Shoulder Hubs Part 2

 

The shoulder hub are a little tricky to build. They require quite a few drilling operations and some of them have to be done in a specific order.

The first step in building the hubs is to cut the disks. These are made from 3/4 plywood and two are needed for each leg. I cut them using my router table and circle jig just like I did with the frame disks.

Once the disks are cut the next thing to do is mark them so you know which ones go on each leg and which is the inside layer (nearest the body) and which is the outside layer (nearest the leg). As I have mentioned before, if you are really accurate with your drill holes, which one goes with which leg isn’t important, but since these operations sometimes aren’t as accurate as we want it’s better to keep things matched up.

Next I worked on mounting the flange to one of the disks. I didn’t want to measure to the outside of the flange since it isn’t machined and is a little inconsistent.  Since the threads in the center are machined it was a more accurate place to make measurements. I put a nail in the hole in the disk and used calipers to measure around the nail to be sure it is centered. Once it was centered I marked the position of the holes. I also put a mark on the flange and disc so they could be put back together in the right orientation.

With the holes marked I drilled them with a drill press.

On the other layer I needed to cut out a 3/16” deep area to accommodate the bottom part of the flange. To do this I used a fly cutter in my drill press to make a template. This cut out doesn’t need to be perfect so I made the template slight larger then the diameter of the flange to be sure it would fit properly. I marked the position of the flange on the disc and then screwed the template on. Finally I used a router with a guide collar to cut out the area within the template.

With that cut-out complete I used a 1 5/8” forstner bit to drill a hole through the center of the disc to accommodate the smaller portion of the flange. The area where smaller part of the flange meets the larger part is slightly rounded so you may need to file the inside edge of the hole so it will all fit together properly. There was also some raised lettering on the flange which I had to grind down a bit to make everything fit. Here is the flange sandwiched between the two discs. If done properly the disc should fit tightly together.

Shoulder Hubs

 

The next thing I want to show is how I built the shoulder hubs. There seems to be two parts on a droid that are referred to as shoulder hubs. The first is show here, that silver part within the shoulder horse shoes:

The part I will be talking about in the next couple posts is this one, the hub that attaches the legs to the body.

After doings some research I found that attaching the legs to the body was one of the trickier parts of building a droid. The legs need to be able to rotate so that the droid can be switched from two leg position to three leg and when in two leg position all the weight of the droid in on this connection point. One of the most popular ways of doing this is what is called the “gas pipe method”. To do this, two different size steel gas pipes are used, one screwed into a flange on each leg and then slipped inside each other. The hard part turns out to be finding pipes that will slide into each other but not be to loose. You will find that these pipes often have a ridge down the inside of the pipe that prevent them from filling together.

I eventually found pipes that will work at Home Depot, but did a slight variation of this method. Instead of using two different size pipes on the legs, I used the same size, and then used a third large pipe to connect them together. Here is what the finished product will look like.

Here is a diagram of the hubs I built. It starts with a metal pipe flange that the pipes will eventually screw into. The flange is sandwiched between two plywood discs and bolted to the one that is closest to the leg. The entire assembly is then bolted to the leg with t-nuts installed on the leg. In my next post I will start to describe how I made the hubs.

Front Vent Housing

Early on in my build I decided to try my hand at some styrene work just to see how easily I could produce some of the body details. I decided to start with the front vents, and particularly the vent housings.

 

The wall of the housing is a little over 1/8” thick. I initially thought it might be possible to bend some styrene that thickness but the curves were to tight. I also tried heating and bending a piece of styrene but that didn’t work either. Bending the 1/8” is probably possible if done right, but I decided on a different approach, building up the thickness with multiple pieces of thinner styrene.

I started by building a form. I cut three pieces of 3/4” thick pine to the rough dimension of the vent and then glued them together to make a 2 1/4” high block. Next I attached a template for the interior size of the vent housing cut from one of the scale plans.

With the template attached I cut the block to the exact size of the template and also cut most of the material on the corners. Finally I used a drum sander to round the corners down to the template and the screwed it to a piece of scrap plywood.

The upper vent is 1.938” deep at it’s largest point so I cut a strip of .03 styrene 2” wide (although in hindsight I would have gone a little wider to leave some room for error) and long enough to go all the way around the form with some room to spare. To hold the first layer together I beveled the opposing edges of the strip so that they overlap and cleanly as possible:

 

To do this I beveled one edge with a file, wrapped the piece tightly around the form holding it in place with clamps and then marked it for length leaving about a 3/16” overlap. I then removed it from the form and filed the other end. With the piece prepared I re-attached it to the form, holding it in place with some squeeze clamps and finally joined the edges with some liquid styrene glue and then clamping over the seam to hold it together until the glue dried.

When the first piece dried I remove the clamps and left the piece on the form. Next I cut another piece of styrene the same width as the first one. I did not try to cut the exact length on each layer since each one will need to be a little longer then the previous so I just started with a piece that was long enough with a little to spare. To start the second layer I glued one end to the side of the first layer opposite where the other one started so that the seams will alternate from one side to the other. When applying each layer try to keep the piece tight down to the plywood base. The edges won’t come out perfect but this can easily be cleaned up later. Once the first edge has dried I started working my way around the piece, gluing  and clamping a small section at a time. Once I got 3/4 of the way around I bent the piece the rest of the way without glue, marked the length and then removed the piece from the form to make the length cut. Finally I put the piece back on the form and glued the end.

