Octocanum Drive/ Mecanum Suspension Designs?
 

As an off season project for our team we are looking at creating an Octocanum drivebase. We have experience with our own custom chassis, and have been using Mecanum drive for the last many years.

We have seen a few designs around (1086 / Blue Cheese, 3847 / Spectrum, 488 / Xbot, and 1540 / Flaming Chickens).

From my research, I can only find one example of an Octocanum that provides suspension when in the Mecanum mode (team 1540). It seems like with this drivebase we wouldn't want to miss that opportunity. Does anyone have any experience with that? And can anyone point me to any CAD designs around that are set up like that?

Re: Octocanum Drive/ Mecanum Suspension Designs?
 

Mecanum wheels apply force to the side when in use, so it is generally safer to be mounted to the frame rather than on a module. Plus, you tend to spend most of your time on mecanum, only using the traction wheels when you are interacting with the opposing alliance. In the event you are low on pressure, you can still use your main drive mode without issue.

Re: Octocanum Drive/ Mecanum Suspension Designs?
 

Agreed on the point of spending most of our time on mecanum. I guess the trade off you made on your chassis was that suspension for the mecanum was not worth as much as the possibility of losing pressure and having the system fall back to the traction wheels?

Re: Octocanum Drive/ Mecanum Suspension Designs?
 

2386 used mecanum for the first time this year and I too was concerned with suspension/ full wheel contact. In order to help keep our masts from swaying at the front of the robot, we used tensioned steel cables going from the front upper most point to the opposite rear low point. Although this did help with the sway of our masts, it also worked as a phenomenal way of ensuring all wheels were in contact with the ground. if the rear wheels off the ground, we loosened the cable lowering the wheels and vice-versa.

Should we ever go mecanum again, we will most certainly use this method of ensuring the wheels all touch the floor. To make it work you just need a rigid, tall super structure and build some flex into your chassis. Would highly recommend this method to others as it is both simple and easy to execute.

Re: Octocanum Drive/ Mecanum Suspension Designs?
 

Alternatively, you could use a gyro to correct for the drift/inconsistencies and not have a suspension system. I know many teams that have mecanum this year who have no suspension, such as 1983, 2990 ect.

Re: Octocanum Drive/ Mecanum Suspension Designs?
 

Yes, especially as it would turn the robot into a 4 wheel long bot(which can't turn well.) The biggest issue that an octocanum has is it can't turn well in octomode unless you have your traction wheels position inward far enough for it to be a wide base. Defaulting to mecanums fixes this issue.

Re: Octocanum Drive/ Mecanum Suspension Designs?
 

Here's a closeup of how 1540's Octocanum drive works. It pivots on the traction wheel and uses 1" pancake cylinders to switch back and forth and to provide suspension. There's a custom single speed transmission built into the 2x1 frame but you need not do that. There is no chain tensioning, we just CADed it to be the right distance and it's been fine.

We started out with a variable air pressure system for the cylinder so that we could change how stiff the suspension was depending on how many toes we were carrying. We ended up dropping that feature because we needed the weight elsewhere. In the end, while we found Mecanum performance was better (more consistent strafing) with the suspension, our software with a heading sensor could do what we needed for this game. We actually don't strafe as often as we thought we would.

For St. Louis we ended up dropping the cylinders to get the weight for a can-grabber. We still have the traction wheels but they are just used to go over the scoring platforms and are just fixed a quarter inch above the ground.

Re: Octocanum Drive/ Mecanum Suspension Designs?
 

Be careful with this statement. Mecanum wheels absolutely requirement a certain amount of flex in a chassis system so that all 4 wheels maintain contact with the ground a majority of the time.

So either build a flexible chassis, or use suspension: one of the two.

A gyro can only do so much. With one wheel off the ground, you will run into a situation where the robot cannot correct itself and strafe at the same time. It will end up driving forward, backward, or sitting in place while the airborne wheel spins instead of sliding sideways like you want.

We ended up changing out our entire drivetrain to a slide drive at state champs. It ended up being lighter than mecanum and it always goes the direction you want it to.

Re: Octocanum Drive/ Mecanum Suspension Designs?
 

3309 used an octacanum drive in 2014 with suspended mecanum. We had the mecanum geared for 17 ft/sec and the traction for 4 ft/sec. It worked well but we had to make sure to conserve our air so as not to run out and drive on eight wheels going at two different speeds (yikes). Although we did well and that never happened in a match. Also looking back on it we probably would have used a 6 wheel west coast drive last year to maintain traction when doing turning maneuvers quickly (it depends on the game obviously). I will look for some photos and post it here if I find them.

