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Archive for June, 2013

Care and Feeding of KAP Batteries

Posted by Tom Benedict on 23/06/2013

There are a lot of choices when it comes to the batteries used for kite aerial photography. Over the years I’ve used alkalines, nickel-metal hydrides, lithium ion, and now lithium polymer. Each has its own requirements for care and feeding. Here’s a look at some of these, and how to make sure you get the most out of them:


These are single-use batteries, and typically come in AAA, AA, C, and D cell sizes. For most KAP applications, AAA and AA are the only sizes that really apply. Alkaline chemistry provides 1.5V per cell, so a 2-cell battery pack will provide 3V, a 3-cell provides 4.5V, and a 4-cell provides 6V. Because alkalines aren’t rechargeable, I don’t like to use them for applications that will draw a lot of power. But for something like a small autoKAP rig, these can be an ideal choice. In case batteries go dead in the field, these can be found practically anywhere in the world.


NiMH batteries can be built into packs, or can be used as individual cells. I like using the individual AAA and AA cells Sanyo sells under the Eneloop label. These will fit anywhere an alkaline AAA or AA battery will fit, so you don’t have to change your battery holders in order to make this switch. NiMH chemistry provides 1.2V per cell, so a 2-cell battery pack will provide 2.4V, a 3-cell provides 3.6V, and a 4-cell provides 4.8V. Depending on the manufacturer, NiMH batteries can sometimes have a high self-drain rate, so it’s worth checking. Eneloops tend to have a very low self-drain rate, so you can install them in a rig and leave them until they need charging. For transmitter batteries, I re-charge after each session. For KAP rig batteries, I’ll run on the same set for a month before pulling them out to charge.

NiMH batteries charge at a 1C rate or lower. The “C” in 1C refers to the cell’s current capacity. A 2000mAh cell can be charged at 2000mA, or 2A, but they can be charged at lower rates as well. Some chargers will charge until a particular voltage is reached. Others will charge until the current the battery is drawing during charge drops below a certain level. An inherent characteristic of NiMH chemistry is that the cell’s temperature will rise sharply when it reaches full charge, so some chargers have a temperature sensor that will tell the charger when to stop charging. In all of these cases, to charge a NiMH AAA or AA cell, the batteries are loaded into a charger, plugged in, and left until the charger indicates full charge.


Lithium Ion

When I started flying a DSLR, I could no longer use Eneloop AA batteries for my camera. As with most cameras these days, the Canon T2i uses a Li-Ion battery pack. Li-Ion batteries have a low self-discharge rate, so they’re great for applications like digital cameras, in which the camera may sit for long periods of time without use. Li-Ion chemistry provides 3.7V per cell, so a 2-cell battery provides 7.4V, and a 3-cell provides 11.1V. (I’m not going above 12V on cell voltage, because there isn’t much on a KAP rig that requires more than that.)

So far the only Li-Ion batteries I’ve used for KAP have been camera batteries, so these have all had dedicated chargers. Just like the Eneloops, I pop the battery into the charger and plug it in. When the charger says the battery is ready, I put it back in the camera.

Lithium Polymer

These are the real bugaboo when it comes to batteries. We’ve all heard the horror stories: unbalanced batteries gone bad, batteries burning or exploding, brimstone and hellfire. While all this is true to some degree, as long as you treat Lipo batteries kindly, they can provide excellent long-term service. I first started using these when I started flying RC airplanes, and have since introduced them into my KAP bag.

Lipo batteries provide 3.7V per cell, just like Li-Ion batteries. This makes things a little awkward for 5V systems like RC radios, but it’s perfect for 12V systems like video transmitters, receivers, and monitors. Some RC gear is designed for Lipo chemistry, and can handle the 7.4V of a 2S pack. But unless your radio and servos all claim this capability, though, don’t plug a raw 2S pack into your gear. It’ll fry gear that’s designed for 5V supplies. In order to use Lipo batteries on a 5V system, some sort of voltage regulator is required. I use a 5V 3A UBEC on my KAP rig. It provides regulated 5V power to the radio and servos, while still allowing me to use the 11.1V of the battery to power my video gear.

