Originally Posted by roystur44 (Post 1389477)

IMHO steel is a acceptable material for making a robot drive train. I like it because it will keep the weight down low to improve your COG. Steel is appx 3 times heavier than alum but designed correctly can be much stronger/ less costly in the same size package.

Steel is much cheaper in terms of cost/lbs vs alum. CRS and stainless sheet is readily available from material suppliers. Steel can be easily spotwelded and mig welded. Welding steel is much easier than welding alum. Laser cutting light guage steel is significantly faster than cutting the same thickness aluminum.

Here's some stats you can use for you analysis
Cost/lbs of Cold roll sheet sheet is appx. .55/lbs
Cost of Alum 5052 is appx 2.00/lbs
density of steel is .29 lbs/sqft alum .098 for alum.

Take a look at using .036 or .048 CRS for your sheet stock and using .065" thin wall 2x1 , 1x1 tube.

Here's a website of a company that can laser cut tubes. Think of designing tab and notches to click together your frame and use the sheet metal as gussets and brackets


http://www.tubeservice.com/index.html

Originally Posted by roystur44 (Post 1389477)

IMHO steel is a acceptable material for making a robot drive train. I like it because it will keep the weight down low to improve your COG. Steel is appx 3 times heavier than alum but designed correctly can be much stronger/ less costly in the same size package.

Steel is much cheaper in terms of cost/lbs vs alum. CRS and stainless sheet is readily available from material suppliers. Steel can be easily spotwelded and mig welded. Welding steel is much easier than welding alum. Laser cutting light guage steel is significantly faster than cutting the same thickness aluminum.

Here's some stats you can use for you analysis
Cost/lbs of Cold roll sheet sheet is appx. .55/lbs
Cost of Alum 5052 is appx 2.00/lbs
density of steel is .29 lbs/sqft alum .098 for alum.

Take a look at using .036 or .048 CRS for your sheet stock and using .065" thin wall 2x1 , 1x1 tube.

Here's a website of a company that can laser cut tubes. Think of designing tab and notches to click together your frame and use the sheet metal as gussets and brackets


http://www.tubeservice.com/index.html

Originally Posted by daliberator (Post 1389374)

Hey CD!
I didn't know exactly how much to drop the center bearings, so I just guessed at 3/16ths of an inch.

daliberator

Originally Posted by highlander (Post 1389967)

Having 1/8" of drop is pretty standard, +/- how much sponginess your tread will have. 3/16" should be ok for most drivetrains, although I don't know what tread you are using.

Originally Posted by Andrew Lawrence (Post 1389969)

A rule of thumb I've always followed is 1/8" for flat wheels (ie colsons, kit wheels, etc), and 5/32" or 3/16" for blue nitrile. The properties of the blue nitrile tread allow for even the slightest amount of contact to affect turning, and because they grip the carpet so well the increased drop is sometimes needed to ensure there is no contact.

Originally Posted by Boe (Post 1389979)

We ran 1/8 drop with blue nitrile in both 2013 (6 wheel WCD long base) and 2012 (10 wheel center 6 dropped wide base) and ran it with a 1/16 drop this year (wide base 6 wheel WCD) all wheels being between an inch and an inch and a quarter. We haven't experienced any turning problems, but one of the things we are hoping to look into this summer is playing around with the drop amount.

Originally Posted by Andrew Lawrence (Post 1389981)

I'm surprised you could get to 1/16 drop without experiencing drag. The diffierence between 5/32 drop and 1/8 becomes more apparent in 1.5" - 2" wide wheels, but it should still be a factor in 1" wheels. Could you provide more information (pictures or CAD models, maybe?) on your 2013 and 2014 drives?

Originally Posted by Chris is me (Post 1389983)

We ran 1/8" drop this year on Colsons and that was probably too much. I'd rather have gone 1/16".

Originally Posted by Andrew Lawrence (Post 1389984)

Did you cut tread into your colsons?

Originally Posted by Chris is me (Post 1389985)

We left them untreaded for one event and cut treads in them for our second event. Turned great both times but was a bit rockier than I wanted. Perhaps that's just the tradeoff one has to make.

Back in 2011, 1/8" was just right for a long base with Colsons.

Originally Posted by Andrew Lawrence (Post 1389981)

I'm surprised you could get to 1/16 drop without experiencing drag. The diffierence between 5/32 drop and 1/8 becomes more apparent in 1.5" - 2" wide wheels, but it should still be a factor in 1" wheels. Could you provide more information (pictures or CAD models, maybe?) on your 2013 and 2014 drives?

Originally Posted by Boe (Post 1389987)

I dont have easy access to all the CAD right now but here's some more information on the two drives.

2013:
6 wheel WCD with two speed 4 CIM custom shifters geared for 9/19 fps before frictional losses. The wheels were 6inch custom 3d printed and if memory serves they were 1 inch wide. The robot frame was 30"x24", dont rember wheel spacing exactly but it was ~11 inches give or take. Here's a CAD render of it.

2014:
6 wheel WCD with two 3 CIM Ballshifters geared to 6/16 fps before losses. The wheels were the 4 inch AM performance wheels and the frame was 23.5"x32" with about 8" between wheels. We almost went with no drop on this but decided to go with a very slight drop to be safe. Wheel also almost made it a four wheel WCD but decided against it. Here's a render of the robot.

Originally Posted by Chris is me (Post 1389460)

I'm definitely getting to the point where I'm just splitting hairs here, but I interpreted Andrew's post as "buying a COTS part is the exact same amount of design as making your own", which it isn't since one stops doing component design. That's not to say component design is better or necessary, it's just not the same set of skills being used and practiced.

The parts that I would refer to as the system design (excluding the choice to use VersaChassis itself) would be the choice in gear ratio, gearboxes, and motors (perhaps power transmission as well). Certainly few real world situations involve engineers doing detailed design of every component - lots of off the shelf parts or reused designs are implemented in lieu of all this extra work.

My point is essentially that it's the off season, and the OP is building an off-season drive. The constraints likely are in favor of more time and less money rather than the other way around. This I don't think the notion of doing something custom should be inherently knocked in favor of a COTS chassis. They could just buy and build it in the build season if it makes sense to run then.

Originally Posted by cadandcookies (Post 1390006)

(because you know what they say about assumptions...).

Originally Posted by asid61 (Post 1390032)

Out of random curiosity, what do they say about assumptions?

Originally Posted by Andrew Lawrence (Post 1389986)

For clarification - was it rocky both times because of the drop, or was it rocky after you cut the treads? Also, did the treads affect the smoothness of the wheel's ride (did driving feel more bumpy)?