pic: Simple Chain-in-Tube Concept
 

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I really like the use of tubing to mount the ballshifter, very clever.

Re: pic: Simple Chain-in-Tube Concept
 

Thanks. I basically got rid of the plate and standoffs that come with the 3rd stage kit and made the output shaft and gear part of the drive rail. The gearbox then bolts on. I had reservations about putting 3 bearings on the same shaft, but since it's bolt tolerances holding the 3rd one on, I'm fairly comfortable with it.

Here's a pic with one gearbox removed.

Re: pic: Simple Chain-in-Tube Concept
 

Brilliant. This is the current weakness in our chain in tube design using the ball shifters. Consider this stolen :cough: I mean borrowed.

Re: pic: Simple Chain-in-Tube Concept
 

Send me a PM if you'd like the CAD model.

EDIT: Link below.

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Very nice Ty!

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You mention reducing the diameter of the outer wheels, have you considered increasing the diameter of the middle wheel?

I'm thinking that versawheels with blue nitrile might have a large enough OD to give a decent amount of rock with 4" Colson wheels on the outside.

Alternatively, you could use 4" wheels on the back and middle and a 3.5" wheel on the front. That gives you the same amount of rock as a 1/8" center drop.

Edit: You can also use a vex 16 tooth sprocket on the 3.5" wheel down from the 17 tooth sprocket on the 4" wheels to try to get the surface speeds of the wheels more closely matched. This should reduce wheel wear.

Re: pic: Simple Chain-in-Tube Concept
 

There's definitely a lot you can do with the wheels, I'm just a huge fan of the durability of Colson wheels and we have a lathe handy right in our workshop.

I've had a few extra requests for the CAD model, so here it is.

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Thanks for the CAD, looks pretty darn simple and bulletproof.

As far as colsons, Vexpro has 4", 3.5", and 3" Colsons. If we build something like your design I think we will use 1/2" smaller dia front wheels, whether we use 4" or 3.5" wheels for the rest.

Re: pic: Simple Chain-in-Tube Concept
 

How are you going to attach the two vertical pieces of tubing to the horizontal frame tube on each side? It looks like there is not a lot of surface area and any fasteners that protrude into the frame tube may interfere with the chain and/or sprocket.

Re: pic: Simple Chain-in-Tube Concept
 

What's the reason for the slots in the tube that mount the gearbox?

Re: pic: Simple Chain-in-Tube Concept
 

Probably to not overconstrain things.

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You want the gearbox position to be driven by the third bearing in the plastic housing piloting onto the shaft captured in the tube. This sets the appropriate gear spacing and prevents misalignment of any the bearings or the shaft. Then the bolts just clamp everything in place wherever it ended up.

I also really like the boxtube standoffs. I'd played around with this same idea, but still using a version of Vex's third stage plate, requiring more pieces and more disassembly to get the gearbox away from the final gear. The boxtube cleans this up a lot.

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Really nice job Ty....thank you for posting your model. I think this design concept will start to become more popular in the near future.

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We have a TIG welder in our shop, so they'll be welded in place. If you don't have access to a welder, basically any motorcycle shop near you will have one and you could work with them for a sponsorship.

Mostly to not over constrain things as stated above. Secondarily to make it so that I don't have to keep track of left and right versions of the tubes since putting a hole in the middle of the tube would cause the tube to interfere with the gear on the rail.

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Nice! Do you have a cutaway of the inside of the tube-in-chain? I'm not quite sure what the inside would look like. How do you assemble this? are there access slots/holes to access the chain?

Call this a stupid question but how do you assemble the chains and sprockets inside the tubing.

Re: pic: Simple Chain-in-Tube Concept
 

Very carefully.

What we have is a piece of hex shaft that is cut to the width of the sprocket(s). Then loop the chain around the sprockets, and drop that into the tube. Last push the axles through the sprockets when they are in place and slide the bearings over the axles.

Re: pic: Simple Chain-in-Tube Concept
 

If you're using the 17t sprockets from 221, a wheel c-c distance that's divisible by .25 won't work without using a half link, which gave us problems. The distance should be something like 11.625 where if you divide it by .25 the remainder is .125.

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Thanks. I've gotten rid of the incorrect information.

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Have you been successful with #25 chain in the drivetrain? Im working on one right now and it is spaced for #25 chain.

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We've used it for three drivetrains now without any issues. I've never seen a chain break, only get thrown when there is angular misalignment between two sprockets.

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Yes, for the past 3 years. Our 2013 and 2014 bots used the team221 COTS side rails with tensionable outer bearing blocks. Our 2015 bot used a chain in tube design that we developed during the summer of 2014. You can download the CAD models, including the chain in tube design, at FRCdesigns.com.

