Mecanum Drivetrains

[Gabe1511]

Hello, my team is planning on developing a mecanum drive train to test with, and I was wondering what designs have been successful for other teams. So, what designs have yielded the most success, and where have there been failures and limitations with your designs?

[Pendulum^-1]

Limitation number one: Mecanum wheels are very easy to push. A problem on a field with well-defined chokepoints, such as the 2013 arena.

[Jay O'Donnell]

The Mecanum drive train that 1058 has been successful with in the past is a simple one-CIM gearbox for each wheel and a c-channel frame. When I'm not on a school computer I will edit this post and add a video my team made a couple of years ago explaining our mecanum drive and how it was field oriented (meaning that if you pushed the joystick away from you the robot always goes in that direction, no matter what orientation it is in).

[JeremyLansing]

For the mecanum drives Team 967 built in 2010 and 2011, we used the kit frame with four AndyMark Toughboxes (2010) or AM Toughbox Nanos (2011). It worked out pretty well for us, and although it isn't entirely required, we did use a gyro both years. I put a link to a video of our 2010 robot at the bottom of my post. You will hear a lot of opinions about whether mecanums are worth the effort, and I'm sure someone will bring up the mecanums on Einstein statistic, but if you implement them right, you can still be effective. Just don't expect mecanums to be a magic bullet that makes your robots better. Mecanums are not necessarily better or worse, they play to different abilities that need to be balanced in your decision making process. But since this is the offseason, prototype away!

Edit, added the link
http://youtu.be/fqeAReWKA6s

[Brandon Zalinsky]

To add to Jay's post, we used 4x 30:1/11:1 supershifters with one CIM each. In the past, we have run each of a Jaguar, but we have blown out so many Jags that we have switched back to Victors.

If you want to get creative, you can do all kinds of crazy things with mecanums. For example, in 2011, 1058 built this simple 4-cim mecanum drive with a twist. Each wheel had a third mecanum plate with cut-up pieces of truck mud flap on it. This plate could be actuated into the rollers, freezing the rollers in place, but not the wheel. With these activated, the robot would be a high-traction 4WD that could push other robots around. At the press of a button this would switch to the normal mecanum drive, giving it unmatched speed and maneuverability.

Coming from one of the biggest mecanum fanboys in FIRST- have fun, drive fast, and forget the haters.

[Gabe1511]

Thanks for offering to post the video! My team has been wanting to rig up a mecanum drive train for the past few years, but we've never done it, and I've decided to spearhead the effort this year. Through scouting I've learned the advantages and disadvantages that accompany mecanum drive trains, but I've just wanted to be able to play with one.

[Koko Ed]

Hello, my team is planning on developing a mecanum drive train to test with, and I was wondering what designs have been successful for other teams. So, what designs have yielded the most success, and where have there been failures and limitations with your designs?

Well you guys got to see our drive base in action plenty of times this year and it worked great-until someone focused defense on us.

[Akash Rastogi]

If you want to get creative, you can do all kinds of crazy things with mecanums. For example, in 2011, 1058 built this simple 4-cim mecanum drive with a twist. Each wheel had a third mecanum plate with cut-up pieces of truck mud flap on it. This plate could be actuated into the rollers, freezing the rollers in place, but not the wheel. With these activated, the robot would be a high-traction 4WD that could push other robots around. At the press of a button this would switch to the normal mecanum drive, giving it unmatched speed and maneuverability.


This sounds pretty creative! Do you have pictures or videos of it in action?

[MechEng83]

There are technical and strategic challenges to implement a mecanum drive effectively. I will attempt to briefly address both.

Technical - We've done mecanum for the last 2 years in 1 form or another. Our gearbox of choice is the AndyMark Toughbox Nano - 1 per wheel. I definitely recommend driving the wheel directly out of the gearbox rather than through a chain. We use quadrature encoders on each wheel and have PID tuning to make certain we control each wheel's speed, rather than just input voltage. We use a gyro on the robot to allow field oriented drive, while having an alternate robot oriented drive. Make sure that your frame is not too rigid. The robot can drive eratically if all 4 wheels are not on the ground. Our 2012 robot had what is sometimes called octocanum drive, where we switched between mecanum and traditional wheels. We designed the shifting pistons to support the robot weight on more than 3 wheels. This level of active suspension is not required, but was a side benefit in our 2012 design. Test with the robot weighed down to final competition weight - drives function differently with varying amounts of load.

