Give me a big enough lever...

The real servos finally arrived! here is the Hi-Tech HS-805BB Mega Giant Scale Servo being tested. I simply attached one of the many great horns and plates that it comes with to my fish-line spool, using its own screw and voilà! 19.8 / 24.7 kg*cm (4.8V/6V) of torque! It is temporarily held in place with straps as you can see because as you can imagine the square holes of the Vex plates don't line up with anything but their own stuff (I promised I would stop bitching about it!)

For the rest of the controls I am using the HS-645MG UltraTorque Metal Gear Servos that have 7.7 / 9.6 kg*cm (4.8V/6V) of torque, very much on the safe side.

On the left of the picture you see Vex's red optical encoder which I planned to use to determine the position of the continuous rotation motors that lift the arms, but again, not even the extremely versatile Make controller could recognize the simple signal. I am sure it can be done but why waste time. I ordered a set of high-res 10 turn potentiometers that are not only more precise but can "hold" the last position even when the power is turned off.

Divide and conquer?

That seems to be the design philosophy of the VEX guys. I promise (well, a weak promise) that I won't waste more time bitching about their horrible "close source" design decisions. But someone has to say something. Of course I used their stuff to prototype my project since I had bought 5 or 6 kits with the hope of actually using them for the final project. Now, to be fair, their nuts and screws are first rate and I have no complaints, as well as their cute chain transports if you use their square shafts of course, but the rest...


It was obvious pretty soon that the electronic/hardware side would not work due to their very flimsy nature and weak linkage (or lack of it). Take their servo for example. Not only is it far from standard, so that you cannot mix with any other brand, but it lacks fundamental elements like a horn or attachment plate of some sort so that you can drive something more than their absurd square shafts. Guess what, you cannot even screw anything to it, you can only use their "clutch" (the small cylinder with a short square stub) to attach another square shaft to drive any square holed device! BTW the clutch and therefore anything attached to it, will simply fall off if you turn it upside down. Am I missing a screw here?

You cannot see it in this next picture, but those arms or extensions that I need to drive the limbs of the marionette with have as much strength and stability as an apple stuck on the tip of a drinking straw and balanced on the edge of a glass, can you picture that? perhaps David Copperfield could use such a trick. The main reason being that as I explained, the servos connect to anything else through the wimpy clutch mechanism that cannot stand any side pressure, only direct transmission to a wheel at the most.


To be fair, after a great deal of literally hacking away with a saw, drilling and cutting and bending, I was able to put together a somewhat functional scaffolding for the stage. If I had the money I would simply make everything from scratch out of aluminum and some steel pieces. And, yes, chuck those servos away. I opened one to convert it, I was so shocked by the poor craftsmanship inside, probably built on a Chinese sweatshop (badly soldered by hand), that I just closed it and proceeded to order a set of excellent Hi-Tech servos.

What was I thinking...

Just to finish the pulley rant, I created a template to drill the round wood pieces that I bought (99c/bag) at the local craft store. They seemed perfectly round in the bag...



Much to my surprise (am I new? or what!) they were far from round, I found out when I tried to fit them in my template. To make it short, I sanded them enough to fit, drilled and glued them together. As I was venting my frustration for not finding proper pulleys, my wife who works next to me in the studio, asked why I did not use the spools that she uses for her beading or the ones that I use for stringing (fish line) the marionette.

DUH!

I must be very tired, been sleeping 4 hours max for months now. why didn't I think of the spools which were in front of me? So, here, I have a steady supply of the perfect size/weight spools.


I only needed to create bushings to adapt to the servos, real servos that is, not the modified ones by Vex which of course have a "proprietary" square shaft that only fits their kit stuff, I still cannot get over their lack of foresight and integration with the rest of the world. So much for Open Anything! Dean Kamen, you know much better than that!

I created the bushings with an aluminum rod that happened to have the right diameter.
I drilled the shaft hole to attach the Hi-Tech servos I will probably use, notched them to hold the adhesive better and epoxied them to the spools.