That’s the good. Now for the ugly: Lithium Polymer chemistry is inherently unbalanced. That is to say, if you build a 3-cell pack and charge it with a 12V charger, one cell will inevitably draw more than the other two, and will charge to a different base voltage. Or… it will over-charge, self-destruct, possibly catch fire, or explode. The solution is simple: keep your batteries balanced. More on this in a sec.

The other drawback of Lipo batteries – one that’s shared with Li-Ion and to some degree NiMH – is that once they discharge below a certain level, they cannot (or should not!) be recharged. So it becomes imperative to monitor the battery level to make sure they don’t drop below that threshold. The solution to this is simple as well: monitor your battery voltage and keep your batteries charged.

There are a couple of tools that will let you do both of these jobs.

Rig Lipo

In this photo I show one of my rig batteries – a 500mAh 3S pack – with a low voltage monitor on the left, and a battery balance monitor on the right. The low voltage monitor was about 2 USD off of Ebay, and the battery balance monitor was about 6 USD off of Amazon. Both will monitor the battery voltage and let out an ear-piercing shriek if the voltage drops below 3V per cell. The low voltage monitor also gives you visual feedback with a set of LEDs. Three green LEDs mean all three cells are good. If one goes red, that cell has dropped below the threshold voltage, and the battery should be balance charged. I use a low voltage monitor on my rig when it’s in the air.

Rig Lipo - Reads 11.4V

The battery balance monitor has some nice added features: It’ll cycle through the voltages on each of the cells in the pack, as well as a total for the entire pack. Here you can see my pack can provide 11.4V. A fully-charged Lipo battery will provide closer to 12.6V. I keep one of these in my KAP bag so I can check all the cells in each of my batteries prior to use. Since these also have a low-voltage alarm, you could just fly with one of these on your rig. But I opt to keep mine on the ground and use the lighter weight low voltage alarm.

Earlier I referred to “balance charging”. Remember that Lithium Polymer chemistry is inherently unbalanced. You can get chargers that will charge the entire pack, but they will do nothing to try to maintain balance between the cells. These are dangerous to use! They assume that the battery has balance circuitry built into it. Unless your battery explicitly says it has built-in balancing circuitry, don’t assume that it does.

Lipo Charger

Since I got into Lipo chemistry for flying RC airplanes, I splurged and picked up a nice charger. Most chargers require 12V power, assuming you’ll either be using your car to run the charger, or that you have a 12V bench supply. The one I got will take either 12VDC, or 110/220AC. This is a really nice feature to look for in a charger if you don’t already have a 12V bench supply.

This charger will charge NiCd (a battery chemistry I haven’t discussed), NiMH, Li-Ion, Lipo, and LiFe (another chemistry I haven’t discussed), as well as lead-acid batteries like gel cells or SLAs. For inherently unbalanced battery chemistries like Lipo and LiFe, it offers balance charging. All this means is that it monitors each cell individually, and makes sure that all of the cells in a battery pack finish charging at the same voltage. So far it’s been able to charge my Lipo batteries to within 0.01V per cell. Not bad.

If you take the plunge and jump into Lipo chemistry for your KAP gear, I highly highly recommend doing some homework and splurging on a good balance charger. Unfortunately there are hundreds of chargers out there, so there’s a lot of homework to be done. Most of these cater to the RC aircraft market, however, so some of their features may not be as useful for KAP. For example, some chargers can charge multiple batteries simultaneously. This is great if you have a power-hungry airplane or helicopter that can drain a battery in fifteen minutes. Put four of them on the charger, and in half an hour you have an hour’s worth of battery ready to go. Neat! But for KAP this feature doesn’t really help much. Our power requirements are so low, batteries last for hours. There’s really no need to charge multiple batteries at once.

