Thursday, January 13, 2011

Mega Review: Two MicroMaxx Monocopters and One Bi-Copter

In 2002, I had become interested in monocopters and had MicroMaxx fever.  So, why not a MicroMaxx Monocopter?  I experimented with two versions.  Art Applewhite took interest and said that, if I came up with a kit, he'd sell it through his site  However, my progress was slow and the designs were too complicated so he did what he does best - make a simple minimalistic version from cardstock.  After seeing this, I suspended work on mine.  So this 'mega review' will present my MicroMaxx monocopters and one bi-copter, which I based on Art's work.  The plans for Art's Mark 4 are available through the MicroMaxRockets Yahoo Group (membership required, look in the files section).

The Amazing Underperforming Mono-Nano-Copter

This prototype was my first attempt at building a monocopter. It is powered by Micro-Maxx motors and is truly underpowered. The MMX motors have too short of a burn to be a good choice for a monocopter, even if it is "nano" sized. Not too impressive by most standards. Well, one man's curiosity is another man's triumph (or something like that).

Parts required:

* 1/4" balsa, 1" x 1"
* 1/16" balsa, 1 3/8" x 4"
* Ink tube from a Bic pen
* One sheet of drafting vellum (any paper will probably do)
* 1/16" x 12" aluminum tube
* 1/4" x 1" dowel
* Masking tape
* Lead for nose weight (see assy instructions)
* Carpenter's glue
* Black, CA (I can't remember the actual name)
* Thin, CA

The central hub is a 1" square of 1/4" balsa, soaked in thin CA. I carefully drilled a hole in the center to hold the launch lug. This is, hopefully, the point about which the monocopter will spin. I also drilled holes in the middle of each side to mount the balance beams. I used pieces of the ink tube from a Bic pen for both the launch lug and the mounting points for the beams.

The single wing is a clipped delta with the following dimensions: root - 1 3/8", tip - 7/8", span - 4". It is balsa strengthened with drafting vellum and ProBond glue. I wanted to add a bit of strength and had never tried vellum before. I spread a thin layer of glue on each side, placed the wing between a folded sheet of vellum, and compressed it with a stack of books. The wing seems strong enough, but the surface is not as uniform as I would have liked. I attached the wing at an angle of about 10 degrees from the monocopter's X-Y plane using black Bob Smith CA. It is mounted such that the swept face is on the trailing edge and the leading edge is raised. I oriented the swept face on the trailing edge to allow me to more easily position the CP of the pod behind this edge (a tip I got from the book "Monocopters", by Francis Graham).

The motor pod is the length of three MMX-II motors and was scratch built from drafting vellum (someday I'll actually buy some MMX tubing). It is both light and strong. The cone was turned from a dowel. It turns out that the motor pod must be angle upward to counteract the torque caused by the single wing. Some of Francis Graham's designs have their pods angled at up to 40 degrees. However, I chose the start with an angle of 30 degrees (in the opposite direction from the wing). To get the CP behind the trailing edge of the fin, I added several #7.5 lead shot to its nose. I should have counted the shot, but forgot to. The CG is at the little green 'x' that's barely visible on the photo. This 'x' is positioned approximately at the trailing edge of the wing's root, and since the wing is swept in the opposite direction, it is behind the trailing edge of the rest of the wing.

I had wanted to use some light 0.03" carbon rods for the balance beams, but didn't find any at my favorite hobby shop. Instead, I used a 12" long, 1/16" diameter aluminum tube. This was cut in half and CA'ed into the ink tubing that was previously mounted in the hub. I didn't add much ballast at the ends of these beams, wrapping about 1 1/2" of masking tape (very high tech) around each end.

The second photo shows the MMX launch pad with its special launch 'rod'. The rod is a piece of a heavy paper clip. It wasn't the right size so some masking tape was used to hold it tight. A piece of ink tube was used as a standoff to keep the monocopter from hitting the MMX launcher and to help it spin.

I used MMX-II motors, Estes igniters, and my Pratt GO-Box for ignition duties. The monocopter did fly. On its 1st flight, it rose to a whopping two feet, at an angle of about 30 degrees from the vertical, before the motor ejected and stopped the spin abruptly. I should have removed the ejection charge! Still, it didn't just flop around. I never expected much performance so I think it was a good first try!

On its second flight, all conditions were the same except I removed the ejection charge from the Micro-Maxx motor. This time, the monocopter barely cleared the launch rod. I think that the igniter may have hung up ever so slightly. With so little upwards thrust, it wouldn't take much to affect its flight.

Flights three and four were similar. For these flights, I bent the igniters, carefully fit them it into the nozzle, and arranged the clips so they held it in place without any tape. Both times the monocopter rose to about a foot and went off sideways at a steep angle. It landed maybe 4 - 5 feet from the pad. This seemed lower than the first flight but definitely higher than the second did!

In summary, I consider this experiment a complete success. The performance was poor, but I didn't have any expectations in this regard. When I decided to build it, I wasn't at all sure it would even take off or be stable. The Amazing Under-performing Mono-Nano-Copter met both of these criteria. My next try may be a lighter MMX-powered monocopter, but then, I have these long-burn, OOP Apogee B2 motors...

UPDATE 10/02:  Sitting at the computer, and in between steps of other projects, I decided to revise The Amazing Underperforming Mono-Nano-Copter. It isn't so underperforming any more!

