971's chassis

[craigboez]

Based on the pictures it looks like you're adding a countersink before putting in your rivets. This seems rather time consuming, so I'm guessing there is a good reason. Care to elaborate?

[Madison]

Originally Posted by AustinSchuh

We ran the "original" 3 piece design in 2012 and 2013, and it has served us very well.

We couldn't find a way to make an octagon with a 3 piece chassis, which means it probably isn't possible or easily to machine. We wanted an unbroken flange to help form a backbone to tie everything to and to tie everything together. The best way to do that that we found was to set the chassis up as you see this year. We started by figuring out where to put the wheels and pulleys, and then built the frame to hold everything in place. This resulted in the jog on the inner face, which resulted in an internal corner which couldn't be bent without breaking things up into more pieces. We also needed a parallel face to bolt the wheel tensioners to, which drove the inner frame rail shape that you see. You can see the set of 8 #6 holes that define the tensioner location in one of the pictures.

Austin,

Is the CAD model for this available somewhere? I'd like to take a closer look at how you worked around the internal bends on that inner face.

[James Kuszmaul]

Originally Posted by craigboez

Based on the pictures it looks like you're adding a countersink before putting in your rivets. This seems rather time consuming, so I'm guessing there is a good reason. Care to elaborate?

If we had to do the countersinks ourselves, yes it would be time consuming, but it is relatively easy for our sponsors to quickly do the countersinks (and to do them right for the rivets). This then reduces the number of protrusions that we have to avoid interfering with or that might catch on things.

[AustinSchuh]

Originally Posted by craigboez

Based on the pictures it looks like you're adding a countersink before putting in your rivets. This seems rather time consuming, so I'm guessing there is a good reason. Care to elaborate?

We use countersunk rivets. There are punches on the CNC turret punch which will make a .129 hole that is countersunk to 120 degrees, all in 1 hit. This makes it so the bottom, front, and sides of our bot are perfectly smooth and can't catch on anything.

[AustinSchuh]

Madison,

Originally Posted by Madison

Is the CAD model for this available somewhere? I'd like to take a closer look at how you worked around the internal bends on that inner face.

The CAD model isn't available, and we have no plans to release it. We subscribe to the 254 CAD release philosophy, and choose to share pictures and explain the why about what we do rather than directly share the model. We have a team meeting tonight though, and I'll (try to) have one of the students put together an exploded view that should answer your question.

[AustinSchuh]

Originally Posted by saikiranra

What is the advantage of having the center drive wheels offset right/left, compared to other traditional 6 wheel drive set-ups?

We wanted our frame perimeter to be an octagon to change how the robot interacts with the field and other robots. The wheel placement was chosen to maximize the space in the center of the frame once we had decided on the frame perimeter.

[Madison]

Originally Posted by AustinSchuh

Madison,



The CAD model isn't available, and we have no plans to release it. We subscribe to the 254 CAD release philosophy, and choose to share pictures and explain the why about what we do rather than directly share the model. We have a team meeting tonight though, and I'll (try to) have one of the students put together an exploded view that should answer your question.

An exploded view would be great. I think I have a pretty good idea of what those pieces look like, but the exploded view will help me to figure out if I'm missing anything.

Thanks!

[SeanKennedy]

Pem nuts are great. They come in multiple different designs for different applications. We typically use an f- series nut because it is flush on both sides and is extremely to install correctly. They are much much stronger than just threading aluminum and they are a blind fastener when it comes to the installation aspect, so there is no need for any access to reach a nut or other piece of hardware on the back side. An f series nut can be installed with any hydraulic or arbor press, and most rivet squeezers.

When we cant access the back of a part, we used a rivnut which is a completely blind fastener as only one side of the material needs to be accessed to install the part. these parts are great for putting threads in tubes or in really odd spots. They can be found at our sponsors web site: enfasco.com

[James Kuszmaul]

Originally Posted by Madison

An exploded view would be great. I think I have a pretty good idea of what those pieces look like, but the exploded view will help me to figure out if I'm missing anything.

Thanks!

We've put up some shots of our drivebase CAD on our picasa page.

[Madison]

Originally Posted by James Kuszmaul

We've put up some shots of our drivebase CAD on our picasa page.

That was speedy. Thanks so much.

[AdamHeard]

Originally Posted by James Kuszmaul

We've put up some shots of our drivebase CAD on our picasa page.

I love that axle retention method.

[AustinSchuh]

Originally Posted by AdamHeard

I love that axle retention method.

I also like that the bushings that the axle go into. They both make it easy to get the axle out, and stick out a bit to replace spacers so that the bearing race on the wheels doesn't rub on the tensioner.

[BrianSilverman]

Originally Posted by Travis Schuh

We align the wheel angle by eye. It turns out that the human eye is pretty good at judging this, we typically sight if the wheel is parallel to the lightening hole. We have never had an issue of having a miss-aligned wheel.

However, it's important to check the lightening hole is straight first (they weren't in 2012 and it was a pain)...

In addition to doing it by eye, the belts always track to one side or the other of the pulley as they spin. When we tighten the belts, we sometimes spin the drivetrain by hand to see which side the belts move to and then tweak it the other way to fine-tune it.

Also, I've seen some wheels that were fairly crooked (I'd guess 10-15 degrees eyeballing it) after running matches or practice (usually caused by a bad job tensioning and/or one of the tensioner bolts backing out), and the belts seem fine afterwards, so it doesn't seem to be a very big deal.

[Bryce2471]

If you don't mind, I've got a few questions.

1. How much does the assembly weigh?
2. How much is the drop center?
3. What is the gear ratios on the drive gearbox?
4. What is the diameter of you wheels?
5. What is the thickness of your sheet metal?

Thanks in advance!

[highlander]

and/or one of the tensioner bolts backing out

have you tried screw lock helical inserts to prevent the bolts from backing out due to vibration?