For me, I wanted something that would take AC or DC power, charge a wide range of battery chemistries, and could balance charge Lipo batteries up to 24V. And that’s exactly what I got.

Why Lipo?

Fair question! For years I didn’t have a compelling reason to switch to Lipo chemistry for KAP. Think about it: The voltages are weird, they require special monitoring and charging equipment, and there’s the risk of fire or explosion. Why go there if you don’t have to? The only reason I started using Lipo batteries for KAP was because I finally had a reason that outweighed all the negatives: I needed 12V power for video.

Even using AAA batteries, sticking with alkaline chemistry would’ve required eight batteries to get the 12V I needed to power a video transmitter. I tried it, and the resulting battery pack was ungainly, heavy, and an incredible pain to use. I even tried a battery pack that had the batteries separated into two banks of four each so my video gear would get 12V while the radio gear got 6V off the same pack by only using half the batteries. I almost fried my GentLED cable doing this, and wound up with all sorts of other problems. My last ditch effort to avoid Lipo chemistry was a 4xAAA NiMH pack powering a boost-buck regulator that output 12V for the video system. But the resulting power was so glitchy, I never got a decent video signal.

Using a 3S Lipo battery on the rig solved that so cleanly, I couldn’t go back. Eventually I ditched the 4xAAA NiMH pack I’d been using to power the radio and servos, and replaced it with a 5V UBEC, fed by the same Lipo battery that was powering the video transmitter. The weight of my rig went down, the overall complexity of the power system went down, and the video no longer had power glitches.

Once you take the leap to using Lipo batteries, most of the real heartache is behind you. One charger will charge all your Lipo batteries. One battery balance monitor will monitor all your Lipo batteries. Adding one more battery to the mix doesn’t make life any harder than you’ve already made it. So I started looking for other places I could use them.

Monitor with Lipo

My video receiver and monitor was a good application. Both required about 12V and had fairly small current requirements. One of the real marvels of Lipo batteries is that they come in all sorts of sizes and shapes, provided those shapes are all rectilinear. (Lipo, Li-Ion, and Li-Fe cells are all flat rectangles. NiMH, NiCd, and alkaline cells are all cylinders.) The monitor had a rectangular cavity on the rear right side of the case. All I had to do was measure it and find a 3S Lipo battery of that size that could provide at least 2500mAh of current. It took less than ten minutes of cruising the web to find just the battery I needed. It fit perfectly, and provided plenty of capacity to power both the receiver and the monitor. Powering my ground-side video system went from being a logistical nightmare to being a simple click-n-ship web purchase.

Why use batteries at all?

All this talk of batteries and KAP assumes that batteries are required at all. Honestly, they’re not. If you’re willing to use film cameras, the requirement for batteries goes away. A wound timer can trigger a shutter as well as any battery mechanism. One of my KAP rigs holds the camera lens-down – no pan, no tilt, no motion at all. Even rigs that move don’t strictly require batteries. Most early KAP rigs used spring-wound or rubberband-wound mechanisms to pan and trigger the camera. One of my favorites – a rig built by Timonoko – uses a propeller to turn a worm drive that pans the rig slowly using wind power alone.

If you don’t need batteries, don’t use them. If you need batteries but don’t need the benefits that bizarre chemistries like Lithium Polymer provide, skip the headaches that come with them. But if you find yourself in a corner, trying to design around something that a Lipo battery would solve, don’t worry. They’re not that nasty to work with.

– Tom

P.S. Bonus points to you if you saw that I had the charge leads plugged into my balance charger backward! When I plugged it in after taking that picture, it came up with a warning, “Polarity Reversed!” and refused to let me charge the battery until I’d plugged the cables in correctly. See what splurging on a charger does? It pampers you!