Stategic - Mecanum is not better or worse than a more traditional drive. It is different. Teams who do not make strategic changes will be ineffective in using a more versatile, albiet, less pushy drive. Almost everyone understands that in a pure pushing match, mecanums will lose. What many people don't realize is that you can maneuver around a robot much more easily to avoid them or get out of a sticky situation. Driver practice is key, as the extra degree of freedom means the driver has an additonal drive component to control. Practice avoidance maneuvers around pushing robots. Practice lining up in the positions you need on the field. It pained me to see teams with mecanum drives this year driving them as a tank robot to get into a specific location, when they just needed to move sideways 6 inches.

[BBray_T1296]

Several Very VERY critical points for a successful mecanum drive:

-SQUARE FRAME. Not as in length (though a square shape IS the most efficient for mecanum), but as in straightness and lack of vertical warping. That is, all 4 wheels need to be perfectly level to get ideal force distribution. If you are worried about having a lifted wheel, put some sort of rubber or spring mount to allow the robot to settle in a planar configuration. When you design the robot, try to create close to a square shape too. We did rectangles both years, but the only way that works is with a "narrow 'bot" configuration. ("wide 'bots" will not work well!)

-WEIGHT DISTRIBUTION. When you construct your 'bot, try to keep your CoG in the center. Not forward, not backward, not left/right, but dead center (ideally). Having a shifted CoG will cause one wheel to have more traction than others (f=uN) and will cause the robot to skew, particularly when strafing. In all drivetrains, low CoG is ideal, so that too, but less importantly.

-DRIVER EXPERIENCE. your drivers need TONS of practice, even if that means playing around with just a base for a while. Know the ins-and-outs of mecanum, and it is advantages. As previously mentioned, mecanum has poor pushing power, but with a skillful driver and well made mecanum (coding is a major factor), you can use the agility to dodge even the toughest defensive 'bot. In 2011, we burned a jag mid competition, and had to compete a match with just 3 operating wheels. From a spectator's perspective, you would not have even known the difference. Of course, holding "up" on the joystick did some funky things, but it was easily correctable for a guy who knew what was going on.

-CODING. Make sure you use encoders, as wheel speed is the single most critical factor. I'm not a coding expert (hardly a grasshopper), but perfectly calculating wheel speeds in all situations (try driving forward, while strafing left, while turning clockwise. Imagine what the wheels have to do!) will really give you an advantage. This is probably the most daunting problem teams have when building mecanums, and where most teams who have tried it and hated it went wrong.

If you don't already, depending on your driver's preference (Xbox or Playstation) get either a wired Xbox controller, or a Logitech controller (http://gaming.logitech.com/en-us/product/f310-gamepad). (wireless Xbox 360 and PS3 controllers are illegal, and I dont think there is a wired PS3 controller, hence the basically identical Logitech). Driving a mecanum robot is a lot like playing a first-person-shooter. Configure the joysticks to replicate how you would play Halo or Call of Duty, except without the "look up/look down" axis. This will make driving feel far more natural to drivers, and will let almost anyone have the basic ability to drive the robot instantly

Both years we did mecanum (2011, 2012) we used toughbox nanos (I dont know the ratio) with mecanum wheels directly on the output shafts. We built custom assemblies to house each wheel including our deflector plates (http://www.youtube.com/watch?v=jl8pHpCjQtY) for hopping the bump in 2012.

[Brandon Zalinsky]

This sounds pretty creative! Do you have pictures or videos of it in action?

Yep! They're around somewhere, i'll find them and post them tonight.

[Gabe1511]

If you want to get creative, you can do all kinds of crazy things with mecanums. For example, in 2011, 1058 built this simple 4-cim mecanum drive with a twist. Each wheel had a third mecanum plate with cut-up pieces of truck mud flap on it. This plate could be actuated into the rollers, freezing the rollers in place, but not the wheel. With these activated, the robot would be a high-traction 4WD that could push other robots around. At the press of a button this would switch to the normal mecanum drive, giving it unmatched speed and maneuverability.

How effective was that strategy? It definitely sounds like it would appeal to my team, giving the best of both worlds.

