hey robot fans welcome back to my chopper build when we left off last time
we had some functional dome rotation and even got choppers nod functionality
working in this video we're going to try to tackle what is arguably choppers
coolest feature the head arms so let's get started by reviewing that okay so if
we go back to the file I used in part one we can review the functionality of
the head arm we want the arm to come out of the head obviously from there they
can rotate from the shoulder along the z-axis rotate from the elbow along the
z-axis rotate from the shoulder again but this time along the x axis which
would rotate the entire arm and on top of all that we want to get the pincers
at the top to open and close the next step is going to be building the models
for all the parts of the arm while keeping this functionality in mind you
can see I've masked everything out for the arm according to some pictures I
found online my plan is to attack this in stages where I'll refine the parts
both aesthetically and functionally as I go Stage one will be the pincers I think
in my head at least this one is the most straightforward for how it's going to
work I'll have to modify the size of the forearm to fit the servo so that will
affect everything else down the line so I want to get this one out of the way
stage 2 will be the elbow again this one is pretty straightforward so getting
these first two easier stages functional before I tackle the rest is probably a
good idea stage 3 will arguably be the trickiest it's the shoulder mechanism
that will control the movement along both of the axes and right behind that
on the tricky scale we'll be getting everything to move in and out of the
head this is the only stage where I don't really have a good solid plan of
attack yet but hopefully by the time I get there I'll have thought of something
but for now let's get moving on stage one with the pincers okay here's what I
came up with for the main part of stage 1 here's my pincer piece if we move it
off you can see it has a recess for the hub here and a recess for the axle so if
we move it back an axle thread through their chopper has a couple little end
caps on the sides of his axle the rotation from there will go from here to
here and I have an end stop setup right here on the hub and then there's a
natural end stop at the bottom from where the pincer hits the hub so the
rotation is constrained a little bit by its own end stops which is perfect
because I did some testing without those end stops and they were super floppy and
went all over the place so from here I have a hole in the back
of the pincer if we go into x-ray view you can see that that hole starts off
pretty big moves down to practically nothing and then reopens up here what
I'm going to do is thread a piece of wire through there tie it off inside the
big recess it'll travel through that little hole through the hole in the end
stop and then down into this hole here which will put it covered it up which
will put it into the arm and then from there it'll travel down the arm and
there'll be a servo right here which will pull the whole thing and when the
servo pulls it'll come to here when it releases it'll go there so pull release
pull release and that'll give us our pincers closing and opening obviously
this will happen on both sides not just on the right side here so let's get
those printed out and see what that looks like okay this is what that looks
like all assembled after I printed out the parts I added in a temporary three
millimeter brass axle to each of the pincers then instead of tying off the
wire I thought it would be a good idea to solder the end of it which is a
little bulb of solder this will catch on to that recess in the back of the pincer
after that i threaded the wire through all the holes on both sides and we end
up with this you can see we could pull it closed and open just like the servo
is going to do on the inside so the next step is going to be printing out a
little test arm which we can insert the servo and write up some code to see if
we can get the servo to do the open and close action okay I printed out a little
test arm here with a cutout and I mounted a nano server to the bottom I
then attach the wire to the arms of the servo horn I just used the Arduino servo
example sketch and made a simple so all this is all the code is doing is telling
the servo to write to 180 degrees and then wait a second write to 90 degrees
wait a second right 180 90 so on and so on
here's that a little bit faster I think this is working pretty well the only
problem I'm running into right now is that when gravity's not on your side the
claw doesn't open quite as much so basically this light gauge wire is an ax
be pushing the claw open it's just creating slack and then gravity's
pulling the claw down so I'm going to experiment with some heavier gauge wire
to see what that does even if it does nothing and it stays like this I would
be totally happy it's just a little bit of a less opening when it's not upright
so I'm going to move on to the elbow for now and see if we can get that working
okay so phase 2 in this elbow you can see it here if we remove this lower arm
