Learn how to build a sturdy, light-weight, fast Micro Magic, whether you have one of the old German racing MM kits or one of the new Asian Graupner SJ kits.
Building a Sturdy, Light, and Fast Micro Magic
by Greg Norris in close collaboration with Ralf Bohnenberger and Jack Chambers
Meet the authors
Ralf Bohnenberger is one of the leading German Micro Magic skippers and he’s very active on the in MM International website. He’s a
n engineer and an excellent modeler. His boats are very well built and full of good of ideas. He would not dream of sacrificing complexity for simplicity.
Jack Chambers is one of the Azura MYC MM skippers. He is actually very new to sailboat racing. However, he used to make wind tunnel models for a living and he now builds gorgeous RC-gliders from scratch. His mode is over the top perfection. His favorite noun is Reynold’s number and he studies aerodynamics as a hobby.
Greg Norris (no picture) is an ok MM racer, also out
of the Azura MYC, who is also the US class secretary. He is an adequate modeler. He is into light, sturdy, fast and bright colored. He doesn’t spend much time with pretty or very cool, even less with complexity or perfection.
Note: All photographs are by Ralf Bohnenberger and Greg Norris.
In this article, we will show you how to build a sturdy, light-weight, fast Micro Magic, whether you have one of the old German racing MM kits or one of the new Asian Graupner SJ kits. For the rest of this article, we will refer to the old kit as v1 and the new one as v2. If you happen to have a v2 Carbon Edition kit, we will discuss that as well.
If you are going to build a Micro Magic, you will rather quickly note that the directions that come with the kit are not exactly what you had in mind, no matter what it was that you actually had in mind. Happily, the instructions seem to be slowly improving and there’s lots of other help:
Separately, there is a nice short piece on how to make a v2 boat class legal. Read this if you are interested, but both of our boats will be class legal and we will discuss and make all of the (minor) adjustments necessary to do this.
Lastly, we will build two fast, sturdy, simple boats, but we’ll have plenty of pictures of Ralf’s beautiful work if you are inclined to the really cool, as well as pictures of Jack’s artwork if you are artistic and like really slippery stuff.
Instead of giving supplier information throughout the article, there is a supplier list at the end of the article.
v1 and v2
One thing that we will not be discussing are the pros and cons of the various differences between v1s and v2s. You can read about that in Ralf’s link above, though I would stress that v2 MMs are steadily improving, and the kits that we are building now are a good bit nicer than the very early one he reviewed in his piece. The most important thing to know about the relative performance of v1s and v2s is that at the 2016 MM European Championship v2s won and came in 3rd, while a v1 came in second.
Right out of the box both kits look great. The v2 is of slightly thicker ABS than the v1, but more importantly, in places where the material is pulled thin by the mold (bow, bottom of the hull) the v2 feels noticeably sturdier. The weight of the hull, deck, keelbox, and hatch is 208 grams on the v2, 185 on the v1.
The bulkheads and strengtheners on the v2 are mostly ABS, plywood on the v1. And they used to come glued in place, but more recent versions have some plywood pieces and aren’t pre-glued. Just play that by ear. I’m really happy that the v2 kit seems to be under slow, steady continuous quality improvement! You’ll also note that we don’t use many of the strengtheners on either the v1 or v2. Actually, if Ralf had his way, we’d have used almost none of them.
The first step on the v2 is to drill the hull rudder post hole. It goes 210 mm from the aft edge of the keelbox, measured on the bottom side of the hull and centered with calipers. Remember that the ABS grabs drill bits badly, so start with a small bit and work up to the final size. Ralf says that you only need the rudder post reinforcements if you are an amateur. Well then call me an amateur. I used the bottom one, but agree that the top one is not important. There is no reason to drill the deck rudder post hole now. It’s easier later. Now glue the rudder post reinforcement in place. When dry, drill out the hole until the rudder post can be inserted easily. Then put the rudder post aside.