[Taylor]

Several Very VERY critical points for a successful mecanum drive:

-SQUARE FRAME. Not as in length (though a square shape IS the most efficient for mecanum), but as in straightness and lack of vertical warping. That is, all 4 wheels need to be perfectly level to get ideal force distribution. If you are worried about having a lifted wheel, put some sort of rubber or spring mount to allow the robot to settle in a planar configuration. When you design the robot, try to create close to a square shape too. We did rectangles both years, but the only way that works is with a "narrow 'bot" configuration. ("wide 'bots" will not work well!)
I disagree with this. Many teams encountered difficulties when driving over uneven field. When field components are placed under the carpet, as they often can be, this takes your carefully tuned 'square' base and lifts up a corner or two. I'd recommend taking Nathan's advice and leaving the chassis 'loose' or having some sort of suspension to negate 'imperfections' in the field.

-DRIVER EXPERIENCE. your drivers need TONS of practice, even if that means playing around with just a base for a while. Know the ins-and-outs of mecanum, and it is advantages. As previously mentioned, mecanum has poor pushing power, but with a skillful driver and well made mecanum (coding is a major factor), you can use the agility to dodge even the toughest defensive 'bot. In 2011, we burned a jag mid competition, and had to compete a match with just 3 operating wheels. From a spectator's perspective, you would not have even known the difference. Of course, holding "up" on the joystick did some funky things, but it was easily correctable for a guy who knew what was going on.
We found quite the opposite during our offseason event - rookie drivers with very little practice driving a robot had no preconceived notions about how a tank-style drive handles, so they bobbed and weaved and spun around traffic with ease using our sensor-less and simply-programmed mecanum drive.

[Andrew Schreiber]

I disagree with this. Many teams encountered difficulties when driving over uneven field. When field components are placed under the carpet, as they often can be, this takes your carefully tuned 'square' base and lifts up a corner or two. I'd recommend taking Nathan's advice and leaving the chassis 'loose' or having some sort of suspension to negate 'imperfections' in the field.

This. 1000 times this.

Rigid frames are the death of holonomic systems like this (omni or mecanum drive, swerve is a whole different ball game I don't have enough experience with to talk about).

You want flex because you want each wheel on the ground at all times. Not doing this will result in unpredictable behavior... well, ok, it's completely predictable given that you know that you're driving over uneven terrain and what the normal force on the wheels is and... blah blah blah.

[Jay O'Donnell]

How effective was that strategy? It definitely sounds like it would appeal to my team, giving the best of both worlds.

The locking mecanums were both effective and cool to show off and demonstrate. It's also fun being able to tell people we pushed a traction drive with mecanums.

[Aren_Hill]

The locking mecanums were both effective and cool to show off and demonstrate. It's also fun being able to tell people we pushed a traction drive with mecanums.

Well considering you pushed a traction drive with a traction drive....

I'm also curious for any pictures/videos you have of this system in action, I've played with some locking wheel concepts, but never found anything truly elegant.

-Aren

[nuttle]

A BaneBots P80 on each corner is another option, if the gear ratio works well with the chosen wheel size. This provides a compact, simple, and, in my experience with this application, very reliable drive train.

[pfreivald]

We found quite the opposite during our offseason event - rookie drivers with very little practice driving a robot had no preconceived notions about how a tank-style drive handles, so they bobbed and weaved and spun around traffic with ease using our sensor-less and simply-programmed mecanum drive.

Our first mecanum drive (2010) used 9:1 Banebots p60 gear boxes direct driving four mecanum wheels (and supported on the far side with pillow blocks), and default mecanum code without sensors. The drivers had instant, intuitive control of the machine, because it handles exactly like a 3rd-person shooter with move/strafe--if you play COD or Fallout or whatnot, you've got the basics down already.

The thing to realize about uneven terrain is that mecanum drives work just like tank drive (or close enough that it makes little matter to a human driver) when going forward, backward, or turning normally...the concerns about uneven terrain are, by and large, overblown.

We've since gotten much more sophisticated, with gyros and encoders and octocanum, but the initial mecanum drive we played with was the easiest drive train we've ever built, programmed, or driven--it barely qualified as an afternoon project to get it up and running.

[Jared]

When building a mecanum drive, it can be helpful to create some type of suspension so that each wheel has the same weight above it. It can be as simple as having the pair of back wheels on a pivot.

Remember, driver practice is really important.

Also, be careful of any bumps on the field. When aligning with the pyramid this year, the little 1/2" bump in the floor caught our mecanum wheels, and made it really hard to line up.

