A slightly different B9 Robot
Slightly different Knees
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George Washington had wooden teeth, Does a Robot have to have wooden knees?

plasti-dip_knee.jpg

You can buy knees or build them:
 
If you buy there are a number of different designs and vendors. All of them make knees that are made from molds, a good amount of time and money were put into these molds. The materials (fiberglass, silicone, latex) are sometimes expensive, difficult to find and even toxic. Not always the sort of project that a DIY builder can do at home. And purchased knees will cost between $300 and $500...
 
Many people instead build their own knees. They start with a sheet of plywood, cut, bevel, sand & paint, and in a while they have a set of wooden knees. This can actually be a good design as long as they are hollowed out well to save weight. It is very common for Plasti-dip to be used as a paint, it gives an appearance of a rubber part much like the TV robot appears to have.
 
To make knees that are not made of wood simply build a wood knee, paint it with Plasti-dip and then... REMOVE the wood!
 

Some people may ask why get rid of the wood. It really depends on what sort of Robot you are building. If its just a “stand in the corner and blink lights Robot” then there is no need to have woodless knees.

 

But if your Robot will be a costume then someone’s legs will have to go thru the knees. And less weight is a nice touch. Of course if your Robot will move on its own then weight and Center of Gravity are very important, lighter knees will help.

 

Its not that difficult to go woodless. Make a wood knee, sand it and finish it smooth, apply a mold release, apply Plasti-dip, remove Plasti-dip knee. Repeat as necessary.
 
The idea is to apply the Plasti-dip thick enough so it can be used alone without the wood. Of course there will be one small problem: to peel the Plasti-dip knee from the wood mold you will have to make a cut. No big deal, make the cut so it will be hidden by the inside knee hinge. This can be repaired latter with normal liquid Plasti-dip.  And since this knee will not support weight some sort of means will have to be found to fasten the knee to the rest of the structure.
 
How to do it:
 

Follow all precautions on the Plasti-dip can. Work in a well ventilated area!

 

1. Get your wooden knee ready, its surface should be smooth and clean. Apply mold release evenly!

clean.jpg
 
2. Have some sort of means to support the knee while it is being painted. I made a rotisserie from scrap plywood. Lag bolts on either side of the knee engage in notches in the top of the rotisserie and you can use a small wrench on the bolts to turn it. This worked very well.
stand.jpg
 
3. Start painting. Have a pattern so that you do not miss any areas. Make the coats even and glossy. When a coat is done wait at least 15 minutes or more before you do the next one. A single can of Plasti-dip will do about 3 or 4 coats and give you a layer of around 0.010" thick. This will not be thick enough, 12 or more coats (4 cans worth) will be necessary to get around a 0.040" thick part..

4. I like to limit spraying 2 cans a day and then allow it to dry overnight. So the 4 cans will take a while. When its all done you must wait around a week for it all to dry. If you do not wait the Plasti-dip will not be strong enough and it may not survive being peeled off the mold!
 
5. When its all dry use a sharp blade to cut along the dotted lines. Do the bottom too!

kneelines2.jpg
 
6. Gently peel the Plasti-dip off. Be careful, do not pull too hard or the material will distort and you will have to start over again. This is why it was very important to get the surface smooth and apply mold release.
peeling.jpg

Here is the finished part:

knee.jpg
These knees are not self supporting, they really should have a plate to properly hold them in place. This week I will make a few plates and threaded rods/stand offs to support them

knee_assy.jpg

Above is a picture of the knees and knee plates during assy. It is important to use the correct spices...

knee_assyii.jpg

Here are the knees in place on the structure. The small brackets hold up the knee plates and the knees. While not a very elegant design solution these brackets allow both disassembly and future attachment of the legs.