And it’s a great time to talk about glues: ABS to ABS you should use an acetone based glue. I screwed up and missed an early tip from Ralf to use Uhu Plast Special (hereafter “Plast”). Instead, I used Testor’s model cement and it was very much less “hot” than the European stuff that I’d used previously. For wood or brass to ABS, as well as for ABS to ABS when I couldn’t clamp well, I used a German epoxy not available for purchase in the US – Pattex Stabilit or Uhu Acrylit (hereafter “Stabilit”). It’s clamp time is about 10 minutes, which means that you can hold pieces in place while they are drying when clamping is hard. And the bonding of whatever to ABS is fabulous. Highly recommended. Just a reminder: be sure to rough up any surfaces being glued with 100 grit sandpaper, then clean them with naphtha (lighter fluid) prior to gluing.
V2 Carbon Edition Kit
And it’s also a great time to discuss the v2 Carbon Edition kit. These boats look really trick. They are transparent ABS with carbon fiber looking paint on the inside. Assembly is identical to the usual kits, except that you need to sand off the CF paint at all glue junctions. You’ll be thinking that this will screw up the look, but really it’s just a great opportunity for some really cool racing stripes.
Glue the keelbox together with Plast and clamp till dry as in the photo. Glue the mast ram reinforcements to the keelbox with Plast on
the v2, Stabilit on the v1.
Glue in the keel box with stabilit. Just hold it down and in place till the glue hardens. Be sure to get the stabilit under the little lip on the hull and cover lightly over the edges from above as shown.
Sail Servo Holder
If you’re building a v1, use the plywood sail servo holder provided, but cut away the plywood on the right intended to hold on a jib servo (which is not class legal). On the v2 you’ve likely got some choices. In my kit, I received a plywood servo holder and two plastic ones. All three were too flexible. I could have glued two of them together, but instead I just cut out a copy of the plywood one out of 1mm CF plate. Looks trick and is very light and stiff. (Be sure to wear a mask and eye protection when working with carbon fiber!)
Or you can copy Jack’s work of art (DSCN8268)
v2 style rudder servo plates (DSCN0102).
Rudder Servo Mount
The rudder servo mount on the v2 is really trick. If you’re building a v1, just make a copy of the v2 version out of 1 mm CF plate, a piece of thin plywood or some spare plastic (like an old credit card). I liked the CF one I made for the v1 so much that I made another for the v2. That was unnecessary though. The stock plastic one is fine. Since it was CF plate, I glued this on with Stabilit.
Concerning the bow reinforcement, you need to make a choice, but you can’t really make a mistake. Take a look at the diagram below. This is how Ralf fastens his jib boom to the deck. It is ultra-cool and saves a gram or two. Alternatively, you can just use a cotter pin glued to the deck as in photo x (No photo). Both methods work fine. But if you opt for the cotter pin, I think that it’s better to include the bow reinforcement, since
this gives a much greater area to glue the front of the deck to the hull so that the tension on the jib boom doesn’t separate the deck from the hull. Since both of these boats will sail out of the Azura MYC and all Azura rigs use the cotter pin method, we opted for this. But for most new builds I think that Ralf’s method is a better choice.
To the right are the deck layouts for the v1 and v2.
Hatch and Power Switch
Now glue in the little blocks to hold the hatch fasteners in place. Ralf doesn’t use them, he tapes his hatch in place. But he also uses a cool magnetic power switch for the hull electronics. I don’t bother a switch. (A 700 mAh battery will easily get you through half of the longest full race day without any switch at all. Just change batteries at lunch.) You decide.
I did use the transom braces. Actually, after I destroyed the v2 transom brace while trying to lighten it, I made a new one out of 1mm CF plate. I liked it so much that I made one for each boat. This is however unnecessary. The kit ones are fine. We did not use either of the big main bulkheads on either boat (more about that further down). You do not need the stern deck reinforcements. Glue a ~1.5mm cotter pin in place for the backstay using Stabilit and similarly glue your bracing and hook or your bracing and cotter pin in place for the jib boom attachment. The hook/cotter pin should be 176 mm from the center of hole for the mast. On the v2 ignore the dimple on the deck. It is in error.
If you’re planning to use the cotter pin method for the jib boom deck hook, the reinforcement for the little screw should be 65 mm in front of the center of the hole for the mast. You do not need to use the entire deck reinforcement piece for either method. You will not need side stays, so leave out the reinforcements, and indeed if there are any other reinforcements that we’ve failed to discuss, leave them out. Finally, varnish any wooden reinforcements with a single coat of varnish.
