14 Jun 2012

This is a review/guide I did of this fantastic RC Aircraft, the Multiplex Twinstar II electric I had built several years ago.  Its a fantastic model to fly, made of foam and fairly indestructible.  The standard kit comes with regular electric motors and nicad batteries.  For my build I upped things a bit and went brushless and Lipo (lithium polymer).  I also have some newer FPV keychain HD 720p video which you can view by clicking here.

Twinstar II Specs

 

Wingspan 1020 mm 56"
Fuselage Length 1085 mm 43"
Wing area approximation 43 dm2 4.7 sq. ft
Weight Approx (on stock motors/nicads) 1500 g 53 oz
Wing Loading 35 g / dm2 11.5 oz/sq. ft
Power System (stock) 2 x Permax 400 6v  
Receiver Power Supply Through BEC  
RC Functions Aileron, Elevator, Rudder, Throttle  

Twinstar II Manual
Twinstar WebSite

 Requirements

  1. Base Kit (MPUM214210), Price $99 shipped, includes the plane, two speed 400 brushed motors and a brushed ESC (not used in this guide), control rods, etc
  2. Two Brushless Motors (See Brushless Guide for help on deciding which size would be adequate)
  3. Two Brushless ESCs rated slightly above the max amps of the motor, in our case we chose ThunderBird 18s by Castle Creations
  4. Fine tip (1/8") Soldering Iron (30 watt) and some solder
  5. Hot Glue gun (Low temperature) and glue
  6. Four HS-81 Micro Servos, Price $62 shipped
  7. Micro Receiver (Dual Conversion best), in my case a 72mhz 6 channel was $60 shipped
  8. Medium Viscosity CA Glue (the type that doesnt say foam safe on the label) and Kicker/Accelerant
  9. Long thin wire for threading the Rx antenna (in our case we had some Copper wire for the job)
  10. Lithium Polymer Battery Pack (Lipos), See the Lipos/Charger guide;
  11. Lipo capable charger (and Balancer if not built in)
  12. Lipo fire safe device for charging the batteries when indoors
  13. Power Supply of some kind for powering the Lipo Charger (if using a CellPro 4s, it does not have an AC plug, so a Regulated Power Supply or Battery Jump Start device can be used if not connecting to a car battery)  See the Power Supply Guide for more information
  14. Hobby Knife
  15. 16 gauge wire (if using the Castle ThunderBird 18 escs)
  16. Two 3" Futaba J style extensions
  17. Three 6" Futaba J style extensions
  18. Two 12" Futaba J style extensions
  19. Deans Connectors for the Y cable (Two Female, One male, plus heatshrink)
  20. Deans connectors for the Battery Extension cables on the ESC (two male)
  21. Deans connector for the Lipo Battery (Female)
  22. Krylon Spray Paint for painting the body (if desired) or Acrylic Paint
  23. Magic Marker for drawing in the windows if preferred over Paint
  24. 4 or more channel Radio Transmitter (Mine Futaba 6XA PCM/PPM 72 MHz)
  25. Two Propellers (8x4e or 7x5e), in our Case 8x4e by APC
  26. Y harness for the throttle lead from the ESC (if not using 2 channel throttle)

Specific Equipment

  1. RipMax Xtra 2829/10 (TWO): 1210KV, 10 Turns, Max current of 15 amps, Price: ~$65 shipped (for two)
  2. ThunderBird 18 ESC(TWO): 18 amps, 3 amps BEC (can run both ESCs at same time without disabling one BEC with any Castle brand ESC), Price: $50 shipped (two)
  3. APC 8x4e Prop (model LP08040E), Price: $14 shipped (for two)
  4. Cell Pro 4S Balancing Charger: Up to 3 amps/1C, can use adapters for brands like E-Flite, Great Plains, ThunderPower/PolyQuest/CommonsenseRC etc, Price $60 shipped
  5. CellPro 4S Extension Cable(To make it possible to charge the batteries in the firebox while charger is outside of the box), $7 shipped
  6. CellPro Revolution Lipo Battery Pack Model CP-3200-3S-N, 3s 3200mah 11.1v, 20C, 9.2oz, 0.767 inches thick x 5.31 inches long x 1.77" wide; 500 Cycle lifetime (at 1C or less) or an equivalent such as the Venom, Price:  $47 shipped

