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Archive for October, 2012

Damped KAP Rig Plans

Posted by Tom Benedict on 10/10/2012

I got out with my new panorama rig last weekend. Despite really crummy light because of the buildup of volcanic gases on our end of the island I was able to fly the rig and test the first of several ideas for rig damping: adding a long stick with a weight at the end.

The rig I built uses a Brooxes Utility Frame for its backbone. The Utility Frame offers numerous options for attaching servos, pan gear boxes, or whatever other doodads a KAP experimenter might want to add to their rig. In this case there was already a hole at the opposite end of the frame from the pan axis, so this is where I attached my long stick.

The “long stick” is a left-over from an earlier rig I built, but never really used. I had a need to fly a GoPro HD Hero over a building and shoot HD video. I could take out minor rig motion with Virtual Dub running Deshaker, but I couldn’t tolerate high frequency jitter. So I got a 4′ length of 3/8″ aluminum bar and threaded some #8 holes at either end. The top hole got a Picavet cross (also from Brooxes). The bottom hole was used to bolt a 500g block of steel to the bottom of the bar. The GoPro was then taped onto this block and flown.

As scary as this sounds (yeah, if it fell the GoPro would act as the rod’s landing gear when it hit), it performed quite well. Rig motion was very gradual, and the total excursions were quite small. The test video looked entirely usable. But because of a change in priorities at work the intended flight never took place. So the thing wound up in my closet collecting dust next to my spare kite spars.

Using it to damp my new pano rig was a straightforward matter of removing the Picavet from the top of the rod and bolting the rod to the bottom of the KAP rig. This increased the weight of the rig significantly, but not so much it couldn’t fly.

Now for the results:

It worked. Hands-down, it worked. Looking at the photos I made with and without the weight bar, it’s clear the bar reduced blur in pitch and roll. Already Picavet suspensions damp yaw quite well, and the acceleration/deceleration profile I set up for the pan axis of this rig in the Micro Maestro controller reduce yaw oscillations even further. So just adding this weight bar results in a more stable rig that’s entirely usable for late-day KAP.

But when letting line out or taking line in, I did see an odd coupling between forces acting along the kite line and motion in the yaw axis. Clearly something is going on here. Since gusts affect the line in much the same way that taking in or letting out line does, this indicates that further yaw damping would be a good idea.

I’ve got two approaches I want to try. The first is to use the Nye Lubricants damping grease to make a viscous coupling for the pan axis on the rig. This de-couples the Picavet from the pan axis, and should act as an additional damper on yaw motion.

The second is a little more drastic. I want to take the idea of the weight bar and instead of having it extend below the rig, I’ll extend it out around the rig in space:


I played with this idea some years ago, but thought that sufficiently stiff arms would negate the need for cross-bracing. I was wrong! But I abandoned those experiments before trying cross-bracing on the arms. My plan is to build this using standard length kite spars with light Dacron for cross-bracing. At the end of each arm of the cross is a 100-200g weight – more than I tried when I first tested this, but closer to the total weight at the bottom of my weight bar.

Having this cross-like arrangement should slow the rig’s oscillations in roll and pitch, similar to the weight bar, but should also slow oscillations in yaw. The Picavet does a good job of damping oscillations in these axes, and the addition of the viscous coupling on the pan axis should further damp yaw oscillations.

Until this is tested in the field, though, it’s all just conjecture. The first step is to build the prototype cross and put it in the air. I hope to be able to report those results in the next couple of weeks.

– Tom

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Parts, Parts, Parts!

Posted by Tom Benedict on 08/10/2012

I’m done with the external parts on these cameras, and now I’m working on the internal parts. Some of them are already complete, but others – such as the cold strap and cold foot – are still just CAD phantoms waiting to be made real.

Meanwhile the outside parts are all set to go out for anodizing:

Sitelle Parts

About 1600 square inches of surface area spread over 73 parts. I’m excited to see these things wearing their colors for the first time.

There was a lot of debate about that color. There were a couple of outliers who liked purple, green (that was me), and a few other oddballs. But everyone else fell into two camps: blue or gold. I like blue, but gold won out in the end. (There are benefits to being project manager on an instrument: your opinion counts more than everyone else’s!) When the parts come back I’ll start posting assembly pictures.

– Tom

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