Magnus Electric Build Thread

[Lothar]

Flap and aileron wiring harnesses.

I will glue in the fuselage side male 6 way Multiplex connectors, and leave the wing sides floating. I don't like the idea of hard mounting both sides. the fuselage side is a very snug fit. I will have to open the wing side openings slightly.

 

[Lothar]

Mounting the tailplane:

The elevator horn epoxy has cured, so I have fitted the tailplane. I had to grind down the ridge in the elevator saddle with a Dremel, caused by the two fuselage halves being joined. I had planned to only attach the tailplane with the two screws, but the one screw thread seems to be stripped, so I have run a small bead of Clear Gorilla Glue around the fuselage to tailplane joins, to provide a bit more support. I don't plan to DS, so that should be sufficient.



I have also made some 'el cheapo' wing bags from a foil windscreen sunshade and packing and gaffer tape. I use a folded piece of heavy duty packing tape to join the wing bag halves on the inside. I then add an external piece of gaffer tape folded over the outside of the mating pieces. The inside tape avoids the wings snagging on any exposed bits of gaffer tape. Finally I add bits of velcro to assist in keeping them in place.

 

[Konrad]

Can I ask why you didn't repair the threads, composite build up/insert or just move up a thread size?

Gorilla Glue is an American brand, I assume you mean a clear polyurethane adhesives. Why the polyurethane adhesives and not epoxy? Does the polyurethane adhesives have some beneficial property that I may not be taking into account when bonding the tail plane.

 

[Lothar]

I don’t think there is room to increase the thread size to M4. If I can find a slim M3 brass threaded insert I will use that.

I like the Clear Gorilla Glue, is is strong but not brittle. I thought that a tiny bead of epoxy bonded to the paint might pop loose if the stab is knocked.

 

[Konrad]

Thank you. I'm always trying to learn how others are thinking.

 

[Lothar]

I just made a pleasant discovery - there was a blob of resin inside the tail of the fuselage preventing the short screw from engaging with the rearmost thread in the stab. I used a round needle file to remove it, and the screw is now securely in place. This is quite tricky because the stainless steel screws supplied are non-magnetic, making it difficult to balance the screw on the screwdriver while inserting it at the correct upward angle to find the thread.

 

[Lothar]

Trial CG balance:

The following equipment is temporarily installed:
1. Typhoon 4W-25 motor.
2. Aloft spinner with 4mm collet, and Aeronaut 9x7 blades.
3. Hobbywing Platinum 60A ESC - front of ESC is 40mm back from the front of the canopy opening.
4. Frsky SR8 rx with wing wiring, pushed all the way back in the fuselage (to just in front of the elevator servo well).
5. 4 x BMS-115HV servos taped into the wing pockets, with wiring harness inside the wing. These will be replaced by thinner servos with IDS drives, watch this space.
6. BMS-127WV in the elevator position.
7. Elevator pushrod with clevises in place.
8. CG markers (short pieces of skewer) taped into place underneath the wing at 79mm from the leading edge.

Note that I have not purchased 4S batteries yet, pending initial test flights with the 3S LiPos I have on hand. I also plan to use 2 x 2S Lipos to simulate a 4S setup - should be pretty hot according to my ecalc simulation!

Test #1:
a) Plane balances with battery #1 sticking out 35mm from the rear of the canopy opening. The battery is mounted inside my velcro battery securing contraption, see picture below. Battery # 1 measures 105 x 34W x 27H weighing 200g.

The battery mount consists of a timber moulding that has a shallow curve on one side, and has been sanded down to a low flat profile on the other side. Coated with WBPU to facilitate velcro sticking to it. I will place some 50mm wide velcro in the bottom of the fuselage for this LiPo carrier to adhere to.





Test #2:
a) Plane balances with battery #2 sticking out 25mm from the rear of the canopy opening. Battery # 2 measures 115 x 34W x 33H weighing 200g.

Please note that batteries 44mm wide will not fit! The canopy opening is 43mm at its widest point, and I suspect anything over 40 will not fit. Note that wider batteries (of course) also sit higher in the fuselage.

I think the test batteries are a good compromise between good access and the largest batteries I plan to use. I may also get a 150g one for light days.

 

[Glenn Beer]

On Gorilla Glue: More and more, I’m finding that bottles of Epoxy just don’t have the shelf life I remember.

I can also mix some water into a dollop* of Clear GG and use that pretty much as I would 30 min epoxy.

* Dollup - from the Imprecise measurement system, superior to both Imperial and metric systems.

 

[Lothar]

On Gorilla Glue: More and more, I’m finding that bottles of Epoxy just don’t have the shelf life I remember.

I can also mix some water into a dollop* of Clear GG and use that pretty much as I would 30 min epoxy.

