Author: davesharp

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Experiments in Garden Hose Hydraulics

I recently decided to make a proof-of-concept for a simple hydraulics kit. Ultimately you would be able to take this kit, get some standard PVC pipe from the local hardware store, and very quickly build your own simple hydraulic devices. Use it to learn about the principles of hydraulics while staying cool on a hot summer day, or use it to power your homemade tools like simple presses, lifts, or even an articulated digging arm.

Double-acting PVC hydraulic cylinder and control valve

The pressure in your typical garden hose is nominally around 40 psi or so, so my first hydraulic cylinder should be able to develop about 125 pounds of force if it had really good seals. This is a proof of concept so I didn’t bother with o-rings or anything, so it leaks like crazy and thus is unable to develop quite those kinds of pressures, although it is quite strong. Moving from a 2″ to a 3″ hydraulic cylinder would bring this up to about 282 pounds of force, not too shabby for garden hose power!

The hydraulic cylinder is made of standard PVC pipe (2″ for the cylinder and 1.5″ for the ram), although I had to use my lathe to turn down a 1.5″ pipe cap to fit inside the outer cylinder. The control valve is made of 1/2″ CPVC fittings and tubing, with the exception of the spool which is a length of 1/2″ solid PVC rod. I had to turn down the spool on my lathe to the appropriate profile and also had to drill out the valve to fit it. The fit is fairly poor but it shows that the concept definitely works. Eventually I am hoping to be able to have all the custom parts injection molded to get the unit cost down cheap enough that it would make a good toy for DIY doodlers and budding engineers everywhere.

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Magnetic Dip, Illustrated

I was surprised at the absence of a concise illustration of magnetic dip available on the internet, so I cobbled together a short 3D animation using the excellent free software Blender. Magnetic dip is a very simple phenomenon but one which can quickly get confusing since it deals with 3-dimensional fields through space that can be difficult to visualize. The gist of it is that the Earth’s magnetic field lines are only parallel with the ground around the equator, and everywhere else the field lines actually dive downwards into the Earth by some angle, the steepest of which are found at the magnetic North and South poles. In the Philly area this angle is surprisingly steep, about 67 degrees below the horizontal — it’s actually more vertical than horizontal! This means that in areas far from the equator, tilting to the East or West will result in a compass error since the needle can align more closely with the magnetic field by deviating from the projection of the field lines onto the ground, which is what we normally think of as North. Tilt to the West in the Northern hemisphere, and the compass needle will tilt to the West as well.

It gets even more confusing when you are talking about traditional non-gyro-stabilized compasses, such as those normally found in small aircraft. The compass needle is usually weighted carefully such that it rests level with the ground under normal circumstances, but this means that when you accelerate in certain directions, that weight’s inertia keeps it lagging behind somewhat, resulting in yet more compass errors. These acceleration effects are not directly the result of magnetic dip, but they are partly the result of an incomplete attempt to deal with magnetic dip. Normally pilots are just taught to remember that this happens and vaguely what to do about it, but if you level out and stop accelerating the problem takes care of itself.

Blender allowed me to put this simple animation together in a very short time. It has a challenging learning curve, but it is a very powerful set of tools. Hopefully this animation will be useful to somebody out there other than me.

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My Blade mCP X Mods

She ain't pretty, but she flies great

I’m a noob when it comes to RC helicopters. I got a Syma S107 for about $30 a year or two ago and it is incredibly stable while being ridiculously bulletproof. I can fly it into walls, and I’ve never replaced a part. If it’s laying on its side on the floor, I can often get it to right itself by just gunning the throttle. (Do I recommend it? No. Do I do it? Sometimes.) A wire fatigued off the board once but that was the only thing I’ve had to fix. It’s a hell of a bargain and it’s treated me great, but being so stable and easy to fly, it has some inherent performance limitations. So I decided to step up a few levels.

