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Archive for July, 2011

Self-Injury and First Responder Training

Posted by Tom Benedict on 27/07/2011

I’m about six months away from taking my first responder refresher course. One question I know will come up is whether I’ve had the opportunity to apply what I’ve learned. The answer: yes and no.

I haven’t helped anyone through insulin shock, and haven’t applied CPR. I haven’t performed any water rescues, carries, drags, or had occasion to participate in a mass-casualty incident. I haven’t delivered any babies, either (thank goodness!) But I’ve had too many opportunities to apply the first-aid training we received. Unfortunately most of them were on myself.

I’m injury prone. This is just a fact of life with me. In the past two weeks I’ve burned my foot, given myself reef-rash on the chest, and cut a nice 1/8″ thick slice off my left index finger. I’d love to say this was a busy two weeks, but it’s really not. And calling it two weeks is honestly stretching it. It’s closer to the last ten days.

The irony is I’ve never broken a bone, I still have all ten fingers despite doing machining at high altitude, and on the whole I’m a fairly healthy person. But life leaves scars. I do what I can to learn from my mistakes, and keep a well-stocked first aid kit with me at all times.

Even if they’re not accident-prone like me, I still urge everyone I know to take a first aid and CPR course. (This now includes you, since you’re reading this!) If the opportunity arises, I urge people to take a first-responder course as well, and keep their training current. It has been said that knowledge is power. This is true. And the knowledge of how to treat injury and sickness is powerful indeed.

I also urge people to keep first aid kits close to hand, and to keep them stocked. By definition, practically everything within a first aid kit is a consumable. That means at some point or another it will be consumed and will need to be replaced. Most first aid kits have a restocking list in them. This tells you what the kit came with in the first place. If your kit doesn’t have a restock list, take inventory the day you get it and make your own. A restock list is a start, but it’s by no means an end. When restocking your kit, try to get a feel for what you use the most and double up on those items. Make notations to this effect in the kit’s restock list. If there’s something you wish the kit had (like a flashlight!) add it to the restock list and put one in your kit.

One item that’s missing from most kits is gloves. When treating someone who’s not in your immediate family, body substance isolation is a must. This typically starts with gloves and a pair of eye shields. Glasses do an ok job of protecting the eyes, but nothing takes the place of gloves. I keep two pairs in all my kits, even the ones that never leave my house.

But even the best first aid kit is useless without training. A person with a full-blown trauma kit can still bleed to death if they don’t apply basic techniques. When I cut the tip off my finger I hit some blood vessels that put on a pretty good show. Nothing close to arterial bleeding, but it was pumping at a fairly good clip. Our first responder trainer drilled this one into us on a daily basis for a solid week: The best way to stop bleeding is to apply pressure. Even though it hurt like bejeebers, I applied pressure and the bleeding stopped within minutes. I even got to practice my fingertip dressing afterward!

Do yourself and the people around you a favor. Get trained. Then go out and use that training to help others.

Oh, by the way, helping others is one of the key aspects of a superhero. Congratulations.

– Tom

P.S. Don’t make your gloves part of your costume.

P.P.S. No capes!

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Offroad Camera Project

Posted by Tom Benedict on 11/07/2011

I’m building an offroad camera for a fellow photographer. The goal is to have a remotely controllable camera platform that can drive over rough terrain, position a camera, orient it, and release the shutter. It’s almost done, but not quite.

All in all it’s been a really fun project to work on, but I’d be lying if I said it was all clear sailing. It’s unfortunately been a case of one step up and two steps back, or on good days two steps up and one step back. And just when I thought the end was in sight, I managed to set myself back by a week.

The vehicle is a 6WD Dagu Wild Thumper from Pololu Robotics.  Since the goal is controllability rather than speed, we went with the 75:1 gear train for the drive motors rather than the speedier 30:1. The motors are driven by a pair of Pololu Simple High-Power Motor Controller 18v25 electronic speed controllers. These are really nice units that can be configured using a USB cable and software from Pololu. They can be driven by an R/C signal, or via an analog input, or over a TTL serial connection. Even better, you can use a pair of Y-splitter cables to feed them a steering/velocity signal, and the two ESCs will do the channel mixing necessary to drive a tank-style steering chassis like the Dagu.

