The MiniRaceWing build and FPV maiden

I’ve been championing the MiniRaceWing for a while now.  For those not familiar with the background, it started as a Kickstarter project for a new type of wing.  The basic premise was to use a mini-quad like carbon fiber centre section with wings that would detach in a crash to avoid any damage.  I made a video about it and backed the project as I thought it was something interesting, and I liked the idea that there were people trying to innovate in wing design.  Whilst the kickstarter didn’t reach it’s goal, the designers managed to find funding elsewhere to produce their plane and make it available to the public.

At last, it’s here.  Originally my wife was going to buy me a MiniRaceWing for my birthday (which is in May) lucky she didn’t in the end as I didn’t get a wing until July and she would have been fuming.  The reason she ended up not buying me the wing, is because I was kindly offered one to review – so I jumped at the chance.  Just to be clear though, although the wing was supplied free of charge for review, the rest of the gear, i.e all the electronics, I purchased myself.

Obviously, the first thing I did was make a YouTube video showing what had just arrived

Before moving on to the more serious business of how to put it together.  The first thing I did was take a good look at the kit provided.  We get a pair of wings, with pre-cut servo holes, some slots for wing spars, and if you notice two small holes close to the tip of the wing – this is to attach the winglets with two plastic button head screws.  The elevons are nicely shaped wedges made of balsa.

The rest of the kit contained the centre frame section pieces, which really are very close to what you might find in a mini-quad frame kit.  We also get some nice ball-joint linkages, camera mounts, a motor mount, decals, battery straps etc

I mentioned it in the “first look” video, but it’s worth reiterating.  The downloadable manual for the MiniRaceWing is quite outstanding (take a look at it here) so really it was now just a case of working through it.  First up was the wing assembly, starting with gluing in the carbon spars.  I did find that I immediately wanted to check something with Markus at MiniRaceWing though, as the manual says to use superglue on the spars, and usually superglue melts foam.  Not this foam though, sosuperglue it was.  I stuck the spars in and let them dry.

Next up was attaching the elevons to the wings. Just lining them up against the wing, I noticed that they come out a little further than the wing tip.

So I did what the manual suggested, and sanded away a little of the elevons until they were flush with the wing tips.

Clearly, I couldn’t put plain wooden coloured elevons onto a new, super-whizzy plane though.  As some of the decals had a red theme running through them, I located some red spray paint in my garage and started spraying the elevons a nice bright red colour.  This didn’t last long because after half a coat on one elevon, the paint can coughed up some splats of paint and decided it was empty.

Needing something that would cover up this small splash of red, I decided to go with black instead.  Black goes with everything doesn’t it ?  The manual, again, has an excellent section about how to attach the elevons to the wing using tape.  Now, I’ve been attaching control surfaces to wings for ages with tape, but as far as my method goes I’d kind of developed my own way through a bit of trial and error,  so it was interesting to see how it’s done “properly”.  They certainly felt secure.  I used some extra tape to wrap over the elevon as a means of protecting it as well.

Control horn mounting was the next task, and this time the manual is pretty critical.  That’s because it has some templates to cut out.  You put them over each elevon which gives you a reference for where the control horn needs to go.  I used a knife to score a line through the template and into the elevon.

Next, I used a small hand drill with a 1mm bit to make several holes across the score line.

Before using the knife once again to turn those holes into a single slot

Finally, the control horn was pushed into the slot, and secured in place with superglue.

Getting the servos installed and the control rods in was the next order of the day.  I’m using my old favorite in terms of servos, the Tower Pro MG90S.  An inexpensive metal geared small servo with a good torque.  I’ve used these in several models now and they are holding up very well.  There was a minor change to make to the wings here though, as when the servo was held over the pre-cut hole, the bottom of the servo extended down further than the hole.  The was easily resolved by just cutting a few mm more of foam out.

I really like the use of the ball joint in the linkages, they have a far better range of movement than using  clevis or a z-bend and are very easy to remove and adjust if needed.  The kit came with two push rods, threaded at one of the ends.  These needed to be cut to 75mm.

One of the ball joints is glued onto the non-threaded end, whilst the other one is screwed into the thread until the surface is completely neutral with the servo in it’s centre position (I plugged the servo into a servo tester to make sure I had it’s centre position).  The manual is very specific about using the 3rd hole on the servo arm, or 9mm from the servo arm axis.  This is lower than I’d generally use – my default position is to go with a lot of movement and use dual rates to tune that down if needed.  I followed the instructions for this build though.  Only when you have this linkage perfect should you go ahead and glue the servo in place.

