The Grim Reaper is a audio animatronic that has a head that can entertain your guests. The head uses small DC servos the ones used for RC cars to get life like movement. Unlike a lot of homemade animatronic heads out there all the servos for this project are located in the skull. There are no external servos and this is better because it gives a more life like effect. This project will use an anatomically correct size skull that will be able to move side to side, tilt up and down, have jaw movement and have side to side eye movement. This project will involve a lot of finagling to get to work correctly. The instructions that I am providing are a guide in where and how to mount the servos and linkages in the skull. Out of all the projects I have this is the most time consuming to get to work correctly but once you do get it to work I found it to be reliable.
One skull that is anatomically correct (make sure the top of the skull comes off this will be easier then cutting it)
4, servos are used for movement (look in the servo section of this project to see the kind used)
A 6 X 6 inch piece of 1/4 inch thick plywood to use as the platform to mount the servos on
A 1 foot piece of 3/8 inch diameter shaft (this will be used for the neck)
A 1 foot piece of shaft to fit the ball linkages for the servos (I will go into detail of this in the servo section)
4, ball linkages for the servos (I will go into detail of this in the servo section)
3, gears used to move the eyes that are mounted to a servo (I will go into detail of this in the servo section)
2, eyes that will fit the skull
A servo control board
To start off this project Im going to talk about the servos that used first. There are a total of 4 servos used, two standard servos and two micro servos. These servos where bought from ServoCity an online store.
There are 2,Futaba S3004standard servos used to control side to side and up and down movement.
There are 2, Futaba S3107 micro servos used to control jaw and eye movement.
There are 2, 24inch Futaba servo extension (light duty) cables used for the micro servos.
There are 2, 12inch Futaba servo extension (light duty) cables used for the standard servos.
There is 1, Futaba Servo Arm used for the up and down movement servo they are sold in a package of 8
There is one Shaft coupler for standard servo to attach to a steel shaft. You want to get the 3/8inch bore one. The weight of the skull sits on this shaft and servo that gives the side to side movement.
The reason for the servo extension cables are, the cables on the servos are on the short side and your going to need the slack. The cables on the standard servos are 12 inches long and the micro servos are 6 inches long. Im trying to get the cables to be close to length to each other. But you are welcome to use shorter or longer cables but the rule of thumb with these servos is to keep the total cable length under 3 feet long for each servo. Over three feet long you can start to run into single problems with the servos.
The ball linkages that I used I found for a random RC car I found on ebay. But you can used bearings from ServoCity and I would recommend the ball linkage package these are closes that I have used. Your also going to need some brass rod or different metal that fits the linkages. I found some small brass rod at my local hobby store and I am sure you can find this at a craft store as well.
First thing to happen is the servos need a platfrom to sit on. Take the top portion of the skull off and trace the top using a pencil and paper. Cut the trace out and see how it lines up with the skull and make any adjustments and then trace this to the plywood and cut out. You can see in the picture on the right the wood platform Iím using. The micro servo on the front left has special cut out that allows the linkage to go to the jaw. I ended up just cutting a square out. The patfrom is attached to the skull with three little wood blocks hot glued to the rim of the skull. In the picture you can see a screw to the left of the wires. The slotted hole in the back left is not used for anything and you donít need to make it.
This is the hardest servo to mount because it is on a different axis from the rest of the skull. This servo mounted will give the side to side movement. If you look closely at the picture on the right you will see the servo is mounted downward and there is a rectangle of cutout wood that the servo is mounted to. The red line represents a shaft that was drill using an extra long 1/8inch drill bit. The skull will pivot on this axis which gives the up and down movement without the neck (steel shaft) bending. All the weight of the skull is held up by this shaft. Also in the picture you can see yellow colored ball linkages that are attached to a short piece of steel rod. This linkage pulls and pushes giving the up and down movement. So two things are happening in this picture the side to side movement and the up and down movement. The servo shown has a 3/8inch steel shaft attached to the servo using a servo shaft linkage as I listed it in the servo section.