The robot is powered by a pair of 7.4v 3000mAh NiMH batteries. They’re wired in parallel to provide 6000mAh of capacity, so it can run with one or both batteries installed.

The Pololu ESCs offer a battery elimination circuit (BEC) for powering the radios and other servos, but they can only source a small amount of current. The other R/C components of the robot draw several amps, so the on-board BECs couldn’t be used. Instead we used a 5V 3A BEC that is installed in the same enclosure as the ESCs. Pololu now offers a BEC of similar capacity, but at about a quarter the size of the BEC we used. In the future, I’d probably go with the Pololu unit.

The pan/tilt unit is a combination of two gearboxes from ServoCity. The pan unit is an SPG400A set up for 360 degree rotation, with a Hitec HS-7985MG servo and 5:1 metal gears.  The tilt unit is an SPT400 with a Hitec HS-7985MG servo and 5:1 metal gears. This provides ample torque for holding the camera and lens combination in position, regardless of the orientation of the chassis. The pan/tilt unit is attached to the Dagu chassis via six standoffs and a custom machined aluminum plate. The plate also serves to distribute the load of the pan/tilt unit to the lower chassis through four of the eight standoffs that attach the two halves of the chassis.

One problem I ran into with the ServoCity units is the exposed gear trains. In most situations exposed gears are no-nos. This is why most equipment that contains gear trains also includes safety covers. The ServoCity units didn’t have a provision for a safety cover, so initially I ran without one. Sure enough, the pan gear box ate the tilt unit’s servo cable during initial integration and testing. I added a simple ABS cover to keep the cables from getting chewed in the future.

Crawler 2

I’m still waiting on a couple of parts, one of which is a 50′ length of heavy duty servo cable to replace the one the pan gearbox ate. But this is the current state of the thing:

Crawler 1

It uses a 75MHz surface radio to drive the chassis and control the pan/tilt unit, and a Hahnel Inspire 2.4GHz remote unit to control the camera. I’m waiting until the owner has had a chance to drive it around before deciding how to mount the Hahnel unit, if at all.

One surprise I had was that the center of gravity of the thing is below the level of the top deck. At first glance it appears to be horrifically top heavy, but that isn’t the case. Even more surprising was how hard it is to push over. The wheels all move independently, which gives the chassis an incredible amount of compliance. It’s quite hard to tip it over.

How this will play out in use I don’t yet know. It’s one thing to test a system when static and declare it stable. It’s quite another to test it in motion and see what the real dynamics are. I have a couple of good test spots where I plan to run it with a dummy weight in place of the camera, just to be sure. Once I know it’s safe and won’t tip over in normal use, it’s on to testing in the field.

– Tom

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Re-Thinking the T2i Rig

Posted by Tom Benedict on 08/07/2011

I’m still finishing up a number of projects, so I haven’t been able to begin construction of the T2i panorama rig just yet. In some ways I wish I had the rig in-hand this very moment. In others I’m glad it’s taking a while: I re-designed it. Again. And as soon as I thought I was done, I re-designed it again.

The initial design called for a Geneva mechanism that would index the camera through a number of pan positions at a fixed rate. I planned in a Hall-effect sensor and magnet so I could compare the rotation rate to a watch crystal and continuously tune it through a PID loop so it would remain consistent even as the rig’s batteries drained. This had all the benefits of Vertigo’s burst-KAP technique without the drawback of the high shutter speeds required to freeze the action. Since the goal of this rig is to do nighttime or late-evening panoramas, stopping the camera at each position is a requirement, and the Geneva fit the requirements perfectly.

Since then I’ve revised the design several times. The first revision was to add the ability to install a two-axis flywheel on the rig’s pan axis. This is to damp the high frequency rig motion in roll, pitch, and yaw, and allow for the slower shutter speeds necessary for late evening photography. I still think there’s a lot to be said for this approach, and plan to pursue it in the future. But for now I’m just adding the bolt pattern so the flywheels can be added later.

