Thanks Forest for the file, I am looking for mounting motor and tube plates as you have used. Is it possible to buy from you these g10 pieces or do you have cad files to let it cnc produce from china? motors will be hp2212 1000 kv and 12 mm tubes for a v octa.
I found a producer for nomex sheets:
what do you think about them?
Nomex core carbon sandwich panels do not survive as motor mounts. the material needs to withstand high point loads. But, end-core balsa carbon sandwich panels are excellent. These are even harder to find in the appropriate thickness.
yes ... i could cut the motor mounts for you. but first, let's talk requirements.
Are you flying over grass or granite? This affects how durable the motor mount needs to be and if it is a single or double plate.
Do you have access to Scotch Weld 2216 adhesive (mandatory for bonded joints)? I can get a tube for you if you can't, but it's expensive, especially the applicator.
With 12mm tubes using the hp2212 with 19mm bolt pattern, you have 13.4mm bolt separation, which will make getting the bolts into the motor back-plate difficult (but not impossible). As an example, i use the T-Motor MN3508-29 motor with 24mm bolt pattern, which is just wide enough. A slotted system would work where you push the bolts up through the motor mount and then slide them inwards as you evenly tighten all four bolts.
Have you cut your mast yet? Or is there room for the mast to extend farther out to provide more room/area for the adhesive bond?
Nomex core carbon sandwich i was planning to use for the EP! Not for Motor mounts, there i like the balsa solution.
I can get the scotch 2216 see in switzerland:
some recommended uhu 300 is there any result out in the meantime?
I was planning to use 12 mm carbon braided tubes from:
If I am using the HP2212 with 19 mm do you think if fixed with the alu x cross delivered with the motors will work because there are 33mm wide?
for the flightcontroller i will use not apm anymore trying pixhawk clone.
stay with scotch 2216 on any critical bond (motor mounts & structural gussets)
the tubes are a bit heavy but they look durable so not bad
some Al X w/ screws weigh about 3g each for 18g total for a hex. so one possibility is to bond the Al X to the tube as a + and secure the motor with 2 screws (all that's needed; but check before each flight to ensure they are still tight).
also, to save a little weight, you can trim the part of the X that sticks out on each side but not the part of the X that would be bonded to the tube (it needs the full 40mm of length (about 30mm of bond length).
i prefer your balsacarbon mounts to make an octa!leave the idea of alu x fixation!
then i take your advice for the scotch 2216.
So can you supply me the 4 motor mounts and the 4 motor/x mast combination for zip fixation?
Let me know your costs? I will glue the middle x tubes one full length and the other half.
Where do you buy the tubes and whats there weight?
hi Forrest, in the meantime i read most of your points in this forum, just fantastic!
I got 2216 scotch in switzerland. The carbon tubes i will get from here:
carbon balsa also in switzerland. I try to build your x2 built in your custom octa, what diameter for the motor mast did you use? mast width 0.86, what does this mean?
Do you have any videos of your x2 built? Whats your experience in the meantime with it?
the octa X2 was my first ship and the first to set the world record for flight duration. then i went to a quad but will soon complete the octa X2. but getting there has taken a lot of steps.
- Figure out the gimbal (that was completed about 6 months ago)
- Learn FPV before i fly a valuable octa X2.
so now i'm focusing on a durable quad X spider to learn FPV. once i learn FPV, then I'll build another much larger quad to set the next record and thenl get back to an octa X2 when my payload costs go up.
i remember once losing an engine on a octa X2 and not even knowing it (really not paying attention). Started it up, took off, hovered for a bit, started flying and my brother says, "Hey, i think one of your motors is dead." The ESC wire had come loose. So really stable platforms.
The .86 was inches. The key on the mast is stiffness. You can do the calculations pretty easy.
- Let us say that a 15 mm carbon tube with 0.6 mm wall = 1 on a stiffness scale.
- A stiffness of 1 is more than adequate for a 17" prop quad
- A stiffness of 5.5 is adequate for a 17" prop octa X2 (a 24 mm dia. carbon tube with 0.8 mm wall)
On the Swiss site for tubing, use the following equation.
Stiffness Factor = (WallThickness/0.6) x (OD/15)^3
Use that equation on the 24 mm tube with 0.8 mm walls to make sure you get 5.5
Order that the tube you want and then to verify, give it the "Twang" test.
- Figure out how much of the tube will be unsupported
... a quad with a 17" prop this is about 9" to 12" on a spider
... on an octa X2 with 17" props this is about 26" to 29"
... the rest of the mast might be supported or stiffened by the Electronics Platform.
- Lay the full length tube to be used for the mast (most come in 1 to 2 meters long) on a table.
- Extend one end of the tube over the end of the table the unsupported distance calculated above.
- Press the rest of the tube tightly to the top of the table
- Twang the end of the tube that is hanging over the table
- Excellent is that there is no harmonic.
- Good is that the harmonic only lasts for one or at most two cycles and stops.
- Bad is that you hear a twang (any sustained note).
So make your best guess. Buy the tube. Then test it
It is also OK to:
- buy tubes that fit within tubes. The second ship that broke the world record used that method. Big OD on the mid section with normal OD on the final section.
- use two smaller tubes that are bonded on top of each other for z stiffness and then use the side spars between the masts to create x/y stiffness.
In your excel file you are using very small Minimum Prop to Prop Spacing, do you really recommand 0.1" spacing? Interferences could have a great influence! Some people recomand 27% of Prop size, what is your advice?
I did a test on RC prop system. Put dual props on a test stand at various separations (something like -50% to +10%). Results showed not a huge impact on efficiency until overlapping quite a bit. But there is a significant noise difference. If you want maximum quiet, try 1". If you want compactness, 0.1" is also OK but a bit noisier. Most of my frames so far have been for world records so have used minimum spacing of 0.1" to remove weight.