Optional

1.  Wattmeter  (AstroFlight Super WhattMeter or similar)
2.  Prop Balancer  **Even simple $5 finger balancers work well on wood blocks
3.  Temperature Gauge  (DuraTrax Temperature gauge or similar
4.  Scale  (5- 11lb Digital scale/a> or similar)

  Assembly Part 1

First check your kit to make sure the contents are all there.

Main kit contents, plus some of the other required items


Fuselage and Tail Panels

You can safely ignore the manual, where it recommends cutting the control snakes and tubes, as it seems this was already done, at least in our kit.  Next we install the Elevator and Rudder tubes (sleeves).  Make sure these are glued along their full length to give stiffness to the aircraft.  Then feed the control rods through the tubes.  **Note that we don't connect the control rods to any of their surfaces, simply get them close for now, as we cant set the "center position" with battery and TX turned on just yet (last few steps).  Note the basic positioning of the ends of each rod/sleeve in Fig. 2

Figure2:

Assembly Part 2

Installation of the Wing retainer screw plates is next.  You simply glue these together using the CA glue (spray activator on one side, wait 2 minutes then put CA on the other side and join, they will bond instantly with the activator).  We then mount these plates in the shell #4.  (Fig. 5)

Fig 5:  Screw plates

 Canopy Latch System

Now we install the canopy latches (See Figure 6), so that the latch tongues (Figure 6) can be engaged between the latches and the fuselage sides.  Spray activator in the latch recesses in the fuselage, then apply thick CA to the joints of the latches and place them immediately.  Use more glue later on if needed.  You can also glue the canopy tongue inserts into the canopy as shown below.  Be sure to push these in as far as possible.

Figure 6:  Canopy Latches and Tongues

**Time saver:  Note the position of the tongues in the photo.. if not exactly like this, the canopy wont likely close and stay closed.. this is very important, otherwise you'll find yourself gouging out foam to make room for Velcro or magnets (warning, do not use magnets near a camera system).  Note it was painted in this photo, I found out in the end the tongues didnt quite work, so I had to pull them out and realign them.

 Assembly Part 3

Installing the servos

Next up is putting the servo's in the fuselage.  Only install the servo's with glue, if you either know the neutral position already (you've already hooked up a battery and found the neutral position by first turning on the transmitter, then the battery/receiver with servos plugged in;  IE:  always turn on the TX first before plugging in the battery!).

I went ahead and put the servos in the fuselage, as its easy to remove the screw later on and adjust them for center once the battery is in place and working with the receiver.  Be sure to use Hot Glue for this step.  Apply the hot glue to the screw hole areas on the servo.  You can add more glue to the general area around the servo later on if you feel there is not enough.  See Fig 7 for all the photos.

Fusing the Fuselage shells

Do a practice run of joining the two shells.  Make sure they fit closely, do any trimming if needed.

Take the aerial/receiver antenna sleeve and line it up in the recess at the bottom of the right hand fuselage.  Glue this one on as you did for the others before.

TIP:  **If you join them together and notice that the wing fastener screw plate or plate holes don't perfectly align with the foam holes, don't panic, you can still work the screw in later on

Once you are sure everything lines up.. Spray activator into the recessed holes in the left shell, then apply thick CA to the joints on the other shell and join.

TIP:  **You can either then immediately apply the CA, thickly, to the raised join surfaces on the other shell and join before waiting 2 minutes, giving you more time to align things, or simply don't use activator on the other surface, but if you don't you'll have to make sure the shells stay firmly together till the CA begins to cure!  Make sure the fuselage is a straight line too.

 

Fig 7:  Servos and the joined shells after gluing


Attaching the horn on the rudder

Now take the push rod connector and put it in the outer whole of the rudder horn and secure with the washer and nut.

