Our team was planning on implementing swerve drive over the offseason, but all the designs we could find online required two motors per wheel, and we were thinking of having only one motor, like a NEO provide steering for all 4 drive wheels. Are there any CAD designs online for something similar? Thank You
1 Like
Flasbacks in nonagon
16 Likes
Search for crab drives. 1717 did some pre 2012 but I donāt know of CAD existing for those years.
5 Likes
Typically youād see this referred to as ācrab driveā where all the motors are linked together. Might help in your searches.
Sniped by the other Andrew from a team with a number in the format of 5X1X.
4 Likes
There is apparently CAD of 118s 2007 robot that used crab drive. At least in the preview you can see the chain that links the different pods together: https://ccisdrobonauts.org/?p=robots
4 Likes
#seriousanswersonly
Thereāre no CADās I could find but hereās a very helpful presentation on Holonomic drives by Andy Baker: https://files.andymark.com/2008CON-Omni-Baker-McKenzie.pdf
On top of that hereās a good CD thread: how does crab drive work?
IIRC team 141 Wobot did a crab drive a few seasons back.
Last year 1108 did a front-side/back-side crab. In theory, it looks great. The front steered independently from the back, or we could steer together. Mostly driven as Ackermann like an R/C car, but with the āfrontā able to switch ends. Or driven in four-wheel steer, strafing
We placed near the bottom at both regionals. Not a good experience.
And it was Because of the drivetrain.
So, yes, it is cautionary tale. We did get an engineering award for the motor-in-the-wheel, which I still love, but we had real problems steeringāboth with the pulleys, spectra and snowblower motors steering and with the software trying to keep track of where the wheels were.
The driver couldnāt really predict where the robot would go. Wandering centers. But sometimes it worked great. Even though we think weāve beaten most of the problems, we couldnāt convince the kids to go this way this year. Probably not again.
Code for ārealā swerve is prolific with lots of people to give advice. Code for crab not so much.
1986 in 2010 Back when Malcolm from HQ was a team member.
2 Likes
I remember @GeeTwo had a small bot that was basically implementing crab drive quite a few years back. Iāll let him give the details, but I remember it using linkages to move the wheels together. I donāt remember if it was ever FULLY functioning or not.
I had never seen 1640ās design before, and mine was linked a bit differently*, but the effect was the same as 1640ās Twitch Drive. I used both ends of rotation for skid/steer. My original idea was to be able to stop about halfway between for pure rotation, but the benefits didnāt come up to the costs of adding a middle position.
https://team1640.com/wiki/index.php/Twitch
* Mine didnāt have linkages across the middle of the robot, but rather each module to the ones adjacent to it. I had two linkages for each pair crossing each other so they only had to work under tension, not compression.
Ok, thank you so much for all the help!
This used to be pretty common, back when motor options were much more restrictive. Use the search term āCrab Drive,ā which referred to swerve with all four wheels steered together. āSwerveā prior to 2013-ish, when six CIMs became legal/miniCIMs were introduced, more often meant wheels steered in pairs, or less commonly, independantly steered wheels with a central power plant, as in 118ās 2007-2008 robots. I remember whatās now standard practice, four independently steered and powered wheels with options for field-centric control being referred to as āunicorn drive,ā because it seemed so implausible ā pretty much only 1640 and a select few others were doing it for a time.
Some of the prominent teams running pioneering swerve variants in these earlier years to look to include 71, 111, 118, 47, and 16
With brushless options and COTS designs, there is less and less reason to do this.
2 Likes
Though now that I post it I am not sure if that was Crab or Real Swerve ā¢ or dual-ackerman/dual-crab (where two pods are steered together instead of 1 or all 4).
I suppose this is kind of off topic but what advantages does ātrueā swerve give over crab drive? I canāt think of any situation where it would be necessary for wheels to be in different orientations but I havenāt gone too in-depth with that.
Rotation in place.
1 Like
Again Iām probably wrong but canāt rotation in place be achieved the same as a tank drive, by turning all the wheels either clockwise or counterclockwise? How would independently turning the wheels be advantageous?
Eliminates wheel scrub.
Are there any other advantages?
1 Like
True swerve can pivot around arbitrary points. A crab can only pivot around its center.
1 Like