You will have noted that I glued some sponges in place. I think that it makes no sense to have water sloshing around the boat when sailing in heavy air. Also, I built a little two-walled house to catch the aft end of the battery slider. It is made of 2 pieces of 1mm CF plate and a roof of 0.3mm CF plate.
Glue the Deck
Now it’s time for the most exciting part of the build! We are going to glue the deck onto the hull. First, trial fit carefully. This is simple: you want the hole for the mast on the deck to snap into place in the keelbox. On a v1, this means that you’ll need to trim away a little of the flange in the bow, since otherwise the deck will sit about 2 millimeters too far forward. On the v2 the deck fits pretty well right from the start.
In Peter B’s build article, he uses a bunch of rubber bands as his clamps. I like masking tape better. Either way, be sure to practice mounting the deck to the hull about 5 times before actually using any glue. Also, be sure to cut all of your masking tape strips prior to gluing. I
used Stabilit at the keelbox/deck junction and if you used the cotter pin method for the jib boom attachment, use it at the bow reinforcement/ deck junction as well. Use Stabilit in the transom area for sure, but do this as a second step after the hull flange/deck junction is all done. I use Plast for the whole long hull flange to deck junction. Be sure to drill the holes in the deck for the mast ram as well as matching starter holes in the keel box. You will need these for clamping the deck to the keelbox when you glue the deck on.
So, now quickly apply a moderate (not thin) amount of Stabilit to the top of the keelbox (and if so planned, to the bow reinforcement) and a similarly moderate stripe of Plast to the whole long hull flange and to the bottom of the deck where the two will mate. Press everything together as previously practiced, then quickly apply all of your masking tape strips and screw the deck to the keelbox with the two little mast ram screws. I let it dry like this for 12 – 24 hours, deck side down to avoid drips.
Remove the tape. Check carefully that all areas are bonded well. It you find areas where the flange moves against the deck when you squeeze the hull together, fill these with Plast and allow to dry. Don’t use too much or you’ll melt the gunwale. After everything has been dry for a day or two, I apply a ring of thin CA glue all around the gunwale to assure that all is well glued. Ralf and Jack don’t bother with this, since their work is of higher quality initially.
After the gunwale has been dry for over 24 hours, glue the rear quarters and transom with Stabilit.
You will note that on the v1 that the hull sticks out about 1 mm
further than the transom. On the v2 it’s more like 3mm. Almost everyone sands the v1 flush. I have psychological issues with shortening waterlines, so I left the v1 step intact, tiny as it was. On our v2, the hull was about 3 mm longer than the transom. We left this in place. Think of it as a scale swimming platform.
Getting the rudder post exactly right used to be an adventure, but I’ve changed my ways. Put the keel fin in place. Don’t force it in! Rather sand it until it slides in easily but snuggly. Now insert the rudder into the lower deck hole, position it both carefully fore and aft and starboard port and mark where the rudder shaft contacts cockpit. Drill the hole for the rudder tube, insert the tube, and check if it’s perfect. It will be about half of the time. If it’s not, simply enlarge the top hole to about 10 mm. Take a 15 mm square piece of 0.3mmm CF plate or an old credit card, and drill the hole for the rudder tube. Position it exactly perfect, and glue in the plate with Stabilit. When dry then glue in the rudder tube, also with Stabilit. I got the v1 perfect the first time, and I needed the plate for the v2.
Sand & Paint
Now wet sand the hull with 400 grit, then 600 grit paper. If you’re like me, you’ll have a couple of glue drips. Carefully wet sand these away with 220 first, but be very cautious to not take too much hull with the glue. Getting the hull and fins very smooth is really important. RC-sailboats, because of their small sizes and lower speeds, keep laminar flow much longerthan full sized boat.
Now paint the boat with spray enamel and allow to dry for maybe a week. Then wet sand again with 400 and 600 grit paper, even 1200 or 1500 grit if you’re interested.
On to the keel fin and bulb and rudders
There’s not much to it, except that you need to work precisely. Most of the fastest boats use mark 1 fins and mark 2 bulbs. (Mark 1 refers to a now extinct version of MM and mark 2 is the same as a current v1.) You’ve got a mark 2 bulb already, but you’ll need to order the mark 1 fin. Currently Graupner USA does not (yet) carry these, so you’ll need to order one from Europe. Whether you plan to use a mark 1 or 2 fin, it is a good idea to use a mark 1 rudder.
