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Combat Robotics Tutorial

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Step 5: Materials

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One major question is: What material should I use?  There are a lot of different materials that will work, you just have to decide what properties you must have (i.e. strength, weight), and what properties don't matter to you.

Properties:

Material Family - Plastic/Metal
Impact Strength - How much of an impact the material can handle.
Tensile Strength - How well the material can handle being pulled.
Flexibility - How flexible the material is. (Relative i.e. grabs material, twists it, yes it flexes)
Density - Density from Machinist -Materials
Main use - Armor/Base-Plate/Etc.

Here is a list of commonly used materials:

UHMW (Ultra High Molecular Weight)

Material Family - Plastic
Impact Strength - High
Tensile Strength - Low-Medium
Flexibility - Medium-High (I wouldn't make a base-plate out of it)
Density - .034 lbs/in3
Main Use - Armor

This is a great material.  I use it for armor on all of my robots.  I wouldn't worry about the low tensile strength, because with its high impact strength and low weight it is the perfect armor for insect-weight robots.  Also, this material is very affordable.

Delrin

Material Family - Plastic
Impact Strength - Medium-High
Tensile Strength - High
Flexibility - Rigid
Density - .051 lbs/in3
Main Use - Baseplate/Armor

I am using this for a baseplate in my current robot, Slash.  It is very rigid, and is still fairly light.  Also it is affordable.

Polycarbonate

Material Family - Plastic
Impact Strength - High
Tensile Strength - High
Flexibility - Rigid
Density - .043 lbs/in3
Main Use - Baseplate/Armor

This is a good material for armor, but has a tendency to crack after big impacts.  Also it is quite a bit more expensive than Delrin and UHMW.
 

Aluminum

Material Family - Metal
Impact Strength - High
Tensile Strength - High
Flexibility - Rigid
Density - .101 lbs/in3
Main Use - Baseplate/Armor

I don't suggest using aluminum, because once it bends, it doesn't bend back.  The Base-Plate of Titan is proof of that.
 

Carbon Fiber

Material Family - Composite
Impact Strength - High
Tensile Strength - High
Flexibility - Rigid
Density - .0643 lbs/in3
Main Use - Baseplate/Armor

Don't use carbon fiber, or any composite for that matter.  Carbon fiber has great properties, until it breaks.  When a normal material breaks, usually just a little piece breaks off, but not for carbon fiber.  Since carbon fiber is made of woven strips of carbon fiber fabric, when it breaks it ones spot it starts to break all the way through.  In other words, with composites it's all or nothing.  They sound like the best thing ever, but with one little break all those awesome properties go away.

*EDIT: I have since changed my mind a little about carbon fiber.  It will work in lower weight classes (<1lb, 3lb is pushing it), but don't be surprised if it breaks after a big impact.  Personally I would sooner go for delrin, because it is just as rigid, and will stay together better in big impacts.  Also delrin is surprisingly lighter.  
 

Titanium

Material Family - Metal
Impact Strength - High
Tensile Strength - High
Flexibility - Rigid
Density - .16 lbs/in3
Main Use - Baseplate/Armor

Titanium is the perfect blend of strength and weight.  It does weigh more that twice what UHMW and Delrin weight, but it is worth it on some pieces.  Most of the time Titanium wouldn't be used for armor unless the robot is a wedge robot.  It is very useful for use in a weapon though.  It is what I am using on Slash.

 

I picked these materials because they are the most commonly used in insect-weight robots.  I left out some materials like steel, because they are rarely used, and when they are it is for the weapon.  If a material isn't listed here that doesn't mean that you shouldn't use it on a combat robot, it is probably just a material I forgot to mention or didn't know about.

 
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what about carbon nano-fibers? they are very strong and durable. stronger than diamond, actually.
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