Mini tubular and ultralight LOS Acro+FPV Quads - RC Groups
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Apr 15, 2016, 05:18 PM
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Mini tubular and ultralight LOS Acro+FPV Quads


Tubular frame construction

Photos and construction details for a basic bonded carbon frame can be found here on page 5 onwards...

https://www.rcgroups.com/forums/show...2645953&page=5

Great write up and photos of a build from Bexamous here...

https://m.imgur.com/a/hEevI

Other useful photos and details

Carbon tow wrapped centre plate details...
https://www.rcgroups.com/forums/show...postcount=1431

Braided kevlar thread wrapped centre plate details on Christo's 10x8mm, 6" frame...
https://www.rcgroups.com/forums/show...&postcount=530


Components

Woven carbon fibre tube - Ebay!

Motor mounts and centre plates - Armattan Productions

The stores aren't working very well on Armattan Productions and not all products seem to be listed on each store, so best to search for "centre plate" (note spelling of centre) or "motor mount" to find the full range from all stores.

Lightweight LOS, FPV frames and tubular frame components can be found in my Armattan Productions store...

https://armattanproductions.com/page...oduct_grid/671

Ian444’s AP store contains a great selection of centre plates and motor mounts...

http://www.armattanproductions.com/p..._grid/2579/222

Schrodingers Cat's AP store...

https://armattanproductions.com/page...oduct_grid/395


Videos
LOS from Bexamous....

Racecraft 5051 flying just a bit out of control (3 min 19 sec)


Test flight: 5" Tube Frame w/BrotherHobby 1407 3600kv motors 3S 500mah BonkaHV (4 min 58 sec)


Speed Test: F40Pro + RaceKraft 5051 + 1000mah 6S (3 min 5 sec)

--------------------------------------------------------------------------------


Here's my first attempt at a scratchbuild quad. It's a simple 230mm X frame, arms are made from a balsa core with the top bottom and sides capped with 0.5x5mm and 0.5x10mm pultruded carbon strip. 1mm epoxy glass G10 plates in the centre and fluro covering to help with orientation. Frame weighs 30 grms.

Setup is :

Emax 1804 motors
Littlebees ESC
Naze 32 rev6
Lemon Sat Rx
HQ 5x3 (or 6x3 props on 2S)
3S 850mAh

AUW without LiPo - 138 grms.

I flew the quad for the first time the other day. Running the latest Betaflight (2.6.1) with stock Rewrite PIDs, it had some pronounced bounceback oscillations. I’ve reduced the P values to 4.5 and then incrementally increased the D term from stock (18) to currently 90 where they have pretty much now disappeared. It's flying nicely now, but does this D value sound way too high to any tuning experts out there?

Edit : I didn't have damped light enabled on the ESCs. With this enabled, the bounceback issue disappeared and D term could be reduced back down to normal values.

I'm a total newbie and this is my first attempt at tuning one. The way the arms have been constructed makes them vertically and laterally stiff but very torsionally flexible. Tricky to describe how flexible, but with relatively little force you can tweak the motors say around 5 degrees, with a good yank maybe 20 deg or so. I'm wondering whether this torsional flexibility is likely to cause any tuning issues?

It's taken a few decent hits and survived but I'm not too happy with the crush strength of the motor mounting so a mk2 version is in the planning stages….
Last edited by TimR74; Aug 28, 2017 at 08:07 AM.
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Apr 15, 2016, 07:40 PM
Team AlienWarpSquad
Nice build
This is close to the Warp Quad 200 which is a very fun LOS aerobatic copter.
I run RCX1804-2400kv motors, 2S and GF5030 props for very, very tame, 3S and HQ5x4 props for good fun and then 4S for insane.
Like the NanoTech 850 45C batteries in 2s, 3s & 4s.

Have fun.
Apr 15, 2016, 09:14 PM
Gyro, SimonK n call it a day:)
lockwood's Avatar
Very nice!!!
Apr 25, 2016, 07:12 PM
Registered User
Thanks for the comments. I've had near to 100 flights with my first acro quad. It's been, and still is, a surperb flyer and have learn't a lot with it.
Anyway, I decided to build a replacement frame, slightly smaller at 200mm, exclusively for 5"props. I tried a 6" prop and 2S once, found it too light, floaty and underpowered.

I took a few photos during the construction incase anyone else finds them useful to try something similar. It's a old school build - hacksaw, dremel, masking tape, sharp pencil and epoxy.... The carbon tubes and overall frame are an order of magnitude stiffer (and only 1 gram heavier) than my first effort. Having just built it, I reckon 8mm O/D carbon tubes would've been more suitable than the 10mm I used. I think with a light build, 1306/1804 motors, approx 200grms AUW, it'll be indestructable when flown over grass.

Re-maiden tomorrow......
Last edited by TimR74; Apr 26, 2016 at 02:56 AM.
Apr 27, 2016, 05:02 PM
Registered User
I'm pleased with how the new frame turned out, definite improvement over the first. Feels a little more locked in when flying and generally more nippy and manoeuvrable.
It's absolutely rock solid as well. The tubular arms should increase the prop efficiency a little. Would be nice to get a 4in1 esc to clean up the arms further, I've been eyeing up the 4in1 littlebee pro esc which is coming out soon.