Finally, realize that there are many teams that will immediately disregard your robot in alliance selections. While I don't agree that all mecanum robots are bad, many teams have this opinion, and just won't choose a mecanum robot for eliminations.

[Andrew Schreiber]

Finally, realize that there are many teams that will immediately disregard your robot in alliance selections. While I don't agree that all mecanum robots are bad, many teams have this opinion, and just won't choose a mecanum robot for eliminations.

This opinions is based on the fact that given a robot with 6wd or an mecanum drive the 6wd offers more tactical flexibility in that they can hold their ground better should I need to stick them in the way of someone else for a couple seconds. The exception to this was in 2012 - Mecanums were practically DNP for me due to their difficulty with the bridges.

Please don't assume it's a bias AGAINST mecanum, perhaps it is merely a difference in priorities and needs.

[MechEng83]

The exception to this was in 2012 - Mecanums were practically DNP for me due to their difficulty with the bridges.

I would put our 2012 driver using mecanums against any other robot in terms of bridge balancing. We nick named him "bridge-dancer" that year because he could do fancy manuevers on the bridge, including driving across while turning 90 degrees to accomplish a triple balance.

[Jared]

This opinions is based on the fact that given a robot with 6wd or an mecanum drive the 6wd offers more tactical flexibility in that they can hold their ground better should I need to stick them in the way of someone else for a couple seconds. The exception to this was in 2012 - Mecanums were practically DNP for me due to their difficulty with the bridges.

Please don't assume it's a bias AGAINST mecanum, perhaps it is merely a difference in priorities and needs.

For 2012/2013 I agree that mecanum wheels were a poor choice. Our team used them, and now every member on the team hates them with a passion.

At our regional, we only picked other robots that could function as a defensive robot, so mecanum wheeled bots were off the list, even through we had mecanum wheels on our robot, which we quickly decided to remove/replace with hi-grip wheels.

However, for 2011, there were some good first picks that had mecanum.

[pfreivald]

I would put our 2012 driver using mecanums against any other robot in terms of bridge balancing. We nick named him "bridge-dancer" that year because he could do fancy manuevers on the bridge, including driving across while turning 90 degrees to accomplish a triple balance.

Yup. Our mecanum wheels had no issues whatsoever with the bridge.

[Andrew Schreiber]

I would put our 2012 driver using mecanums against any other robot in terms of bridge balancing. We nick named him "bridge-dancer" that year because he could do fancy manuevers on the bridge, including driving across while turning 90 degrees to accomplish a triple balance.

Yup. Our mecanum wheels had no issues whatsoever with the bridge.

Interesting, every mecanum drive system I saw that year (excepting 357) had issues with the bridge. What wheels? Did you do anything to the rollers? What sort of feedback did you have?

[pntbll1313]

Interesting, every mecanum drive system I saw that year (excepting 357) had issues with the bridge. What wheels? Did you do anything to the rollers? What sort of feedback did you have?

Our mecanum was also very good going up the bridge. We had a good bridge lowering device but often had to go up second to help push another mecanum up.

Single Balance
http://www.youtube.com/watch?v=fWYN5xVIyzw&t=11m1s

Here is one of us double balancing
http://www.youtube.com/watch?v=fWYN5xVIyzw&t=13m15s

We just had the 8" andy Mark wheels.

[Caleb Sykes]

Interesting, every mecanum drive system I saw that year (excepting 357) had issues with the bridge. What wheels? Did you do anything to the rollers? What sort of feedback did you have?

One of the important things in 2012 was to set your speed controllers to brake mode and not coast mode if you were using mecanum drive. As much as a problem as this would have been for a 6WD, we found very early on that trying to balance with these settings was near to impossible with mecanum.

I don't know for certain, but I'd be willing to bet that a lot of the bad bridge-balancing mecanums never did this.

[pfreivald]

Interesting, every mecanum drive system I saw that year (excepting 357) had issues with the bridge. What wheels? Did you do anything to the rollers? What sort of feedback did you have?

Andymark wheels, standard, no feedback whatsoever. We were planning on using our traction wheels (octocanum), but found that by and large we just didn't need to. (We did use them to "downshift" to push other robots up the bridge, but we had no issues getting ourselves up/down the bridge.)