First, weigh the keel fin and bulb together. You’ll want to be less than 415 grams. The maximum is 420 grams and you’ll add a little weight in construction. Now, measure the distance from the front tip
of the bulb to the front edge of the fin. Shoot for 26 mm. It has to be more than 25 mm. If you need to lengthen the slot in the bulb, this is easily done by drilling into the area you need to remove with a drill the same diameter as the slot. Then extend the slot using an xacto knife. Now, check that the maximum depth is correct. Shoot for 134 mm, the maximum being 135 mm (measured from where the fin exits the keelbox to the bottom of the bulb. If the bulb slot is all shiny and flat, roughen it a little with a file or some coarse sandpaper. If you need more depth, insert a toothpick into the slot below the fin. If yo
u are using a mark 1 fin in a v2, note that the v2’s keelbox is slightly shorter than the v1. You’ll need to trim a couple of millimeters off the top with an xacto knife and sand a little off of the aft edge of the keel insertion. You can use your own mark 2 fin as a guide for this.
(Not Available) File: DSC00628.jpg Caption: “Jack’s keel and rudder. Developmental work, but very pretty!”
Using a small hammer tap out any larger irregularities in the surface of the bulb. No need for perfection. Do not sand the lead bulb itself. Draw a line carefully from the forward to the aft bulb tip on the side of the bulb. You need a true perpendicular on the keel fin. This is not so simple. Watch a Micro Magic go up wind. It is actually slightly bow down.
Here’s how to get a perpendicular: Put a mark just above the round area at the bottom of the bow (see picture). Put the boat with the keel fin in place in the stand and carefully reposition the boat until the distance between the mark and the table and the bottom of the center of the transom and the table are exactly the same. Now draw a perpendicular on the fin using a right angle. Remove the fin. Put it into the slot on the bulb and measure the angle between the two lines with a protractor. Even though the two lines are not exactly in the same plane, it is easily possible to measure the angle within a degree or so. According to a previous Model Yachting Theory and Practice article, you are shooting for 87-90 degrees, but absolutely not less than 87 or greater than 90. Cocked way up or down is slow.
If your total keel weight (see above) was less than 410 grams and you extended the slot in the bulb to move the fin forward, buy some lead split shot as is used in fly fishing at your local fishing store and tack glue this in place in the excess slot with some thin CA glue. The last step is easy: glue the bulb to the fin with a little bit of Stabilit. No need for a jig, just hold the bulb to the fin at an 87 – 88 degree angle with your hands until the glue sets up (about 10 minutes). This sounds hard, but it’s as easy as can be. Next, fill the slot with Stabilit up to the top of the slot and allow to dry. Get some cheap, clear epoxy at the hardware store along with the cheapest little brush that you can find. Paint the bulb with the epoxy, including the bulb – fin junction and put the keel fin in a vice with the aft bulb tip pointed down. The excess will drip off of the bulb tip leaving you with a very smooth bulb with a sharp tip at the aft end. Let dry for a couple of days. Then wet sand the bulb with 220 grit until it is totally smooth and even. While you are at it, round the forward edge of the fin and the rudder a little. Both are way too sharp as they come in the kit. Fill any irregularities with modeler’s putty. Sand with 220 grit and very lightly spray with whatever color you plan on painting the keel. I suggest a very light color so that you can see attached weeds from a distance. The paint allows you to see irregularities better. Repeat the sanding and filling until all is perfect. I always plan on two iterations, but usually need three or four. Lastly, wet sand the keel and rudder with 400 grit, apply the finish coats, and after 3-4 days, wet sand with 400, 600, and if you want 1500 grit.
