geared for more than that 15.4 one I linked above, so I would try 12:72 x 16:22 AND 11:72 x 16:22 AND 12:72 x 16:32. I would be very interested to see actual results from a team that has tried a fast mecanum.
This is wonderful help, thanks.
Just for the record, If I had it to do I would strongly consider slide drive. I think mecanum will vibrate too much and if the robot (basically a fork truck) is carrying a stack of totes they could vibrate off.
We won’t be having 4 independent suspension wheels with this setup. So that is not going to be a solution.
We also won’t have encoders, but I think for us using the built in libraries this is not an issue.
But the drawback of slide drive is that I think the slide wheels will get caught on the lip of the loading platform even knowing it is tapered. In the best case it may cause an unwanted bump.
I think Chris’ point was that you don’t need 15fps for this game. But you do need fine control at near-zero speeds, as when aligning the bot to place totes and bins. A bot geared for lower top speed will have better fine control at low speeds.
We will be using the clamping gearboxes and 6" mecs with a 20t on the CIM (with 8mm-1/2hex adapter) to a 64t gear. Then the 64t gear’s shaft attaches to a #25 16t sprocket which is linked to a 48t sprocket attached to each wheel. The 6" mecanums are attached to WCD bearing blocks tensioned with the cam.
That certainly does work - that’s how we did our robot last year. We used 6 inch mecanums and (I believe) the 10.7 TB minis Using 4 inch mecanum with the 8.45 is a bit lower, but that’s good because you’ll be carrying a heavier load and this is a slower-moving, though probably much faster scoring, game.
We were conisdering mecanum for our drive this year, but we were worried that the handling would change too much as we picked up the load (we’re lifting outside of our chassis). The drivers even noticed it a bit just when we lowered our pickup arm on the practice 'bot (which was wooden and rather heavy) last year. We’ve opted for an H drive so that at least the direction of thrust will be what we expect, even if the accelerations shift a bit. We’re figuring on putting the strafe wheel at the COG when we’re carrying four or five totes (we’re going to do up to six) so that it behaves well when carrying a full load (during scoring) at the cost of being a bit off-center when empty.
In the past, on our drive station I have been using the Z slider for a “throttle” control. Since it really sets the maximum Y value, it really should be called a speed governor.
The original reason for this convention was that when a new student driver took control of the robot they always ended up gunning it right away. With the slider they could get used to driving the robot fast. After a few sessions the students would max out Z and be comfortable with the controls.
I think this won’t be maxed out this year. Instead the drivers will keep it from 50 to 75 percent. Even lower if it needs to be slowed to a crawl. This takes the guess work out of how far to push the Y control.
With the Toughbox mini’s (standard) gear ratio, that is even more reason to govern speed this year.
My apologies, I did know the right spelling and I’ll carefully blame my computer for “auto-correcting” to the wrong way.
Either way, we like them and have used them for the last 7 or 8 years, and don’t subscribe to the pushing match theory, as our Mecanum drive is more maneuverable - we don’t get in to many pushing matches.
The custom bearing holes in the chassis worked fine for us. We moved the nano’s to the corner spots of the chassis. Two of the nano’s were mounted in stock hole locations, and the other shortened end of the side railes we had to drill the nano’s hole pattern there. We recessed for the bearings, and removed the two screws so that center bearing was just pressed up against the side rail. We did not use any chains or belts, all direct drive.
Although I would say we were primarily cantilevered, we did also cut bearing holes in the outer rails of the chassis and used long drive shafts and had some extra support on the outside of the Mecanum as well.
Agree that having to tap the gearboxes is a weakness of the gearbox, but minor in my opinion. We VHB taped the encoders on last year (and didn’t use them anyway) - which I would not recommend. If we decide to use encoders this year we will tap the boxes. I did take one apart last year, and it was simple and readily re-assembled. And, we duct taped the open sides to prevent debris from entering.
We had a rock-solid drive train all year with the (slightly modified) AM14U, Toughbox Nano’s, and Mecanum wheels, had it up and running in a few days, and absolutely no flaws through the entire season. I would recommend it without hesitation. Although I’m sure some teams could easily have custom gearboxes, for teams with limited resources (as the original poster implied), I’m guessing that is a stretch and I base my recommendation on that.
For purposes of fine control of speeds near zero, that is not as efficacious as reducing top speed via gearing.
But much less expensive than four shifters!
Who said anything about shifting?