I cut down the motor pod to an inch and a quarter, just enough to fit the dowel nose cone and a MMX motor. The business about having the CG behind the trailing edge of the blade is not a requirement as I've later found. I cut the old wing to about 1/4", and added a 4" x 1 1/2" piece of 1/64" Birch. I have also determined that the balance beams were way too long so I cut them to 2 1/2".

The first two flights went to about 9 feet and landed 3 and 5 feet from the pad, respectively. On the third flight, it headed off at a 45-degree angle, smacked the side of my SUV, and still rose to about 7 feet. Much better performance than before!

The main lesson-learned is: build 'em light!

Cicada Killer

This review describes my second-generation Micro-Maxx monocopter. The improvements over my original include a lighter wing, a smaller motor pod, and a carbon rod balance beam. It has undergone numerous minor tweaks and one major revision. The maximum altitude obtained to date is about 9 feet.


* 3/16” balsa for wing and hub (see diagram)
* wrapping tissue paper
* white puzzle glue (pre-thinned white glue)
* ink tube from BiC pen (1/2” used)
* 0.03” carbon rod (7” long in final configuration)
* scrap paper to roll motor tube
* ¼” dowel for nose cone
* black CA

Please refer to the figures while reading the construction notes.

Wing - Make this out of 3/16” balsa as indicated, with the grain oriented with the leading edge. I removed sections to make it lighter and sanded it into an airfoil shape. The entire wing is covered with wrapping tissue attached with puzzle glue. I made it out of a scrap piece of wood, hence the odd shape. My thanks to John McCoy of NARHAMS for suggesting this construction method.

Hub - This, too, is made from 3/16” balsa. The grain should probably also be along the leading edge, although it was perpendicular on my model. I rounded both the leading and trailing edges. I drilled a hole at the lateral CG and installed a half-inch section of ink tubing. This is flush with the top surface and extends below the hub.

Motor tube - This was rolled from drafting vellum and white glue. It is about 1/8” longer than a MMX motor.

Nose cone - This was turned from a ¼” dowel on a hand drill.

Balance beam - I started out using 3/32” wood of varying length (see flight log table). I replaced it with 0.03” carbon rod, which was graciously supplied by John. The wood dowel was simply glued to the bottom of the hub next to the launch lug, while the carbon rod was inserted through the balsa hub.

Assembly - All components were glued together with black CA. The wing and motor tubes are centered on the hub and are angled upwards away from one another. The wing is angled at approximately 12 degrees, and the motor pod at approximately 15 degrees.

All flights were from my MMX pad with a 1/2” long launch rod. The igniters were Estes and the MMX ones with the plastic shell removed. For all but flight #10, I used my Pratt GO Box. The wind was calm except for flight 10, which was 5 - 10 mph in my guestimate.

Flight Beam
Est Alt Est Dist
from Pad
Beam Material Notes
1 7 5+ 7+ 3/32 Wood Hit Roof Rack of SUV
2 9 1 4 "
3 9 2 4 "
4 7 4 9 "
5 7 3 9 "
6 6 5 12 "
7 6 7 8 "
8 6 5 8 "
9 5 9 5 "
10 5 5 20 " NARHAMS Sport Launch
11 12 3 4 0.03 Carbon
12 9 4 5 "
13 8 5 8 "
14 7 9 8 "

I was pleasantly surprised with the performance of this monocopter, considering the short burn time and low thrust of a Micro-Maxx motor. On my next version, I will make the wing slightly longer (for hopefully even better performance), and will use a rectangular shape with a slightly rounded tip (for aesthetics).

Push me Pull You (Bi-copter)

This is two-motor, two-winged helicopter model that employs MicroMaxx motors. Thus, it's a bi-copter as opposed to monocopter. The Push Me Pull You uses cardstock construction and is based on a design concept developed by Art Applewhite for his Mark 4 monocopter. You can see his Mark 4 in the files section of the MicroMaxRockets Yahoo group.

You will need enough card stock to cut out the components shown below, and a piece of an ink tube from a BiC pen (or equivalent). To construct it, you'll need a ruler, Exacto knife, and white glue.

The component measurements and step-by-step instructions are included in the attached diagram. You should also refer to the two photographs during construction. I have to apologize but I built the bi-copter 'on the fly' and backed into the plans - just like software design, eh? As noted in Step 3, there is one possible issue with those plans. But don't fret, if you refer to the figures, this should become clear while you are constructing the model.

Since the two motors are so far apart, I made an igniter by removing the plastic shell from two MicroMaxx igniters and soldering on wire pigtails. For my first igniter pair, I used stiff wire, which was hard to deal with. For the second set, I used flexible 30 gauge wire-wrap wire.

For a launcher, I clamped a piece of wire from a thick paper clip into a low power pad that I made from a drill chuck. I used a second piece of ink tube as a standoff to keep the monocopter elevated. You must make sure that nothing will obstruct the wings, which hang below the plane formed by the beams. To supply the juice, I used my Pratt GO Box.

I removed the ejection charge from the motors and used some tape to hold them in. The bi-copter flew great to an altitude of about 20-25 feet

This is a unique-looking rocket and flies great. You should give it a try, and while you're at it, build one of Art's Mark 4's also.