KAP | Building the Pan Mechanism

Home Page KAP Rig Main Page The History Of Photography

One you have a pan servo modified to continuous rotation, it is time to build the mechanism that will actually use this servo. This page describes building the pan mechanism.

There are a number of different ways to actually implement the pan mechanism. You can pore over other people's pages or, if you meet another KAP person, examine their rig and see how they did it. I don't think my design is exactly like anyone else's, but it is very similar to many and certainly derivative of the ideas of others. Whether you choose to built a pan mechanism like mine or not, it is another example of the amount of work that goes into even the small assemblies on a KAP rig.

My pan mechanism is simple in concept. The rig hangs off a bolt, a 4" long 8-32 bolt (I originally used a 6-32 but bent a couple and decided to go bigger). On this bolt is a large gear, 35-tooth in this case. The bolt passes through the upper deck of the KAP rig and then through a small aluminum plate an inch above the top deck. Mounted to this small aluminum plate is the continuous-rotation servo with a small gear (13 tooth, in this case). The bolt and big gear are essentially non-moving, the aluminum plate and small gear "crawl" around the big gear. The small plate is attached to the top deck of the KAP rig by three one-inch long threaded aluminum spacers, so when the servo crawls around, it takes the rig with it.

What I like about this design is that the precision work comes in the alignment of the servo and the hole for the 8-32 bolt. These will keep the gears spaced at the right distance. The structure can be built separately from the rest of the rig and attached at the end, something you'll see below. This allows the balance point of the rig to be determined, which tells you where the 8-32 bolt needs to hit the top deck of the rig, which then tells you where to drill the holes for the aluminum spacers. There is no stress on the servo, which supports no weight in this arrangement (all the weight is borne by the 8-32 bolt). It simply walks the rig around the big gear. The gearing makes the speed manageable. I don't consciously pick my ratios, I just took the biggest gear they had in the hobby store that day and the smallest I figured would fit. I like these aluminum gears, figuring that aluminum should wear well. I haven't flown enough to wear out equipment yet, so don't know if gear wear matters relative to plastic gears, but I like the concept.

Anyway, with all that, here's how I build my mechanism.

