To Strafe or not to Strafe

[cglrcng]

To Strafe, w/ an Omni Crawler Drive though. This is the year to do it. The year without real defense and no bumpers required or necessary. If you use the triangular 1 it can tip over and still keep going....and going....

https://www.youtube.com/watch?v=BTp2UAaihaI

Hee, hee...Then there's the Water Game! (Ok, that water is slightly frozen...But the 2016 Game could be held in outdoor colder locations and the field just a wee bit larger and colder is all). Posted to try and give the GDC ideas to give the fans what they have always prayed for...A Water Game! Using the 1929 Fordson Snow Machine concept of course. (There has to be a way we could tweak that so it wouldn't turn the carpets into huge balls of yarn). Any ideas?

https://www.youtube.com/watch?v=zBjlSJf4274

So what happens when the field melts in those warmer regions? Still a water game. (Only wetter and muddier).

https://www.youtube.com/watch?v=H5NsmZcLAdM

"Guardrails can't hold us!"....I know how I'm getting to the ski slopes from now on....Anyone still have a 1929 Ford around that's still running or in decent shape? Lol. I'm going to make me 1 of those Fordson Snow Machines.

[Caleb Sykes]

Originally Posted by Lewis Nerone

You also need to make sure that your chassis is designed to run mecanum (wheels must be in a perfect square, neutral camber, etc.). These were challenges last year.

Why do you think that a square chassis is required to run mecanum?

[JorgeReyes]

Has anyone had any luck with having two traction wheels in the front and omni wheels in the back? This would allow you to pivot at the front rather than the center which makes getting totes easier

[jijiglobe]

Originally Posted by JorgeReyes

Has anyone had any luck with having two traction wheels in the front and omni wheels in the back? This would allow you to pivot at the front rather than the center which makes getting totes easier

We did it in 2008 and it worked fine but you need to make sure that turning around the ends of your robot is what you really want.

[cglrcng]

I found the kitbot for that crane we have been looking for, and it Strafes nice at 2:14 of the video.

https://www.youtube.com/watch?v=0nWFA8wv0-I

[MrJohnston]

Originally Posted by alopex_rex

What kind of creative programming are you going to use? In my experience with tank drive I haven't done anything more fancy than limiting the rate of acceleration, I'm curious as to what can be done.

Tank allows for fairly precise movements with pre-programmed routines.... It's one of the reasons I'm certain we'll have a strong autonomous....

[Abhishek R]

Originally Posted by MrJohnston

Tank allows for fairly precise movements with pre-programmed routines.... It's one of the reasons I'm certain we'll have a strong autonomous....

What is it about tank that lets it accomplish tasks more precisely than other drive systems?

[MrJohnston]

With good traction tires on a tanks system, there is very little slippage, allowing you to program precise numbers of rotations, etc.... I am not a programmer, so I really can't give much detail. I do know that as we were discussing the pros and cons of different drive systems, that our programmers were very clear that they could have more precise autonomous routines with the tank system. In the past, I've seen them consistently get our robots to autonomous go to an exact location (within an inch, or two) repeatedly.

Perhaps we simply aren't experienced enough in mecanum - Okay, I know we aren't. However, I think very highly of our programming team - both students and mentors - and tend to trust them when they say, "We can program much more precise movement with this drive than with that."

[Physicguy]

Originally Posted by MrJohnston

Perhaps we simply aren't experienced enough in mecanum - Okay, I know we aren't. However, I think very highly of our programming team - both students and mentors - and tend to trust them when they say, "We can program much more precise movement with this drive than with that."

This is true in past events tank drive system that have been used has been really successful in competition. We are at the same crossroads on whether or not to go with an omni-directional drive or to just stick with tank. We had our fair share of trouble with mecanums before.

[Ether]

Originally Posted by MrJohnston

With good traction tires on a tanks system, there is very little slippage

When turning there is a lot of slippage. That's why it's called skidsteer.

[Abhishek R]

Originally Posted by MrJohnston

With good traction tires on a tanks system, there is very little slippage, allowing you to program precise numbers of rotations, etc.... I am not a programmer, so I really can't give much detail. I do know that as we were discussing the pros and cons of different drive systems, that our programmers were very clear that they could have more precise autonomous routines with the tank system. In the past, I've seen them consistently get our robots to autonomous go to an exact location (within an inch, or two) repeatedly.

Perhaps we simply aren't experienced enough in mecanum - Okay, I know we aren't. However, I think very highly of our programming team - both students and mentors - and tend to trust them when they say, "We can program much more precise movement with this drive than with that."

I would encourage you to try omni's in the offseason if you have already ruled them out for this year. I don't have experience with mecanum, but we used omni's as our main drive system on our 2014 robot. Our autonomous worked pretty well consistently; we didn't have many accuracy issues.

[SenorZ]

We, Team 4276, tested pushing totes on carpet and up ramps using our 2014 drive: 6" AM Mecanums with 10.7:1 TBMini's.

We pushed 4 totes with bin and we're happy with the results. We drove the robot on top of poly sheets (not HDPE, sticker missing so not sure what it was exactly) and there was little difference in ability to push totes.

That coupled with the ease of strafing and rotation has led us to keep Mecanum for this year. We'll be upping the gear ratios though.

[MrJohnston]

Originally Posted by Abhishek R

I would encourage you to try omni's in the offseason if you have already ruled them out for this year. I don't have experience with mecanum, but we used omni's as our main drive system on our 2014 robot. Our autonomous worked pretty well consistently; we didn't have many accuracy issues.

We are looking at some possibilities with omni wheels... The increased ability to turn (over a tank system) is appealing.

[GeeTwo]

Originally Posted by GeeTwo

We miscalculated on the amount of defense last year, and went mecanum. Our programmers got mecanum working from the libraries in about two weeks from a cold start. We're going omni H-drive this year - we're doing a "bottom stacker", and feel that a bit of strafing is going to be essential to quickly and precisely line up on the totes. We decided to pass on mecanum this year because of the issues with a moving center of gravity.

Originally Posted by Ether

When you experimented with H drive in the off-season, did you find that it was less affected by variations in center of gravity than mecanum is?

Did I say we experimented with H drive in the off season? Actually, we built a tank drive for a prototype chassis because we recognized that it was the best chassis for 90% of the games for teams without massive funding or the ability to crank out a swerve drive in the shop (like us).

Anyway, we do not expect a major variation due to (front-to-back) variation in the COG on an H-drive. We're going to put the COG at the transverse wheel when we have about a 75% load. The short moment arm to this wheel should keep the torque about the COG small when we have 3-6 totes. We'll have to learn to adjust at lighter loads, when it's less critical. I also can't think of a reason why, in a tank-mode spin, an H-drive wouldn't rotate around its COG - lateral forces balance about the new COG, leaving only torque.

Actually, when I later thought about the forces on a mecanum with a COG that moves forward and in reverse, I became a little less concerned, but still glad that we switched. Moving forward and back would be largely unaffected by moving the COG forward or back. Strafing or translation with a strafing component introduces a torque so that the robot will rotate towards the strafe direction. On an attempt to simply rotate, the robot will tend to strafe in the direction of rotation on the side to which the COG moved. Also, the axis of rotation seems to move to in the opposite direction of the COG, which sounds likely to cause the robot to fall on its face eventually. I did not think about combination maneuvers involving both translation and rotation. Disclosure: this is all based on pictures in my head, not on paper or even a whiteboard, and certainly not experience.

[Ether]

Originally Posted by GeeTwo

Did I say we experimented with H drive in the off season?

Reading between the lines. It sounded like you had some supporting test data you might be willing to share.