for the time being you can see it's just a cap that attaches to the bottom of the
forearm and it's going to operate in the same way as the pincers do where it's
just being pulled into place only I don't think we're going to be able to
get away with those loose wires that don't defy gravity so we're going to use
a 2 millimeter rod to push and pull this one so the way that's attached if we put
this elbow joint into x-ray mode you can see I have a little axle that threads
through just above the center there also be an axle in the center but this one's
just above and then there's this little coupler here this will be 3d printed it
accepts the axle for this and also has an opening for the 2 millimeter rod
that'll come out and when that's being pulled the whole elbow gets pulled up 90
degrees so what's pulling that elbow is if we just unhide that arm again and we
unhide the servo here we can see I have a servo that's going to attach to the
back of the arm and then that is going to pull that rod from here and just give
us that little bit of movement that we need to pull the elbow up right 90
degrees okay so I glued the elbow onto the back of the upper arm and I glued
the servo onto the back of the lower arm I threaded that axle through that hole
to attach to the coupling which will pull the rod then I slipped that rod
through the lower arm I added in the main axle which everything will pivot
around and then I attach the servo using a couple of screws and finally attached
to the server horn which brings us to here if I move this manually you can see
that the servo is moving this whole piece is kind of needs to be refined a
little bit I had to cut out some parts here and back over here I had to cut out
a little bit just to make all these rods fit and everything I'm going to have to
move this servo a little bit back but for now this is
to the test I've wired it into the arduino and i have the arduino running
the example sweep sketch I just changed the values of the sweep from 180 to 90
just to give it a little less movement so if we turn this on you can see that
it moves but the problem is that it moves past its endpoints if I can guide
it so that it doesn't go past this endpoints the servo is fine but once it
goes past those endpoints that a servo that isn't have enough torque to hold it
so basically the servo doesn't have enough torque to hold it at its soft
endpoints so I'm going to have to install some hard endpoints on the model
here just to get it to stop where it needs to stop so I want it to stop here
and I want it to stop here you see it's just very happy to go past those two
endpoints ok I've added in a hard end stop here at the bottom and here at the
top that will constrain the rotation from 90 degrees down to flat so if we
power this back on see that you get the motion it's pretty good it's hitting
those end stops pretty hard so I probably have to change the values of
the rotation a little bit but for most parts working there's definitely enough
torque in the servo to at least pull it and this is only running at 5 volts to
servos actually rated to run 6 volts which is what it will run in the final
version so I can see the servo wire here is getting stuck so that's got to be
routed a little bit better but I think that works for the most part so let's
move on to the shoulder joint which will definitely be the hardest part of this
mechanism okay so here's the arm in the current state I have those end stops
that I printed out in the digital file here when I go through and do the final
refinements for the final arm I'm going to integrate these into the lower arm
here it'll make it look a little bit more finished it a little bit more
buttoned up but for now they're fine for these tests so moving on to the shoulder
we have the elbow rotating like this and we need the shoulder to rotate along the
same just to do that we're going to use the
HS 805 BB + servo the same one that we used for the nod function and that's
going to rotate the whole arm like this but in addition to that the arm also
needs to rotate along this axis here so I made a amount that goes on to the
cross style servo horn of the 805 BB servo so that will attach here and it
also has a mount for another servo and this is what's going to control our
rotation I'm not going to use a continuous rotation servo because I
don't want to have to deal with adding up slippering in here so this is going
to rotate 90 degrees in each direction so from here it's going to rotate that's
not the rate from here it's going to rotate 90 degrees this way and then 90
degrees this way and that's going to be our main rotation and that's going to be
controlled by a standard servo and how that's going to attach is with a servo
horn that has a m5 rod coming out of it it's actually an m5 screw you can see it
here at x-ray mode make it white so this is going to start here at the servo horn
and travel through where we have the other servo and into the arm here and
here you can see it ends there I'll probably glue that in just for some
extra support and then as that rotates this whole piece will rotate as well
so that there's a little bit of support for the screw and it's not just hanging
