So, Siccario flies great and is perfectly balanced. Insider can fly a surprising amount of weight as a 4” ducted quad. It follows that their unholy spawn would be amazing, right? RIGHT????

Let’s take Siccario’s main body and make it a 5” ducted quad instead of an X8. I made the Insider ducts super deep to maximize thrust, but if we’re going up to 5” then maybe we can shorten the ducts for better performance in the wind. Since Siccario was already fully realized, I just drew up one arm and duct for this.

I built it up with 2806.5 1750kv motors and some transplanted parts from other prototypes. It flew pretty well with dummy weights so Justin and I went out and mounted his Komodo on it. It looked great.

It flew quite well, but the fc kept rebooting, thankfully when the quad was close to the ground (not my Komodo!!!). A teardown revealed that somehow the caps got lost in the transplantation process. So I added some caps and we tried again, but now it flew like crap. Not wanting to destroy Justin’s Komodo I landed it asap.

Now, this setup had flown great at one point, but now it wasn’t cooperating. I was too distracted to think clearly so I decided that more thrust would solve my problems, and redesigned the motor mount to take deeper ducts. It didn’t help as much as I’d hoped.

When I first built this baby there was just one high kv option in this stator size. Since then Brotherhobby came up with some options, so I swapped out the motors hoping that higher quality motors were the problem. It was not.

At this point business kinda blew up with the emerging Cinelifter market. I basically became a full time shipping clerk with no time to fly and test. The winter weather didn’t help, either, and so testing slowed way down for me.

I did try to reduce the noise level with a suggestion from Nathan Powell. Sadly this change did nothing.

Luckily I’d sent a frame to Fincky, along with all the variants of the ducts. He felt that the taller ducts didn’t produce enough additional thrust to offset the increase in drag and loss of agility, so he reverted to the original design. He got it flying so well that it became part of his working fleet. That’s the Fenster from 3:30 to 5:00, as well as 7:40 to 7:52.

Molds!

Troy hooked me up with Zhong at HQ for a molded 85mm duct, and that got me thinking that I should get these ducts molded. Obviously there’s a substantial initial investment with molding, but I was getting increasingly tired of dealing with big nylon prints. I adapted the file and sent it off to HQ, then waited about 5 weeks for the first samples to arrive. The samples were gorgeous, but sadly they were porky at 88g compared to 55 for nylon. Stupid me could’ve seen this coming had I done a simple calculation using Solidworks, but someone was a little too excited to think straight.

I slapped them on and tried to hover it. The quad lifted off and set itself back down, with motors smoking hot. I put the original printed ducts back on and it was normal again. Fincky suggested that it might be a resonance issue, so I printed some TPU spacers and put them between the duct and the carbon, and it finally hovered normally.

Justin, Clint, and I arranged a big session of prototype testing at Calvert Veaux. It turned out to be a disastrous and frustrating day. The worst mishap happened when I tried to fly Fenster fpv. Even though it hovered normally at home, it went straight into a flyaway and I was forced to disarm. Right around the moment of impact Justin’s video froze and his Siccario, which he had just tuned to perfection, got body slammed to the ground. There were several other quads in the air at the time, so we have no idea if I caused his freeze, but for me the two events are just timed too closely to be coincidence.

Three of the motor mounts cracked on impact, right where the arm ends. I wanted to the arm to end short of the motor for easy access to the motor screws, but it was becoming obvious that this design was too weak. Clint also pointed out that having your motor on a diving board surely wasn’t ideal if you’re having resonance issues. Duh.

Lick the Wounds

It’s hard to believe that I had a great test flight 6 months ago and thought I was almost done with the design. Fincky’s two builds had become part of his arsenal and been used in multiple shoots. Not only that, Fenster was becoming an underground thing – even though I never listed it as an official product people kept messaging me asking for one, so quite a few of them got out in the wild and were flying well.

And yet I was back to square one. This whole resonance issue was giving me PTSD, I’d gone through it with Micheru and was never able to defeat it.

First I had to lighten the ducts. Luckily it was way stronger than necessary so I reduced the wall thickness. I was prepared to pay for a whole new mold (because my relationship with Fenster had developed into a Wile E. Coyote/Road Runner situation and there was no stopping me now) but Zhong let me know that the existing mold could be reworked. Phew.

As for the arm, I extended the arm out all the way. This meant the motor mount had to be countersunk and the screws would be inaccessible once assembled.

I hadn’t gotten the new ducts yet, so I built it up with the existing ducts and tried to hover it. One motor let out a puff of smoke and the quad put itself down. As I feared the previous flyaway crash had damaged the motors. So it was time for yet another set of motors. Fincky tried a few different stator sizes and 2808 was his sweet spot, so I went for a set of Brotherhobby 2808 1500kv’s. Now, the real test would be to mount the ducts with no TPU spacers, but I didn’t want to smoke the new motors immediately. I built it with the spacers in place and it hovered normally. (Fincky has since confirmed that the ideal motor is 2808 1900kv)

With the lighter ducts just a few days away, I decided to hold off on a full fpv test flight. The lighter ducts will have a different resonant frequency, so there was no reason to risk the new setup on the old ducts.

The new ducts finally arrived and they came in at 66g, not as light as Solidworks predicted but a nice improvement nonetheless. I mounted them with spacers for a couple reasons. #1, fear of flyaways. #2, stators have gotten taller since my initial design, and the props are rising a bit above the sweet spot of the duct. So the spacer dampens vibes AND raises the duct to match the taller motors, or, as Pee Wee Herman said, ‘I meant to do that’.

Fenster flew just fine on a quick fpv test, time for a small run and more testesrs.

Meanwhile, a quick beauty shot with the new cam mount.

Fenster continues to do work, despite not being officially launched. Here it is, along with Siccario, flown by Vanover.