[BBray_T1296]

I disagree with this. Many teams encountered difficulties when driving over uneven field. When field components are placed under the carpet, as they often can be, this takes your carefully tuned 'square' base and lifts up a corner or two. I'd recommend taking Nathan's advice and leaving the chassis 'loose' or having some sort of suspension to negate 'imperfections' in the field.

We found quite the opposite during our offseason event - rookie drivers with very little practice driving a robot had no preconceived notions about how a tank-style drive handles, so they bobbed and weaved and spun around traffic with ease using our sensor-less and simply-programmed mecanum drive.

Brace yourselves, a text wall is coming! :ahh:

After some distraction, that post really was badly typed. Red: You will notice my post did mention the recommendation of using of some sort of springy material to absorb deformities. That being said, on both of our robots, in 2011, and in 2012, we had our typical solid-as-a-rock welded aluminum box tubing frames. These were set and welded by one particular employee at our sponsor's shop, with precision as a top priority. For this reason our frames are extremely rigid and (realistically) perfectly 'square'. Like the instance I mentioned in the first post, we were subject to, and did experience raised/disabled wheels in the competition. But! because (Blue:) we controlled our drive not with motor power, but with motor RPM (using encoders), we had almost no trouble at all. When a wheel is lost (for whatever reason) and the driver attempts to do anything, the left side with only 1 wheel suddenly finds itself with half the torque of the right side with both wheels at matching PWM input. The code detects that the only left wheel is not spinning as fast as the right wheels while the robot tries to go, so it amps up the power to the lacking wheel to match RPMs, and thus balances the torques*. This operation was also the case when the robots were strafing. This whole scenario was a very rare occasion though, as most obstacles in 2011-2012 were faced head on anyways (ramps/key in 2012, minibot poles in 2011), so 2 wheels climbed the bank at the same time, making the leveling problem a non-issue. I concede the obstacle of 2013's pyramid, and who knows what 2014 will have in store, so I concur, I am making the recommendation to put springs or some other form of 'loose' configuration on future mecanum 'bots.

*while the 3 wheels are not slipping (or in mecanum's case: equally slipping), the only way they can all turn at the same speed is with the lone wheel compensating for it's disadvantage with double the torque

As for (Green:) driver experience. Like I said, This will make driving feel far more natural to drivers, and will let almost anyone have the basic ability to drive the robot instantly.
That being said, a driver with hours of practice will be able to more efficiently and more effectively traverse the field, avoiding defense 'bots and evading traps. Magenta: These guys are trying mecanum for the first time, likely from some variant of tank drive last year. Any drivers-to-be on the team (who will more than likely NOT be rookies) will have probably driven this year's robot, an thus will, likely, have "preconceived notions about how a tank-style drive handles." Sometimes it can be easy to forget the strafing ability, especially in the heat of a match when you are used to driving tank from an event in the past (or simply spending hours driving a tank 'bot while waiting for the mecanum base to be finished).

One last rant: Green again: In every single last instance possibly imaginable, tons of practice is superior to a lack thereof. Commercial pilots spend thousands of hours training in flight simulators before they operate a real jet. Imagine handing me a copy of Flight Simulator X and saying "you have one hour". After that one hour, you stick me in the captains seat of a 747 and tell me to fly to Seattle. Not the best idea, I have to say. Same goes for a FRC robot. If practice is so worthless, and anyone can drive the robot as well as a trained 'pro', why not hold a school wide raffle on Thursday before your regional. One lucky student gets to drive the robot in competition, be it a band kid or a cheerleader. Maybe you could sell the tickets-what a great fundraising idea!

have fun, drive fast, and forget the haters.

[MechEng83]

Interesting, every mecanum drive system I saw that year (excepting 357) had issues with the bridge. What wheels? Did you do anything to the rollers? What sort of feedback did you have?

Encoders on all 4 motors (rationale and details would require a separate post with lots of minutiae and some drawings) for closed loop speed control with tuned PID values. Andymark 6" regular mecanums. No special modifications to the rollers other than making sure each one spun freely on its axis.

[colin340]

i love Mecanums!!

But in competitive applications like first, i believe is the words of Colin Chapman (founder of Lotus cars) -- “Simplify, then add lightness" Mecanums do neither!!

now i'm hugely biased as the gang of mentors i hang with is all about 6 or 8 WCD.

granted some 340 students are working on a Mecanum as we speak.

[yash101]

Limitation number one: Mecanum wheels are very easy to push. A problem on a field with well-defined chokepoints, such as the 2013 arena.

