Robostangs 548 2016 Offseason Rocker- Z6

[jnicho15]

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The Robostangs present Z6! Another generic chassis with the following:

• 6 Wheels! (that don't all touch the ground at once like our comp bot)
• Lexan Side Plates! (remember to make sure the bearings can't fall out)
• Flanges! (FYI: cold-bent lexan cracks)
• Multi-Level Belly Pan!
• 4-CIM Drive!
• Dual-Reduction Versa Gearboxes! (9.52:1)
• Finite-position Chain Tensioners!
• A roboRIO!
• A Battery!

Download SOLIDWORKS CADs!

[cbale2000]

Interesting Chassis! I am a bit curious as to what its intended purpose is though.

The only reason I could think of to use what appears to be thin polycarbonate on the side plates (and nowhere else) and to arrange the drive the way it is would be for a demonstrator of some kind.

Care to elaborate?

[jnicho15]

Originally Posted by cbale2000

Interesting Chassis! I am a bit curious as to what its intended purpose is though.

The only reason I could think of to use what appears to be thin polycarbonate on the side plates (and nowhere else) and to arrange the drive the way it is would be for a demonstrator of some kind.

Care to elaborate?

Every offseason, we design and build a simple chassis in order to give design and machining kiddos practice. Them we drive it around at outreach events. This time, we tried lexan sideplates for fun. Also, we may use this design as our drive base in the season.

[tickspe15]

What are the perceived benefits of using polycarbonate for the plates? It looks like you're relying heavily on two zip ties to hold everything together.

[BigHorse]

The choice to use lexan was an experiment to see how durable the lexan would be and to see if we could shave some weight off the drive base. Plus it looks cool.

We ended up switching to matching aluminum sideplates after our 2016 robot trampled this little guy at an outreach event.

I think with the protection of bumpers it is worth using lexan to shave off some weight during the season.

[cbale2000]

Don't get me wrong, I don't have a problem with using polycarbonate (we've used it extensively throughout our chassis for years) but it looks like you're using maybe 1/8" at the most?

On our drive system we use 3/8" polycarbonate for durability. Granted we're not bending flanges into it, but I personally don't think I would ever use less than 1/4" thick on a chassis. Polycarbonate is roughly 44% the weight of 6061 aluminum so you do still save weight even with twice the material thickness compared to a typical aluminum frame.
Additionally, if you use thicker polycarbonate, you could potentially replace even more of the aluminum frame with polycarbonate like the interior plates that you mounted the gearboxes to. I think I would still leave the front and back parts aluminum though for rigidity.

The other trick we've found is it has to be supported with standoffs and such otherwise you get too much flex between attachment points (as it seems you experienced).

[s_forbes]

Polycarbonate is a neat building material; it has a lower density than aluminum, but is much more flexible. It has some good applications, but I don't think that replacing aluminum channels in a drivetrain is usually one of them. Being lighter isn't always the best attribute. Sometimes you need a material that is stiffer rather than lighter.

That said, it's great to see you built the design and tested it, that's worth way more experience than just hearing people on Chief Delphi say "that won't work very well". Kudos for that!

The zip tie bearing retainers are great, I highly approve of that fix.

[Cothron Theiss]

Looks great! Few questions though. How are you bending the lexan? I'm always curious about the different ways people manipulate the stuff. Also, is there any reason you made the 2nd level of the belly pan out of aluminum instead of lexan? That seems like a perfect application for it.

As far as using the lexan for sideplates, I think you'd do well to add some standoffs in between your side plates. They'd support and strengthen the plates much more than the zipties, and in both directions as well.

Also, when relying on bends in sheet metal or lexan or paper, the length and bend angle of the flange is important. In the middle of the top bend in the plate closest to the viewer, your flange seems to be flexing upwards such that the bend angle is greater than 90 degrees. This will not impart as much rigidity to the plate as a 90 degree bend, so don't expect it to.

[jnicho15]

Originally Posted by s_forbes

The zip tie bearing retainers are great, I highly approve of that fix.

Look closer at the "bearings".

[cbale2000]

Originally Posted by s_forbes

Polycarbonate is a neat building material; it has a lower density than aluminum, but is much more flexible. It has some good applications, but I don't think that replacing aluminum channels in a drivetrain is usually one of them. Being lighter isn't always the best attribute. Sometimes you need a material that is stiffer rather than lighter.

Sometimes flexible is good though. Aluminum will deform when it takes an impact which can be difficult to fix without replacing the part, whereas polycarbonate will just flex and return to its original position. That little bit of flex can make a big difference when it comes to frame durability and longevity long-term. Granted, you do still have to make sure it's strong enough to not fail catastrophically during typical use.