pic: 6wd chassis - need feedback

[R.C.]

Originally Posted by JHSmentor

for the 1/2" aluminum shafts - how do you attach them? I can see welding them to the inside rail but not the outside - or do you tap the ends and bolt them on that way?

Ok, got this. We have used cotter pins for the past 3 years and they work beautifully. Use 1/8 cotter pins and drill 1/8 inch holes on the mill toward the end of the shaft, both sides.

[MrForbes]

(28 / 2) x 6 / 80 = a bit over a pound per half of the robot, for a little over two pounds overall. But you better double check!

[JHSmentor]

Well - it sounds like gussets or a bedpan are the way to go. I'll look at various options for material and weight considerations. if we are going to be adding something for the electronics and everything else anyway, then maybe the bedpan would be better - but it also can limit you to where you can mount everything. Plus, if we use Lexan or wood then it would be easy to cheeze hole it to cut some weight as well if needed.


I'll fool around with Inventor to get the weights - most of the pieces are duplicates of each other anyway so it could be fairly easy I'm thinking.

thx again.

[artdutra04]

If you possess a means (such as a sheet metal bend/brake) to bend the edges of all of the 1/8" aluminum components into flanges, you'll drastically increase their strength.

Now if you do decide to go this route, you can't really use 6061, as that doesn't like being bent (you'll get stress fractures everywhere and the joint will be as good as useless).

A more preferable grade would be 5052, as you can usually bend this with a bend radius equal to the material thickness without any problems. However 5052 isn't real fun to machine, so everything would have to be punched or cut out with a laser/waterjet.

It's all about the design trade-offs.

[sanddrag]

Keep in mind anywhere you weld the aluminum, it will become significantly weaker.

[BGiraud]

What size wheels do you plan to use? At first look it seems like your wheels may hit your outer rails. If so, you will need to slide the dead axle mounts toward the center a bit. You can get an inventor wheel assy and add it to see how it fits. Also, I recommend dropping the center wheel 1/8-1/16. You can use chain tensioners like those on AndyMark's site. If you add sprockets to your wheels then you can also check your chain clearances. Make sure your sprocket size is such that you do not hit cross members. You should be able to cantilever your center wheel off of your direct drive axle, so no bearing in outer plate.

[JHSmentor]

The design is a refined copy of last years robot where we used Omni's on the 4 corners and AndyMarks for the center drive wheels (all 6" obviously). Really worked well for us with 0 drop on the center wheel. I have this particular design completed with shifters and wheels so there appears to be plenty of clearance for everything (although I need to double check the sprockets for interference with standoffs in the wheel modules. We will consider different design options depending on the game.

we don't have the option of bending the aluminum - at least not that I know of. The shop we were going to use for the welding may have something though.


thx again for the suggestions.

[Raumiester2010]

Quick Question, are you planning to bias your center wheel? My team is notorious for our crazy tough 6 wheel drive chassis (sorry i dont know a huge part on the structure of it) and we always bias our center two wheels down just a little. this allows you to be able to turn much better than with all 6 wheels planted on the ground. another thing we prototyped in '07 was a 6wd, center biased. we cut part of the front section, re welded part of it in while installing some hinges, and made it so the front third of the robot, just the part holding the wheels, would articulate downward using some pneumatics. this way, with the push of a button, we could switch from having only 4 wheels on the ground for maneuverability to having 6 down for brute pushing power.

just an idea but you can look into it.

message me if you have any questions, i might be able to get you some schematics.