Install the servos. Not much new or fancy here. Obviously, bolt the sail servo onto the mounting plate and screw the plate onto the keelbox with wood screws. Screw in the rudder servo with wood screws. Otherwise, you’ll have future trouble replacing them. No need to mount the sail servo arm yet. Jack and Ralf both mount their receivers on the starboard forward area of the sail servo mounting plate. I mount mine on the port underside of the deck immediately adjacent to the keelbox. Likely not much difference here functionally, both methods seem markedly preferable to the usual method of sealing it in a pill bottle or plastic bag and then velcroing to the side of the boat. You’ll note that I used positive arms for rudder control. I had felt for a long time that the standard pull-pull system on stock v1s was actually preferable, being lighter and more gentle on the rudder servo. Jack agrees with this, as you’ll see i
n the pictures. But Ralf’s single arm method is really slick, and I used it in both boats. The main point is that the Z-spring makes it obvious when the rudder is hanging up, and you can look into it easily and promptly (even easier than the standard pull-pull system). Also, Mike Eades had reported frozen junctions on single arm systems blowing rudder servos. If you look carefully, I devised a simple no-freeze system. When you mount the rudder, check it out carefully with the transmitter and sail servo to assure that you’re getting unimpeded movement through the entire range of motion. This is really easy to see if you watch the rudder and the Z-spring together.
(Not Available) File: IMG_3276.jpg Caption: “Ralf’s boat doesn’t use a standard rear brace. Note the ABS rear strut braces instead. I did the same thing on the v1 and v2 except with 4mm CF tubing.
I was going to build one boat with an angled sail servo arm (in order to preferentially ease the main before the jib), but I ditched that when Dutch champion Elmer Boon scolded me to keep it simple, stupid. (See the great interview with Elmer elsewhere in this issue.) So, we’re running dead stock with the sail servo arms. You can get a little of the “let the main out first” geometry just by bringing the jib sheet block in a screw hole or two. That’s a marginal change, though.
To the rig
Since you have already joined the AMYA and sent in your boat registration to me, now is a good time to put the numbers on your sails.
Build the Mast
Then build your mast: Jack (Mr. Reynold’s Number) uses nothing but 5 mm masts. I have used both stock v1 five mm masts and Skyshark 2Ps (slightly more than 6 mm diameter). The v2 comes with a 6 mm mast with 4 mm extensions on each end. It was a good bit heavier than either the stock mark 1 or Skyshark masts, so I did not use it. I put a stock v1 five mm mast into the mark 2. I use tiny 1mm cotter-pins instead of the stock plastic piece for the jib-stay attachment and 2 pieces of 1mm CF rod for the mast crane. Jack modifies the stock plastic pieces to the point of unrecognizability. See the photos. Don’t cut the bottom of the mast for length yet, but do fashion a 6mm diameter shim for the bottom of the mast using either the stock aluminum tube that comes with the v1 or an old left-over piece of 6 mm mast. This should be cut to extend a mm or so above the top of the gooseneck.
(No photo) File: DSC00633.jpg Caption: “Jack’s gooseneck, strictly developmental, but very cool”
Goosenecks and Vangs
Jack built a work of art of more than questionable legality, but a work of art nonetheless. Actually, his boat is very much a developmental boat, he really isn’t very much concerned with legality. If you see him at a regional regatta, you will likely note that he’ll be racing the v1 boat that we’re building here, not his developmental boat pictured here. In the picture, you’ll note a stock VAM ball bearing gooseneck, an example of the typical Azura ball bearing goosenecks, and our best try of mocking up the gooseneck described by Elmer Boon in his article. Pick which you like best. The Azura design is from one of our ancient Keith Molen/Punta Gorda boats. The Azura gooseneck is made of a 20 by 52 mm piece of 0.40 mm (0.016”) aluminum plate bent around two sealed 6mm internal diameter bearings and glued with epoxy. Don’t forget the little cotter pin. This is used for the downhaul which leads to a piece of surgical tubing on the main boom. The boom a la Boon is a chopped-up stock gooseneck and glued to a piece of credit card or 0.3 mm CF plate. The idea here is that the boom stays in place for multiple rigs. Note the little hook on the downhaul for quick rig changes. Note that if you have the downhaul coming through the fixed piece of the gooseneck, you will need to trim it to the deck and if it goes on the boom side of the turning axis, it will need to be trimmed on the main boom.
I have always used 4mm job and main booms. Jack’s boat has them, too. VAM booms are made of Skyshark 2P. Elmer thinks that larger booms function as endplates. I am skeptical about this claim (not
that endplates aren’t a good idea), but willing to give this a try, hence the 6mm main and jib booms on the v2 boat. In my endeavor never to use any stock Graupner parts, I fashioned the main boom to gooseneck junctions from left-over servo arms. This works great and is easy. Ralf use stock jib boom counterweights, predictably, Jack uses a markedly modified one. I use custom ones made from 4mm brass rod. These look cool and are very quickly made with a dremel with a cutting disk and a drill press. For a 4 mm boom use a 32 mm piece of rod, and turn down a 10 mm piece at the end to 3 mm to insert into the boom. For a 6 mm boom, make a 10 mm shim out of some 5 mm CF tube and simply insert a 32 mm piece of 4 mm brass rod into it.
