To clarify polycarbonate (minibots)

[Halliday]

The rules state we can use polycarbonate on the minibots. My mentor wanted me to make sure before I started building that there is no limit on how much polycarbonate we can use.

So would it be safe to say I can create my minibot out of 90% polycarbonate? The only things that wouldn't be are the motors, battery, NXT, ect....

Thanks in advance

[MrForbes]

The rules don't specify how much of which materials you can use, aside from things like motors, switches, batteries, etc.

Although making a rigid structure from polycarbonate might make it weigh more than making it from aluminum. If you need a rigid structure.

[Halliday]

Originally Posted by squirrel

The rules don't specify how much of which materials you can use, aside from things like motors, switches, batteries, etc.

Although making a rigid structure from polycarbonate might make it weigh more than making it from aluminum. If you need a rigid structure.

Thanks for the helpful answer and the even more helpful advice. If using aluminum makes it lighter then I'll use it. I just rather not modify the aluminum materials for my design but if it makes a difference then I'll do it. Going to get out a scale and weight materials now.

[MrForbes]

In general, polycarbonate is roughly half the density of aluminum. But it's modulus of elasticity is much lower, so to make a part as rigid as aluminum it needs to be more than twice as thick.

If you can make angles or channels from polycarbonate, you can make a light, rigid structure. It's not easy to bend it a full 90 degrees though. You can bend it with a brake, and adding heat from a heat gun helps, but still it's not easy to do it.

[Chris is me]

Originally Posted by squirrel

In general, polycarbonate is roughly half the density of aluminum. But it's modulus of elasticity is much lower, so to make a part as rigid as aluminum it needs to be more than twice as thick.

In general, yes. However, what's usually the limiting factor in rigidity in structures, especially tiny minibots, is not your material but your cross-section. "Thick enough" for both polycarbonate and aluminium is usually very close to doable, as long as your pieces are arranged and put together in a nice, rigid manner.

If you don't want to cut Tetrix aluminium, you can use various kinds of "standard" aluminium parts.

[thefro526]

Originally Posted by squirrel

If you can make angles or channels from polycarbonate, you can make a light, rigid structure. It's not easy to bend it a full 90 degrees though. You can bend it with a brake, and adding heat from a heat gun helps, but still it's not easy to do it.

McMaster car sells polycarbonate in most common shapes, Angles, U-Channels, Tubes, etc, so building a rigid structure from some off the shelf polycarbonate pieces wouldn't be all that difficult. And as far as I can tell, any form of Polycarbonate seems to be legal, since the manual doesn't refer to any specific shape or form in the same way they do with Aluminum.

[MrForbes]

Great suggestion Dustin! I hadn't thought of that...even though we used a round polycarb tube from McM on our 2007 robot

[thefro526]

Originally Posted by squirrel

Great suggestion Dustin! I hadn't thought of that...even though we used a round polycarb tube from McM on our 2007 robot

How well does Polycarb tube hold up? I've been wanting to play with some for quite some time and now I finally have an excuse to.

[MrForbes]

We've also used it on our underwater robots (6" diameter). And for the torpedoes for the underwater robot (1.5" diameter). The arm from 2007 held up fine. The underwater robots are doing great. It's good stuff. But like any other material, you need to use it in a reasonable design if you want it to work well.

[GaryVoshol]

Originally Posted by Halliday

So would it be safe to say I can create my minibot out of 90% polycarbonate? The only things that wouldn't be are the motors, battery, NXT, ect....

Well, your percentage is off - 90% means you'll have up to 13.5 pounds of polycarb and 1.5 pounds for the rest of your bot. As I recall, the battery and motors themselves weigh somewhat over 2 pounds; if you're using the NXT (with it's batteries) would likely push that to 3 pounds total.

So maybe 60-70% polycarb is possible ...

But no, there are no restrictions on how much of any material you can use as long as it fits in the weight limits.

[Halliday]

Originally Posted by GaryVoshol

Well, your percentage is off - 90% means you'll have up to 13.5 pounds of polycarb and 1.5 pounds for the rest of your bot. As I recall, the battery and motors themselves weigh somewhat over 2 pounds; if you're using the NXT (with it's batteries) would likely push that to 3 pounds total.

So maybe 60-70% polycarb is possible ...

But no, there are no restrictions on how much of any material you can use as long as it fits in the weight limits.

lol, I wasn't trying to get too technical but I should have known better to do that on Chief Delphi.