I have to disagree with this. We were able to easily push around the other robots. We used four CIMs, one on each wheel.

Even if you are being pushed around, the maneuverability of mecanum allows you to typically free yourself easily.

Mecanums are quite a friendly drivetrain if you want to have full control on how you move, without getting way too complicated. It will go on just as regular wheels would, however, using a separate transmission for each wheel. The rest of the changes required are all in the robot code. Also, if your mecanum robot code isn't ready, your standard code will work, only without support for the advanced features like sideways driving
:D :D :D :D :D

[cmrnpizzo14]

There are enough teams in the FLR area that you can find some easy resources right in town. 3173 has used mecanums this year and 2011. 191 has used it prettymuch every year I believe. 1551 has used mecanum or octocanum.

Honestly, we enjoyed our experience with it but we felt that we could accomplish equal or better driving with a simple kitbot on steroids. We prototyped it over the summer and loved it.

Tips:

-Remember to have your wheels in the "X" configuration as opposed to the "O"
-Nanotubes make construction very easy and helps save the hassle of chains but they are heavy and rather difficult to get to the bolts. If these are used, purchase spares for competition so that you can simply swap the whole nanotube instead of trying to pull one wheel off. We have found this to be faster.
-Keep the frame square but flexible. We found that this was difficult this year. If a frisbee became jammed in our hopper the best method to free it in match was to ram the wall. This freed the frisbee (most times) but unfortunately would mess up our nice square frame because we could not keep it perfectly rigid. We had a strategy this year that was not too reliant on driving so it wasn't a huge deal but our chassis team did have to resquare the frame after many matches.


For fun, ask 578 about their mecanum tank treads that Eric D. created. Inefficient, heavy, largely useless, but very cool.

[EricH]

It will go on just as regular wheels would, however, using a separate transmission for each wheel. The rest of the changes required are all in the robot code.

This is a HUGE benefit of mecanum if it's your first time doing it. You can even (should you build a practice robot) build for an easy switch. 330 did that in 2005--never did put the extra trannies onto the competition robot, though; it stayed as a 2-gearbox, 6WD despite having the ability to go mecanum.

One thing I haven't seen brought up, but I've seen on a mecanum drivetrain (not on the competition robot for that year, just a test mule): If you have a heavy-ish load located well outside your frame perimeter, don't expect to be able to strafe straight without closed-loop control. This goes back to the whole "keep all 4 wheels on the floor" principle, but more along the lines of "keep the same weight on all 4 wheels" to the best extent that you can.


Oh, and my opinion of mecanum is this: If properly executed, and in a game that actually requires the extra mobility, and properly used, it's a pretty big advantage, until you run up against a swerve. The swerve is better in terms of traction, and worse in terms of complexity. If, however, the mecanum is not properly executed, or used properly, or the game doesn't actually require the extra mobility, then the team could have probably used the weight better by building a 6WD (or similar tank drive) and allowing for more material elsewhere in the robot. Probably. (Note that this does not apply if "cool" is a driving factor in the design more than "competition effectiveness" is, or to any offseason robot built for non-competition purposes.)

[pfreivald]

1551 has used mecanum or octocanum.

We've used octocanum the past two years, and mecanum three others--and we're always upping our capabilities, especially with control. One thing I have my programmers working on this fall is using the gyro to compensate for wheels not working the way you want them to because you're driving over an irregular surface.

It's...interesting, anyway!

Either way, if you want to come down and check out what we've done in more detail, let me know and we'll set something up.

[Chadfrom308]

Our team in 2012 used mecanum wheels with regular traction wheels. The mecanums were on an offset axle that got pushed down with pnumatics. We were able to drive really well and place some nice defense.

I will say though, you have to be careful. Mecanums are can be dangerous. We got stuck on a ball one match and literally tore it to shreds in seconds. We also ran over team 67's go pro and spun our mecanums on it by accident. Luckily it was okay! I wish I could've saw that video though...

[pfreivald]

I will say though, you have to be careful. Mecanums are can be dangerous. We got stuck on a ball one match and literally tore it to shreds in seconds. We also ran over team 67's go pro and spun our mecanums on it by accident.

Is that more dangerous than any other drive train?

Also, I would like to see that video, too!

[Brandon Zalinsky]

This sounds pretty creative! Do you have pictures or videos of it in action?

