Mecanum Drivetrains

[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

[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.

[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.

[Akash Rastogi]

Originally Posted by Flak-Bait

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?

[Brandon Zalinsky]

Originally Posted by Akash Rastogi

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.

[Brandon Zalinsky]

Originally Posted by Akash Rastogi

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

Here'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's a video for that.

[Madison]

Originally Posted by Flak-Bait

Here'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'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?

[Brandon Zalinsky]

Originally Posted by Madison

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]

Originally Posted by Flak-Bait

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]

Originally Posted by Akash Rastogi

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.

[pfreivald]

Originally Posted by Flak-Bait

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]

Originally Posted by 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.

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.