pic: 319 Octagonal Drive Isometric

[Ty Tremblay]

Originally Posted by Conor Ryan

I'm not convinced it will make a significant/reasonable difference in any scenario, but all I got is anecdotal stuff.

I made the decision to go with the octagonal shape after many long talks with 971 and 973. If you watch 971's matches, you'll see that they're still quite mobile even when in a friction pin. It also made quite a difference for 971 when they were jammed in corners trying to shoot during the finals of Chezy Champs.

[Ty Tremblay]

Here's an updated version without the secondary bumper frame. Weight is now 31 lbs!

[asid61]

If your goal is to take advantage of the greater area you get with an octogonal shape, won't the wheels take up a lot of space on the bellypan, thereby canceling out the benefits?
I can see how manipulators get extra space though, but I like electronics space more than manipulator mounting space.

[Jay O'Donnell]

Originally Posted by Ty Tremblay

It depends on how you intend to use them. Are you using them for a WCD?

Not for a WCD. Probably something similar to the VEXPro Drive in a day (not exactly like it but pretty similar).

[Ty Tremblay]

Originally Posted by asid61

If your goal is to take advantage of the greater area you get with an octogonal shape, won't the wheels take up a lot of space on the bellypan, thereby canceling out the benefits?
I can see how manipulators get extra space though, but I like electronics space more than manipulator mounting space.

While the inboard wheels do take up a little space, the space gained by moving the wheels inboard is much greater. Moving the wheels inboard allows me to move the side rails of my frame outward by 2.25 inches.

Quick math shows that I gained 135 square inches by moving my rails outward by 2.25 inches on a 30 inch long frame, and lost 45 square inches by making 4.5 by 2.5 holes inside my belly pan. This gives me a net gain of 90 square inches for electronics on top of the additional space above that for mechanisms.

Originally Posted by Jay O'Donnell

Not for a WCD. Probably something similar to the VEXPro Drive in a day (not exactly like it but pretty similar).

Ok, I would mount the gearbox using the 4 bolt holes in line with the output shaft. If you support the other end of the shaft, the fact that the holes are practically in a line won't matter.

[M. Mellott]

I can't tell from the image...are all 6 wheels in contact with the ground, or is one pair dropped/lifted?

[Ty Tremblay]

Originally Posted by M. Mellott

I can't tell from the image...are all 6 wheels in contact with the ground, or is one pair dropped/lifted?

The middle wheels are dropped a fairly standard 1/8".

[asid61]

Originally Posted by Ty Tremblay

While the inboard wheels do take up a little space, the space gained by moving the wheels inboard is much greater. Moving the wheels inboard allows me to move the side rails of my frame outward by 2.25 inches.

Quick math shows that I gained 135 square inches by moving my rails outward by 2.25 inches on a 30 inch long frame, and lost 45 square inches by making 4.5 by 2.5 holes inside my belly pan. This gives me a net gain of 90 square inches for electronics on top of the additional space above that for mechanisms.

Very impressive gain then!

[75vs1885]

Originally Posted by AdamHeard

Are you worried about something coming under your bumpers and hitting the chain/sprocket?

Also, it seems like the 2nd frame is a LOT just to support the bumpers.

Assuming similar bumper rules as previous, something inplane with the existing drive frame could support it for far less pieces/weight/fab.

I think its so early to say w/o knowing the game, but I do agree, if it was the frisbee game then youd probably see that

[RonnieS]

Originally Posted by Ty Tremblay

Here's an updated version without the secondary bumper frame. Weight is now 31 lbs!

Are you using chain or belt? I always like to be able to put new chain on without having to take off bumpers for scenarios like elims. Although I do know this might be hard with the chain(or belt) running outside of the chassis.
-Ronnie

[Ty Tremblay]

Originally Posted by Ronnie314

Are you using chain or belt? I always like to be able to put new chain on without having to take off bumpers for scenarios like elims. Although I do know this might be hard with the chain(or belt) running outside of the chassis.
-Ronnie

I'm using chain simply because it's not as wide and thus reduces the cantilever needed.

I'm glad you asked, though. I slept on it for a day or two and realized that the only reason I was running chain on the outside of the rails was because it was on the opposite side of most of the wheels. After thinking it through, however, I realized that the center wheels are probably the WORST wheels to add extra cantilever to. If the shaft were to shear despite it's factor of safety, we'd have to rebuild the entire gearbox with a new shaft. If one of the shafts on the outer wheels was to shear, it'd be much less difficult to change out. The center wheels also experience the heaviest loads and impacts.

I made the switch to VEXPro 2 CIM Ball Shifters due to their stock encoder mounts and reliability. I then stole 973's WCD modifications for the ball shifters and ran the chain inside of the rails. This significantly simplified the exterior of my bot, allowing me to easily mount the standoffs that make my frame perimeter.

You'll also see that I switched to WCP bearing blocks and forgot to add my battery holder.

Here's the result. Weight is now about 36lbs.

[JesseK]

Originally Posted by Ty Tremblay

If the shaft were to shear despite it's factor of safety, we'd have to rebuild the entire gearbox with a new shaft.

FWIW the 2 CIM Ball shifter with 3rd stage option looks like it has an output shaft that would be extremely simple to create out of steel hex on a lathe. Cut to length, face on the lathe, 3 lathe operations, then tap and you're done. Would take about an hour for both axles. It'd give you 2 spare axles for the outer wheels as well.

This assumes the steel hex fits everything though.

[Ty Tremblay]

Originally Posted by JesseK

FWIW the 2 CIM Ball shifter with 3rd stage option looks like it has an output shaft that would be extremely simple to create out of steel hex on a lathe. Cut to length, face on the lathe, 3 lathe operations, then tap and you're done. Would take about an hour for both axles. It'd give you 2 spare axles for the outer wheels as well.

This assumes the steel hex fits everything though.

Yeah. It's easy enough to make out of steel. The FEA I ran put our factor of safety at >2 with 7075-T6, I could even go with another Al alloy (2024-T4, I think it was) and get an even better FOS. The benefits of running the chains on the inside of the rails just outweigh the benefits of running them on the outside now.

[TD78]

Ty, looks really good. Straightforward and configurable if need be. Seems like basic milling and turning could complete this chassis in little time.

I've loved the methodology of using pop rivets to get everything aligned. Throw a few weld tacks here and everything gets tied together quite nicely.

Would you be able to post a top down view?

Thanks as well to the teams in which parts of the design drew inspiration. Amazing how chassis design has evolved over the years.

[Ty Tremblay]

Originally Posted by TD78

Would you be able to post a top down view?.

Here you go.

Note that the cantilever could be reduced further by the use of wheels other than Colsons.