hey robot fans this is part 4 of my Star Wars rebels chopper build in Episode
three we got a test hit armed operational this was really just a
brute-force construction to prove the concepts and test the motors by the end
we had a pretty gnarly looking arm with some pieces glued on and some stuff
bolted on and hacked off but it works which is awesome the first part of this
video is going to be refining all of those parts down to a more finalized
version so we can have the final footprint of each arm in place as we
begin to design the interior of the final head model so let's go through
each of the areas of the arm to see what kind of refinements we can make the
pincers went under a pretty major overhaul the nano server pulling the
wire worked pretty okay but I was never really satisfied with the wires
durability and I definitely wasn't happy with its inability to forcibly open the
pincer relying on gravity was a bit of a cop-out and luckily when I posted this
video a few weeks ago I also shared it on reddit and the robotic sub and a user
named H Willis sent me this picture it shows some gears that open and close
with a pincer type device and a worm gear I kind of immediately dismissed it
thinking my pincer was too small for something like that it kind of stuck
with me though and I started messing around with the idea in 3d studio max
and found it was definitely possible I went back to that gear generator website
that I used for the dome gear and made some new gears for the pincer on the
site if you set the tooth count of one of your gears to zero you end up with a
rack to match your gear I could use the servo to push the rack up through the
gears which would eliminate the problem of not being able to hold the claw in
the open position because the rigid rack would hold the gears in place so this is
what that looks like I printed out a little stick with a rack at the top and
when I pushed that through the claw opens the claw is happy to stay open in
any position which is already better than we are dealing with with the wire
solution when you pull on the stick the claw closes I think this is going to
work my only concern right now is that the stick requires a pretty smooth
linear motion the servo is obviously not going to give us that because the servo
is going to be rotating like this so the stick isn't going to go straight up and
down and I'm worried that when you combine that inefficiency with the
power of that nano server it's not going to be enough force to open and close
this claw how we want to so I think I'm going to experiment with using a
solenoid a solenoid is a little electromagnet that pushes or pulls a
plunger when the surrounding coil is charged you don't get the position
control of a servo but the only function here is going to be opening and closing
the claw so no position control is fine with me I attach the rack stick to the
end of the solenoid and installed it into the lower arm and place of the
servo in this configuration when the solenoid is receiving no charge the claw
will be closed then when I charge the magnet it'll push the rack stick about
eight millimeters and that will open the claw I have two main concerns with using
a solenoid the first is speed control these things are pretty crazy fast so
hopefully I can use a PWM to at least slow it down a little bit and give it a
smoother motion to the opening and closing of the claw the second is heat
generation solenoids get really hot really fast because they draw a lot of
power I'm trying to realistically think about how much continuous use the
pincers are going to get and if it'll be enough for the heat to be a real concern
as a precautionary measure I'm going to print the arms in Tolman alloy nine ten
which is pretty heat resistant but if that's not enough then I guess I can
always revert back to the servo the good thing about these arms is that they're
totally modular so if something doesn't work I can just print out one little
part and they reattach it to the rest of the arm so after a few rounds of testing
for fit and function here's the arm with the solenoid installed in the bottom and
the pincers reattached this arm is printed in abs for now I'll use the
Tollman alloy for the final because it's a little bit more expensive than the ABS
I also printed out this cap which will cover over the access to the solenoid
then I'll give you your completed arm the elbow is pretty much unchanged from
the last round I just had to move around a couple of the little access holes and
I also routed the wires through the solid part of the model rather than
having it dangle where the arm was flexing so hopefully that'll clean up
the rotation a little bit if we power this on there's gonna be an initial
freakout I'm not sure what that's all about there it is I'm just writing the
blink sketch from the Arduino library the speed of the tois isn't as bad as I
thought it was going to be I can obviously
control the rate of it but the speed of how it opens and closes isn't too awful
so that should work now this is all gonna connect to the updated lower arm I
built those end stops which were glued on to the test arm into the actual model
to make it a little bit cleaner and along those same lines I subtracted out
all the areas I cut off from the previous arm also I combined the two
main sections so now there's one long piece instead of an arm glue to a servo
holder and all of this gets connected to a heavily modified shoulder assembly the
old shoulder worked pretty great but it was a little overkill with that
giant-scale servant rolling rotation I was willing to let it go but I ran into
some problems one is power consumption those mega scale servos are pretty
hungry beasts and I'm worried about how much power I'm going to be able to
transfer to the head the second is the size of their body as I went through my
3d model and I was building out the head I realized if I was gonna have these big
guys in there there was no way I would be able to put a working periscope in
because having those giant servos sliding in and out of the head with the
arms would clip any installation that I put in that spot so I opted to switch it