I use 20 lb. Spiderwire for everything except the jib boom to deck eye loop which is 80 lb. Spiderwire. Jack uses 20 lb. Spiderwire for some stuff and 5 lb. for the rest. (Note that this is not a typo.) Ralf fainted when he read that last sentence and hasn’t been heard from since. I hope that he is recovering well. I use 3mm internal diameter silicone tubing for 4 mm boom sliders, and 5mm silicone tubing for 6 mm boom sliders. Both Jack and Ralf use many more Graupner connectors, in Jack’s case always highly modified. Ralf likes little metal hook sliders made of piano wire for the tacks and clews. I tie mine out of Spiderwire hoping for more flexibility. I avoid bowsies like the plague in the wind stream, and when use the tiny stainless steel ones. I use 1 mm CF rod for my forestays. Ralf uses a more standard luff wire.
(No photo) DSC00669.jpg Caption: “Jack’s extremely developmental, but also extremely interesting rig.”
Lastly, note that both Jack and Ralf use trick outside adjusters for both the main and jib sheet. I use a simple internal bowsie on the jib sheet only. I adjust the main and jib together with the transmitter trim adjustment, and use the internal bowsie only to adjust the slot.
The stock v1 sails are fast, so I used them. The newer v2 sails are much improved from the original v2 sails, but the material is still quite heavy, so I used sailmaker sails on the v2. The simplest way to get the proper mast height is to tape the head of your mainsail ¼” below the bottom of the masthead crane and cut the mast such that you get about 1/8” of downhaul adjustment.
There are 3 good choices. You can use NiMh AAA 4 or 5 cell battery packs. These are ~700 mAh. The 4 cell pack weighs 51 grams, the 5 cell packs 64 grams. HobbyKing makes a really nice 700 mAh LiFe battery. It is 2 cell (2s) and weighs 55 grams. Since it has 2 cells, it requires balance charging, but this is not really a big deal after you get used to it. It is 6.6 volts. This is not too much for the servos. Lastly, if you have a boat which is over the 860 gram minimum weight, consider cell phone batteries from HobbyKing. These are single cell LiPOs, implying 3.7 volts and no balance charging. The 3.7 volts works fine with most receivers. They are 600 – 750 mAh, and almost magically they weigh only 15 – 20 grams. You do have to solder the connector wires on yourself and you have to know how to figure out which is the positive pole. (Both tasks are easy.) We use them routinely at Azura. We package them in little ziplocks and tape watertight with strapping tape. They do have the disadvantage that some of them swell with gas after 18 – 24 months. When this happens, they should no longer be used and they should be disposed of properly.
File: DSC00674.jpg Caption: 3 options for batteries. Note that some skippers also use 5 cell NiMh AAA packs.
(Not Available) File: DSC00686.jpg Caption: “Pumpkin is the v2. Just by chance, she weighs 860 grams on the head.”
That’s about it
All three of us wish you fun with your building and even more fun sailing your new Micro Magic! We really had a good time with this project, and we recommend it to all of you. The boats are fun to build and come out just great!
Servos – ServoCity, Graupner USA
Carbon Fiber Plate and Rod – HobbyKing, Midwest Carbon Fiber, Goodwinds Kites
Rudder Fasteners – Tower City
Rudder Fasteners – Tower City
Ball Bearings – Fast Eddy Bearings
Aluminum Sheet – Most hobby shops
Goosenecks – VAM
Silicone Tubing – Aquarium shops, Amazon
Piano Wire – Most hobby shops
Keel Fins and Rudders – Graupner.de, RC-Zeilen.nl
Goosenecks – VAM
European Glues – RC-Zeilen.nl, Conrad.de
Sails – Black Magick, Carr, Cat, Ken Bauser, VAM, Sirius
This article contains hints and ideas for building. This document was scanned from the magazine. It’s images are difficult to interpret. But, if used with the Graupner instructions the images become more understandable.