The latest Betaflight really is ace, can't get over how stable this 210 gram quad is, even in turbulent, gusty winds. I've waterproofed the FC and ESC with silicone conformal compound also. Tested it out flying in some light rain, landing in wet grass with no issues so far...

Waltr, how do you find the HQ 5x4 compared with the HQ 5x3 on your RCX 1804 motors? I'm looking for a little more bite on the initial acceleration without going to 4S. Will try out the 5x4 when my current stash of HQ 5x3 run out.
May 01, 2016, 04:24 PM
Build and rebuild
Brainstorm's Avatar
Quote:
Originally Posted by TimR74
Thanks for the comments. I've had near to 100 flights with my first acro quad. It's been, and still is, a surperb flyer and have learn't a lot with it.
Anyway, I decided to build a replacement frame, slightly smaller at 200mm, exclusively for 5"props. I tried a 6" prop and 2S once, found it too light, floaty and underpowered.
Truly impressive scratch-builds, TimR! Both the original balsa frame and the updated carbon-tube version.

Interestingly, this is the same building technique that people (e.g. End Of Days) use to build larger quads for record-setting endurance flights. Really cool to see this applied -- elegantly and successfully -- to a smaller acro quad!

May 02, 2016, 05:10 PM
Registered User
Thanks for the kind comments, Brainstorm. I think scratch building quads with tubular arms is a good option for small LOS quads as their lack of mass greatly reduces the chances of crash damage. Weight for weight, tubular arms have hugely increased stiffness over flat plate arms as well as being superior aerodynamically in minimising thrust blockage and airframe drag.

The frames are cheap as well, this one was a total of about £6-7 worth of carbon, there’s also the epoxy as well. If anyone’s thinking of doing similar, I'd strongly recommend the slow setting 12/24hr epoxy rather than the rapid 5 min type. It has far better bonding strength and flexibility, it's tough stuff. Be sure to file/sand the bonding surfaces also.
May 03, 2016, 05:38 AM
Build and rebuild
Brainstorm's Avatar
Quote:
Originally Posted by TimR74
I think scratch building quads with tubular arms is a good option for small LOS quads as their lack of mass greatly reduces the chances of crash damage. Weight for weight, tubular arms have hugely increased stiffness over flat plate arms as well as being superior aerodynamically in minimising thrust blockage and airframe drag.
All these advantages apply across the entire spectrum of multirotor sizes. The main challenge with using CF tubes is assembly. If you use tube clamps, tubular arms are easy enough to work with. However, you gain a lot of weight and complexity. Bonding the tubular arms with epoxy reduces complexity. However, it dramatically increases labor cost and build time. That's why CF tubes are great for your scratch-built acro mini as well as record-setting endurance fliers. For the mass market, CNC cutting out of flat CF stock is hard to beat in terms of production as well as easy assembly.

Quote:
The frames are cheap as well, this one was a total of about £6-7 worth of carbon, there’s also the epoxy as well. If anyone’s thinking of doing similar, I'd strongly recommend the slow setting 12/24hr epoxy rather than the rapid 5 min type. It has far better bonding strength and flexibility, it's tough stuff. Be sure to file/sand the bonding surfaces also.
Excellent points on cost, strength of slow-setting epoxy, and sanding prep work. That mirrors two other tubular frames that I've enjoyed watching come together. Have a look at these two builds:
  • Frickler's "Light Flight" 500g gimbal quadcopter, and
  • Ferdinand's Projekt 12mm from 2013, which led to his later record-setting frames.

You're in good company!
Last edited by Brainstorm; May 03, 2016 at 05:47 AM.
May 04, 2016, 05:24 AM
Registered User
Totally agree with your comments, this type of construction does not lend itself to mass production at all. You never know, we may see tubular arms coming back in for the very dedicated racers that are looking for marginal gains after all the designs have converged on a Kraken style minimal frame with aero pod.

Thanks for the links. Interesting builds, at the other end of the spectrum to what I'm doing. The 0.5mm wall thickness tubing wouldn't last too long in a crash when used in those lengths, but that's not what they're designed for. I've had a couple of hefty crashes with my latest frame now with nothing worse than broken props and the CF tube filling with mud. I've solved the last problem with these plastic end caps which fit neatly to the ends....
May 13, 2016, 12:15 PM
Registered User
I've been thinking about making a mk3 quad frame with the possible view to making a dedicated battery on top LOS mini quad. I've read a few times that the vertical CofG of a quad should ideally be in line with the thrust line of the props to give the best handling as the rotational moment of inertia is at a minimum. One disadvantage with the bonded tubular design like I've made is the vertical thickness is high compared with a flat plate design - 12mm as opposed to say 3-5mm. This pushes the battery further away from from the plane of the props, which isn't ideal.

I've wondered how much of a noticeable difference in flight it would make, reconfiguring the battery position on top of the quad to get the perfect vertical CofG. I thought I'd try out a few flight tests with the battery relocated to achieve this.

The two photos below show the current layout, and the position where the battery needs to be (surprisingly high) for the CofG to be exactly inline with the props.The upper standoff heights were lowered slightly to achieve this.