out for a smaller servo this is the HS 645 mg which is the same servo that is
being used for the spin of the head arms they also have a metal tooth spline
which is really great because all the weight of this is going to be hinging on
the servo I actually think it's a little too much weight for that spline to
handle so I built a servo block it's entirely 3d printed except for the round
part that connects to the actual spline and that's also gonna be made of
aluminum so it'll be metal on metal which will rotate the shoulder and the
servo block will take most of the weight of the arm off of that spline and since
everything else has pretty much changed why not change the linear slides also
this was the one I used in the last episode I really liked the linear motion
of it but what doesn't work about it is the fact that it rotates along its own
axis here so if the arm was mounted onto here it wouldn't stay flat I thought I
could fix this by printing out a carriage that went along two rails the
problem there is that the rails have to be mounted perfectly parallel or else
the motion isn't gonna really work too well and besides that why should I use
two rails when I can just use one so I figured I would just abandon that whole
track and one of these linear slides this doesn't
rotate and the motion is super smooth I might even say it's smoother than the
other one so I think this will be the one that I use for the final slide okay
I have all the components of the new arm printed out assembled and installed on
that rail I have it all powered and wired up and I started doing some
testing with some pre-programmed animations things were going very well
and then just around the time I was going to start really recording this
happened
so I know that looked like some crazy out-of-control stuff but really it was
just one thing that happened this servo that controls the elbow it could handle
the weight pulling it up but if I try to move the arm back down and catch it in
its downward motion and pull it back up that was too much force for this little
servo so I stripped the gears and that freaked out that you saw was the gears
trying to catch back up to the position that it was supposed to be hitting this
is what happens if I try to run this servo I'm just running a sketch telling
the servo to hit 180 degrees crying at homes it's just not powerful enough to
hold that arm and now I think it's pretty much toasted so I'm going to
replace this servo with this servo the original one is the HS 65 MB and the new
one is the HS 85 mg the 65 is a sub micro server and the 85 is a micro
server so it's a little bit bigger you can see the size of them a little bit
better on their sides that one doesn't want to stay on its side so I'm gonna
have to redesign the lower arm to make this larger servo fit which is a bit of
a pain but I think it's a necessary one also the larger servo has over 150
percent the torque of the smaller one and it has a metal gear system so
hopefully it'll prevent that back drive from happening which we saw in that last
test I don't think I need to rebuild and retest I think I've seen what works and
what doesn't so I'm gonna use the footprint from that last test to design
the base of the head so let's take a look at 3d studio max to see how we're
gonna do that after a few design iterations this is the final head base
that I came up with it's pretty big and bulky in fact I posted a picture of it
on Facebook and the first comment was wow that looks humongous which is true
but I think the bigness of it will come in handy once everything is mounted to
it and there's a lot of forces being applied to the base here between the
head spin and the head arms going in and out
the movement of the head arms once they're extended out I don't want to see
any sagging or any movement on this ring itself I needed to stay pretty solid
because it's also going to be nodding and bobbing so the bulkiness will come
in handy as far as features I was able to put in a hole here for the slip ring
there's a periscope Bay here where I will mount the final periscope after I
see how the head arms interfere with this space I have some wire routes here
this little tube will take wires from one side of the head to the other
and beyond that I left everything a little bit open-ended with all these
little tiny holes here I figured things are going to need to be moved around
quite a bit so I'd rather not have anything lis permanently built on to
here I could rather have smaller mounts that are printed separately and can be
tested and attached as needed this is going to attach to the lazy susan using
these larger holes I bought some aluminum standoffs which
will attach to the end of the screws and slip into these larger holes same thing
for the dome that's going to go on top of this they're gonna have these same
standoffs coming down and will attach to these holes the dome itself will slide
right on top of here you can see I kind of beveled this edge down so the dome
will come to here and hide this seam underneath the base of the widest part
of the top and that's about it I think this is ready to print as soon as we get
it printed out I could mount the rails for the head arms to go in and out and
we can start testing the new servo which will move the head arms in and out
and after many hours of printing we have the four main slabs that make up the
bottom of the head I did a rough sanding to remove the supports and get the sides
of each segment ready to glue together and you could see I also have three
screw holes that connect each of the four segments together so here's a look
at the mechanism that'll push the head arms in and out of the head it's just a
servo attached to two arms that pushes that carriage down the linear rail if
this is working great so far with no load on that carriage so we will keep it
as it is and test it out once I get the full arm assembled and attached to that
carriage so I got the lower arms installed onto the rails and I ran into
a little issue here when I redesign the elbow server for the larger one I did
think about his being a little bit bigger but I never actually checked the