Meanwhile two other discussions have happened that changed my mind on a couple of things. The first was a thread on the KAP Forum from Mike LeDuc, who built a 3-axis stabilized pendulum rig that he’s used with great success. In addition to using an IMU to control three servos to take out extraneous motion in roll, pitch, and yaw, it also has the provision to trip the shutter on the camera only when it is at the apex of a swing, when the motion is at a minimum. I loved the idea as soon as I saw it, and still like it. I think it compliments the flywheel in terms of adding rig stability, and would result in sharper pictures at longer shutter speeds.

While trying to design around this idea, another thread on the forums came up, in which a fellow KAPer who goes by the name of yurik_ryba posted a link to a Pololu Robotics product, the Micro Maestro USB servo controller. I have a long-standing love of the design work done by the folks at Pololu, so I had to give it a look-see.

The Maestro line of products are all servo controllers with attached microcontrollers. They’re intended for robotics or animatronics, so there’s a provision for programming a sequence of motions into them. A Windows-based application lets you write the scripts that control what they do. Even better, each I/O slot can either drive a servo, act as a digital input or output, or act as an analog input. The Micro Maestro has six channels, but by the time you get to the largest version there are 24 channels of I/O and the added capability of having your I/O channels act as PWM outputs for DC speed control. They’re wild!

Of course I ordered one.

So for the moment the plan is to go with a mechanically simple rig. It’s basically a Brooxes BEAK with a geared pan axis. No sense re-inventing the wheel, so I plan to use his Deluxe Gear Set, which interfaces directly to the Brooxes Utility Frame I plan to use as the framework of the rig, similar to how it is done in the BEAK. The pan gear will be modified to include a ring of 1/8″ diameter, 1/16″ thick rare earth magnets. A ratiometric Hall-effect sensor will then be wired in on one of the unused I/O channels as an analog input device. Careful placement of the magnets should let me use this as a fairly accurate encoder.

One of the cooler features of the Maestro controllers is that each axis can have its own acceleration and maximum velocity settings. This should let me replicate the behavior of a Geneva without the mechanical complexity, and by using an encoder that gives a continuous near-sinusoidal output, I should be able to have it stop at an arbitrary number of positions as it completes its circle. The scripting language includes a command to detect if all of the axes have stopped, so with a sufficiently slow pan velocity and acceleration, I should be able to time things so the rig has settled down after each move.

Since this rig only has one axis, one shutter, and one encoder input, that still leaves me three I/O lines to play with. Sparkfun offers several three-axis gyro devices that would let me sample the rate of roll, pitch, and yaw. Once the rig is built and tested, if further stabilization is required I should be able to add Mike LeDuc’s apex sensing to my rig as a plug-and-play option. And adding the flywheels is a matter of bolting them on. This wouldn’t offer me the three-axis stabilization that Mike’s rig has, but I can cross that bridge when I get to it. Adding three-axis stabilization of a DSLR camera is not a lightweight affair, and up to this point the rig would weigh very little compared to the weight of the camera and lens. Light, simple, and effective is what I’m after.

In case anyone is reading this and is shaking their head, thinking I’m rushing headlong toward disappointment, please understand I know the risks. Earlier this week I talked about some of this with Michael Layefsky, whose nighttime picture of Jack London Square in 2009 got me started on this whole idea. He convinced me that night time panoramas from a kite probably are a fool’s errand. Even so, it’s a risk I’m willing to take. Look at it this way: At the very worst it won’t work for panoramas, but will occasionally (say 0.5% of the time) produce a good nighttime photograph. So be it. Roll the clock back into the sunset hour and it will still provide better panoramas than I can currently make. Roll the clock back a little further to the golden hour and it will beat my current setup hands-down. No matter how I cut it, this is a good direction for me to go.

And even if the whole thing is an utter and complete flop, the rig is entirely constructed of Brooxes components. That’s like building a KAP rig out of Legos or Meccano parts. If all else fails, take it apart and build something else that does work. Nothing is wasted except for my time, and even that’s not a waste since I’ll come out of it knowing more than when I went in.

All in all, life’s pretty good.

– Tom

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