Here (http://www.youtube.com/watch?v=DdhWSo_4WQ0&feature=youtu.be)'s the design and implementation of the Locking Mecanum Drive 1058 built in 2011. I threw in some match footage for you guys too!

With regards to what Jay said about Field-Oriented Drive, here (http://www.youtube.com/watch?v=HT3WhTcQvw4)'s a video for that.

[Madison]

Here (http://www.youtube.com/watch?v=DdhWSo_4WQ0&feature=youtu.be)'s the design and implementation of the Locking Mecanum Drive 1058 built in 2011. I threw in some match footage for you guys too!

With regards to what Jay said about Field-Oriented Drive, here (http://www.youtube.com/watch?v=HT3WhTcQvw4)'s a video for that.

If I'm understanding this correctly, the rollers are stopped only be the pin / screw / post that goes through the 2nd hole you drilled near each rollers' axle?

[BrendanB]

1058 is definitely one of those teams that has re-defined how to use mecanums effectively in the game. Their 2010 robot with the field oriented drive performed amazingly throughout the 2010 season. It was fast, responsive, very agile, and played some very mean mid-field offense!

I didn't get to see too much of their 2011 robot but I've heard a lot of stories about what they pushed.

Their 2007 and 2008 mecanum drives were also effective players of the game.

While mecanums still aren't my personal choice to use in a drivebase they can make for a great off-season project for a team. Plus they make excellent demo robots.

Use in a competition is a different story but every team needs to make decisions when they design their robots. There have always been times where being able slide sideways is advantageous and mecanums are a very easy way to achieve it. There are downsides that go with them but there are downsides of every mechanism you put on your robot.

In the end, no matter what drivebase you go with the best thing you can do is train your drivers and give them time to practice under realistic circumstances. While our team doesn't use multi directional drives we've trained our drivers to react faster so they can quickly maneuver around obstacles without us giving them another direction. We use old robots, chairs, trash cans, simulations, etc to keep them on their toes so when their path is blocked they don't stop moving while maneuvering.

Practice, practice, practice and the decisions you make at the beginning of the season will pay off no matter what drivebase you use.

[Brandon Zalinsky]

If I'm understanding this correctly, the rollers are stopped only be the pin / screw / post that goes through the 2nd hole you drilled near each rollers' axle?

In the first shot in the video, the new hole that is being drilled is to help hold on a piece of rubber. The wheel itself is left unmodified, and we take a third mecanum plate and put one piece of rubber on each "wing" or flange of the plate. When the piston is activated, it pushes that aluminum bar you see in the video into that third plate, which is mounted parallel to the mecanum wheel. This pushes the rubber piece into the wheel, braking the roller.

The plates are on the same axle as the wheel and are spring loaded, so when the piston retracts, the plate comes off the wheel, unbraking the roller.

[Akash Rastogi]

In the first shot in the video, the new hole that is being drilled is to help hold on a piece of rubber. The wheel itself is left unmodified, and we take a third mecanum plate and put one piece of rubber on each "wing" or flange of the plate. When the piston is activated, it pushes that aluminum bar you see in the video into that third plate, which is mounted parallel to the mecanum wheel. This pushes the rubber piece into the wheel, braking the roller.

The plates are on the same axle as the wheel and are spring loaded, so when the piston retracts, the plate comes off the wheel, unbraking the roller.

I have to admit, that is a great little feature! How well did it work out for you in a real match against defense?

[Brandon Zalinsky]

I have to admit, that is a great little feature! How well did it work out for you in a real match against defense?

Very well, even though we encountered very little defense focused solely on us. We'd do a "roll", where we'd activate the traction drive, plow into the side of the defensive robot, go back to mecanum mode, and push towards the goal while rotating the robot. This would cause us to roll off the side of the defending robot and get past them. In other situations, we could just outdrive them with the agility of the mecanum wheels. The biggest advantage of the locking mecanums is if an opposing robot is pushing you sideways, you can stop dead with a push of the button and, amusingly, confuse the hell out of the opposing robot's drivers.