here on the server horn I printed out this bearing holder so if we hide that
arm you can see that the screw is going to travel through there there's going to
be an m5 bearing here and another one on the other side where you can't really
see it here and that's going to support the screw make sure it stays straight as
it enters into the arm I also printed out a mount for this to go on to my test
head so you can see here I have the side of the test head in the model here and I
printed out this mount which will attach to the 805 servo here and all of this
will screw in and we can start testing the functionality on the test head
here's that all installed on the test head I also printed out this
fancy-schmancy little remote control here just two joysticks to control the
movements okay I'll power it up here we can start testing the functionality we
have the shoulder and while the shoulders up we can move the pincer open
and closed we can move the elbow and the fence there so I definitely need to add
in some stick smoothing these are moving very quickly and pretty harsh and I
don't even have an end stop on the shoulder so I could potentially crash it
right into the top here but with some stick smoothing and some end stuff this
should work really smoothly we also have our spin front to back so if we put our
elbow up we could spin front to back while still using the pincers as well
I think in the end I'm going to do a lot of canned animation on these just
because the control is pretty delicate and a little bit difficult so if I can
program in some like push one button and it does this animation push another
button and it does this and yet even be able to control it manually in a
separate mode but yeah that the controls for this are super delicate and maybe if
I got the hang of it from driving them for a little bit but I think in the
settings of a convention where there's people all around kids running around it
might just be better to have some canned animation rather than sitting here
trying to concentrate on subtle servo movements so one of the main problems
here comes from the shoulder if we look at the actual chopper model there is a
smaller hole that this arm comes out of it doesn't have the full reach to the
top of the head so if we rotate our shoulder joint here we can see that it
really does go way past where that hole would be so that comes from the fact
that the shoulder joint is too far inset into the head if we can move the pivot
point of the shoulder more outward through that hole then we can get more
rotation upward so that's going to come from changing the configuration of this
arm mechanism a bit the current shoulder hub needs to be reduced to allow it to
move closer to the interior wall of the head the interior walls themselves will
have to be refined a bit to allow all this extra room also we're going to have
two arms that theoretically move out of the head along the same plane so we're
going to have to figure out how to make that a little bit more plausible all
this points to the next step of the building the development of the final
head model I was hoping to have the arms moving in and out before I started
building that but there are way too many variables involved so it's probably
smarter to start integrating them into the design as I go I do however have a
pretty good idea of the hardware I'm going to use for the arm movement I
purchased some linear slides which have this little carriage on them the
carriage is loaded up with ball bearings that make the motion really smooth as it
moves along the eight millimeter rail so attaching those carriages to the
assembly should be all we need to get the arms moving out of the head smoothly
so here's our basic head shape you can see the arms fit pretty nicely inside of
there as far as how I'm going to address the
two arms moving out of the same plane I came up with this idea if these pink and
purple lash lines represent the center axis I've offset the openings for the
doors just a little bit about a half an inch in each direction off of that
Center axis to give it a little room and in addition to that I have tilted each
of the arms about three degrees so from a top view it's pretty obvious what I
did but I don't think even the most astute person would be able to see that
from any other angle unless they're you know really looking for something wrong
from the front it should look pretty normal and especially if they are heads
rotating there's no way you're going to be able to detect like half an inch in a
couple degrees rotation so that'll solve a pretty big problem of getting the
heads out the doors so next up is just going to be a lot of refining and
getting these are mechanisms completely optimized to get in and out of the head
and setting up those rails for the actual motion so we have some functional
arms I think that's going to do it for this video between now and the next
video I will really start designing the new head and get everything set up in
the next video we should hopefully see the final versions of both arms moving
in and out of the final head maybe with some canned animation be sure to
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you
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