The servo cable then runs down the pre-cut slot, although this is a tight squeeze, so is worth running a screwdriver (or something similar) down the slot so it’s easier to push the servo cable in place.  You need between 1cm-3cm of servo lead hanging out the end of the wing to join with the centre frame.  Mine was pretty short at 1cm, but within the limits.

The winglets are the next thing to fit.  This is a pretty quick operation, but the holes the screws go through don’t penetrate fully through the wings, so do need to be opened up.  I just poked them through with a screwdriver.  The winglets attach nice and tightly with minimal fuss.

The manual advised reinforcing some of the wing with clear tape.  The leading edge, servo wire slot, and the back of the wing where it joins to the frame.  I’m using clear duck tape, which sticks to the foam well, and is very strong.

I put the decals on next.  This took a bit of work as I had to cut some away to fit around the servos and the control horns.  I also noticed that since I’d tightened up the screws holding the ball joints in place, the nut or screw could hit the foam at their maximum extents, so I cut a little wedge of foam out in order to allow the servos to move freely without any resistance.

With the two wings completed, I turned my attention to the central fuselage.  Truth be told, I’d actually put this together before even looking at the wings, as I wanted to see how the parts all come together.  It was just like putting a quad frame together, aside from the addition of the c-clamps below the fuse that hold the wings in place, and allow them to release in a crash.  It’s worth noting, that all the screws provided use a torx T10 screw head.  You’ll find them in most screw driver sets these days, but if you don’t have any, you’ll need one.

Here’s a quick rundown of what gear I decided to put into the fuselage, and the reasons I’ve chosen those.  First up the power setup.  According to the power setup suggestings on the MiniRaceWing page the fastest setup recommended was to use a T-Motor F80 2500kv Motor.  On a 4s lipo, this should propel the wing at around 200kph.  MiniRaceWing sell the Motor and prop setup here, but were out of stock when I wanted to order.  So I bought the T-Motor, along with 3 Groupner 5×5 Cam speed props from electricwingman.com.  Everyone seemed to be out of the 8mm to 5mm reducer inserts though, but Markus managed to find one to send me in the kit.

I would need a 60A ESC to run this motor on 4s – which I intended to do, although I was happy to run it on 3s as well.  So I bought a HobbyWing Skywalker 60A ESC, as I’d used the 50A version previously in my Mini Talon and it performed well.  The 5A UBEC should also have no issues with running the 2 servos and powering the HD camera I intended to mount.

For the receiver, I chose a FrSky X4R-SB.  Of course, I didn’t need the SBUS version of the receiver, but I already had some, and it would cover the 3 channels I needed as well as supply 5v to my HD camera.

This wing was going to be flown raw, or as we sometimes call it “naked FPV”… but that conjures up some scary images.  All I mean by this is that I wouldn’t be using any type of autopilot,  stabilization, or OSD.  It would be useful to know the state of my lipo voltage in flight though, so I choose the excellent RunCam Swift 2 as my FPV camera.  Aside from giving a superb live image, it has it’s own OSD to display your battery voltage, although you obviously need to wire this to the battery for this function.

I chose the AKK-Tech K33 as my VTX.  The main reason behind this was that I would output 5v to power the camera and so make cabling more straightforward.  I  could position it inside the fuselage and still see the display which tells me the band and channel, and the buttons to set each are on the side – so very accessible.  It’s a 600mw VTX as well, so should give far more range than I’ll actually need.  I matched this up with the AKK-Tech LR2 Skew Planar antenna which I’d used previously and found it to perform very well.  The fuselage had a hole to mount the skew through, so I used an SMA pigtail I had in my spares box so I could position the VTX where I wanted it and use the appropriate antenna hole.  It wasn’t perfect as I had an SMA to SMA pigtail, and the VTX was RP-SMA, so I used an adapter to make everything compatible.

For the HD camera, I used my Firefly Q6, as it’s fairly low profile and handles 1080p at 60fps well.  It’s internal battery is terrible though, so I would be using it’s live out cable, but just for attaching the 5v/ground lines so I knew it would stay powered up.

As far as lipos went, I had a lot of 2200 3s’s around, and also bought a few Zippy 1800 4s lipos which are practically identical in size and weight to the 2200’s.  I took all my gear and attempted to lay it out in the fuselage to see how it would fit.