I repeated this process until I had built up the proper thickness for the housing . You can see that the final seam didn’t come out perfect but I can probably clean this up with some filler and sanding. You may want to apply your layers so that the seam ends up at the bottom of the housing so it will be less noticeable

To finish the part I sanded the back end of the housing on a belt sander to get it level. Not that the back of the lower housing has a small angle to it, but the upper is square. With one edge cleaned up I sanded the other end to being the housing down to it’s final height. If you left a lot of extra you could start by cutting some off on a band saw. The front edges of the houses is slightly curved. I handled this by marking lines along the side at the final height and the formed the curves on the belt sander.

Here is what the final part looks like.

Horseshoes Part 2

In my last post I showed how I created the the tempalte for the horeshoes, in this post I will show how I used the template and a pattern cutting bit to cut the actual parts. The first step was to cut a series of blanks out of 1/4” MDF and to trace the pattern on to them.

I then used the traced lines to rought cut the parts on the bandsaw.

Next I screwed the template to the first of the blanks. The template doesn’t need to line up perfectly with the traced lines as long as there is wood from the blank sticking out all the way around the template.

Cutting MDF puts out a lot of fine dust so I wanted to take some precautions before I made the cut. I used some cardboard to make a dust catcher that extended all the way over the cutter. I cut a hole in the back of the dust catcher to put the hose from the shop vac and tapped everything down to the router table. Even with this I still used a dust mask while making the cuts.

In my post on cutting the leg parts I talked about the importance of using a guide pin to start cuts on a router table. In this case I found the pin was really getting in way so I chose not to use it. If you don’t use the pin you just need to be very careful when you start the cut. With everything setup I cut all the pieces.

The final operation I did on the horeshoes for now was to form the ridges that are along the inside edge. To do this I used a pattern cutting bit in the router table just like I did to cut the shape. The difference for the ridges is that I replaced the bearing on the bit with one that was slightly smaller the the diameter of the bit.

I then set the depth of the router so the cut will be exactly half the thickness of the horeshoe pieces. Since the groove is only half the thickness of the part the template isn’t needed, you can just run the pieces without it and you will get perfect groove along the edge.

When stacked together you get the ridge effect.

On the horeshoe part nearest the leg I made this cut all the way around the piece. This provides the groove that is between the horesehoes and the leg frame.

Horseshoes

 

The next element I worked on for the legs was the shoulder horseshoes.The horseshoes attach to the outside of the leg frame that I have been building in my previous posts. The tricky part of making this component is the ridges that you can see along the inside edge of the horseshoe. There is also a groove between the horseshow and the main part of the leg.

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Most people make these using eight thin layers stacked together. The even numbered layers are made a little smaller on the inside then the odd numbered layers so you get the groove effect. I took a slightly different approach. I made each horseshoe out of 4 layers of 1/4” MDF and then used a router to cut the groove on the bottom side of each piece.

To cut the shape of each layer I went back to the router table and a pattern cutting bit, so just like with the leg frames we need a template to start with. I started with a printout of a full size template from the plans which I glued to a piece of 1/4” MDF that was cut to the exact width of the part.

To make the outside cut I went back to my router table circle cutting jig that I used for the body frame components. The cross slide slot on the router table was to far from the bit for this cut so I attached a thin piece of plywood to it to get it close enough.

To make the inside circle I used a circle cutter mounted in a drill press. Cutting MDF generates a lot of dust so I clamped the hose of my shop vac as close to the cutter as possible and wore  dust mask. I also firmly clamped the piece I was cutting in place instead of trying to hold it.

For the straight cuts on the inside I used the table saw.

I made the angle cuts that lead into the center circle on the band saw. There was really no way to guide this cut so I carefully did it freehand. The final cuts were the angle cuts on the bottom, I made these on a miter saw. Here is the final template.

In my next post I will show how I used this template to make the actual parts.

More Leg Work

The final operation I am going to do for now on the leg framework is to cut out the inside of the middle layer. There are two reasons to do this. First it reduces the weight of the let by a little bit. Second, if you plan to motorize the feet, it provides a place to run the wires. The cutout of the shoulder also provides some space for the leg mounting hardware.

On the 3/4” center layer I marked a line 1 1/4” in from the edge of the leg. It wasn’t necessary to follow all the contours of the edge, 1 1/4” provides enough clearance all the way around. The line goes right to the end of the foot leaving an open space to run wires if you want to.

Before making the cuts on the band saw I drilled some holes at key points to make if easier to turn the piece.

Here is the final piece temporarily pinned to the inside layer. This cutout will not be seen so the rough cut it not a problem.

Leg Pockets

 

Where the legs meet the shoulder there is a detail feature that goes into a pocket on both sides of each leg.

This pocket is easier to cut out before the layers of the leg are assembled. To make these cuts I used a router with a guide collar and a template. I stared out by making a template out of a piece of scrap 1/4” MDF. The cut out on the right is the actual template.

The shape is pretty simple so I just laid it out based on the measurements in the plans being sure to add the distance between the edge of the guide collar and the edge of the bit to the measurements so that the template cutout is slightly larger then the final size of the pocket. Since the shape has some tight corners I used the smallest possible router bit, but it will still require some manual cleanup in the corners.

With the legs temporarily assembled I marked the location of the pockets. These lines will be used to align the template.

Next I screwed the template to the inside surface of one of the leg side pieces. The cut does not go all the way through this piece so I adjusted the router for the correct depth and then made the cut.

The center layer is cut the same way, but I put a scrap piece of wood under the leg piece because this cut needs to be all the way through.

With the legs again temporarily re-assembled you can see the finished pocket.