pic: 4 Wheel Strafing Chassis

This is a design I completed in May after championship. It was intended to be a off season project but like so many others, it never materialized due to lack of time, money, and motivation. So I figure I’ll throw it out there and hope somebody gets some use out of the design. I’ll upload a zip file in the discussion thread with more jpegs. The inventor files are available for anyone who wants them.

Technical specs:
4 CIM drive geared for 8.6ftps
1 globe for steering geared 4:1 to the wheels
physical properties puts it at 35 pounds without fasteners or chains. I’d estimate 45 pounds on the safe side as it appears there.

As promised, here are the zip files with additional jpegs. They needed to be shrunk to make the file size limitations.
PM me if you want any closeups.

module.zip (99.5 KB)
wheels and steering asm.zip (72 KB)

module.zip (99.5 KB)
wheels and steering asm.zip (72 KB)

Looks good. I’m just curious, why did you go with sprockets as opposed to gears?

Looks great! One quick question though. Do all four wheels turn or only the wheels on the side of the steering assembly?

And to amend to that question, why was that decided upon?

I choose sprockets were used for a couple reasons. There was quite a debate among team members regarding this. I am not the head designer for my team. This was something I worked on my own. It was my opinion that sprockets were the way to go for these reasons:

  1. cheaper

  2. allows for more flexibility for choosing distances while maintaining gear ratio’s

  3. requires less precision in holding tolerances when machining side plates.

  4. Allows for a change of gear ratio’s easily.

  5. just as efficient as gears if chain is correctly tensioned.
    (I calculated the center distances with Matt Adams sprocket center distance calculator. Thanks Matt)

All 4 wheels turn together, and steering is tank style. Its simpler than having paired wheels for steering, or 4 wheel independent, especially since we don’t get 2 globes in the kit anymore, or 2 of any appropriate motor for that matter.

off topic, but…

link to M.A. center distance calc.
i felt obligated to post a link to the calculator for those who missed it the first time (or weren’t around). its really an invaluable tool, and has saved me some work and frustration.

<edit> FYI, it runs in excel </edit>

It looks like you have all the bases covered. I would look at the upper bearing being a little larger in diameter with a central hole for wiring big enough so as to allow power and control wiring. The lower bearing/followers are a good idea too. Remember though that using the chain and sprocket design raises the steering power demand and allows for objects to block the turning if they get caught between the outside of the wheel module and the robot frame. Tank steering is OK for changing orientation but is not need for normal driving. As always (after it is built) practice, practice, practice.
Good luck!

I am looking to purchase a 4 wheel ‘crab’ or strafing chassis for use on a powered chair project. Can I purchase your design or can you build one for me?

Holy Thread Revival!

You may be interested in http://www.chiefdelphi.com/forums/showthread.php?t=77623 You might not get many results when asking in this thread because it is quite old, but who knows.