I heard about the Blade mCP X helicopter, the first “real” helicopter of its size that came stock with 3-axis attitude-holding stabilization electronics. It weighs maybe double what my S107 does but its performance is amazing. It can do inverted flight, flips, all sorts of crazy stuff. That is, when supplied with an appropriately-skilled pilot, which I certainly am not. But I can fly it in my backyard in 30 mph winds, and this little beast can take it — pretty impressive for something that weighs the same as a good quality 9V battery. Being such a noob, I crash constantly, but I can usually patch things up without needing to buy replacement parts. Here is the list of mods I’ve performed on my helo so far, mostly out of necessity:

  • Grommet mod – tightens up the swash, reduces vibration (not my idea). Works great
  • Tail boom from mCP X2 – comes with a more aggressive tail rotor which helps with yaw authority
  • Created a simple tool to speed up resetting the main gear after crashes – just remove the battery and push this drilled-out rod over the gear hub to click it back in place, no need to remove the canopy or landing gear. I keep it zip-tied to my transmitter since I crash a lot 🙂
  • Lengthened tail boom – added perhaps 1/2″, seems to help with yaw authority
  • Added magnetic breakaway tail boom mount – after a crash the tail boom pops off instead of breaking, can be reset by simply moving it back in place and letting the magnets lock it down. Works very well, but be careful because if you have too much slack then with the right kind of crash the tail motor wires can get wrapped around the head. I’m sure I’ll keep experimenting with this one
  • Masking tape holding my canopy together? Classy
  • Hot glue holding my landing gear together? Not perfect by any means, but it keeps me flying until I buy a spare
Aluminum piece presses into the helo frame like a stock tail boom, but has an embedded magnet. Tail boom is hot-glued to a piece of bamboo skewer that fits into the channel, and has a magnet glued to it using CA and baking soda. Rubberbands or o-rings might be better
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Next open house project: Making Springs!

Ever work on a project and find yourself needing a spring? Ever go to
the hardware store looking for one, and have to compromise because the
offerings are so slim?

At the next Open House (Sept 28th) we will have materials for
making simple coil springs. If you have a project in need of a spring,
or if you’d just like to check it out, come on by. We’re certainly no experts and you wouldn’t want to mass produce them this way, but adding
a new tool to the toolbox is always fun and may come in handy one day.

If you have a project in mind, try to bring as much information as you
can so we can take a stab at making you something that will work. We
can do extension-, compression-, and torsion springs. Note that the
final heat treating process takes about 2 hours so I will probably do
that part at home and bring the completed springs in to the following
Open House.

Home-made springs (torsion, compression, and extension) and some examples of their uses: mini catapult, spring scale, and wear-compensating anti-backlash nut
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Wide-Baseline Stereograms

Thanks to all who attended our first stereo photography class, it was a great turnout with several new faces! If you attended, here is some content that I just created that you can view using either the anaglyph glasses or parallel-viewing stereopticon that you received, or if you have been practicing up on your free-viewing, you can use the cross-eye method or “look-through” method (just set the 3D settings appropriately towards the bottom of the video on YouTube). I’ve created a slideshow of 3D images captured using wide baselines — in other words, the two photos making up each 3D picture were taken very far apart, much farther apart than the distance between a human’s eyes.

So, why wide-baseline? Well, the sense of depth from stereo vision is highly nonlinear, so we generally have exceptional depth perception up close (within a few inches or feet), but we are able to differentiate less and less as the objects get further away. In everyday life our depth perception due to binocular disparity is basically limited to around 20′ or so for most practical purposes. (This is why 3D pictures of landscapes are usually extremely boring and flat — the subject is too far away to make out the depth!) However, it is possible to overcome this limitation by moving the two cameras (one for each eye) farther apart. Some of these images were taken from airplane windows hundreds or thousands of feet apart, making it possible to discern depth between cloud layers many miles away. This tends to produce an effect that is similar to examining a miniature model of the subject up close.

Most of these 3D pictures were captured with the video camera on my phone while on a moving platform (train, car, airplane, etc), with the camera held very still up against the window and facing directly out. I would then open up two copies of the captured video side by side and use the cross-eye method to find two frames of the same subject that provide good depth. I would then copy those frames into Gimp, align the images and crop them down to produce a finished stereogram. It takes time and practice but it can produce some really cool results!

