While Playing around with Autodesk, I’ve come up with a rough design for a unique multidirectional drive concept. Basically, the center platform and center wheels are on a powered turntable (chain driven from CIM in back.) The remaining four wheels are unpowered Omniwheels, which allow the chassis to move in whatever direction the center wheels are facing. The overall effect would be similar to a crab drive, but somewhat easier to build.
That looks interesting…Can I assume the vertical ‘big’ CIM is used to turn the table for steering?
duh…of course it is. I got to read your caption first. Please post any refinements. I’m going to bring this to my team’s resident VEX expert for a prototype.
Shawn??? Are you reading this.
I think that is how it works…
thats really cool
I’m going to try that with VEX
I’m not sure, but ball casters might have less friction than omniwheels
we had a bad history with casters this year. i wouldn’t recommend it. that design is sort of present in our 05 bot. its not multi directional http://www.chiefdelphi.com/media/photos/20299
it shows it with
ball casters but. later we switched them out with omnis and personally its my favorite bot to drive. its a great idea i might want to try that out.
The Champion Lightning Bots of Team 2010 built a somewhat similar drive system this year, but instead of both drive modules on a single turntable, they were on separate pivot points driven by a Globe motor chained to them via a 2:1 sprocket reduction. When pointed straight ahead, the system was laid out the same as in your concept drawing. The four corners of the frame had ball casters instead of omniwheels. Each drive module had 180 degrees of rotation limited by potentiometer feedback.
2010 used 2 A-M traction wheels for their driven wheels, each of which was powered by a custom 2-CIM motor single speed transmission. The wheels were mounted 16" apart, center to center. It proved to be a very maneuverable and reliable design, although the casters did make it next to impossible for them to climb ramps.
The drive modules were inspired by those used on Team 48’s 2002 robot. This style of module requires plenty of clearance for the motors to freely rotate.
Steering Linkage Overhead View
Your solution is definitely unique - If you decide to attempt to build it, best of luck attempting to solve its particular design challenges!
Thats a really cool idea… I would also have to agree that ball casters would be a better idea then omni wheels.
My main concern with this idea is the torque required to move the center ‘module’, because most of your contact with the ground will come from those two middle wheels… and if they provide too much friction you may just end up turning the whole body of the robot. So instead of having a crab drive you have your robots body turreted… with your center two wheels staying put…
To solve this you would have to either program the wheels to turn the direction your are trying to move the middle module, basically running the wheels in opposite directions helping the big CIM turn your center module. Or you may want to use omni wheels over the kit wheels…
This is defiantly something you would want to do some calculations and small prototyping to see if it would actually work, cool idea thou!
Very interesting concept, a nice simplified swerve concept. I think I may also try and find the parts/money to try and test it with Vex (although the bushing around the base of the drive will probably be hard to reproduce, I might have to prototype it without it).
Some thoughts to consider:
As it stands, this drive will have difficulty climbing ramps/inclines/large® steps. When the leading set of wheels starts to go up the incline, the drive wheels will be lifted off the ground, and the bot will roll back down. If you added some form of suspension to the omnis, this could possibly fix the situation, but that increases the weight/complexity. It’s really a game/strategy dependent decision.
You’re going to have to consider your wire runs carefully (but that is true for pretty much any swerve).
It might not be possible, but it would save a considerable amount of chain (and space that cannot be used to mount because chain is there) if the steering motor is moved to the central support.
What makes it so that the wheel bogey in the middle turns across the carpet rather than the frame rotating around the wheels?
Yeah, I was thinking that omniwheels might be needed in the middle, but normal wheels are obviously preferable for traction reasons if it dosen’t push backwards like you suggested. A prototype is really the only way to find out for sure. It’d probably have some programming compensation like you said too.
I agree with Lil’ Lavery that ramp climbing is a problem, omniwheels or casters, but I have a few concepts to play around with for some kind of suspension.
Last year when we were throwing around ideas for drivetrains and such, we came up with a concept similar to one drawn. We tossed it for the very reason that lavery posted, and also for the reason that if we ever got into a pushing match, the slightest bit of lift would lose it for us.
almost as maneuverable as my off season idea; spherebot:)
I think everyone else have covered most of the things about that base. The first thing that caught my eye was the 1x1 that is holding the powered module up. What is the thickness on that? Also… what is the thickness of the shaft that is coming out (going into that 1x1) to connect to the sprocket (in order to turn)? I am assuming its 1/2". Are you worried about that 1x1 bending/sheering? How much does it weigh as is in the picture?
Very interesting concept. I hope after some modifications on the drawing you will be able to manufacture this and share the outcomes. Good luck.
http://www.firstroboticscanada.org/site/node/372
http://www.firstroboticscanada.org/site/node/323
Im guessing you already knew about these when comming up with the design, but my advice is to try to contact whoever did these and discuss the pro’s and con’s with them.
There used to be more pictures of similar drive methods but they seem to have been lost when waterloo moved all its info to FIRSTroboticsCanada
-Simon
those are 111 and 236, respectively.
I designed a concept system similar to this a few years ago. I addressed this problems with the inclusion of traction plates, operated by pneumatics. This plates would drop down and restrict the movement of the outer frame when you rotated the turntable.
Wow! you just designed what 172 imagined and prototyped earlier this season (but got nowhere with…)
Early in the design stage, we were experimenting with drive train ideas. What we ended up with were independent drive sections that could pivot to climb ramps, but we thought, what if we went further than that: what if the independent drive sections could turn independently as well, much like the front yoke on a toy wagon.
We coined this type of swerve drive as “Little Red Wagon Drive” and basically mulled it over in the background while this year’s robot was built. We even got as far as building a Vex prototype (although it isn’t documented as far as I know of, and it has probably been disassembled by now)
The main difference between Little Red Wagon drive and your design is the placement of the pivot. Instead of having the turntable on the middle, it would be located in the front of the robot, with casters (or omnis) supporting the back. The pivoting drive section in front would simply pull the rest of the robot along, much like, well, a wagon (or almost like a front wheel drive automobile)
If I can find any pictures of our vex prototype, I will be sure to post them. I’m sure everyone at 172 would be happy to see our pet design project actually get somewhere, even if it is designed and built by a team elsewhere!
If you were to power your omniwheels then that would give you the ability to fully control the rotation of the robot.
Thanks for all the feedback!
I’ll probably be building a full scale prototype early this summer once all our offseason events are done. Right now I’m working on an improved CAD verison.
Some improvements:
-Better turret support
-lighter
-Central platform can move vertically downward 2.5 inches via spring if it is lifted off the ground, solving the pushing problem and allowing it to climb ramps to some degree.
You already can, just drive the left and right middle wheels in opposite directions and hold the turret control motor still.