Review: Kit #34, the Delta Twister

(Cover taken from the Otona no Kagaku site.)

Kit #34, the Delta Twister, is now out.  2940 yen.

Otona no Kagaku is pretty pleased with this one, advertising it as a unique design for a wind-up plane never seen before. Designed by Yusuke Takahashi, this entomopter gets it’s name from the triangular front wing, and the “twisting” way the wing flaps.  It is a much more impressive craft than the entomopter or ornithoper were from kit #31.  I haven’t had a chance to take it outside yet (it’s raining), but Gakken claims a flying time of 10 to 30 seconds, with a distance up to 30 meters.  With the rubber band only partially wound, it’s safe to fly indoors as long as you don’t aim at people’s faces.  The key point is that it’s very light at only a few grams without the DC motor.  Made from carbon fiber rods and mylar sheeting, the Twister is powered either by the wound rubber band, or a coreless motor connected to a charged capacitor.  The drive rod at the front connects the crank handle to the front wing, and causes the wing to flap at a relatively slow rate of 1-2 complete beats per second (with the band partly wound; 5-10 bps with the motor).  Normally, this would be too slow, but the greater surface area of the front wing pumps a lot of air, and the back wing acts as a stabilizer/parachute to help keep the Twister aloft.  The launching instructions state that you should toss the Twister as you let it go, but simply dropping it works fine, too.

The operating principle is very simple.  You wind up the rubber band with the hand crank at the front and when you let go, the twisting crank makes the drive arm move up and down.  Since the arm is connected to the front wing about half an inch off-center, the wing then wiggles, with one side going up, then the other. The mylar sheet is big and loose enough to generate a wind strong enough to feel against your hand, for forward propulsion, and the tail wing acts as a stabilizer, as well grabbing enough air to slow any downward motion ala a parachute.

(Rubber band version. Note the handcrank at the front.)

Initially, I decided to build the rubber band version because it looked like that would make the construction of the wings easier.  This version only has 17 parts, not including the double-sided tape.  There’s a 60 minute suggested assembly time, but I focused so hard on understanding the instructions and trying to get it right the first time, that I was stunned to discover that 2 hours had passed.  The basic idea is very straight forward.  You have a small white silicon tube, 6 carbon rods (1mm by 170mm, three 0.8mm by 220mm, and two 0.8mm by 170mm), a couple mounting pieces, 2 large sheets of mylar, and a folded paper guide. Cut six 3mm pieces from the silicon tube (it may help to mark out a 3mm line on a piece of cardboard and use it like a cutting board) and put five of them on the carbon rods as shown in the diagram. The 1mm rod is used for the central rod for the front wing.  The rest are structural supports for the two wings.  Put the 1mm rod and two of the 220mm rods into the three hole holder as shown, and slide the flexible skeletal bar on to the other end as shown.  Don’t worry about positioning the bar yet.  This gives you the skeleton of the front wing. For the back wing, connect the two 170mm 0.8mm rods to the straw holder and put the wing tip bars on the opposite ends.  Put the remaining rod into the middle hole of the straw holder and slide the end straw holder onto the rod from the opposite end.  This completes the back wing skeleton.

You’ll notice that the plastic pieces that attach to the mylar have a flat side and a ridged side.  As you put them on the carbon rods, make sure the ridged side is face up.  When you’re done with the skeleton frames, cut the double-sided tape as shown in the diagram on page 3. Lay the folded guide sheet out flat on the table and tape one of the mylar sheets onto the guide with Scotch tape.  The instructions state to start with the big wing first, but it doesn’t really matter. You can get both wings from one mylar sheet; the other is just a spare in case you need it.  Pre-position the two wing skeletons so they lie evenly within the gray areas of the guide sheet (this is where you adjust the skeleton bar on the front wing to the correct position).  Put the double-sided tape on the mylar, with the backing still on the other side, as shown on the guide sheet.  When you’re ready, take the backing off one piece at a time and put the skeleton on each piece of tape, centering the carbon rods within the gray boxes of the guide sheet.  Make sure now that the flat sides of the plastic pieces are face down on the tape.  When the rods are affixed to each piece, cut the mylar along the guide lines with an x-acto knife and wrap the excess mylar around the rods.  Remove the extra paper from the guide sheet, reposition the mylar for the other wing, tape the edges of the mylar to the guide sheet and repeat for the other wing.

Make the rubber elastic into a loop and knot the ends.  Put the loop over the crank hook of the front wing and use the puller tool to pull the band through the body straw.  Put the straw in place on the front straw holder, slide the back wing holder over the straw, wrap the band around the back wing end cap and put the end cap in place.  Remove the puller tool.  You’ll probably want to wrap a piece of Scotch tape around the end cap to keep it from spinning when the rubber band is wound up.  Connect the free end of the front wing central carbon rod to the back wing tip piece and you’re done.  Wind up the Twister using the front crank and let go.

(DC motor (silver cylinder above the white gear) and cap (blue cylinder at the back.)

To use the DC motor, pull off the back end cap, remove the band and front crank piece.  Replace the front crank piece with the gear holder.  Attach the gears and DC motor.  Route the wires, and mount the capacitor board at the back.  Check positioning to allow for easily plugging into the battery holder.  Assemble the launcher/battery holder.  Put in 2 AAA batteries.  Plug the Twister into the launcher using the 2 pins on the capacitor board.  Press the battery switch and let the wing flap for 10 seconds to charge the cap.  Pull the trigger to launch.


