Sharing motor(s) tranmissions in Swerve drive

[Andrew Schuetze]

For some background on our team's first ever summer prototype work read this thread.

What I am posting here is a request for what you think would be the pros and cons of having a single motor and transmission per side of a crab-steer drive system. (What is a side in a swerve system?) Consider having a single transmission with one or two motors being shared with two modules per side. Front/Rear or Left/Right. Add to that the concept of also steering modules in the same pairs. I'd like to reference a white paper by team 79 Krunch for info on steering options in swerve drives.

Anyhow,
Post your thoughts

[Tristan Lall]

With regard to driving them together, it's feasible, but be aware that you'll limit yourself a little bit in the area of complex motions (because you can't get all 4 wheels spinning at different speeds). This probably won't be too big a deal, though, because it's difficult to control that sort of motion by hand. In autonomous mode, it might limit your options a little, but you should be able to work around it.

Also, if you steer them together, you're limiting yourself (under most circumstances) to either a lot of sliding, or to translations only. As long as you're happy with a skid-steer component to some of your turns, this is quite possible. In fact, most robots forego the ability to steer modules independently, because they'd rather use the motors elsewhere, and don't really need fancy rotational moves (like orbiting an object while revolving around the robot's own axis).

I'm trying to remember if 47's 2002 robot had 4 independently-driven and independently-steered modules; I think that it did, and that would make it one of the very few with that capability.

[Karthik]

Originally Posted by Tristan Lall

I'm trying to remember if 47's 2002 robot had 4 independently-driven and independently-steered modules; I think that it did, and that would make it one of the very few with that capability.

Their 2001 robot had this capability, and I believe it is the only FIRST robot to ever do so.

[Tristan Lall]

Originally Posted by Karthik

Their 2001 robot had this capability, and I believe it is the only FIRST robot to ever do so.

2002 being the one with the mini-treads, and 2001 being the one with the fancy ball-holding arm. To be honest, I thought the 2002 could do this too, but it's been so long, that I don't remember.

[RogerR]

Originally Posted by Tristan Lall

2002 being the one with the mini-treads, and 2001 being the one with the fancy ball-holding arm. To be honest, I thought the 2002 could do this too, but it's been so long, that I don't remember.

actually, 2001 had the mini-treads to help it ride over the mid-field 2x4. i still can't believe that they got the whole thing to fit under the bar.

[edit] pics can be found here and here [/edit]

[Tristan Lall]

Originally Posted by RogerR

actually, 2001 had the mini-treads to help it ride over the mid-field 2x4. i still can't believe that they got the whole thing to fit under the bar.

That explains it. I was off by a year. Oops. Also, the 2000 robot didn't have the 4 driven and steerable wheels...that makes sense now.

[Karthik]

Originally Posted by RogerR

actually, 2001 had the mini-treads to help it ride over the mid-field 2x4. i still can't believe that they got the whole thing to fit under the bar.
[/edit]

From 1998 to 2002, Team 47 had some of the most awe-inspiring robots that I have ever seen. Each year they'd make your jaw drop. It seemed like there was no limit to what they could accomplish. They managed to pack loads of functionality into simple and elegant designs.

[Mike Martus]

Thanks for the compliments guys.

Our team used "Swerve" drive systems for several years. Some independant (all 4 wheels) configurations and a - Four Wheel configuration moved by a single motor. All had their good and bad points. The nature of the game in recent years has made swerve drives to be shelved in place of powererful fast systems that can climb.

Due to resources required both mechanical and physical the need for swerve has been very low as it would impact the game very little. I see an opening for FIRST to have a game that will require the felexability of a swerve drive system.

Swerve is many times confused with a steerable chassis (like a car).

[Tristan Lall]

Originally Posted by Karthik

Their 2001 robot had this capability, and I believe it is the only FIRST robot to ever do so.

I was just thinking, 67's 2005 robot (the 3-wheeled omnidirectional system) might have had 3 independently rotated drive modules. (A robot with 3 independently steered modules can perform the same maneouvres as one with 4.) See here for apparent confirmation of this fact.

[RogerR]

Originally Posted by Tristan Lall

I was just thinking, 67's 2005 robot (the 3-wheeled omnidirectional system) might have had 3 independently rotated drive modules. (A robot with 3 independently steered modules can perform the same maneouvres as one with 4.) See here for apparent confirmation of this fact.

67's 2005 machine definitely had it, as did 312's 2006 machine (the latter heavily influenced by the former). the drive configuration of the simswerve would also lend itself to the same maneuverability of the 4 wheel independent. i think what is notable about the 47 bots' modules is not the fact that they are independently steered, but rather the fact that there are 4 of them that were independently steered.

[Tristan Lall]

Originally Posted by RogerR

i think what is notable about the 47 bots' modules is not the fact that they are independently steered, but rather the fact that there are 4 of them that were independently steered.

I know, and of course Karthik knows, given SimSwerve; I'm just pointing that out so that others realize that 47's implementation wasn't the only one that allowed for arbitrary planar motion.

Incidentally, 47's 2001 and 67's 2005 designs drive all of their points of contact; 47's 2000 and 1114's 2005 drive only two points of contact, and leave the other two as casters—this retains maneouverability, but sacrifices maximum pushing force (because the total normal force on the driven wheels is lower, and they therefore exert less friction).