I presented our original idea for the Quick Build Drivetrain at the Hampton Roads FRC Summit in 2012. I gave an update and a description of our West Coast drive train development program at the 2014 FRC Summit.

Correction: While our 2015 bot used WCD side rails, it technically was not a true a west coast drive. We took the center mounted gearbox and moved it to the end opposite the crate stack. Then we omitted the center wheels and replaced the front Colson wheels with omnis. (Pics in the picasa galleries linked in my sig.) The internal power transmission components, however, are identical to the West Coast drive train we developed over the summer of 2014. This fixed-spacing chain-in-tube design, won us two regionals and took us to the quarter-finals at CMP with literally zero maintenance. I think that once we got to St. Louis someone said, "Hey, shouldn't we put some more grease on the gearbox gears?" Caveat: the 2015 game was super easy on drivetrains, requiring neither high speed nor pushing power.

Re: pic: Simple Chain-in-Tube Concept
 

I've made a few updates to this drive train.

• Switched to 4" wheels after taking another look at the numbers. This should give me actual speeds of 6/14 fps
• Moved to retaining the wheels with screws and washers to better reflect my team's machining capabilities.
• Added features for the box tubing to set into on the rails, this will help us make sure everything is aligned before welding.
• Created an example for a no-welding setup for teams without access to welding. This also allows for all VexPro 3rd stage reductions to be used (box tubing option doesn't allow for 60- and 64-tooth gears).
• Added basic bumper framing.

Updated model
No welding setup
No welding drive rail

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Have you run those bumper rails before?

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I have not. I used the mantra of "copy the best and invent the rest" (thanks Mike Corsetto).

I took inspiration from 118's 2014 CAD as well as 971's one-bumper manufacturing style with reinforced corners.



We plan to do our own testing, but if 118's design lasted the season in Aerial Assault, my initial hunch is that our more conservative design will too.

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That round tube you see on their drive was actually only to fulfill the rule that there should be no "unsupported" side of the bumper greater than 8" After seeing it at competition it really didn't even support the bumper but it was there only to pass inspection.

I'm not quite sure how they mounted it but my guess is they just tapped the ends of that tube or round stock and bolted it onto those large 2x1 uprights. IIRC the inspectors made them lift their robot by their "Bumper supports" (The round stock in the screenshot) in order for them to pass the inspection proving that "Those actually do support the bumpers". They used those large holes with large threaded bolts attached to the bumpers to mount their bumpers to their robot.

If I were to use what 118 did, I would in fact just use a piece of aluminum rod or even thunderhex shaft that is tapped to do what they did in a similar fashion.

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Right, but like I said, this is a more conservative approach.

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I really like this design and may consider proposing it, if it makes sence for the game.
I do think there is a problem with it though. Assembling the transmissions to the chassis. (Please correct me if I wrong here.)

If I am seeing this correctly, the tube mounts need to be installed to the frame first, then the transmissions to the mounts. The problem is, the drive shaft is long enough that motors will not allow correct alignment to the two rail bearings because the belly pan is in the way. Servicing this, or replacing a motor might be a bit difficult.

If these issues are easy to address, please explain how. I like this design and would love to use it!

Re: pic: Simple Chain-in-Tube Concept
 

The drive shaft on the middle wheel, along with the gear on that shaft, remains in the tube when the transmission is removed. The interface between the removable transmission and the frame consists of the mounting bolts and the gear interface.

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Right, forgot about the third stage! That make perfect sense. OK, supper easy assembly and repair them, got it.

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I cant believe I missed this thread earlier. We may look into this.
Even with the relatively small amount of space saved, makes a big difference on the footprint of the control system parts on the bellypan.
With a modulated frame that we are using, this is even easier to access our chain.

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Realized I've been having a 7 month long brain fart.

If you increase the spacing of the output gear from the rail by .25", you can bolt on 1"x1"x.125" tubing and use that to mount your gearbox. VexPro sells .25" acetal spacers with a .5" hex broach.

Top-down view

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How difficult will it be to install those gearbox mount bolts?

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I thought your original version that started this thread was basically this with a 1"x0.75" tube for the gearbox mount...

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If you can easily find 1x.75 tubing, then that's a great way to go. It's not easily acquirable for our team, so we'll be milling down a piece of 1x1 and welding it on.

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The bolts holding the gearbox to the 1x1 tubing? Very easy.

If you're talking about the bolts/screws used to attach the tubing to the drive rail, it's just a matter of lining up the holes and getting a bit started on the other side. I'd suggest doing it before installing any wheels, bearings, or chain.

I'm about to hop on a plane, I'll get a couple more screen shots and the updated CAD as soon as I can.

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Or .75x.75, or .75 x 1.5, or something... but ok.