[yash101]

Team 1165's Mecanum Test! Mecanum is nothing but pure amazing, and it actually seems like magic, especially with the wheels covered up so no one can see them
http://www.youtube.com/watch?v=_Lrosi-WA7A

[pfreivald]

Very well, even though we encountered very little defense focused solely on us. We'd do a "roll", where we'd activate the traction drive, plow into the side of the defensive robot, go back to mecanum mode, and push towards the goal while rotating the robot. This would cause us to roll off the side of the defending robot and get past them. In other situations, we could just outdrive them with the agility of the mecanum wheels. The biggest advantage of the locking mecanums is if an opposing robot is pushing you sideways, you can stop dead with a push of the button and, amusingly, confuse the hell out of the opposing robot's drivers.

A lot of the same advantages of octocanum, though with octocanum you can do a 5:1 or greater downshift with little weight and cost built in.

[Lil' Lavery]

Being able to execute a "roll" maneuver is pretty much the tempts me towards omni-directional drivebases (and some fine tuning near goals like 2005, 2007, or 2011). That being said, I don't anticipate it happening anytime soon on 1712 and it's only useful if the field has enough space for it to be executed (so it rarely solves choke point defense). 1640's swerve drive roll maneuver is probably my favorite, though. So beautifully executed this season.

[pfreivald]

Being able to execute a "roll" maneuver is pretty much the tempts me towards omni-directional drivebases (and some fine tuning near goals like 2005, 2007, or 2011). That being said, I don't anticipate it happening anytime soon on 1712 and it's only useful if the field has enough space for it to be executed (so it rarely solves choke point defense). 1640's swerve drive roll maneuver is probably my favorite, though. So beautifully executed this season.

In terms of actual competitiveness, I wouldn't recommend straight mecanum for teams seeking to become elite. Some kind of omnidirectional drive combined with high-torque pushing is, I think, the best of both worlds, and of those kinds of drives, octocanum has been the best solution for us so far--it's certainly a lot simpler and lighter than swerve.

[wilsonmw04]

In terms of actual competitiveness, I wouldn't recommend straight mecanum for teams seeking to become elite. Some kind of omnidirectional drive combined with high-torque pushing is, I think, the best of both worlds, and of those kinds of drives, octocanum has been the best solution for us so far--it's certainly a lot simpler and lighter than swerve.

no matter how accurate your statement is, mecanum is a great solution for many small teams. They are easy to build. They are easy to drive. They give young and/or small teams a reliable with a relatively small investment.

Octocanum is a wicked drive train. we developed a version last summer, Ran it with some success last year and perfected it this summer. I really hope the game allows us to use it this year.

[pfreivald]

no matter how accurate your statement is, mecanum is a great solution for many small teams.

I disagree. They're a neat application for many small teams (trust me, it doesn't get smaller than 1551, or at least not by much). For competitive advantage, the KBOS is a better solution for those who can't to octocanum or some other variant which provides pushing/shoving/defense/plowing-through-defense capabilities.

Octocanum is a wicked drive train. we developed a version last summer, Ran it with some success last year and perfected it this summer. I really hope the game allows us to use it this year.

It's a rare game that won't. We're very happy with ours, but I'd love to see how you've "perfected" it.

[wilsonmw04]

It's a rare game that won't. We're very happy with ours, but I'd love to see how you've "perfected" it.

Not to hijack the thread, but... :-)

Here is our prototype last summer

http://www.youtube.com/watch?v=QPBly4Hin9o

We have two major issues:
1. The chain kept jumping/ alignment issues during shifting

2. There was so much tension on the chain that is was stretching and needing to be replaced every few days.


We did some mods with the piston and changed from #25 to #35 chain. Created spacers to fix the small alignment issues and we now have a pretty darned good drive train. We had rookies driving it this fall and went through 10 or so off season matching without a chain coming off or any major issues. We are looking at optimizing the weight of our modules, but I am pleased with the results:

http://www.youtube.com/watch?v=oBP3pLThZls

When I stated I hope the game allows us to use the octocanum, I'm hoping not to have large obstacles to traverse like Breakaway or Rebound Rumble.

[yash101]

The idea of locking mecanums is a great idea and I will share it with my team. We were going to switch to Swerve/Crab because it gives a greater traction, allowing the robot to defend well. This will allow us to implement a "Defend Mode" or a "Hybrid mode", where the root automatically switches after the wheel RPM reaches a certain amount!

[pfreivald]

Not to hijack the thread, but... :-)

We reduced the weight of ours like crazy by using 2" Colson wheels and belts instead of chains. The difference in wheel size allowed us to get a 5:1 reduction in mecanum vs. traction drive with very, very little weight or complexity.