Re: Octocanum Drive/ Mecanum Suspension Designs?
 

Perhaps a crazy idea, but what if you did a "duodecanum" with the default being traction wheels?

This would have eight traction wheels, two on the same drive train as each mecanum wheel. The traction wheels are all at the same gear ratio as each other, and the mecanum all at the same gear ratio as each other.
Four of the wheels, one on each drive train, are located at the center front-to-back, and share the same axis of rotation. The other four are "outboard" of their respective mecanum wheels. The eight traction wheels form a standard 6-wheel drop-center drive chassis, with an extra pair of wheels. The four mecanum are off the carpet normally, but lift the chassis high enough that the drop-center wheel is off the carpet when the pistons are actuated.

What I'm thinking is that the center-axle wheels' interactions with the carpet will serve to clutch the front and rear half drive trains together when in traction mode, but these drive trains will operate independently in mecanum mode. I'm thinking that the corner and mecanum wheels would be in a traditional octanum butterfly configuration rotating about the traction wheels, with the center wheels being driven from the corner wheels.

It would look sort of like this from overhead, with a-d indicating which drive train each wheel is on. [L] is a traction wheel, /L/ or \L\ is a mecanum wheel.

Another edit: Another possibility would be to have ten wheels (decanum?), and a clutch on the center axle that engaged/disengaged the two drive trains on that side. Either of these systems would be programmed exactly like octanum, presuming that you're already constraining the outputs so that the two left axes and the two right axes match each other when in traction mode.

Re: Octocanum Drive/ Mecanum Suspension Designs?
 

Having one of four wheels airborne sounds like more of a manufacturing problem to me, rather than a mecanum specific issue. There's a crazy amount of teams using mecanum this year without suspension and very rigid (for FRC) frames, you don't NEED it. The bigger issue (for the vast majority of mecanum teams) is the center of gravity distribution and strafing, which can either be corrected by a gyro, encoders and some code or not using mecanum.

Edit: I should clarify, varying weight on mecanum wheels is one of the larger issues with mecanum. Having no contact with the ground for one of the four wheels isn't a problem that is specific to mecanum, it's a manufacturing issue.

Re: Octocanum Drive/ Mecanum Suspension Designs?
 

Yes, but it is often a manufacturing problem with the floor, rather than the robot. This year, as with many, it's a manufacturing design. There are these things called scoring platforms that disrupt the planarity of the field. Even in that lovely land of theory where everything works, this will result in one or more wheels becoming airborne when the robot meets one at an oblique angle.

Re: Octocanum Drive/ Mecanum Suspension Designs?
 

Snipped quotes above and referencing everyone else's subsequent quotes as well here:

I don't have any hard measured evidence, but it certainly seems like the drive-ability gets worse over time. I believe this is due to slowly degrading the chassis alignment over time from hard use (maybe due to chassis warping from hard bumps, post-competition demos where someone runs it into a wall, etc).

We did our first gyro corrected drive system this year, and it makes a difference, but cant account for everything. Now in our post-season, if we look at the wheels when strafing one always seems to be slightly off from the others; maybe it's not resting on the ground with the same force as the others.

That's what led me to inquire about the utility of the pneumatic suspension benefits of the octocanum drive. I agree we want mecanum to be our primary, higher speed drive, but its seems if all the parts are right there because of the octocanum, it would be a shame not to find a way to add the suspension to the mecanum mode.

But, there's trade-offs with every engineering decision, and we will have to decide if the potential for a loss of pressure and reverting to traction, or some other octocanum failure is too big a risk to take. Or find a solution that doesn't suffer from that drawback.

Re: Octocanum Drive/ Mecanum Suspension Designs?
 

Sure, the scoring platforms disrupt the planarity of the field, but when would you ever need to strafe ON the scoring platform? The primary use of holonomic drives have been in alignment to feeder station and landfill. Expecting mecanums to behave normally while going over or on the scoring platform isn't realistic, with or without suspension.

Re: Octocanum Drive/ Mecanum Suspension Designs?
 

Even when you're driving forward, mecanum doesn't behave as you expect when a wheel is off the floor. The front of the robot will rotate towards the side of the airborne wheel. If it's a front wheel that comes off the carpet, this will tend to rotate the robot so that it is more nearly parallel with the edge you are climbing, usually making matters worse.

