01-12-2015 16:46

Harman341

Re: pic: WCD off season chassis from 2471

I don't see any chain. Is that chain-in-tube or are you just powering the middle wheels?

01-12-2015 16:47

KrazyCarl92

Re: pic: WCD off season chassis from 2471

Are you going chain-in-tube to power the corner wheels?

Are the two vertical 2" x 1" tubing pieces on the left side (as pictured) corner wheels encoder mounts? Why do they stick up above the height of the frame?

01-12-2015 17:12

Zebra_Fact_Man

Re: pic: WCD off season chassis from 2471

Is see the question I was going to post has already been asked...

OP please to tell.

01-12-2015 17:25

Bryce2471

Re: pic: WCD off season chassis from 2471

It's a chain in tube design
They are encoder mounts. They stick up to accommodate the gears that run the encoders. I'm not sure why they were done that way, as I was not involved in their design.

01-12-2015 17:50

Ty Tremblay

Re: pic: WCD off season chassis from 2471

What lead you to choose to use tensioners with your design?

One of the major benefits of the in-tube design is that it's practically impossible for a chain to jump the sprocket, especially if the center-to-center distance between the sprockets is correct.

01-12-2015 18:24

Bryce2471

Re: pic: WCD off season chassis from 2471

I was not involved in that decision, so I can't say for sure. However, I do know that bearing blocks were used so that the the frame could use .0625in wall tubing.

01-12-2015 18:46

JesseK

Re: pic: WCD off season chassis from 2471

Do I spy shock absorbers? Or is that black ABS for spacing?

01-12-2015 21:44

RobotsThatWork

Re: pic: WCD off season chassis from 2471

for your chain in tube design, are you using 2"x1" tubing? if so, are you using COTS sprockets? I haven't been able to fit 2 COTS sprockets into the tube. It would be great if anyone could tell me how everything was packaged together.

01-12-2015 22:00

Greg Woelki

Re: pic: WCD off season chassis from 2471

I can't speak for team 2471, but these fit. A version broached for 1/2" hex is available in the drop down selection box.

01-12-2015 22:12

R.C.

Re: pic: WCD off season chassis from 2471

I'm not sure how cots sprocket don't fit? Do they not fit due to the diameter or the width of the sprocket or both?

01-12-2015 22:15

Bryce2471

Re: pic: WCD off season chassis from 2471

Yes, and yes. They are plastic spacers. We designed the bumper mounts that way to help insulate the frame from impact. This year's BunnyBots competition has no rule against high speed ramming, and looks to be highly violent.
It was designed to use standard vex spockets, but because they were out of stock, we ended up using steel sprockets with shortened hubs. I don't know the exact layout.
Very nice, I was unaware that they were availible in hex.

01-12-2015 23:06

RobotsThatWork

Re: pic: WCD off season chassis from 2471

Two 16 tooth vexpro sprockets do not sit next to each other inside the 2x1x1/8 (so width). This is true for both when bearings are press-fitted, and when I use a versa bearing block. The Sprocket with Chain attached to it has a total diameter of 0.491 inches. When I put 2 back to back it would be too wide to fit inside the boxtubing. Any solutions?

I haven't looked into the 17 tooth double sprocket, but can you create a dropcenter with the larger diameter? I know the clearance is pretty slim already for 16t, but I don't know for sure with 17t.

02-12-2015 07:59

pribusin

Re: pic: WCD off season chassis from 2471

Very nice and clean drive base. I want our team to look into a chain-in-tube design this year but I've always wondered how you assemble the chain and sprockets in the tube Care to give me some insight on the procedure? Are there access hole on the underside? Has anyone ever done this with belts?

02-12-2015 08:09

notmattlythgoe

Re: pic: WCD off season chassis from 2471

What we've done is loop the chains around the sprockets and then drop the entire thing down into the tube. Then slide the axles through the sprockets and the bearings over the axles. This is of course 100x easier if the tubes are not attached to the robot already.

If you are using 2 sprockets in the middle like we do we have a small piece of axle that we'll put through the two sprockets to hold them together during the drop and push that piece out with the final axle.

02-12-2015 08:52

pribusin

Re: pic: WCD off season chassis from 2471

Got it - thanks.

Are those 3" x 0.875" wheels? How are they kept from slipping off the hex shaft?

02-12-2015 10:23

Nate Laverdure

Re: pic: WCD off season chassis from 2471

We chose to avoid this problem by using 2 x 1.5 x 1/8 tube.

