Saturday, April 20, 2013

Improvements to the center foot

Its been a while!

I haven't forgotten about my first R2-D2!  While I have been doing a lot of work on the second one, I am still tweaking the first.

One of the bigger challenges with driving R2 around is going across uneven surfaces, for example, going onto an elevator.  The center foot only has so much room and due to the shape, fitting one or two wheel casters, depending on the diameter of the wheels.  Two 2.5 inch wheels fit nicely but being smaller than a 3 inch wheel, get stuck easier. 

A while back, I found that replacing the wheel that comes in the casters with a roller blade wheel works great.  The neoprene material offers superior shock-absorption.  However, those uneven surface crossings were still nail biters!

While reading what another R2 Builder's blog posts, I noticed he had found some shock and vibration dampening parts that could help my droid out.  The shock dampeners are HERE

The center foot and caster mount and support structure are made by JAG.  It's a fantastic design and works great.  The support structure bolts inside, into the side (half moon) detail pieces.  The support structure has 4 thick stand offs, which the caster plate attaches to.  Add casters and off you go!

For the past few years, I've worked on getting softer wheels.  I hadn't though about changing how shock could be absorbed much beyond that.  I had marginal success with a rubber muffler hanger between the casters and mount, but that's it.  After seeing those vibration dampeners, I had some ideas.

One important angle that I had missed was, in hindsight, really obvious.  When the caster plate is bolted on, it lays not only on the metal standoffs, but the edges of the support structure and the heads of the hex-head bolts that attach the structure inside the foot.  (You might have to read that twice, slowly!)

In order to take advantage of the new, shock absorbing stand mounts, I have to either trim or make a new caster mount plate that doesn't touch anything else.

First, the vibration-dampening sandwich mounts (as McMaster calls them) are attached.  These are male on one side, female on the other using 1/4-20 threads.  They have a compression rating of 55 pounds each, plenty for my R2.  (When I placed a scale under the center foot a while back, the weight showed 97 pounds.)

I consulted with my good friend, Fred, about trimming the steel plate or making a new one.  Fred, put simply, is a genius.  We think oppositely yet alike.  We come up with interesting ideas on how to solve challenges like these.  He suggested using some of the 1/4 inch aluminum leftovers we have kicking around the shop (from the dome gear I made a few weeks ago for R2 #2).   Before I could debate him on going from the existing 1/8th inch anodized steel plate to 1/4" aluminum, he was cutting up cardboard and making a template on the bandsaw.  That's just how we work together!

He came up with another good idea....instead or just cutting to length and width, he suggested cutting around the offending hex heads.  So, not only would the new piece not touch the inner foot structure, it would clear those too. 

Then, on to using the old plate to cut the mounting holes, plus the holes where the casters mount. 

After counter-sinking the holes for mounting into the new dampeners, in they go!

Pushing against the surface, you can feel some I think this may work out pretty well!

I'll install the casters and see how this works!