Custom West-Coast Design Feedback

[asid61]

Originally Posted by roystur44

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

I would use 6061, not 5052 for a cost analysis unless it is a sheet metal chassis. 6061 is cheaper and stronger, but harder to bend.

[daliberator]

Originally Posted by roystur44

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

Thanks for replying!
This is main reason I wanted to go with steel in the first place; we don't have a massive budget and I wanted to incorporate some welding into the project.

Thanks,
daliberator

[highlander]

Originally Posted by daliberator

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

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 highlander

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.

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.

[Boe]

Originally Posted by Andrew Lawrence

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.

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 Boe

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.

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?

[Chris is me]

Originally Posted by Andrew Lawrence

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?

The new chassis size restrictions of the last 2 years have changed the dynamics of drop center drives a lot. The old rules of thumb kind of go out the window. As chassis tend to be squarer rather than longer, the need for drop is substantially less than in previous years. With the right wheels you can probably get away with 6WD no drop in a square configuration and still turn fine. Maybe you still need a bit of drop for wide roughtop, though.

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 Chris is me

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

Did you cut tread into your colsons?

[Chris is me]

Originally Posted by Andrew Lawrence

Did you cut tread into your colsons?

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 Chris is me

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.

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)?

[Boe]

Originally Posted by Andrew Lawrence

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?

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 Boe

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.

Very interesting. And very beautiful robots as well - thank you got sharing. As Chris said above, with the new frame perimeter, it appears less drop can be run with these wheels than before.

[cadandcookies]

Originally Posted by Chris is me

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.

Just a thought along the side-- I interpreted the post as "we include everything in the CAD, whether we're building it or buying it"-- not "since we downloaded the model, it's the same as designing it" (which I think anyone would agree is a ridiculous statement). In that regard, I'm certainly in favor of having as complete of a CAD model as you can-- when I've designed drive trains and assemblies for robotics in the past, I've found that it's nearly always worth taking the extra 10-15 minutes to make sure all the bolts and rivets fit where they're supposed to (because you know what they say about assumptions...). Just my requisite money paid to mail a letter to the editor.

[asid61]

Originally Posted by cadandcookies

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

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

[Dunngeon]

Originally Posted by asid61

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

They make an a*s out of you and me (assume)

Originally Posted by Andrew Lawrence

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)?

By rocky, I think he means actual rock back and forth due to the drop center. Along the axis of the drop center