clearance between the two arms and in hindsight I remember that I did make
that clearance pretty little so now they are going to crash into each other and
even if I can get them to clear like they are right now once I attach the
upper part of the arm which is a little bit wider it's definitely not going to
make it these are going to hit each other they overlap by about ten
millimeters so what I'm going to do to fix that is one I'm going to shift each
of these arms back inside of this little carriage here about eight millimeters to
give me an extra 16 millimeter gap in the middle and I'm also going to rotate
out these rails a little bit so give it one extra degree of rotation away from
each other so hopefully that'll clear up all the issues of clearance and even
give me a little bit of breathing room since these things aren't totally
straight and they have a little play in them another issue that came up which I
hadn't actually thought about was the wire management here we have one two
three servos and eventually a solenoid that's going to go into the top part of
the arm and then all these wires are going to be traveling back and forth so
wire maintenance could get a little bit tricky so what I'm thinking about doing
actually is using one of those old linear rails that I had if I can figure
out a way to install two of them in the center here above everything I can have
each group of wires attached to the carriage and slide around there and then
all I need to do is get one connector to connect to the edge of the rail which
can then go down to the Power Distribution maybe here I can use some
kind of a last thing to pull it back and forth to keep
it taut while it's going back and forth and there's nothing drooping but I
really think that attaching it to a carriage that's also sliding with the
arm is pretty important I'm not sure how I'm going to do that
my main goal for this whole entire thing is to keep as much mounted to this
bottom base as possible such that the top of the head is really just a cap
that comes on and whenever I need to maintenance anything I could just pop
that cap off and here's all the mechanics I don't want to have too much
attached to the top where it's half attached to the top half attached to the
bottom and maintenance everything is really tricky with disconnecting all
different kinds of cables and mechanisms so for the most part I'm going to try to
keep as much mounted to this base as possible so I think I can mount those
two rails to the base here somehow and keep the whole arm structure on to the
bottom so let's take a look in 3d studio max we'll take a look at shifting these
arms back in their carriages we'll take a look at potentially putting those
rails in and moving the rails out an extra degree this is the rails in their
current position I want to rotate both of them out on the servo side about one
degree so this one's gonna rotate this way and this one's gonna rotate this way
while keeping the position of the opposite end the same this is the side
of the rail where the arm actually exits the head so if I can keep this position
relatively the same it shouldn't affect too much where those arms end up once
they exit the head the degree of rotation will be just a little bit more
but the look of the actual head on the side should remain the same that whole
change is going to look like this I know it's very subtle but if I keep flipping
back and forth you can see that that's exactly what happens is the servo side
rotates out about one degree and that will give me enough clearance probably
by itself to make the two arms pass each other smoothly but just in case it isn't
enough room I also I'm going to do this this servo block was updated so that the
servo is pushed back about eight degrees if we look at the current one you can
see here the base is the same the base is what attaches to that carriage on the
rail and just the housing for the servo has moved back so the whole servo wall
here gets pushed to the back and even the bearing hole
here at the front is now pushed into the base itself instead of sitting right in
front of it like it is here this will give me about eight millimeters on each
side which is an additional 16 so this alone is enough space to clear the gap
and the other modification of swinging those rails is enough distance to clear
the gap so hopefully I don't need both of them but we'll see how it looks when
everything's installed okay everything is installed on the rails the original
carriage is work I didn't have to use the ones that shifted back the servo
those extra eight millimeters just swinging out the two rails was enough to
clear everything and the servo is clear both the lower arms which are installed
and the additional servo I also have the in out mechanism attached to both arms
and I have that wired up to test the in/out mechanism and if we turn this on
you can see everything moving in and out of the head I'm using the variable speed
servo library here the full speed of the servos was way too much for those arms
coming off the servo horn to handle they kept snapping off their splines and
bending and turning down the speed was a definite must so now it's moving much
smoothly and I think this is fast enough for the final form anyway so everything
is good choppers wingspan is pretty impressive this is going to be a really
big project when it's all said and done the next step here is going to be
getting all of these servos wired up and functional to do that I will need to
start building a proper control board for the head my little rinky-dink tester
board that I've been using so far has met its end I don't think it's going to
work anymore but fear not well most likely use it for the body just like I
did for the head and for now we're gonna have to move on to something a little
bit more concrete so yeah the next video will take a little break from these head
arms and deal with power distribution and our dinos and getting all that wired
up we're also gonna get the slip ring installed and installed the base of the
head onto the body and start having this thing function as it will in its final
form so stay tuned for that see you next time
you