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Unread 31-10-2014, 08:05
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Re: pic: 319 Octagonal Drive Isometric

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Originally Posted by Ty Tremblay View Post
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
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Unread 31-10-2014, 09:29
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Re: pic: 319 Octagonal Drive Isometric

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Originally Posted by Ronnie314 View Post
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.
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Unread 31-10-2014, 10:01
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Re: pic: 319 Octagonal Drive Isometric

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Originally Posted by Ty Tremblay View Post
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.
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Unread 31-10-2014, 10:33
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Re: pic: 319 Octagonal Drive Isometric

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Originally Posted by JesseK View Post
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.
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Unread 31-10-2014, 10:40
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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.
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Unread 31-10-2014, 10:53
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Re: pic: 319 Octagonal Drive Isometric

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Originally Posted by TD78 View Post
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.
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Unread 31-10-2014, 11:02
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Re: pic: 319 Octagonal Drive Isometric

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Originally Posted by Ty Tremblay View Post
Here you go.

Note that the cantilever could be reduced further by the use of wheels other than Colsons.
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...
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Unread 31-10-2014, 10:58
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Re: pic: 319 Octagonal Drive Isometric

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Originally Posted by Ty Tremblay View Post
Here's the result. Weight is now about 36lbs.
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.
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Unread 31-10-2014, 11:18
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Re: pic: 319 Octagonal Drive Isometric

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Originally Posted by BrendanB View Post
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.
Brendan, I'm curious, did you guys opt for manual or automatic shifting? Did you find any pros/cons with your chosen approach?
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Unread 31-10-2014, 12:25
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Re: pic: 319 Octagonal Drive Isometric

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Originally Posted by lineskier View Post
Brendan, I'm curious, did you guys opt for manual or automatic shifting? Did you find any pros/cons with your chosen approach?
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.
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Unread 31-10-2014, 12:46
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Re: pic: 319 Octagonal Drive Isometric

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Originally Posted by BrendanB View Post
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.
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.
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