TIME SAVER:  **Make sure the connector can revolve smoothly, but doesn't wobble, if it doesn't revolve you will have servo groaning and push rod binding later on!

Orientation is very important here.  Look at Figure 8 for proper orientation.  The instructions say to add CA after you have the nut secure, but don't do this right now, because if you need to move the connector to a different whole to give you more throw later on, you wont be able to.  Wait until you have everything secured and trimmed out on the ground before adding the drop of CA

Screw the Grubcrew into the push rod connector with the supplied allen key.  Make sure this is tight.

Apply activator to the horn recess on the rudder then apply the CA to the horn and place on the rudder with the holes at the leading edge facing the hinge pivot line as in Figure 8.

Figure 8:  Rudder/Aileron Horn assembly

Note:  I didn't include a photo of the elevator control horn, but it can be seen in the Assembly of the Tail Section Figure.  The same hole positioning is used for the other horn controls, just repeat the procedure noting the position (Aileron one should have the connector facing inward toward the fuselage, same for the control rod).

Time Saver:  Be sure to flex all control surface hinges until moving smoothly, if you don't do this enough, it will cause binding in the servo's later on.

Assembly Part 4

Tail Section

At this point we do a dry run of pushing the tail section into its place.  See if it fits ok, trim / adjust as needed.  We want to make sure it fits snugly and is parallel to the wing saddle at the front of the fuselage.  The fit must set exactly 90 degrees to the tailplane.  Don't use activator here, as it will set too quickly.  The fit is usually snug enough to not need the activator.  See Figure 9 for the after photo.

Figure 9:

Motor and ESC installation and Tips

Now we get to the installation of the Xtra 2829/10 motors and the Thunderbird 18 ESCs.  See Figure 10 for photos.  We will use the original brackets meant for the stock motors, combined with the screws from this kit.  Orientation of the motors in the nacelles is very important.  It is very difficult and causes issues if you try to run the wires on the underside of the motor mounts, therefore look at the pictures below for proper positioning.

I did the soldering of the wires from the motor to the ESC before putting the motor inside the nacelle.

Figure 10:

Wiring and the Y deans cable

As you can see from the last photo, I've chosen to go ahead and use the bullet style connectors that came with the brushless motors.  This will make it easier to swap motors out if needed.  Try to strip back only at most about 1/4" of wire before soldering on the connectors.  You can basically heat up the connector where they go together, causing the solder to pool up in the little cup and then attach the wire.  The bullet ends go on the the battery wires coming off of the ESC.

In order to connect the two ESCS to the battery, it will be necessary to make a Y cable or adapter for the two sets of wires.  In this case its  a deans cable with male on the single end, for connecting to the battery deans and then two sets of male deans on the other end.  I used matching 26 gauge wire obtained from the local auto shop for the deans cable (same gauge that comes with the ESC).

Note that I used about 9" of this wire to make each ESC battery deans "end" for each ESC (figure 11).  It has been suggested that the total battery to ESC wire length not exceed 12 inches.  This can also go beyond 12 inches by using resistors or higher gauge wire.  In our application, combined with the actual Y cable, the length becomes more like 16" or so, but in testing it works fine, so we didn't worry about shortening the length.  The same rules apply with soldering on the wires to the deans connectors, I left about 1/4" wire bare, soldered that wire first (pre-tin), then using either a set of plyers or a vice grip (because the deans connector gets very hot) I then soldered the wire onto the appropriate positive and negative locations per Figure 11.

TIP:  Be sure to use heat shrink on all soldered connections, you can obtain this from your local hobby shop or radio shack.  I also used some black electrical tape to make the bond even more secure.

Figure 11:

Gluing the motor mounts and tidying up the wires in the nacelle/wing section

We then move onto putting the motors and the mounts in the nacelles.  Here we can use activator fairly easily, note the final position of the motor and prop/nut once glued (This position may vary, but balancing will be a little different) See Figure 12  Note:  It was necessary to cut away at some of the foam in the nacelle so the whole length of the motor mount would fit.  We also cut some of the foam where the ESC fits in and also applied some CA to ensure the ESC and the wires don't come loose, this included CA'ing the motor wires (via the electrical tape around them).  You can also see how we ran the wires in the wing panel and applied CA or hot glue in spots to secure those wires, leaving room for the wing insert.

