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Where were we? Ah yes. Last thing I documented was the regulator
board I built. That is most likely out right now. I simply don't have the
weight to spare (this is a common repeating theme that you will hear a couple
more times for the rest of this build report.) As I said before I was having
problems with the 225MG's stripping the one plastic gear in em without even
having been in combat. This was not good as I had planned on these nice
light powerful servos. Let this be a lesson to you. Always overplan the
drive motors for a walker!!! After a call to hitec to see if there was some
way to get hold a metal gear, with no results, I tried a couple of local
clockmakers (I thought that clock/watchmakers could cut gears which they
can just not mine) yielded the following results " Well, we send stuff
like that out, about 60 day turnaround, but our guy is on vacation this
month ". There was then a brief moment of insanity where I thought I
might be able to cut myself some gears with the lathe and a lot of patience.
With bourbon removed from the system logic kicked back in (good thing too),
so I decided to bite the bullet and just get some new servos. Enter the
645MG. "Guaranteed Unbreakable Drivetrain" sounded like just the
ticket to me, plus hitec support recomended them as gears that I most likely
would not be able to strip. Only problem is they weigh 2.1oz each as opposed
to just over 1oz for the 225's. Oh well, I had a little weight to play with.
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As time wore on, I found that I had less and less to play
with. A call to Batteries America
helped me decide on the Sanyo N800AR which is an "A" sized cell,
just a bit bigger in diameter than a "AA" cell. The AR means that
the have a higher current output capacity than standard or extra cells.
So they are comparitively more heavy per capacity, but my motor draws a
lot of current quickly so they are needed in this application. They are
also capable of handling a more rapid charge than standard cells. My original
choice was some 1100mah AA cells which could not give me the kind of current
that I needed. The only bad part about the 800s was that they weighed a
bit more than the 1100's. Yet another thing to eat into my rapidly shrinking
weight budget. |
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As a result of all this, some semi-radical changes were made.
First I ditched the .125 UHMW plastic in favor of some .125 lexan on the
top plate (this was actually not a weight savings but it made the top stiffer)
and some .0625 lexan for the side skirts. The top plate also now serves
to mount the servos via nylon blocks that I made up. The overall width was
reduced by ~3/4 inch to lose some weight. This also had the effect of reducing
my interior room somewhat significantly. Great. The legs too were replaced
by nylon ones. I was concered about the aluminum ones getting bent and staying
that way. The nylon will bend and return, plus it weighs about half of what
the aluminum ones do, and that is without the milling that aluminum ones
had. I milled off a bit of material from the side plates as well. And to
complete my drilling out, I drilled holes in the leg cams (after making
these things about 5 times already I vowed not to have to do it again.) |
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In this pic you can also see the new weapon mounting system.
The original had the motor and the disk mounted to a single piece of 3/4"
square aluminum tube. Good idea, but I had to mill out too much from it
to clear the drive wheel. This made the beam too weak and it flexed at this
thin point causing the drive wheel to have intermittent contact with the
weapon disk. This was no good. To remedy this I made the triangular arangement
you see in the front. Two pieces of .125" al plate sandwich a .5"
bar of nylon which hold the drive spindle, a 1/4" stainless bolt. Nice
and rigid. The motor is then sprung against this. You can see the purple
beam across the center with the spring holder. |
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Here is the motor in it's mount. It's actually flipped over
backwards at this point. It's a speed 400. I turned the drive wheel on the
lathe to fit the "prop adapter" that I got with it. Yeah, I could
have made this myself, but I didn't have a drill to fit the motor shaft
(of course metric) and paying $3.50 for less of a headache seems like the
ticket at this point. I had tried a full rubber drive wheel but it was too
hard to get it balanced right at this tiny size (and that high an RPM) so
I opted for an al wheel with a heavy rubber "O" ring tire. Works
like a charm. The entire assembly pivots in the holes in the uprights that
were for mounting the origninal beam, you can see the spring that keeps
the motor firmly against the wheel. This way I also get a bit of shock compliance
if the disk happens to stall (one hit has yet to stall this disk, it's really
powerful, most likely capable of removing a digit or three, lets not find
out.) |
