pic: Coaxial Swerve drive, lightened.

[CraigHickman]

[cdm-description=photo]25168[/cdm-description]

[Joe_Widen]

That looks super cool. Instead of all that machining to make it lighter, you could try just using a thinner plate, such as 1/8'' or 3/16" (it looks like you have 1/4''). You can never have to many speed holes though.

[Tytus Gerrish]

allot of sharp edges i see. this thing is awfully tall. you know how much side load those bushings are taking and how much shear that creates between those plates up there? i know modules that i make out of legos that are that tall don't last long. it would be nice if it were supported closer to the Axel.

[Madison]

I've been curious as to why you've opted to mill pockets into the plates rather than entirely cut out large sections. Any insight?

[CraigHickman]

The reasons for the lightening style is structure. As a whole, the entire module is only 8 inches tall, from the top of the power transmission shaft to the bottom of the tread.

The plates used are 1/4", and it can't be any thinner, as it's held together with bolts. As for sideload issues, Inventor 11's stress analysis tells me that it can take about 900 pounds of sideload as a whole, which just might be enough for a FIRST bot.

[Joe_Widen]

You could try using Al tubing and be crafty with the cnc mill. It would have zero bolts (...gasp....). Thats how im designing mine atleast. No fancy stuff, no coaxial, just plain old spur gears and motor mounted on each module. Fancy gears are not my friend, especially after using worm gears (a thousand and one to many headaches there), although, I think helical gears are crazy cool. Good Luck to ya.

[Nuttyman54]

You could try using Al tubing and be crafty with the cnc mill. It would have zero bolts (...gasp....).

Maintinence would be a pain though, even more so w/ the extra stuff due to the coaxial design

[CraigHickman]

The gear sytem for said module is a set of bevel gears (under martin sprocket as miter gears.) They give me a 1:1 ratio, which matches all of the ratios in the module. This is to make calculations for the gearboxes (maybe 2 speed?) which are elsewhere on the robot.

[Stephen Kowski]

The plates used are 1/4", and it can't be any thinner, as it's held together with bolts. As for sideload issues, Inventor 11's stress analysis tells me that it can take about 900 pounds of sideload as a whole, which just might be enough for a FIRST bot.

I would recommend you re-evaluate you 1/4" plate idea....1/8" bent sheet metal is more than capable.....
http://static.flickr.com/16/91417384_4550cf91c0.jpg

[Greg Needel]

Inventor 11's stress analysis tells me that it can take about 900 pounds of sideload as a whole, which just might be enough for a FIRST bot.


This quote scares me a bit. I just want to warn you and everyone else about integrated FEA in software, especially inventor. FEA is good when you have an idea about how strong something is and you just want a verification. ie. you have already calculated an approximation using a number of other methods, or you are familiar with your mechanical properties of the materials and their metal working abilities. IT is NOT OK just to click a couple buttons and assume that the number that it gives you is what you are going to get. First of all nothing that is build comes out exactly like the cad model, no matter how good your machining abilities are. Next there are a number of mistakes that can exist in a cad model from small keystroke errors or incorrect constraints.

I am not trying to come down on you i am just trying to warn people that if you blindly trust a number that the computer gives you without understanding what it is calculating you have the possibility of large errors, which could be catastrophic in your machine.

[Nuttyman54]

i'm not familiar w/ the stress analysis tools in Inventor, but you might want to check that it's not just telling you that if you apply uniform pressure along all lateral surfaces you can survive up to 900 lbs before deforming. Looking at weak points, i'd be VERRRY surprised if it could take 900 lbs at the joint.

EDIT: Thought of another thing: are you treating this as one solid object? It occurred to me that the bolts might sheer off before you reach that 900 lb limit....

[CraigHickman]

I believe I did something wrong in the stress test... not sure what yet... I'll let y'all know when I find out where I messed up...

[DB_UPS]

I would recommend you re-evaluate you 1/4" plate idea....1/8" bent sheet metal is more than capable.....
http://static.flickr.com/16/91417384_4550cf91c0.jpg

The bent sheet metal looks easy to make and harder to screw up. Joe, you should look in to make a version this way too. So if swerve drive is a optional next year we have two ways to make it. But i do like the milling way too.

[Cory]

The bent sheet metal looks easy to make and harder to screw up. Joe, you should look in to make a version this way too. So if swerve drive is a optional next year we have two ways to make it. But i do like the milling way too.

Sheetmetal is only easier if you have the resources to precisely punch and bend it. Otherwise it's a disaster waiting to happen.

[Stephen Kowski]

the resources to precisely punch

You don't have to use a punch....you could get it done by a waterjet or laser just as easy....

[Greg Needel]

You don't have to use a punch....you could get it done by a waterjet or laser just as easy....



something tells me that teams are more likely to have a punch then a waterjet... :rolleyes:

[DB_UPS]

Sheetmetal is only easier if you have the resources to precisely punch and bend it. Otherwise it's a disaster waiting to happen.

Good point. But 1/8 sheet metal bends really nice in a vise. You can also mill holes in it, thats if you now to do it right. So you do need a punch.

[Cory]

Good point. But 1/8 sheet metal bends really nice in a vise. You can also mill holes in it, thats if you now to do it right. So you do need a punch.


There's absolutely no way you can fabricate a swerve module out of sheetmetal by bending it in a vise--it needs to be very precise, far more than you can ever be by using such a method.

[DB_UPS]

If you want to make some thing works. You can do. It may not look pretty, but it would work.

[CraigHickman]

Just in case people are wondering why we would go with 1/4" plate rather than sheet metal, here are our reason: it's light enough, we get mass amounts of it for free, our CNC sponsor prefers doing machining on this plate, and it's quite strong for its use.