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  #106   Spotlight this post!  
Unread 14-04-2014, 21:31
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Tyler2517 Tyler2517 is offline
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Re: Swerve Drive vs Mecanum Wheel drive?

As a Team who has had both a swerve drive and a mecanum drive. I love our swerve drive. In our teams history we have built 2 mecanum drives 2 tank drive's(if lunancy counts) 1 crab drive(failed so bad) and 1 swerve(2014).

In 2010 my team attempted a crab drive(they call it a swerve). At that time my team did not use cad. The drive was huge 80/90 pounds and did not work... ended up trying to keep it driving straight with zip ties....

In 2011 we did the first mecanum drive. This was the best performing robot up to this point we used the standard AM frame. When using it we never had problems with being pushed. It was very slow though much slower then i would have liked and the drive frame was heavy.(i think our team just builds heavy drives) But it was still a good drive.


2013 We went back to our mecanum drive this time using lighter gear box's. this drive could not strafe very well at all. The rollers had way to much friction. We got pushed around a lot. Even though it was geared on the high end it never reached that speed. Could not drive straight at all. We got it to work in the end but not nearly as well as in 2011

2014 We built a 4 wheel independent swerve.

My team has never had very good metal working tools. We had a plazma cam that we used a lot but when our metal shop teacher passed the new one wanted nothing to do with us. Losing us all of our metal working tools. We do have a very small CNC that breaks a lot. (it was on a total of 30 minutes the whole year). but one of our mentors has access to a cnc shop that we can use.(limited use) The day of kick off we lost our best mechanical student and our coach.
But that did not stop us. We had to travel to Portland Community Collage they have mills and laths we can use their (all manual). Me and my sister managed to manual mill/lath the swerve in 4 weeks. The first week was updating the design. We then pulled 3 weeks of going to school/machining as our whole life. We used a mentors CNC shop for some parts that their were to many of to manually make or to tight on tolerances for a total of less then 5 hours of CNC work.
If their is a want their is a way.

The performance of the swerve drive was a dream. It is the fastest drive we have ever built. It can also plow our mecanum drive our of the way in static tests in the shop.(on official carpet) It was very powerful. It was also 4 pounds lighter then last years mecanum drive and 10 lighter then 2011. With each modular weighing in at 7 pounds 4-8 ounces. The swerve drive out performed every drive we have ever built up to date.

Half of the reason i am in favor of the swerve drive over mecanum is that it presents real engineering problems. The felling our team got when it was driving for the first time was truly amazing. We got our first engineering awards this year because of it. It was a lot of work but it was worth it even if we did not win.
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Unread 28-05-2014, 17:07
Happy Birthday! RRLedford RRLedford is offline
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Re: Swerve Drive vs Mecanum Wheel drive?

After reading through most of this thread, I am posting ONLY in regard to the question of whether the performance level of a poorly designed/build mecanum drive is very much different from an excellently designed and built mecanum drive.

My teams mecanum drive experience is limited to this year's 2014 FTC competition (we do both FRC: 3135 & FTC: 3507). After evaluating VEX 4" mecanum wheel, we made a last minute decision to switch to mecanum midway through our FTC bot tank build (but completed the tank too in case mecanum was a bust).

The PICS below show the basic concept of our design. This was a more robust implementation of a mecanum drive than what your typical FTC mecanum efforts are like. Twice when a slightly errant autonomous route had us collide with the scoring buckets' balance beam, we became wedged under it, going back on our rear wheels only, and totally lifting one entire side of the hanging bridge, while doing a wheelie, as we pushet it across the field, yet no damage to drive train resulted.

We were not pushed around very much by tank drive bots and could play decent defense. Granted that at FTC level, not as much drive train differences can be seen between drive type designs (compared to at FRC level). However, the point I make is that, compared to the other mecanum drive bots we saw, there was a lot of difference between a good design and a weak design.

Our "H" frame had just enough flex to help keep all wheels down most of the time, yet stiff enough to deal with high stress situations. We were able to position accurately on the sloped bridge and were stable once locations were reached. The soft urethane of VEX wheels was very grippy and gave excellent traction, better than Andy Mark 4" mecanum wheels. Our weight was fairly evenly balanced. We won a design innovation award at our 2nd regional qualifier and were first seeded team captaining the winning alliance at 1st regional. We were 2nd seed in state after qualifying rounds.

Bottom line is there was a significant range of performance difference between the weaker mecanum designs/builds of bots (not very many though) compared to ours. We plan to add field oriented gyro control, improve our speed, and do an independent wheel suspension scheme for our next year's FTC mecanum build, unless the game design makes mecanum an inappropriate option. Our first FRC mecanum drive could also be happening later in 2014.





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Last edited by RRLedford : 28-05-2014 at 17:09.
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  #108   Spotlight this post!  
Unread 01-06-2014, 02:50
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Re: Swerve Drive vs Mecanum Wheel drive?

Quote:
Originally Posted by Alan Anderson View Post
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.
It's been a while, but I'll reply anyway...

While it's true that you can make improvements like these, they are more design solutions and optimizations rather than conceptual changes. A mecanum wheel, no matter how well deisgned, will still be just that: a mecanum wheel. Rollers tilted at 45* angles on a wheel. There can't be any kind of mecanum revolution unless somebody figures out how to lock the rollers without wasting weight.
This is not a bad thing, as optimization is a very good thing and makes good ideas better, but it does show inherent limitations in mecanums. Other kinds of drives can be done in many different ways by comparison.
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Unread 01-06-2014, 16:11
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Jalerre Jalerre is offline
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Re: Swerve Drive vs Mecanum Wheel drive?

I haven't used both but I say choose swerve over mecanum. Mecanums don't have as much power and most teams write them automatically and will be hesitant when choosing a team with mecanum drive train for an alliance. However, don't listen to those people who that say mecanums are horrible. We've used them before in the past and their not that bad. They are much easier much to build and program than swerve.
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Unread 02-06-2014, 01:55
Spencer Chinske Spencer Chinske is offline
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Our team is currently going through a similar debate. We think a swerve drive is great but are unsure if we can get one working reliably over the summer. In the event that we can't, we will be trying an octacanum drive train. For those of you who don't know, with an octacanum drive train you can toggle between high grip wheels and mecanum wheels. Secret city wildbots (4265) built a fabulous octacanum chassis this year. I would possibly look up an octacanum drivetrain because you can get the pushing power of a standard drive with the maneuverability of an omnidirectional drivetrain like a swerve or mecanum. Secret city wildbots (4265) can be found on YouTube under "dragonfly reveal".
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