Boats outside Dave & Buster's on the Delaware River. Click to view entire slideshow
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New Class: Intro to Stereo Photography

On June 18th from noon to about 3pm, Hive 76 will be sponsoring an introductory class on Stereo Photography. We will cover a lot of fun things, including: basics of how stereo vision (“3D”) works; how to take stereo photos with an ordinary digital camera; tips on getting the best results in your photos; and an overview of several available 3D viewing methods, many of which will be available for in-person demonstration. Students will be able to try their hand at creating their own stereo photos, and each ticket holder will receive a small take-home element to help with their experiments. Tickets are available for $20.

lion statue
Stereo photo of a lion statue (view cross-eyed to see 3D). Click for full size

Bring yourselves, and if you can:
– A digital camera
– A laptop with image editing software (Gimp / Photoshop, etc)
– Any cool 3D stuff you might want to share (ViewMaster reels, toys, antique stereopticons, etc)

It should be a great opportunity to meet some cool people, share a fun hobby, and hopefully learn something new. See you there!

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How I Became A Maker

Growing up, my dad worked overseas for the State Department so we moved all over the Middle East. DaveI always wanted to know how everything worked, and my dad had a hint of an interest in electronics and other hobbies, but resources were always a little limited and there weren’t any skilled mentors I could learn as much as I wanted from. I recall spending a lot of time coming up with wacky invention ideas, most of which in hindsight are probably infeasible, but coming up with the ideas was always half the fun anyway. My dad would bring home articles from magazines on topics he thought I’d find interesting, like building simple robots, or making red jello lasers. Periodically I would get an inkling to try realizing one of my inventions and I would save up my allowance money, eventually putting together an order from a surplus catalog in the States. It would take 2 weeks for my snail-mail order to arrive there through the diplomatic pouch, and another 2 weeks to receive my parts, and as you can imagine of a young kid, I usually ended up getting bored with waiting and abandoned the original idea for something I could do much sooner. I had a great set of books, a silver hard-bound set called “How Things Work”, which was wonderful for fueling the inner mad scientist in me. In about 4th grade I remember spending a fair bit of time designing the space ship that I hoped would eventually rescue me from homework and school, and also allow me to explore and perhaps begin colonizing Titan, one of the moons of Saturn. (Needless to say, that one hasn’t panned out. Yet.)

I really had an interest in how almost everything worked, picking up as many things as I could. One day my dad brought home the first Magic Eye picture I’d ever seen, and after struggling with it for an hour it was an incredible feeling when the image of the earth finally popped out at me in all its 3D splendor, and I’d been bitten by the 3D bug. Living where I did, we didn’t have access to hardware stores or Radio Shack, but there were petrified forests, ripe with geodes and other marvels of geology that I loved to learn about. In slightly later years I learned some interesting things about chemistry, and am probably fairly lucky to have all of my fingers and toes. After figuring out how to make a surprisingly effective blowgun with quite nasty darts, I got a taste of what fun working with projectiles can be, going on in much later years to build a high-power rocket that is fired from a pneumatic cannon.

I was always interested in computers, and had a burning desire to learn how to write my own software. In elementary school I stumbled onto HyperCard (an incredible thing at the time), and I was off and running teaching myself some basics of algorithms, and writing simple tools and games. (I was never particularly interested in actually playing games, much preferring to explore and learn, or take things apart and dream of what I could do with the pieces.) Discovering programming was a bit of a boon for me, because it was a way of inventing for free — no materials to buy or wait for in the mail, no tools to wear out, if I could dream it and if I had the motivation, I could make it happen for nothing. From that point on I think I just assumed that I would go on to major in Computer Science when I got old enough. Little did I know that when that time came, I would abandon it after feeling like the educational system was beating all the fun out of it for me.

I’ve always found myself wanting to understand things, but having to teach myself. While that has been frustrating, usually taking much longer than simply being taught by an expert, I think it has been valuable for shaping how I approach challenges. Making things can be a puzzle, an adventure, or a game, and it’s so much more rewarding in the end than something you’ve bought or watched on TV.