The only tool needed is the x-acto knife.  All pieces are snap-fit plastic, and they will need to be removed from the form frames and any excess plastic removed.  However, if you’re using the battery holder, you’ll need a small Phillips driver for the 2 screws used to keep the case closed.

(Front of launcher.  The 2 pins on the capacitor board plug into the jack of the launcher.  When you pull down on the battery switch at the back, the wing immediately starts flapping and the cap. begins charging.  Wait 10 seconds, then squeeze the pusher trigger.  This simply pushes the circuit board forward and frees the 2 pins from the jack.)

I did find the process of switching from the rubber band to the motor to be very difficult (maybe another 17 pieces, and took 1 hour to complete).  The rubber band crankshaft piece and the gear holder shaft both pressure fit onto the 1mm carbon rod, and I needed to do a lot of pushing and pulling that could have damaged the mylar.  This is not something I want to do often.  I also had trouble with the gears.  Initially, the gears were very stiff, and the way the middle gear fits into the teeth part of the motor kept causing the motor to pop out of the shaft when I put them together.  The cap wouldn’t hold a charge, and the motor got really hot when I tried to run it.  The problem was that the motor pressure fits into the hole in the gear shaft, and it wasn’t completely pushed into place.  After really mashing in the motor, the gear assembly turned much more easily.  If you find that the gears require work to turn with your fingers, try pushing the motor in a little farther (but be careful to not snap the gear shaft).  The next problem is that the capacitor mounting piece on the straw body slides too easy and the Twister will rotate onto its side as you’re charging it with the launcher.  If this happens, just hold the Twister in place with your free hand.

(DC motor version of the Twister with the cap. circuit board pins plugged into the launcher.)

While this kit, and the next one, aren’t numbered on the packaging, the website URLs indicate that this one is #34, and the next will be #35.  So, technically, the Delta Twister isn’t actually a “special kit”.  The mook reflects this.  The first 4 pages are examples of flapping-wing aircraft from the Studio Ghibli movies, mainly from Laputa, Castle in the Sky.  The next 14 pages are various descriptions of the principles of flight, starting with air flow, then including dragonflies, bees, planes and helicopters.  There’s a 10-page interview with the designer and photos of the Twister in a wind tunnel.  Another 4 pages on descriptions of the technology behind the coreless DC motor and capacitor, and an 8-page photo essay on the proper way to launch the Twister (two pages demonstrate an extender pole for launching the DC motor version from an additional 6 foot height).  We get into the suggested mods in the next 8 pages, including changing the wing material to make a big gold fish, hanging two twisters upside-down from a small dirigible, and adding a second motor to drive an RC-controlled tail fin.  2 pages showing a hand-built 1-seater wooden glider, and 4 pages showing an amateur project using a Primer-V2 robot that can ride a scaled-down bicycle without training wheels or falling over.  An 8-page interview and photo essay on Fujitsu’s new super computer (currently the world’s fastest), and 7 pages on the principles of geodynamics and fossil formation.  The mook wraps up with the assembly instructions for the Twister, and a 16-page manga by Yoshitoo Asari that originally ran in Gakken’s school kid science books back in the 70’s. Asari started out at Gakken drawing the Manga Science sections before going off to create his own Space Family Carlvinson and Lucu Lucu gag manga.  This particular installment teaches the principles of aerodynamics.

Overall, the mook is again a great collection of photos, but there’s not much in the way of historical objects this time.  Lots of interviews and theory in Japanese. I personally really like the Asari manga at the end, and will eventually get around to translating it.  The Delta Twister itself is very eye catching, and the Japanese people I’ve shown it to find it very cute and fun to play with.  The mylar can be damaged by strong winds and won’t fly well if damp, so there’s a limit to how often you can fly it.  You’ll want either an open field like a baseball diamond, or an indoor basketball court (I think it would be good for frisbee golf).  It is a fun kit, and if you’re a science teacher you may want to get two (they’re still relatively cheap even after the import mark-up) to have one each rubber band-, and DC motor-powered (since it’s difficult having to switch between them).

Next up: Kit #35, two-cylinder steam engine

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  1. A follow-up.
    I finally had the chance to take the Twister out to an open field and play test it. The capacitor generally held a charge for about 5 seconds, and flight distance was about 10-20 feet. When I pushed the trigger, the pusher fingers would slip off the capacitor circuit board and the Twister would fail to launch. The last problem is because of the angle I was holding the plane at relative to the launcher – the nose of the plane has to be kept down when you pull the trigger. As for the cap. discharge time, that may be partly due to the batteries running down, or it may be an actual problem with the cap. circuit itself.

    The biggest issue, though, was that the Twister kept self-destructing. I put a piece of cellophane tape around the plug part of the gear strut that fits into the front of the body straw, which helped keep it in place for the most part, but because the wing flaps as the cap. is being charged, the plug works its way out of the straw anyway, and then the two wings come apart. It may be better to use masking tape, or to just glue the plug into the straw (which then prevents you from changing back to a rubber band drive).

    There may be a reason why most of Gakken’s demo videos are for the rubber band driven version.

  1. Yoshitoo Asari’s early Science Manga « threestepsoverjapan

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