* Dollup - from the Imprecise measurement system, superior to both Imperial and metric systems.

That is great to know, thanks for the tip!

 

[Konrad]

Normally I like Stackhouse's thought process, but I wonder how many "hair" there are to a foot? (Sorry for the link to RCGoofs)

As to glue I find polyurethane adhesives to have a short self life. The humidity in the coastal air helps accelerate this. I try to store with no head room in the bottle.

I get good shelf life with epoxy hobby grade (Smith Industries). I often get crystal precipitating out. (This is an indication of purity) I will heat the epoxy components in a water bath to melt these crystals and reconstitute the components. I bring the parts back down to room temp before mixing.

 

[Wayne]

Bob Smith Epoxy - I don't know that I have ever had any go bad on me, it is really good stuff in that regard. I have a bottle of 5 minute at home that I am still using up, it predates Aloft
Hobbies, bought it in So Cal at Gyro Hobbies, and nice shop that is no longer with us. Must be at least 10 years old. It is almost empty, and I can get a new bottle with an Aloft sticker.

Lothar - Glad you got the second screw working! Wow, that battery is really back there, I didn't expect it to be that far back. Like the battery tray, I think I will have to copy that idea in some future planes.

 

[Hank GB Z]

Hey Wayne,


Crazy you mention Gyro Hobbies. I used to work there wayyyyyyyy back in 2001-2002 before i left for USF. I loved that store. I wish it was still around.

Hank

 

[Wayne]

Yeah, great shop. I may have bought stuff from you, maybe my Epoxy. LOL

I worked at Hobby Shack in the 90's.

 

[Lothar]

Lothar - Glad you got the second screw working! Wow, that battery is really back there, I didn't expect it to be that far back. Like the battery tray, I think I will have to copy that idea in some future planes.

I have just done some interesting balance experiments with more square drone batteries. I have ordered a Tattu R-Line 1800mAh 4S which weighs 197g and measures 78mm x 39mm x 38mm (L x W x H). It will stick out about 35mm, but being much shorter will be easier to get in and out. I made a dummy battery to check the fit, and it looks like 39W x 38W will just squeeze in under the wing joiner. I will post details when the battery arrives.

I will also use the 1300mAh one which will fit easily.

 

[Lothar]

The 4S Tattu's arrived today.

Target CG = 79mm from front of wing at the root.

Test #1:
a) Plane balances with 1800mAh R-Line 120C Tattu sticking out 18mm from the rear of the canopy opening. The battery measures 76 x 38W x 35H weighing 197g. AUW 1130 + 197 = 1327g. The rear of the battery just fits under the wing joiner without being squashed.



Test #2:
a) Plane balances with 1550mAh R-Line 120C Tattu sticking out 25mm from the rear of the canopy opening. The battery measures 76 x 38W x 35H weighing 175g. AUW 1130 + 197 = 1305g.



Test #3:
a) Plane balances with 1300mAh 120C Tattu sticking out 30mm from the rear of the canopy opening. The battery measures 74 x 35W x 27H weighing 148g. AUW 1130 + 148 = 1278g.



Note that I have left my velcro strap open so you can see the battery.

 

[Lothar]

Sorry about the pause in posting progress, have been tied up with a few other things.
As mentioned in post #5, the servo pocket measurements caused me to rethink my servo choices. In the end I went with FrSky HV5611 servos for the flaps and ailerons. They are only 8mm thick, are metal cased and have metal gears. At 8.4V they are very fast - 0.05s/60deg.

Note that they ship with only 45deg rotation per side. I had to connect via F.Port to change them to 60deg rotation, which is needed for the flaps.

Another major plus is that FrSky make IDS drive kits for them.

 

[Lothar]

Installing the IDS drives​

Step 1. Determine the servo horn offsets​

The servo horns must be aligned with the bump in the servo covers. This distance is 11mm on the Magnus.



The distance of the flap servo horns from the wing root is 154mm, while the aileron horns are 328mm from the root.

 

[Lothar]

Step 2. Transfer the horn distances to other side of wing​

The horn distances must be transferred to the top side of the wing as guidelines for cutting the slots in the wing wipers and the servo arm access holes.

 

[Lothar]

Step 3. Mark the wipers for cutting the access slot.​

An access slot must be cut in the epoxy wipers to give clearance for the IDS paddles or horns, which will be fitted into the flaps and ailerons. The width of the paddles for the HV5611 servos is 11mm.

 

[Lothar]

Step 4. Cut the wipers for the IDS access slot.​

A good tool for cutting the slots in the epoxy wipers is a Dremel tool with the 2.1mm diameter tungsten carbide cutter 9904.



I used blue masking tape to hold the flaps and ailerons as far down as possible, to fully expose the wipers. A steady hand is required!


The slots can be cleaned up with a small flat file and a scalpel.