I flew about 10 back to back flights swapping between the two configurations for each flight to evaluate any differences. The change in battery position looks dramatic but actually had a minimal effect on the flight characteristics. I was expecting a little larger difference, but it was noticeable. With the battery on top, the quad settled back fractionally quicker after fast roll or flip. Flips in fast forward flight felt a little nicer as they stopped very crisply. The other area of the envelope where a difference could be felt was in small radius, high throttle turns. These were a little easier with less tendancy to blow out I found if you were a bit over eager and messed up your coordination a little, but again not a huge difference. I guess for FPV racing on tight courses, it may make a difference but for general big sky zooming LOS aerobatics, there was no real difference, to me anyway. I did have to be a little careful as any heavy crash would have smashed up the FC stack with the battery strapped to the top of it.

I can see a couple of disadvantages having the flight battery on top of the quad. Just being personal, I wasn't so keen on the aesthetics for a LOS quad. It just looks imbalanced and top heavy (even though it clearly isn't!) as it's flying along, compared with the usual config. Also, to enable the same strength and crash resistance, the quad would need a beefed up battery tray, separate from the FC stack, which would add a little weight. As a side issue, I find the battery useful to hand catch the quad with at the end of a flight.

Anyway, overall it was a worthwhile little experiment, but having done it I'll stick with the same layout for the 8mm Mk3….
May 14, 2016, 07:24 AM
Build and rebuild
Brainstorm's Avatar
Really excellent data, Tim!

I admire you systematic approach. Takes a lot of dedication to run 10 packs back to back with two different setups. Flying a symmetrical quad LOS, you also eliminated the two variables that tend to complicate data collection: asymmetrical thrust (e.g. H-quad, dead-cat) and FPV.

Keep up the good work! Looking forward to Mk3!

PS: Interesting to note that you attach your LiPo with velcro only, and no strap. Especially with LiPo on top, I'd be afraid of the battery accidentally falling off and into the props for rapid shredding.
May 14, 2016, 07:31 AM
Registered User
Quote:
Originally Posted by Brainstorm

PS: Interesting to note that you attach your LiPo with velcro only, and no strap. Especially with LiPo on top, I'd be afraid of the battery accidentally falling off and into the props for rapid shredding.
I used a strap as well (can see it in the 3rd picture) no way it would have stayed on otherwise!. Just twisted it 180 deg when the LiPo was on top.
May 14, 2016, 07:44 AM
Build and rebuild
Brainstorm's Avatar
Aha! Thanks for the clarification. Never mind, then.
May 16, 2016, 05:18 AM
Registered User
X3 Acro

Despite only weighing 31 grms, the mk2 feels a bit overbuilt for its intended purpose. It's survived countless crashes, one onto a road, a few cartwheels across the patio.

The X3 has the same construction as before. The arms have been slimmed down using 8mm x 6mm tube. I've increased the motor to motor distance slightly to 210mm. This will theoretically make it marginally less manoeuvrable and a little more stable but the main reason was I prefer the look of a little more space between the ‘discs’. 210mm also still allows a frame to be made from a single 500mm piece of tube and still retain enough of the arms outside of the motors for protection in crashes.

The centre plates have been kept small to minimise the profile. The holes drilled for the ESC and FC stack will act as a stress riser at the root of the arms, if this causes an issue I'll have to increase the size to the centre plates a little. The holes are 2mm as I plan to use small 2mm standoffs to save a little weight and give room for a 4in1ESC.

Weight came out at 23.3 grms which is a useful reduction over the last frame. This was 146 grms AUW without LiPo. (I think I must have weighed the first one without the LiPo strap, as it was heavier than the 138 grams stated). I want to try and shed 20 or so grams over the X2. Plan is a separate build and keep the X2 as a spare/backup. Same Emax 1804 motors, 4in1 ESC (Littlebee pro), minimise all wires and direct solder them to the FC, no case for the rx, lighter battery strap. Multishot and an F3 FC for this one....

Here's a couple of photos before I go and ruin it with some fluro covering...
May 17, 2016, 10:07 PM
Build and rebuild
Brainstorm's Avatar
Quote:
Originally Posted by TimR74
Weight came out at 23.3 grms which is a useful reduction over the last frame. ... I want to try and shed 20 or so grams over the X2.
Nuts to think you got a 200+ mm frame down to 23g. At this rate, you might run into trouble with it blowing away in the wind like a leaf.

Quote:
Plan is a separate build and keep the X2 as a spare/backup. Same Emax 1804 motors, 4in1 ESC (Littlebee pro), minimise all wires and direct solder them to the FC, no case for the rx, lighter battery strap. Multishot and an F3 FC for this one....
I'd be curious to hear more about the Emax 1804 motors as well as the LB Pro 4-in-1 ESC. Somebody wrote in another thread that the 1804's not only have better torque than 1306 motors (that's expected), but are also more efficient.

Quote:
Here's a couple of photos before I go and ruin it with some fluro covering...
Thank goodness you took some clean photos before you ruined another perfectly good scratch-built frame with horrific fluorescent paint!


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