05-01-2017 21:34

Bob Steele

Re: pic: SkunkWorks 8 wheel 6 CIM drivebase

We used this basic drivebase last year. The model utilizes Colson wheels with the VEX hex hubs. We actually used 6" pneumatics last year from WCD that worked great. The six inch solid rubber Colson wheels with these hubs are drop in substitutes. They didn't even require extra spacers.

This is a powerful 6 CIM SINGLE speed belt driven drive base. It performed extremely well in last year's game and we have altered the design to be a very strong platform that could be adapted to nearly any game. Our Stronghold robot had a section cut out of the bumper to allow the ball to be picked up easier.
This design could also be altered to make a cutout on one end if necessary.

The center of mass for this is extremely low and it is a very stable platform to start with.

We anticipate using this a test bed for programming as the electronics (not shown) are modular.

FYI we did current limiting in our code and never had a single issue with brownout for the entire season. The acceleration was impressive.
It is the first time in many years that we have gone with a single speed transmission solution (not counting 2015)
We probably won't be going back to a shifting transmission. This drive base did everything we could ask for.

05-01-2017 22:00

Ari423

Re: pic: SkunkWorks 8 wheel 6 CIM drivebase

Are you sure the model is 6" Colsons? They look a lot more like WCP Pneumatics to me.

On that note, how hard is it to remove the existing hubs from the Colsons before inserting the VexPro hubs? I've never tried it myself but I imagine it's not easy otherwise they would come out on their own.


Also, what kind of current-limitations did you implement? Current-limiting can be as simple as basic input ramping to complicated current feedback loops (or probably even more complicated things that I don't know about). I have yet to see a good engineering analysis of the differences between the methods (i.e. whether it's worth it to put in a lot of time and effort for complicated current-limiting software over the basic stuff).

05-01-2017 22:08

BrendanB

Re: pic: SkunkWorks 8 wheel 6 CIM drivebase

For sizes larger than what Vexpro sells in their current lineup, you can go the old fashion route and buy your Colson wheels here. The wheels with a 1 3/16" bore are what the Vexpro/WCP hubs are designed for.

Considering your location if you have more local sources for Colsons with hubs I'm not sure what the best method would be is to remove them is or if it would damage pressing a new hub in.

Thanks for sharing your 2016 chassis Skunks! Any information on your gearing and speeds from this season?

05-01-2017 22:22

Bob Steele

Re: pic: SkunkWorks 8 wheel 6 CIM drivebase

I will refer your question regarding current limiting to our programmers although I do think it was ramping.

You are correct that the model shows pneumatics. We substituted Colsons for the as built version. We purchased the colson wheels without any hubs to push out.

I got them that way from The Robot Market Place. They have a really nice selection of all kinds of wheels and shipped quickly.

http://www.robotmarketplace.com/prod...5-6-456-2.html

They also have the hubs
http://www.robotmarketplace.com/prod...-217-3430.html

We purchased them directly from VEX though...

I just pushed the VEX hubs into them with a press. Easy....

We are going to be testing the wheels at our practice field soon. We know that on concrete, the Colson's don't have the traction that the WCP Pneumatics have. They aren't bad... and we wore out quite a large number of the WCP pneumatics during the competition season.

We initially wanted to use them primarily for demos and parade activities so that we didn't wear out our pneumatics. We will be looking at using them for competition this year too. They are heavier than the pneumatic wheels but not a great deal.

05-01-2017 22:40

Bob Steele

Re: pic: SkunkWorks 8 wheel 6 CIM drivebase

You can check the actual drawings but as I remember our calculated top speed was 16 feet per second... (whatever that translates to in field performance is just relative.... we really want good acceleration and not top speed.)

As I remember we came off the CIM with a 12 tooth spur gear that ran a 48 tooth spur gear that ran a pulley-belt-pulley (same size) that ran a 24 tooth spur gear that ran a 48 tooth gear connected to the wheel. On each side all four wheels are belted together and run off all three CIMS.