Posted in Engineering, Kite Aerial Photography, RC Airplanes | Leave a Comment »

Video KAP Rig – Status Update

Posted by Tom Benedict on 22/06/2013

It took a few weeks, but I finally had a chance to make some small changes to my KAP rig and give the video downlink another try. I had much better results this time – a clear indicator that my antenna mounting was suspect. But I got another clue, too. I’ll get to that in a sec. First, the current rev of the setup:

KAP Rig 2013-06-17

The new monitor is about the same size (and weight!) as my RC transmitter. With the exception of the extension cable on the antenna, the KAP rig is almost completely unmodified.

The ground unit is a little ungainly. The mounting arm was made for a much smaller monitor, so it wobbles around more than I’d like. I can fix this pretty easily by making a thicker one. The monitor mounts to it using a T-nut that rides in a slot on the back of the monitor, so even using a thicker arm won’t require changes on the monitor side.

The larger monitor had an added benefit: I found myself placing the ground unit on the ground, and looking at the monitor as I let kite line out to get over the subject. By pointing the camera down, I could tell exactly where the camera was, and once it was in position I could pick up the ground unit and aim the camera to get the framing I wanted for the photograph. Once I’d done this a few times, I decided the larger monitor was well worth the extra weight, encumbrance, and cost.

This second flight was over the Mala`ai garden in Waimea:

Mala Ai Garden - 2013-06-16

This time I flew with my Canon Powershot A650IS, but the rig will take a Gopro or my T2i DSLR as well. I’m running CHDK on my A650, which lets you use a bitmap as a focusing reticle. The reticle I’m using has the “rule of thirds” grid on it with circles around the intersection points of the grid. The reticle image is also sent through the video out on the camera, so the combination of the big screen, the reticle, and good wind made it very easy to position the subject in the frame just the way I wanted it.

The video glitching I was getting during my previous test was completely absent, even with the rig more than 500′ away from me. No surprise with this video Tx/Rx, but it was nice to finally see it work. The only real gotcha I ran into was that the antenna connector on the video Rx was corroded. CORRODED?! Yep. EVERYTHING is gold-plated except for that one connector. The nut that holds it in the case was showing actual signs of iron rust. GAAAH! So at some point I need to unsolder the crummy connector and put a better one on. But that’s for another time.

I’m not 100% happy with the extension cable on the transmitter antenna, so I’m trying to come up with better ideas. So far this keeps the antenna clear of the rig, well out of the camera’s line of sight, and low enough to always have clear air between it and the receiver. But something a little more robust would be good.

The wind this weekend is (yet again) questionable, but I’m bound and determined to get out at least once to do some KAP with the new setup. Whether I can will actually depend a lot on my cat, Ember. He’s slated to come home this weekend. Depending on how things go, I may be spending the weekend with him.

– Tom

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Survival Part II

Posted by Tom Benedict on 21/06/2013

Ember, Coned

Ember came home Friday before last, but from the moment he came in the house he was in steady decline. He went right back to the vet Sunday morning, a day and a half later. His abdomen was swollen and hard, he was in complete renal failure, and he had popped one of the wires holding his femur together. The vet wound up draining over 280ml of urine from his abdominal cavity. It turns out the force of the impact with the car had perforated his bladder, and unfortunately his urethra as well. She stitched his bladder shut, and put in a catheter to give his urethra something to regrow around. The next two days were a real low-point in my life.

Not everyone I know has as firm an attachment to their pets as I do. I know this, and yet it’s still strange when people tell me, “I’d have put him down.” Maybe. But he wasn’t done yet! So how could I give up on him?

Over the next week Ember recovered while perfecting the art of removing his own catheter, even with an Elizabethan collar on (also known as “The Cone of Shame”.) In the end the vet extended the collar by about a centimeter by wrapping the cone with duct tape. (“Hey, Bubba! The vet fixed my cat with DUCT TAPE!”) A blood transfusion and a change of antibiotics to deal with a new infection in his urinary tract finally saw him solidly on the road to recovery. The popped wire in his femur was fixed using external pins and a cast. For now, every part of him is on the mend.

