Fixing a wobbly leg
Hurrying a build will always come back to bite you later!
When I originally built my R2, I was in a building frenzy. In a way, it was almost therapeutic for me, as I needed to get my mind off things, and really focused as much as I could into the build.
The legs was one of those first things I made, and I did not let the fact that I did not have a drill press stop me!
So, instead of .. I don’t know .. ask any of my friends if any of they had access to one, I basically drilled the holes in my ankles freehand. I know for a fact, that these holes have not been straight.
The symptoms of this, has been that my R2 always drifts towards the left when I drive him, and even though I can compensate, as soon as the drive power stops, and he rolls a few decimeters, he always steers off to the left. This has really been a pet peeve of mine, even though it is something only I was aware of, but isn’t that the definition of a pet peeve anyway, more or less? 😉
So, armed with a plan, I took R2’s legs to my friend Anton’s work (where they have a proper drill press) and got to work.
This is the problem area: (and no it isn’t dirty. It is only painted that way)
A few years ago, I did have the foresight to protect the existing ankle holes, so I had drilled the holes slightly larger and inserted a piece of aluminum tube to not let the threaded bolt eat into the plastic. When the foot was removed, I got proof that my ‘protection plan’ had worked as it should: The threads from the bolt had really eaten into the aluminium bolt! Just imagine what could have happened if it had gone straight into the plastic ankle?
So, the force has been strong enough to not only impress the threads into the aluminium tube, but also to slightly deform the hole!
My plan was to make a new hole, a straight hole this time, and rather than the existing tubes, I would insert some sort of bushings into the hole.
I had these linear ball bearings that will do just fine for the job at hand:
First step was to affix the leg to the drill press… and slowly drill through both ankle and the existing aluminium tube to straighten up the hole..
Since the aluminium tube was only fixed with E-6000 inside, it soon pushed out the other end, while the drill made a straight hole through..
My friend Anton did the first one:
.. and I drilled the second hole. Scary but a VERY quick fix in the end. The new bushings were pushed in to place …
A much better solution, and a more solid contact area towards the plastic!
I also took the opportunity to attach the new motor holders (as seen in “Fixing a hobbled droid” and “Fixing a hobbled droid, part II”). Yes, even though I had made these new motor holders way back, I had to abandon them due to a motor dying on me, but this has since been fixed, and this seemed like a great opportunity to put them in action!
Since fixing this, I have not yet had time to do a proper event with R2, but I’ve got a two day event in September that will be a perfect test. I will bring along my backup motor holders just in case… you never now.