The 17t sprocket works in the 2 x 1 x 1/8 because it has a large enough pitch diameter that the chain clears the 1.125 bearing OD.

02-12-2015 12:37

jman4747

Re: pic: WCD off season chassis from 2471

External retaining rings: http://www.mcmaster.com/#97633a200/=102dny4

02-12-2015 12:48

Nebster

Re: pic: WCD off season chassis from 2471

What are you using to hold the corners of the frame together? It's not clear to me

02-12-2015 12:52

notmattlythgoe

Re: pic: WCD off season chassis from 2471

There are blocks in the ladders with through bolts going through the rails.

02-12-2015 13:00

Ty Tremblay

Re: pic: WCD off season chassis from 2471

http://www.team221.com/order.php?cat=15

See "Chassis Tube Connector"

02-12-2015 14:46

Bryce2471

Re: pic: WCD off season chassis from 2471

This was a point of much discussion while in the design phase. We thought gussets would be stronger, but using blocks would fit with the chain in tube solution better.
This is what we ended up going with, partly because the belly pan is adding a lot of corner to corner strength already.
We did not use these, but they look to be functionally equivalent. The plastic blocks ended up being a good project for younger students to get some training and experience in.

02-12-2015 16:01

cxcad

Re: pic: WCD off season chassis from 2471

It would be interesting to see the FEA for the block vs gusset design. On my team the thought was that blocks were stronger because the blocks were pulling the frame members toward each other.

02-12-2015 21:48

zinthorne

Re: pic: WCD off season chassis from 2471

Does anyone know where to find a cad file for this?
The half inch hex

02-12-2015 23:24

asid61

Re: pic: WCD off season chassis from 2471

Because I couldn't find it, I just downloaded the round version, put a hex bore in it, re-saved it as a STEP file, and reopened it. That gave me the 1/2" hex 17t double sprocket.

03-12-2015 19:20

zinthorne

Re: pic: WCD off season chassis from 2471

I can not find the round version. Am I missing something on the website?

03-12-2015 19:42

Greg Woelki

Re: pic: WCD off season chassis from 2471

I emailed them about it last year. The file can be found here.

03-12-2015 22:42

Jacob Bendicksen

Re: pic: WCD off season chassis from 2471

Wait, Mean Machine's not doing swerve?

Glad to see you're having fun and building robustly for BunnyBots -- should be a fun event.

04-12-2015 17:43

Nebster

Re: pic: WCD off season chassis from 2471

What are you doing for center drop? Do the sprockets you're using inside the tube have enough clearance with the walls of the tubing for a center drop? I haven't seen that done before but since you're using 1/16" tubing it could be possible.

Do you feel 1/16" walled tubing is strong enough for a traditional drive train?

04-12-2015 18:06

Bryce2471

Re: pic: WCD off season chassis from 2471

Yep, I'm looking forward to it!
The bearing blocks we are using have their bearing holes drilled 1/16" off center. The center wheel has its block upside down compared to the outer wheels, so that gives us 0.125" drop. If it tips around too much or is too squirrely, we will flip one of the outside wheels for effectivly a 0.0625" drop. We are using 16t #25 chain sprockets.
I think so, but we'll know for sure by the end of the month.
Anything that survives this BunnBot game will certainly be "strong enough for a traditional drive train"

04-12-2015 18:14

Dunngeon

Re: pic: WCD off season chassis from 2471

Yes, 1/16 wall tubing is easily strong enough for a drivetrain.

07-12-2015 10:45

Chris is me

Re: pic: WCD off season chassis from 2471

This is not a safe general statement to make at all. There are multiple loading conditions to consider, and it entirely depends on how you build your frame, what loads it is exposed to, etc.

Generally, 1/8" wall (or .1" wall) tubing is used on the driveline in order to support the bearings or internal bearing blocks better. 1/16" is too thin for a drivetrain bearing fit not supported by anything else. So regardless of strength many teams run 1/8" wall on the driveline. This could be different for systems like the VersaBlock which don't rely on the internal walls of the tube for support.

As for your cross members, I have heard in the past that teams have dealt with buckling cross members under very heavy defense when they used 1/16" 2x1 tubing. This obviously depends on the number of crossmembers used, any other cross-structural support from other mechanisms, etc. but I wouldn't just say "1/16th is easily strong enough" as a general statement.