But the vet is quick to point out that he’s not out of the woods yet. Using a catheter as a mandrel for an animal to rebuild a damaged body part around is risky. There’s a chance that he’s not repairing the damage to his urethra at all. Catheters can’t stay in place more than about three weeks. So at the end of that time, the catheter will be pulled. Once it is, he’ll either live on to finish healing his broken leg, or he’ll go into complete renal failure again with no way to repair the damage.

For now Ember’s life is hanging by a plastic tube. Only time will tell if he’ll pull through this. If he does, it’s a testament to his will to survive. And if he doesn’t, it wasn’t for his lack of trying.

– Tom

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Posted by Tom Benedict on 06/06/2013

Can your tongue do THIS?!

Last Friday, my cat, Ember, was hit by a car. We heard a thump that we attributed to a car door closing, but in retrospect it’s hard not to recognize the sound of an animal being hit. I doubt I’ll ever make that mistake again.

We didn’t find out it was Ember for another two hours. It took him some part of that time to drag himself from where he’d been hit to our front porch. He lay there for the rest of the two hours before we opened the door and saw him. He made one attempt to move, then thankfully stopped. It was enough for me to see his right rear leg was broken.

Our vet’s office has an on-call doctor, so we were able to get Ember in to be seen in less than twenty minutes. It seems like such a short time after the hours he’d already spent injured and in pain, but time seemed to crawl as we drove him there. His leg was covered in lacerations, some small, some large, and the doctor confirmed his femur was broken. Fifteen minutes later she was starting an IV and we were sent home. There was nothing more we could do.

Before I go any further… If you’re the kind of person who skips to the end of a murder mystery to see whodunnit, don’t worry. I’m about to skip to the end, too. If you’re the kind of person who reads the whole book through so you can be surprised when the detective reveals the killer, sorry. I’m ruining the suspense now.

Ember lives through this.

X-rays showed that he suffered a spiral fracture to his right femur that left the bone in five pieces. His pelvis, spine, hips, and knees were intact. Not the best situation, but not the worst. During surgical prep, the doctor found additional lacerations, including one gash in his belly that almost completely opened him up. She set the bone using a combination of pins and wire, and closed everything up with staples. When we saw him the next day, I lost count of how many staples he had in him, or how many lacerations they were holding shut. He looked like he’d picked a fight with a razor and a stapler, and lost.

The first time I saw him after surgery, I was more terrified than when he’d been hit. Surgery takes a toll on the body, and a patient in post-op, even for trauma, almost always looks worse than when they went in. He could barely lift his head, and that spark in his eyes that’s such a part of who Ember is was gone. His body was on the mend, but I was afraid his spirit was broken.

Yesterday we visited a second time, and I was overjoyed to see some of that spark back. Unlike the previous day, he was alert. Pissed, but alert. And best of all, he was trying to walk. He was born a quadruped, and it was obvious the tripod life wasn’t suiting him well. The doctor said the muscles in both legs and hips were bruised, torn, and generally traumatized, so it would take time. But there was no paralysis, and his spirit was obviously not broken. They decided to keep him an additional 24 hours to make sure he didn’t have any post-operative infection, and to be sure he’s mentally on the road to recovery.

Ember’s the hero of the story. Now on to the swooning bystander: me.

Over the past few years, I’ve been stretched a little thin. My son has been in the ER more than once, and Rydra was diagnosed with a brain tumor. She had a craniotomy, multiple MRIs, cancer scans, you name it. I spent that time being stoic, analytical, supportive, whatever it took to get us through.

But whatever quality it takes to do that, I ran out of it when I saw Ember collapsed outside the front door. I managed to call the vet, but it was Rydra who drove us there. She’s the one who did all the talking. She’s the one who held me while I cried. And she’s the one who’s been keeping tabs with the vet and arranging the daily visits. For my part, I’ve been spending that time in an almost constant state of panic and fear that the next time the phone rings, it’ll be the vet telling us that something went horribly wrong.