In Figure 12 you can also see the wing spar cover after its been glued.  I did not glue it via the instructions, I simply inserted the cover (after first etching out most of the spar covers extra foam, to fit the cover snugly with the wires below) then applied glue and accelerant in the cracks.  This worked well and there were no overly raised edges, it was nearly perfectly flush.

Figure 12:

Assembly Part 5

Wing wiring organization

As you can see from Figure 13, I ended up organizing the wires a little better.  I also added 6" servo extension wires to the receiver to avoid the stress of disconnecting the receiver connectors when I remove the wing.  I also labeled where the connectors come together so I'll remember which pairs go with which connectors.

Figure 13:

Electrifly Ultra E-tote and a custom Lipo charging box

In Figure 14 you can see images of the tote I decided to go with.  This unit will hold two chargers.  Its designed for the TritonJR, but I am using a CellPro 4s with a 3foot extension cable for charging in a box outside of the tote.  I simply velcroed the CellPro onto the box.  It will hold two batteries, possibly one large one and maybe one small 7amp hour battery and a power supply unit as well.  It has easy connectors which take banana plugs for charging.  Keep in mind if you are using a standard 600mah charger from Tower, this can eventually ruin the battery (many seem to think its fine to leave continuously charging but this isnt the case).  Instead I went with the Harbor Freight float charger, which shuts off when fully charged.  It supports batteries ranging from 5amp hour to 125 amp hours.  I also used the drawer as a charging drawer, by adding 600 degree furnace tape ($7).  I had to make a custom fit lid for the box out of a piece of balsa (also added some 3M spray to harden it up a bit).  With the box, I also cut another hole on the other side to make it easy to route the charging cable through the box to the outside and allow more ventilation.

I should also mention that you will probably only get one good charge from the battery (if using a standard lead calcium battery) at the field.  You would be much better off with something 3x the capacity to get at least 3 or more charges in at the field (and it would not fit in the tote and be about 25 lbs too).  At home I acquired a 19amp PSU from online for a reasonable price of $43 shipped (from someone in one of the forums).  You can also make your own PSU from an old PSU from a computer, but there is some work involved.  You could also just directly connect your charger to the car battery, but be careful and let the car run between charges.  Another option is to get a cigarette lighter adapter to bare wires type setup, where you can run extra feet of wire using say 14 or 16 gauge wire, on the other end you would put connectors to attach to the banana leads coming off your charger on the tote.  Note: this method probably only provides about 10-15 amp ability, still more than enough for even 2 or 3 chargers at once, if you want to go that far.

Figure 14:

Final Pre-Paint Photo


Assembly Part 6

Painting and Transport Tips

This step is optional, as you can fly with the plane the way it is or add decals as well.  I chose to add paint to make it easier to see.  Keep in mind, this will add between 1.5 and 2 ounces of weight though.  I used basic masking tape (though painters tape would work well too) to tape off the areas I didnt want to have paint.  I first sprayed the black Krylon spray on the bottom of the wing, then applied the yellow Krylon to the top section of the wing.  This resulted in drippings on each side of the opposite color, which was a little annoying but fixable.  I ended up using the Acrylic paint which I got from Michaels for most of the work, in fact, i'd recommend you just use the Acrylic, it may even hold up better than the spray.  I had to cover over the yellow Krylon since the two yellows weren't an exact match, which probably added some extra weight.  I used a small paint brush for the delicate areas and a marker to do the windows and door.

The other thing I did, which may seem cheesy, but is very effective, is use the box it came with for transport with a few mods.  I taped off the back section of the box and cut a slit for the tail to stick up through, I left a flap on the second half of the box for inserting and removing the parts and added some packing material between pieces.  I also had a spare transmitter strap which I was able to attach to the middle of the box to allow the box to be "thrown over the shoulder" during transport.