Pan Mechanism Plate
Cut Out the Material As always, you need to start off with your raw material. I cut the top plate piece out of my standard 1.5" X 1/16" aluminum bar. I don't like the name "bar" because it sounds so thick, but "sheet" isn't right either. In any case, here's the raw workpiece next to the continuous rotation servo. I didn't do a precise measurement, calculation of likely stress, etc., I just eyeballed it, marked it and cut off a piece. Minolta G500 digital
Pan Mechanism Plate Trimmed Down a Bit
Trim The Workpiece I use three attachment points for the pan mechanism to the main rig. Three points define a plane, you know. I wanted them not to be all lined up and on the first pan mechanism of this nature I built, for the Contax G1 rig, I left this upper plate pretty big. My initial thought was to do the same here, to which end I have here trimmed off the corners using my hacksaw. As I worked on this, I decided it didn't need to be even this big and trimmed off some more, though I didn't photograph it. You can see that I have also marked the plate for the spot where I'll need to make a servo-shaped hole. Minolta G500 digital
First Cuts for Servo Hole
First Cuts for Servo Holes Here I have clamped the workpiece in the vise to make the initial cuts. For the hole for the servo, I hacksawed the two sides of the piece I needed to removed and then used my Nibbler to nibble out the rest of the material. I show the use of the Nibbler elsewhere in these Rig-building pages. It is a fun tool, one I bought for KAP rig building and invaluable in making rectangular holes in the middle of workpieces. Minolta G500 digital
First Cuts for Servo Hole
Servo Hole Nibbled Out This is the Klein Nibbler and the pan mechanism workpiece with the servo hole nibbled out. You can see the little bits of nibbling waste lying there on the workbench. That larger piece is one I nibbled around. This tool sure builds your grip! Minolta G500 digital
Tidying Up Servo Hole
Servo Hole Tidying Up The Nibbler doesn't give you a finished-looking edge. I nibble close to the outline of the material I want to remove and do the final bit with a file. This way you can hand-fit the servo to make sure that you are getting things just right. Here I file on the servo opening while tidying up. Minolta G500 digital
Fitting the Servo
Fitting the Servo Here I try the servo fit. You can see the aluminum filings on the vise from tidying up the hole. Minolta G500 digital
Cleaning up Holes on Pan Mechanism Plate
Cleaning up Holes on Pan Mechanism Plate I already have photos of drilling holes elsewhere in the site so didn't take them here again, but you can see that I have drilled out the workpiece. On the tabs are the holes to mount the servo, one of which will go right into one of the threaded spaces. Two others are for the other threaded spaces. The big one, the one I'm filing on, is for the black nylon sleeve the 8-32 bolt will pass through. This is the most critical hole in here, since the relationship between the servo and the suspension bolt hole is what sets and holds the relationship between the small and large gears. The only bummer here is that the outside diameter of the sleeve I'm using is .2810" and my largest drill bit smaller than that is .2500" (1/4"), so I am here gently enlarging my hole.Minolta G500 digital
There! It Fits!
There! It Fits! My judicious filing has paid off. The nylon sleeve fits! This sleeve is designed to clear an 8-32 bolt and the black ones are UV-resistant. I figured that since the rig operates in sunshine a lot, the UV-resistant nylon parts make sense. Minolta G500 digital
Finished Pan Mechanism
Finished Pan Mechanism This is what the finished mechanism looks like. You can see how the bolt that is holding the servo on the right goes right into the threaded aluminum spacer. I couldn't do this on the left servo bolt because the wire is in the way. The other two spacers have their own bolts. I have also mounted the shoulder bolt and gear onto the pan servo. You can see how the servo bears no weight in all this--it is just held rigidly in place relative to the large gear which will be on the 8-32 bolt, not shown here. Minolta G500 digital
Finished Pan Mechanism Top View
Finished Pan Mechanism  Top View Another view of the finished mechanism. Here you can clearly see the nylon sleeve the 8-32 suspension bolt will pass through. Minolta G500 digital

The Pan Mechanism in Place!
The Pan Mechanism in Place This is the end result of this bit of work. The bolt running up the middle is the 8-32 bolt the whole rig hangs from. You can see the Picavet cross at the top of the photo. The large black gear is fixed to the bolt (with a small allen locknut); the servo with the small gear crawls around this larger gear. The handy thing about this design is that it's easy to build the rest of the rig and then find the balance point; the downside is that it's kind of tall, and I use a 4-inch suspension bolt. Note that this isn't all bent and crooked, just that this camera seems to suffer a bit of distortion up close in the wide angle setting. Canon A85 digital
The Pan Mechanism in Place!
Another View of the Pan Mechanism An oblique view shows the layout a bit better. With a small camera like the G500 the top deck of the rig can get a bit crowded! The receiver is the black box on the lower left; the battery pack is the yellow thing to the right. I attach both of these using high-strength Velcro so I can move them between rigs. You can also see that on this rig I dispensed with a power switch and just plug the batteries directly into the receiver to activate the rig. Canon A85 digital

The finished pan mechanism is positioned so that the bolt will pass through the top deck of the rig at the balance point. The balance point has do be determined when the rig is basically finished, with the loaded camera, batteries, receiver, antenna, etc all in place.

Probably the main disadvantage of this design is that is a bit tall. The suspension bolt needs to be 4" long to get through this, past the gears and through the Picavet safely (it could actually be just 3.5", but you can't buy that size around here). Some KAP rigs I have seen have managed to make this somewhat shorter, often by mounting the pan servo through the top plate and having a Picavet arrangement requiring a bit less height. Still, I like the convenience of building this separately and positioning it only during final assembly.

Finally, as a later addition, I have a 3.7 Meg video of the Pan Gear in Action. Like most of my videos, this isn't all that exciting, but it makes very clear the way this mechanism works. You can also see how fast the rotation is with this particular combination of servo and gear ratios. I could finally do this sort of thing after my daughter bought a digital camera, a Canon A85. Enjoy!

by Matthew Cole, Saint Paul, Minnesota e mail me