And I can certainly imagine wanting to strafe across the scoring platform to cap a stack that was already built, or to pack the stacks in close to each other to leave room for more.

Re: Octocanum Drive/ Mecanum Suspension Designs?
 

I just thought of something and I was wandering if it had ever been done before. Has anyone done a octicanum-like drivetrain with slide drive that can switch to 6-wheel drop-center? It would definitely push it with weight, but it might make it more worthwhile to go into traction mode for prolonged periods of time.

Re: Octocanum Drive/ Mecanum Suspension Designs?
 

You lost me at "octicanum[sic]-like drivetrain with slide drive". Octanum uses four mecanum and four traction wheels. Slide drive (aka H-drive) uses five omni wheels. 6-wheel drop-center uses six traction wheels. Would you mind backing up and taking another swing at this?

Re: Octocanum Drive/ Mecanum Suspension Designs?
 

He is saying basically your idea for the sixwheel with drop down mec's, except instead of octocanum use nonadrive.

Re: Octocanum Drive/ Mecanum Suspension Designs?
 

We've used the Vex Mecanum wheels with Andmark Nanoboxes with No problems at all this year. We have encoders on each gearbox (3D printed bracket), gyro correction, and a very stiff frame. Wheels are set up to drive on to the scoring platform, and strafe to pickup totes in the landfill.

The Nanoboxes have very limited clearance between the upper mounting bolts and the CIM motor. We had to machine down the mounting bolt head OD to make these gearbox noise free.

Re: Octocanum Drive/ Mecanum Suspension Designs?
 

Yay, I didn't confuse everyone!

Re: Octocanum Drive/ Mecanum Suspension Designs?
 

NOTE: I'm saying "switch" because I haven't a clue what the technical term is

Okay, I said octicanum-like because it still involves the ability to "switch" drive trains. Basically, you have six modules with traction and omnis. Then you have a center omni hard mounted to the center in the normal H-drive way. When you "switch" to traction, the wheel in the center gets raised off the ground. When you "switch" back to omni, the traction wheels go back up and the center wheel gets lowered back down to the ground. Did I better your understanding of it?

Re: Octocanum Drive/ Mecanum Suspension Designs?
 

Team 3844 has been playing around with some firestone air springs as actuators that double as suspension. We will have some to give out at Championships next week if you are interested.

Re: Octocanum Drive/ Mecanum Suspension Designs?
 

Unfortunately we won't be at Championships, but if you had a part number, pictures or CAD of your design we'd love to take a look.

Re: Octocanum Drive/ Mecanum Suspension Designs?
 

^Seconded

Re: Octocanum Drive/ Mecanum Suspension Designs?
 

Please explain how so many robots with mecanum wheels are able to drive over the scoring platform perfectly fine at angles. It has quite a lot to do with the gyro/PID correction. (See videos of 1983, 3574 ect on PNW First youtube channel)

Also, if you're strafing ACROSS the scoring platform with your wheels on it how can you cap? The wheels will be where a stack is, unless you're like the High Tekerz and have you're wheels mounted perpendicular to the front of your robot w/ a cutout.



I'd also encourage teams to seriously consider just how much value holonomic motion is adding to your robot.

Ex: In the case of 4488 where everything is automated it is of high value to their game strategy (auto alignment to feeder station)
However, for a team with a built in ramp (2826) they easily align with the feeder station w/ a 6wd because they designed for imprecision, mecanum is of low value to them.

IN NO WAY am I saying that you should never use mecanum, but that you should honestly evaluate every option available to you in line with what Karthik outlines here. If, after honest analysis you believe that mecanum, octocanum or some other holonomic/holobrid is the best option; then go for it.

This section is a word of warning from a team that had a slide drive, and got rid of it because we weren't getting the value we expected out of it.

Re: Octocanum Drive/ Mecanum Suspension Designs?
 

Sounds like you covered the explanation pretty well. Corrections are always possible, sometimes within the time you have to design, build, and program them.

I was thinking more of aligning new stacks with old to make plenty of room. As we decided early not to climb on the scoring platforms (admittedly not our best decision ever), I haven't spent a whole lot of time thinking through these use cases.

Absolutely. We were planning for significant automation in alignment to totes that would have made slide drive essential. At one point, we had used all of our DIOs and had to use two off of the MXP, plus we were hoping to use a camera for left/right (strafe) alignment on totes. When we realized we were unable to program these cases robustly in time, most of the sensors came off.

