6WD questions

[AdamHeard]

We have a fixed drop, been running .125" drop on ~4" wheeels has served us well.

Originally Posted by JesseK

1/2" axles are almost a must in cantilevered robots. In our past offseasons we have bent 1/2" axles in experimental testing which has led me to believe that 3/8" cantilevered axles during competition will simply make us have a bad day.

We've used 3/8" axles when both ends of the axle are supported by the frame with the wheel somewhere in the middle.

Universally saying X size is required isn't the greatest thing to do.

We had a prototype cantilever drive with 3/8" axles perform and last just fine, we however do 1/2" axles with 7/16" hex on our comp for geometry reasons.

[JesseK]

Originally Posted by AdamHeard

We have a fixed drop, been running .125" drop on ~4" wheeels has served us well.




Universally saying X size is required isn't the greatest thing to do.

We had a prototype cantilever drive with 3/8" axles perform and last just fine, we however do 1/2" axles with 7/16" hex on our comp for geometry reasons.

Rather than being universal, I meant to imply my own conclusions from my own experience. I feel that it is simply confusing to someone with a question when people respond with (in a Brian from Family Guy voice) "it depends, and here are some vague anecdotes of reason from which you cannot possible derive a logical conclusion".

Additionally, I was trying to provide context as well. Very different conclusions are drawn from the statements '1/2" cantilevered axles didn't hold up in our experiments' versus '3/8" cantilevered axles are fine for our prototypes'. Indeed, the original post didn't have anything about the context of competition or extreme environments, however it is implied by the fact that there's a good chance a third party reader who arrives at this post via search will take the information as fact during the build season (regardless of how illogical that can be, does anyone really have time to 'experiment' during the build season?).

[AdamHeard]

Originally Posted by JesseK

Rather than being universal, I meant to imply my own conclusions from my own experience. I feel that it is simply confusing to someone with a question when people respond with (in a Brian from Family Guy voice) "it depends, and here are some vague anecdotes of reason from which you cannot possible derive a logical conclusion".

Additionally, I was trying to provide context as well. Very different conclusions are drawn from the statements '1/2" cantilevered axles didn't hold up in our experiments' versus '3/8" cantilevered axles are fine for our prototypes'. Indeed, the original post didn't have anything about the context of competition or extreme environments, however it is implied by the fact that there's a good chance a third party reader who arrives at this post via search will take the information as fact during the build season (regardless of how illogical that can be, does anyone really have time to 'experiment' during the build season?).

I should have further explained my point I suppose. Saying 1/2" shafts will work is just as dangerous as saying 3/8" shafts will work. The diameter of your wheel, how far it's cantilevered, how many wheels you have, what you're driving over, etc... will all effect the size you really need.

I'm just as guilty of any of doing this, I just hate the thought of a kid browsing chief and seeing, "1/2" axles! they work, we're doing it!", then spend a whole season busting axles. The other end of the spectrum is true as well, but less damaging, I'd dislike to see a team waste a half pound for no net gain.

Before we can really quote shaft sizes, we need more information about their specific shaft setup and design.

[JesseK]

Originally Posted by AdamHeard

I should have further explained my point I suppose. Saying 1/2" shafts will work is just as dangerous as saying 3/8" shafts will work. The diameter of your wheel, how far it's cantilevered, how many wheels you have, what you're driving over, etc... will all effect the size you really need.

Ah, yes, I didn't even think about cantilever distance. Good point.

[EricH]

Which is why I put in that it's a design decision and made reference to doing the analysis...

"It's all about the math."--Mark Leon

Failure to do the proper math correctly in this case could easily end up causing serious drivetrain problems later.

[Andrew Schreiber]

Originally Posted by EricH

Which is why I put in that it's a design decision and made reference to doing the analysis...

"It's all about the math."--Mark Leon

Failure to do the proper math correctly in this case could easily end up causing serious drivetrain problems later.

http://www.chiefdelphi.com/media/papers/1998 I'm just going to leave this paper here.

The thread it was originally posted in may be of some use as well. http://www.chiefdelphi.com/forums/sh...d.php?p=623114

I have to agree with Eric, do the math for your situation. I usually then have someone else check the math and then add some fudge factors in (erring on the side of caution) but YMMV.

[dtengineering]

Not all 6wd trains are cantilevered... nor do all of them use hex shafts. Keyed round stock has served us well for years.

Here's a shot of one side of our 8wd system from this year... but if you just lengthen the spacing between the wheels, you've got a 6wd.

The centre wheel in this shot is mounted directly to an extended output shaft from the KoP toughbox. (Geared down to 14:1)

Tension is adjusted by turning down the nylon rollers until they are "just right".

Jason

[Katie_UPS]

Originally Posted by thefro526

25 has been using their 6WD since 2002/2003 and all 6 wheels touch the floor. It works fantastically for them.

Originally Posted by Dillon Carey

Actually the six wheel swerve did have the center wheel dropped.
About 1/4 of an inch

Whoops!

Thanks for correcting me, I'm still learning.

[ajlapp]

Regarding lowering the center wheel when driven directly from the motor/gearbox. How can you make it adjustable up and down or do you make the outer wheels up and down adjustable? Which method is easier to maintain and more effective over time?

Our Universal Chassis system uses change blocks to allow for adjustable center wheel drop. The axle mount holes in each block are drilled off-center creating different amounts of drop. Universal Chassis

Since the center wheel typically interacts with your gearbox it is easier in my opinon to move the outer wheels.

This option also allows you to indepoendently adjust the front and rear wheel position. In the past we have raised the front wheel only...leaving the center and rear on plane.

[Al Skierkiewicz]

Teams that don't build a little adjustment into this system can run into other problems as teams found out at Champs. When the subsurface floor is neither flat nor smooth, some adjustment should made to the drop wheels in order to get the desired performance. At Champs, the plastic underlayment sagged in the middle. Since the underlayment was a four foot square, robots in the 38" dimension sometimes had difficulty in turns when in the center of a square. Also, if you cannot quickly change wheels, adjustment may allow you to compensate for tread wear on the dropped wheels.