This picture shows the shaft coupler and how the shaft comes out of the bottom of the skull. Also this is where the servo cables come out.
This picture shows the shaft in how it attaches to the neck. The whole skull will pivot on the shaft and the shaft itself will not move.
The next servo to work on will be the one that gives up and down movement. This servo is the one that sits on its side that has a linkage that goes to the back and attaches to the axis that I talk about earlier. This servo is hot glued into place. This servo uses a short arm that is on the servo as you can see. The package of servo arms I mention in getting use the shortest arm to mount to the servo.
This picture on the right gives a close-up. The arm on the servo is adjusted for the movement it does and this is done with the control board. The ball linkages are hand screwed into the servo arm and the extended shaft that is attached to the axis tilt point. I dill have to drill out the hole just a little to get the screw on the ball linkage to screw in. I used a scrap piece of plywood leftover and drilled a hole to allow for the silver color painted shaft shown in the picture to extend to the ball linkage. I hot glued this wood piece to the side of the servo that gives side to side movement.
T h e n e xt s e r v o t o m o u nt is th e one that gives jaw movement the micro servo. The location of this servo is above the jaw on the left side. You can see in the picture how I cut out some of the platform to allow the linkage to move freely. I also drilled a 3/8inch hole in the skull to allow for the linkage to pass threw. I just eyeballed the hole of where the linkage would line up. The wheel that is mounted to the servo comes with the servo when you buy it. Again with attaching the linkage to the servo just screw it into one of the holes provided on the wheel but your going to need to drill out the hole a little. You want a smaller hole then the screw on the ball linkage so when you screw it into the plastic servo wheel it will not come out. The servo is attached to the platform with to little blocks of wood and screwed into place. But you do not need to do this you can just hot glue the servo down to the platform. The hot glue is better anyway but you are welcome to do it the way I did.
The picture on the right shows where the ball linkage attaches to the skull. I drilled a hole where I could screw in the ball linkage to and I painted it black.
This is another view of the skull showing the linkage attached to the jaw.
The micro servo that controls the eyes is located in the center with the big gear on it. I had to cut a slot in the platform to have the servo sit lower to mesh with the two small gears on each side. The eyes are attached to a shaft and go threw the platform and threw the top of the eye socket. I drilled a hole using a 1/16inch drill bit drilling threw the platform and the top of the eye socket. I just eyeballed where the two holes would be. The two small gears are held in place using some of the same linkage shaft I used early. I just hot glue the gear on the top and also added a dap of hot glue on the shaft only where shaft meets the platform. The glue on the shaft keeps the whole eye assembly from siding down but still freely rotates like a shaft collar. The gears themselves can be found in a hobby store I was lucky enough to get these as left over from a project I was working at work. I did look up a place where you can get a bag of plastic gears like these at Edmund Scientific.
The diameter of the big gear is 1-1/4inches
The two small gears are the same size and they are 3/4inch in diameter
The two small gears I had to cut in half to get them to fit in the skull but they donít need to rotate fully.
This is a short video that shows the servos operating in the head. (click on picture)
The picture on the right shows the controller that I used to operate the four servos. This particular controller has a sound chip in it being able to record a 20sec message and the is then played back when the servos operate so you could set the jaw servo to open close the moth when the program is running. This control board is called the Animate Board from Blue Point Engineering. It is a pricey board but it works well and you can cruse around the website and look at other control boards that do more but would work with this setup too. All the boards the company sells come with instructions
The picture on the right shows how the control ler looks form the back of the Grim Reape r. You can use any body you want to mount the skull to and I chose a foam body I got off of ebay for a few bucks. The wires run down the back of the neck to the controller using those servo extension cables.
This shows what the grim reaper looks like when it was done. I used some fabric to make a hood which hides all the wires and just makes it look more like the Grim Reaper. There is a video of this in action on the video page.
If you need any help with this project send me an email.