Same here. At CMP, we'll be driving a 4 wheel omni, and have exactly 3 CIMs and no other actuators. By the time we made the "no strafe" decision, it was too late to go back to 6-wheel to see if it would work better for us, especially if we found out we'd have to switch back. We may very well have a 6-wheel drive for Red Stick Rumble. However, rather than shy away from holonomic, I'm working up some sensor-heavy programming exercises for the summer and fall sessions.

(On a couple of non-drive notes, we now have a better tote lifter that is much more likely to pass inspection than our original spring-cushioned "rake". Despite this, it still has the double end-lift as well as single side-lift capabilities, and is fully capable of doing either on the step as well as the floor. We have also practiced far more tote-flipping since Bayou than we did before. We're striving to make these "inaccessible" totes available to some major stacker 'bots that are running out of "easy" totes. Carson may prove to be the best division we could hope for! )

Re: Octocanum Drive/ Mecanum Suspension Designs?
 

hi all, just thought i would chime in.
this year we used with no suspension and no gyro on a very stiff overbuild 80/20 frame. the only problems we had with driving was when going over the end of the scoring platform when only two wheels were on the floor.

Also though we had some of the most drive practice we have ever had,(about 50-60 hours) As primary driver i already had one years experience.

So my question is this. Is there any advantage to spending an extra week or two in the build season to design these complex drives, coding gyros, and building suspension if those few weeks could have been devoted to the drive team practice? I know this year it paid off to go simple. We made it to the finals in Milwaukee. :D

Re: Octocanum Drive/ Mecanum Suspension Designs?
 

Good point - and I mostly agree. I think you need to have a frame to reference when talking about the benefits that suspension and gyros add to your competitive experience. Over the last 3 years we have gone from a very rigid 80/20 frame, to a kit frame, to kit frame with gyro. In each year we made it to eliminations at our regional. I think a big difference is that (in my opinion) we had better drivers. I think that fact is discounted a lot in the discussions because it's not quantifiable, and by and large, engineers like quantifiable data.

Our rigid mecanum robot did fine over the platform all through competition. I'm sure it would have fared (almost) as well without the gyro. I think the gyro only corrected for direction when we hopped the platform in our auto routine - without that, I definitely would imagine our robot would have hit slightly at an angle and veered off course at least once.

As the starter of this thread, I can say the reason we are looking at a more complex drive (octocanum) is because we love the motion control we have with mecanum, but dislike the "bad defense, no pushing match" stigma it gets. And then, if we are going octocanum, we might as well find a way to get the benefit of suspension if possible. Aside, I do believe our chassis warps over the season and not all wheels make perfect ground contact, and that can skew direction/performance of the mecanum. I believe that is compensated by our drivers, but it would be nice to have something smoother.

100% agree that I'd take a rigid, non-suspended mecanum robot with an amazing driver with lots of practice, over a suspended, gyro-compensated mecanum robot with little drive practice. In my mind driver practice is worth many times more.

Re: Octocanum Drive/ Mecanum Suspension Designs?
 

For 90% of teams, more driver practice is more important than adding extra functionality.
That being said, for that other top 10%, crazy suspensions and drive systems can be worth it.

The other thing to consider in both scenarios is what your students are getting out of it. Cool, crazy drivetrains can be fantastic learning experiences for students. And even if they don't work out competitively, they provide lessons for the future.

This year 20 used mecanum for the first time since 2008. We felt it was appropriate for this game, and with smart programming we could get around the need for a suspension, and we hoped to build a flexible enough chassis.

As usual, though, 20 doesn't really do "non-rigid" when it comes to frame design, and some design hiccups in the middle of build season resulted in 20's weird rigid trapezoidal frame: (https://plus.google.com/108224752813010749343/posts/3qH3xHN5Ghv?pid=6116193614109484338&oid=1082247528 13010749343)

The practice bot strafes and drives perfectly in both autonomous and teleoperated mode, while the competition robot does not. As a result, our practice robot is capable of two stacks/match consistently and a tote stack auto, while our competition robot has yet to show that it can do that.

What this has done was taught the team something. What this hasn't done was win any blue banners (yet. :D)

Was it an off-year for 20? In many respects, yes, but in others, no. We did some really cool things 20 hasn't really done before, and as annoyed as I have been at certain shortcomings of the team this year, in many ways we've stepped up our game.

In summary: Do what's right for your team. (basically the conclusion of every Chief thread these days).