28-10-2014 13:10

Mike Marandola

Re: pic: 319 Octagonal Drive Isometric

Looks awesome, but is the wheel cutout in the bellypan big enough to take the wheels out without taking the shaft and chain off? Then again you won't be swapping out colsons much, if at all.

28-10-2014 13:22

RonnieS

Re: pic: 319 Octagonal Drive Isometric

We are doing something just like this, it looks scary similar haha.

28-10-2014 13:23

AdamHeard

Re: pic: 319 Octagonal Drive Isometric

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.

28-10-2014 13:27

RonnieS

Re: pic: 319 Octagonal Drive Isometric

We adjusted our brackets to make sure our bumper was low enough to not have that problem.

I am think that structure is supported so well for the possibility of that being a second tier and not just bumper mounts.

28-10-2014 13:28

AdamHeard

Re: pic: 319 Octagonal Drive Isometric

Why have a 2nd tier? The superstructure can mount to the drive frame.

28-10-2014 13:29

RonnieS

Re: pic: 319 Octagonal Drive Isometric

Maybe wanting to get something like an intake as far out $@#$@#$@# possible?

28-10-2014 14:35

Ty Tremblay

Re: pic: 319 Octagonal Drive Isometric

Those outer sprockets are my biggest concern with this design. I'm considering taking the hit on wheelbase to extend the front and rear frame members.

I put the second frame that high so that it was supporting the middle of the bumpers. Since the bumpers are as low as possible, I was worried about the moment created when running into a robot with the bumpers in the higher end of the bumper zone.

28-10-2014 14:44

Joe G.

Re: pic: 319 Octagonal Drive Isometric

This strikes me as a prime candidate for belt/chain in tube, in order to protect the chain. It also means the cantilever lever arm on the middle wheel won't be as long.

28-10-2014 15:39

Travis Schuh

Re: pic: 319 Octagonal Drive Isometric

If you do a one piece bumper with the corners well joined, then the moments should be resolved through the bumper wood and transformed into lateral and vertical forces at the frame. We run a very low frame with a one piece bumper that has held up really well (the top of our frame is about 3.5in above the ground).

28-10-2014 15:47

Ty Tremblay

Re: pic: 319 Octagonal Drive Isometric

Excellent. I actually mocked up some bumpers very similar to 971's this year after perusing through your Picasa album.

28-10-2014 15:58

Travis Schuh

Re: pic: 319 Octagonal Drive Isometric

Our cad should be pretty representitive our our bumpers also. We added corner gussets for our 2014 bumpers and found them well worth the added effort. (The 2014 bumpers held up much better than 2013).

28-10-2014 16:35

Jay O'Donnell

Re: pic: 319 Octagonal Drive Isometric

This isn't really a specific question for the drivetrain, but I've been working with the same gearboxes and I was wondering how you are supposed to mount them. Do you just use the bolts from the standoffs in the gearbox?

28-10-2014 16:46

Ty Tremblay

Re: pic: 319 Octagonal Drive Isometric

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

28-10-2014 16:55

Conor Ryan

Re: pic: 319 Octagonal Drive Isometric

Octagonal Drivetrain! Its been a long time since I've seen a good picture of one.

179 did it ?first? in 2005. (Wow I'm surprised I commented on that one too). It was a pretty great robot too. Remember, that was 2005 BB (Before Bumpers Era).

A couple things I'd recommend:

• Studying some match footage to see if it really makes a difference on a T-Bone Pin. (You don't need to go back to 2005 for this)
• Do some math proving that this concept could work in the world of T-Bone Pins.
• Will this make a difference on turning?

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

28-10-2014 17:12

Ty Tremblay

Re: pic: 319 Octagonal Drive Isometric

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.

28-10-2014 17:16

Ty Tremblay

Re: pic: 319 Octagonal Drive Isometric

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

28-10-2014 20:47

asid61

Re: pic: 319 Octagonal Drive Isometric

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.

28-10-2014 21:22

Jay O'Donnell

Re: pic: 319 Octagonal Drive Isometric

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

28-10-2014 21:34

Ty Tremblay

Re: pic: 319 Octagonal Drive Isometric

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.

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.

29-10-2014 12:43

M. Mellott

Re: pic: 319 Octagonal Drive Isometric

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

29-10-2014 13:31

Ty Tremblay

Re: pic: 319 Octagonal Drive Isometric

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

29-10-2014 22:11

asid61

Re: pic: 319 Octagonal Drive Isometric

Very impressive gain then!

30-10-2014 21:38

75vs1885

Re: pic: 319 Octagonal Drive Isometric

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

31-10-2014 08:05

RonnieS

Re: pic: 319 Octagonal Drive Isometric

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

31-10-2014 09:29

Ty Tremblay

Re: pic: 319 Octagonal Drive Isometric

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.

31-10-2014 10:01

JesseK

Re: pic: 319 Octagonal Drive Isometric

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.

31-10-2014 10:33

Ty Tremblay

Re: pic: 319 Octagonal Drive Isometric

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.

31-10-2014 10:40

TD78

Re: pic: 319 Octagonal Drive Isometric

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.

31-10-2014 10:53

Ty Tremblay

Re: pic: 319 Octagonal Drive Isometric

Here you go.

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

31-10-2014 10:58

BrendanB

Re: pic: 319 Octagonal Drive Isometric

This looks really nice. It also looks like you can pick up some more space in the center by shortening your side extensions now that you've moved the chains to the backside of the 2x1.

We haven't use the WCP gearboxes but we were really happy with our 3 CIM ball shifters this year. Something our mechanical guys really liked is the flexibility when removing them from the robot. We designed our chassis with a slot in the side plate as well as a large pocket in the bellypan so we could remove the whole assembly (gearbox, wheel, axle, etc) through the bottom of the robot. They found it was much faster and simpler to just separate the main gearbox from the third stage assembly when we had to replace the encoder gears for the updated version.

31-10-2014 11:02

TD78

Re: pic: 319 Octagonal Drive Isometric

Thanks so much.

Less cantilever is nice, but those Colson wheels are just so robust. No need to replace them throughout the year. When I was on 121, we used them from 2005 through 2008 without issue (and we had to make our own hubs then!).

I know a lot of teams like to use 7075 for the shafts to be lightweight, but for the little extra weight, I would try and go with steel (granted, as stated previously, that the steel hex shaft lines up well with the hex bearings). I saw a few teams last year shear some 7075 shafts (including gearbox direct drive shafts) and replacing those did not look like fun...

31-10-2014 11:18

mwtidd

Re: pic: 319 Octagonal Drive Isometric

Brendan, I'm curious, did you guys opt for manual or automatic shifting? Did you find any pros/cons with your chosen approach?

31-10-2014 12:25

BrendanB

Re: pic: 319 Octagonal Drive Isometric

We've discussed developing an auto shifting program but the conversations usually end with us deciding that the programming effort should be focused on our manipulators and keep our driver in control of the robot so he isn't working against the robot if he feels the need to stay in low gear while an auto shifting program would quickly shift up on him. The biggest downside is we could be pushing a robot while in high gear but our driver was practiced and got into the routine of downshifting just before contacting an opponent so we didn't ram them hard. Both the operator and myself would verbally remind him to be be in low gear while pushing as a precaution.

31-10-2014 12:46

notmattlythgoe

Re: pic: 319 Octagonal Drive Isometric

We've talked about it too, our solution to staying in low gear is when we're in high gear to do the autoshifting, but switching to low gear will stay in low gear. So you basically have an autoshifiting setting and a low gear setting.