So if it seems odd that I spent one of those days at the beach flying kites, understand that it was Rydra who set that up, too. She was right when she told me it was out of our hands at that point. And she was right when she said we needed to get out and get a fresh outlook on things. She was completely right when she told me to go fly a kite. Or two. Or all of them, if that’s what it took.

We saw him again today. He’s still not walking, but he’s starting to get around. The doctor said she’s probably release him tomorrow or Friday, providing he continues to improve. I’m still going into full-blown panic every time we get near the vet. Everyone else, including Ember, seems to be handling the situation a lot better. He’s still hurting, still angry, but the look of determination on his face is humbling.

When we first brought him in, the doctor told us she could heal his leg, but that he had to have the will to survive in order to heal the rest.

He has it.

– Tom

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All Kite No KAP

Posted by Tom Benedict on 03/06/2013

One of Rydra’s friends from high school was on the Big Island, so we set up a get-together at Hapuna Beach over the weekend. The wind was good, and I had all my KAP gear with me, including my new video ground station. It really was perfect for doing aerial photography.

But I’ve done so much KAP at Hapuna, I just couldn’t bring myself to hang a camera from the line.

A year ago I might’ve panicked at the thought, but honestly, I took it as a good sign. In the last two years, a combination of not wanting to be too far from Rydra and an overall shuffling of personal priorities have meant that almost all my KAP has been done at Hapuna. At various times I’ve been afraid that I’ve lost interest in KAP. But I finally realized the root of the problem wasn’t the KAP, it was the flying location. I’m tired of doing KAP at Hapuna!

So with a smile on my face, I pulled out a kite and my winder. Not to do KAP, but just to fly.

The PFK Nighthawk launched smoothly and easily, and flew so well, I decided to pull it in and swap it out for the Flow Form 16. That flew so well, I put the Nighthawk on a 10′ tether and attached it to the line, too. When those two were flying well, I added my green 6′ rokkaku to the line and put all three up. This is the same stack I did back in January. It was fun then, it was just as fun now.

Eventually the wind started to drop, so I pulled those three kites down. The kids wanted to fly them, so I stuck each one on a short tether and handed them off to the kids while I put up my Didakites rokkaku. Eventually the wind dropped enough that the Flow Form wouldn’t stay inflated, so I packed it away and handed my Fled off to my daughter. (If you’ve lost count, I’m up to five kites.)

Toward evening, the crowd began to disperse enough to consider flying a sport kite. I tied my rokkaku off to my kite bag, pulled out Rydra’s and my Widow, and laid out the lines on an open stretch of beach. I got twenty glorious minutes of flying before a group of people walked straight into the area I was flying and dropped their stuff on the sand. I was a little disappointed, but I wasn’t going to risk their safety. I landed the Widow, packed it up, and headed back to our spot on the beach.

The wind continued to die down as the sun began to set, and one by one the kids handed me the kites they’d been flying so I could pack them away. Eventually even the rokkaku didn’t want to stay in the air, so I pulled it down, too. As I was packing it away I realized there was only one kite left in the bag that hadn’t flown: my Dopero. The wind was light, but there was still enough of it to fly!

It only flew for about ten minutes before the wind failed altogether, but I was grinning ear-to-ear as I packed it away. One beach, one afternoon, seven kites. At that point I couldn’t care less that I didn’t get my KAP stuff out of the bag. This is what it’s all about – good company, good wind, a bag full of kites, and no limits. I was in heaven.

This is the difference between KAP and most other forms of aerial photography. The end-all be-all with KAP isn’t getting the shot at all cost. Some days the gear doesn’t even come out of the bag. And sometimes those can be the best days of all.

– Tom

Posted in Kite, Kite Aerial Photography | 2 Comments »