Swerve Drive vs Mecanum Wheel drive?

[Chadfrom308]

We have actually never had any problems with our encoders, even when one broke, the rest of the PIDs made up for it.

As for Field Centric, we never used it. It is way faster to do robot centric.

85% of the time, we don't use the strafing feature of the mecanums. But, the most important 15% we use them. (Like lining up the 1pt goal and lining up for inbounding)

And that has made it worth while

[Ben Wolsieffer]

Originally Posted by Ether

Is there something unique about the way you did it?

Field oriented control has been around for a number of years. It's built-in to LabVIEW and WPILib for Java and C.

It's most unique aspect is that it could automatically correct its orientation when we were pushed or lost traction on a wheel, which made our system much easier to control than it would have been without it and it allowed us to travel in an absolutely straight line, unlike it the past where going sideways often went in an arc instead. This prevented us from needing to be so obsessive about weight distribution, because we could just let software fix our problems.

[Ether]

Originally Posted by lopsided98

It's most unique aspect is that it could automatically correct its orientation when we were pushed or lost traction on a wheel, which made our system much easier to control than it would have been without it and it allowed us to travel in an absolutely straight line, unlike it the past where going sideways often went in an arc instead. This prevented us from needing to be so obsessive about weight distribution, because we could just let software fix our problems.

Share the technology: write a paper!

Originally Posted by lopsided98

I read about the idea on CD and decided to implement it...

... and give credit where credit is due

[Ben Wolsieffer]

Originally Posted by Ether

Share the technology: write a paper!



... and give credit where credit is due

I don't have time to write up about it at the moment but I probably will during the offseason. For now, here is the code for it if anyone is interested in looking at or adapting it for their own use: https://github.com/RobotsByTheC/CMonster2014.

I would tell where specifically I got the idea from on CD, but I don't really remember anymore.

[efoote868]

Originally Posted by lopsided98

As a mecanum lover, it really annoys me when people automatically rule out mecanums when the really don't know what they are capable of. Our robots in 2010 (http://youtu.be/rdAKiuimaY4?t=58s) and 2012 (http://youtu.be/tdAncHeHOEQ?t=1m36s) had mecanums and they could traverse the bump and balance on the bridge.

Yep. Same with my old team, and we were very competitive those years.

[JohnM]

This year is our first year using mecanum wheels, and I have to tell you, I love them. I'm not a big fan of trying to switch to swerve drive next year because we still have not mastered mecanum wheels.

John M

[kk052]

this year was our first time of swerve, that said it saved our robot, it defenetly has its benifits, and if you where just given both drives on the feild without the need to make or program them, swerve will usually win over machanum. but there are businesses that sell machanum (get them from andymark), but there are none that sell full swerve drives, even though you could buy the lower end of the andymark crab drive, so it will come to desighn, if you biuld a good working swerve, it will beat mach, but if your swerve isn't well made, like how our encoders would slip on our's (locktite fixed that) it will not even move. i would recommend adding a third option of a dual drive/octanum, for a well made swerve will nearly always win a machanum.

[asid61]

The problem with mecanum IMO is that they are basically the end. Apart from octacanum drives, mecanums don't have many places to go to design-wise. I think they will remain the same for a long time.

Swerve and tank drives, on the other hand, have a room for improvement. 221's Revolution Swerve weighs only a couple pounds per wheel, and their in-wheel Wild Swerve is fantastic. However, I still think that there is room for improvement- nobody's just found it yet.
Tank drives have changed little over the past few years, but gearboxes get more interesting every year.

[Alan Anderson]

Originally Posted by asid61

The problem with mecanum IMO is that they are basically the end. Apart from octacanum drives, mecanums don't have many places to go to design-wise. I think they will remain the same for a long time.

I can think of several directions for improvement of mecanum-style wheels. Figuring out a way for the rollers to never stick would be at the top of my list, followed by a simple roller lock to improve the maximum forward torque before losing traction, and eventually adding powered rollers to give better sideways power.

Optimizing mecanum material selection and mechanical design isn't done at all. Just increasing robustness while decreasing weight would go a long way toward making mecanum wheels better for FRC team use.

[XaulZan11]

Originally Posted by efoote868

we were very competitive those years.

I'd agree with this 100%. But, at least in 2012, I think you were competitive because of your accurate shooter and probably not your drive train (I wonder if you would have been better on bridges with a traction drive). Like you mentioned earlier with the good teams that build swerve probably are the teams with good scoring mechanisms and good team organization. These teams will be competitive no matter what drive train they select. Drive train selection is even more important for the fringe competitive teams; teams who may or may not have consistent scoring mechanisms or who may or may not have ample time to practice. The competitive teams that will have consistent scoring mechanisms and gave their drivers enough practice will be competitive with a swerve, tank or mecanum drive.

[The Doctor]

My experience with mecanum is that it causes a serious power drain when strafing (going sideways). Our battery is usually at 11.5v when going forward (using 4 CIM motors & Toughboxes), but it drops to 8v when strafing.

[Ether]

Originally Posted by The Doctor

My experience with mecanum is that it causes a serious power drain when strafing (going sideways). Our battery is usually at 11.5v when going forward (using 4 CIM motors & Toughboxes), but it drops to 8v when strafing.

Too much friction in the rollers.

It can be quite tricky to obtain an acceptably small level of roller friction in the affordable COTS mecanum wheels used by most FRC teams.

[ekapalka]

Originally Posted by BBray_T1296

They work an unbelievably better when controlled by encoders and PID

I've heard that PID control begins acting unusually when you have a constantly moving setpoint because the tuning parameters were only set for one particular speed. Is that not so, or has your team found a way to work around this (such as a lookup table for different setpoints)? My team never really got around to putting encoders on our wheels, and as a result wound up tediously multiplying each wheel by a particular constant depending on its direction (because our motors have a 20-30% speed bias in a particular direction), which was a pain to figure out through trial and error.

Originally Posted by lopsided98

I don't have time to write up about it at the moment but I probably will during the offseason. For now, here is the code for it if anyone is interested in looking at or adapting it for their own use: https://github.com/RobotsByTheC/CMonster2014.

I've been tentatively skimming through this code for around half an hour and can't seem to find where the magic happens... I'm not particularly accustomed to the command based model :P Could someone point me in the right direction? Thanks!

[Niezrecki]

Originally Posted by Joe195

Overall, swerve drive has much better control, but is very challenging to design and program. Mecanum is easier to program, but doesn't give you the same power. I would say swerve drive is better, but only if your team can use it to its fullest potential

I am in full agreement. We have done swerve drive before and it has the ability to keep control and deliver some amount of force as well. Swerve also commonly consists of one CIM per wheel which delivers a nice amount of power. Mecanum has a history of being pushed quite easily in FIRST and tends to impress other teams less. Swerve however definitely delivers a better turning capacity than Mecanum. It's also beautiful to watch. I am looking at you Apple Pi (2014).

[Citrus Dad]

From a scouting perspective, we heavily discount robots with mecanum drive because they don't have the same defensive abilities as tank drive. To be honest, we haven't see a high-scoring mecanum drive robot, even at Worlds, so I don't have an opinion about the use there.

Offensive robots with swerve are amazing. 368 was amazing on our alliance at SVR, and of course 1717 has produced some of the best robots possible.

My assessment: if you're not ready to contend for being one of the very best robots at your regionals, then stick with tank drive, but if you're going to make that plunge, choose swerve over mecanum.