I next set about making up the cables I’d need to connect everything together.  I had a lot several different ideas about how to cable up.  The first was to go minimal, shortening every cable to length, solding everything in place (instead of using connectors) and going through the frame for the neatest effect.  However, given that one of the selling points of the wing was the ease that you could change your layout, and replace gear I went in the opposite direction –  making sure I had enough wire to move components and giving everything a connector so I could easily remove/replace things.  It meant that some wires would go around the frame instead of through it, but it offered more flexibility.

This is the wiring harness for the VTX and camera.  The VTX will be powered from the JST connector, and as mentioned, will supply a regulated 5v output to the camera, so we join the 5v, ground and video lines from the VTX to the camera.  The extra thing I’ve done is use the smallest bullet connector I could find and attach it to the blue wire from the camera.  This will connect to the main battery to give the on screen voltage.

On the ESC side of things, I’ve attached an XT60 connector to attach the lipo, but also soldered in a JST connector (to connect to the VTX) and another tiny bullet connector on a length of wire to connect to the camera.  I’ve cut the motor and ESC wires to the right length and attached 3.5mm bullet connectors.  There’s enough length here so that the motor can move in and out of the fuselage in it’s mount.

Before connecting up the fuselage pieces, this is how everything lays out.  There’s actually a mistake made on the top plate, but we’ll come back to that later.  You can see in this picture how the SMA pigtail attaches to the VTX and comes out of the top of the frame.  You’ll also see small servo extensions connected to the receiver.  These will connect to the servos in the wings, but also cable tie on to the posts to act as strain relief if the wings release – stopping any pull on the wire transferring through to the receiver.  Also connecting to the receiver is the USB live out cable for the Firefly Q6.  In this case, I’ve removed the signal (video) wire as I’m just using it to supply the camera with power.

After putting the fuselage together we get this.  It’s not a particularly neat looking job, as I’d deliberately left myself extra cable to move things around, but it’s easily tucked away so it doesn’t cause an issue.  I’ve used the normal mini-quad method of using a combination of cable ties and heat shrink in order to get my receiver antennas up and away from the fuselage.

Here’s a close up of how we use the posts for strain relief if the wings need to detach.  This took a little while to get right, mainly because the amount of servo wire I had at the end of the wing was very small.  This meant I needed to experiment with the position of the extensions so I could attach them to the servo wires in the wing and being able to fold them into the frame neatly.

After slotting the wings into the C-clamps under the fuselage and tightening the screws, the wing is ready to fly.  Well, almost.  I did a few more obvious things – making sure the electronics all worked and no magic smoke was released.  I also set the failsafe on the receiver and made sure WDR was activated on the camera.

What took the longest was getting the CG right.  This is 135mm from the leading edge of the wing.  I found that in the initial positions for attaching the C-clamp wing holders to the fuse, my setup was coming up tail heavy.  However, this, like the rest of the plane, is customizable.  I moved each of the C-clamps back one position which moved the wings backward and so shifted the CG forwards more.  This just about balanced out – I say just about as I found there wasn’t a place on the wing where it would perfectly balance on my fingers, it would tend to fall forward or backwards.

I must admit that not quite knowing if I had hit the CG left me feeling a bit nervous, so I was happy that my friend Neil was able to come and help with the maiden attempt.  This flight, of course, had a YouTube video to go with it.

So things started well, and then went wrong.  This is mainly the fault of the mistake I mentioned before on the top plate… of course at the time I didn’t realise it.  The press nuts were meant protruding through the top of the plate.  Although I had the screws in tight so the motor mount couldn’t move, there was obviously some give in this orientation and so two of the screws came out mid-flight, taking out the prop and making a small hole in the wing.

It only took about 10 minutes to remove the top plate, flip it over and reinstall all the equipment.  Here’s what it looks like in it’s correct orientation, although it should be noted I’m missing two of the screws (on order as I write this)

So, at this point in time, I can’t give my final conclusions on the wing, as it needs to be flown properly, and more aggressively (faster !)  What I can say so far, is having needed to reconfigure things several times, the central fuselage pieces make this very easy.  The wings come off and reattach easily for storage (I haven’t seen if they pop off well in a crash yet !).  The flight characteristics so far are excellent, with the wing handling particularly blustery conditions very well and feeling extremely locked in.  I didn’t touch a single trim tab on the maiden, it just went where I pointed it.  All in all, I’m very impressed so far, and I’m looking forward to getting back out and really putting it through its paces.

Thanks once again to Markus for supplying me with a review model.  You can pick up your own wing at www.miniracewing.com

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