Figure 15

Performance-Stats and Final Thoughts

Initial flight

Before painting, I did take a test flight, see the video for it here.  Initially it was a bit bumpy, almost going straight up from take off.  I had to trim out the elevator (on the elevator itself, though I trimmed it out on the transmitter at first) to make a more level flight at 50% throttle.  I should mention that you, of course, have to balance the plane at the 85mm from the wing leading edge at the "root".  I marked both sides of the fuselage then extrapolated that down to the bottom of the plane drawing a line there (its just behind the leading edge of the wing).  With my 3200mah 9.2oz or so pack, I have the pack velcroed to the side of the fuselage and the position of the main square of the pack ends at about the midpoint of the two servos in the fuselage.

Balancing of the Props

Using the finger balancer or any other balancer, you should also balance the props.  The key to balancing is making sure it swings to the same position each time (not necessarily level position).  If it doesn't balance, use sandpaper to sand down the heavy side or add nail polish to the side that is lighter.

Servo Groan

You will want to eliminate any servo groan prior to flight.  What this means is when the plane is sitting idle, you should not hear the servos.  You should also not hear them groan when you reach your maximum positions with the sticks.  If you do, try several things:  Flexing the control surfaces (the foam), make sure there is no binding on the control rods (ie: bent rods), etc.

Actual Performance Stats

I purchased the Astro Flight meter to test out the performance.  Keep in mind it doesnt come with deans connectors, so you must put your own on, pay close attention to which side has the male and female connectors.  If you have this reversed the readings will not be correct!

My Stats

7x5e:  19.20 amps, 222 watts, 11.55 volts
8x4e:  23.4 amps, 267 watts, 11.48v  (without props, 2.63 amps, 12.33v, 32 watts)
No load:  0.14 amps (with one servo groaning this becomes 0.26 amps)
RPMS:  8x4:  8222 x 2 or about 16,444 combined (initial test), ~19,000 (final config)

Thrust test (standing nose down on kitchen scale)  Roughly 49oz

AUW (no paint):  44.2 oz (with tape on the bottom to protect the plane during landings)
AUW (paint):       45.2 oz (with tape on the bottom)

Flight times:  15 minutes without continually pushing the limits (say 40% aerobatic), probably could max to 20 mins

Vertical ability:  On a fresh battery nearly straight up, so say around 89% of vertical or near vertical for maybe 100 feet     or more before stalling.

Final Thoughts

After having just a few Zagi electrics for years, I must say this plane is very easy to fly.  You become better at making shorter and shorter landings (distance wise it takes some room at first to land, until you become better at it or add some weight to the plane to bring it down quicker).  I chose to stick with the 8x4 prop.  I will eventually be adding 900mhz video equipment to the plane, adding around 4oz of weight (Stay tuned for that guide as well).  This plane should handle the extra load with ease, with this brushless setup.

You can also add wheels to the plane if you want.  There are many ways to do it, most of them if doing it directly, involve attaching plywood plates to the bottom of the fuselage for support.  Another method is to make a frame from tubing at a hardware store and use rubber bands to attach the whole thing to the plane (makes for easy removal in situations where wheels aren't desired)

As far as aerobatics go, this plane did very well for the type of plane it is.  I was able to make very tight loops and some rapid barrel rolls among others with ease.

PROS

  • Fairly easy to build
  • Very good performance from the Xtra motors
  • Easy to fly
  • Ideal for a camera setup, with the props on each side and out of view

CONS

  • A bit pricey for this brushless setup and the whole deal
  • Directions aren't always exactly the best route to take, you must improvise (minor)

Poor                     
Average
Very good
Excellent

                  Ratings
Packaging/Materials
Manual
Ease of Assembly 1/2
Takeoff
Landings
General Flight 1/2
Aerobatics 1/2

            Total:  1/2

Videos

Video version of this how to guide

Maiden Flight from 2007


Use this QR code in a QR reader application on mobile to open quickly on a mobile device

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