The big rig section on these forums seemed to need more action, so I decided to post a little bit about my latest build. It's a frankenquad made from mostly parts I had sitting around. It has a 620mm H style frame with APC 12x4.5mr props, Turnigy Multistar 4822-690kv motors, Turnigy 4s5000 hardcase lipos, Skystar 40A bl32 esc's, Matek F722se, Sony PZ-0420 ccd cam, Rush Tank Ultimate Plus VTX, Matek M10Q, 12V ubec, and an RP1 elrs rx. The frame is a DIY job my buddy made 15yrs ago. He gave it to me 13yrs ago after he gave up on it... saying he couldn't get it to fly for jack with Arducopter. I already had most of the parts needed at the time, but ended up starting a family, which meant a lot less FPV time. Now that my kids are older I found myself with enough time this summer to get the big rig done.



Before going into the specs and all, I gotta mention how I installed a 12V ubec that happened to be putting out lipo voltage! This let the magic smoke out of my beloved PZ0420 within a few minutes. When that happened I got hella pissed... luckily I had one more spare PZ0420 on hand to use, as well as some more 12V ubecs. You know those ubecs got tested first on the second round, lol!

The main part of the frame was more or less ready to go. I just removed some standoffs, velcro, and drilled the mounts to fit my motors. The camera mount was a design I drew/printed in ABS for an old 330mm rig I don't have anymore. I did draw/print some antenna mounts, and the GPS mount came from thingiverse. The ELRS antenna is actually a ghost antenna, and there is a 2mm cf rod between the TPU base and head. The VTx antenna mount was resin printed.

It's running the latest iNav (6.1.1 IIRC). I've seen a lot of questions on tuning these kind of rigs. After getting this rig tuned, I now understand why hehe. Back in the day the biggest I flew was FW450's with 10" props, and I was one of the first to start going smaller amongst the locals with my 330 7" rig. So going 12" was interesting for me. From my smaller quad learnings, I thought esc rampup power would have to be dropped below like 20% (this works on 7" for example). However on this rig, it wouldn't even fly until I pumped rampup to 30%. I also didn't have to crank my PIDs as high as I normally would on larger rigs. I did start right off dropping filter low cutoffs to 60hz though. Even 50hz may be appropriate on a rig this size. I attached my diff in case anyone is interested in more detail.

It flies great... for such a giant! The sound is very, very quiet and low like other heavy lifter rigs you may have seen on YT. It has no issue loitering hands free in my backyard for 20min straight, taking just 4000mah. It can do flips etc, but it only has about a 3:1 thust:weight, so freestyle is mild if at all. I built this for utility anyways... things like dropping a rope in a tree to recover a quad, blowing leaves off the roof, etc is what this thing will do.

I plan on adding a servo drop mechanism, and I also have an old storm32 3-axis brushless gimbal I'd like to mount on it. The F722se has 2 camera inputs and can switch between them using a switch. This, with a gimbal and gps hold, will be very nice for general camera work as well.

Cheers,
Kev

Yesterday I put this rig up in my backyard with not one, but two 4s5000 packs on board... connected in parallel of course. It flew appreciably higher up on the throttle, needing almost half throttle to hover, which burned at 21A. It also felt a lot heavier so I didn't push it hard. It was also more stable in position hold/alt hold. I got bored after 16min of flight, and landed with the OSD showing 5200mAh used. Everything was cold to the touch after landing.

The 2 pack config weighs just over 5lbs... you can feel it's presence in the air. It completely flattens out a 6' radius on my cut lawn grass when hovering 8' high over it.

I did notice one problem with position hold during this flight; an occasionally very strong yaw bounce back. When I was flying around with purpose (banging harder on sticks), pos hold tracked well on all axis. However while I was in a stable hover, if I gave very small yaw inputs to reorient a few degrees left or right, the yaw would bounce back hard. I played with this a bit to see how unstable it would get. When I tickly the yaw just right I could actually get the quad to end up rotating in the opposite direction! Say I have a very small input to rotate slowly like 3deg left... it rotates slowly left, but when I let go of the stick it bounces back 5deg to the right... leaving the quad pointing the opposite direction I intended.

I checked logs, and discovered what appears to be way too much yaw feed forward... or at least that's what it looks like to me:



I'll play with turning that down and hopefully get a well behaved pos hold yaw. Could there be some other cause of this (thought maybe elrs smoothing or similar could also be at play).

It's probably not compass calibration or alignment... it can spin on yaw axis without losing position at all. In fact it's kinda funny to watch a full yaw spin because the quad is so big, and the compass+gps are on the back of the frame. The whole frame pivots around the gps... does an awesome job holding that gps within a few inches as it goes. At first sight this was a little unsettling to me, but after I saw what was going on it was actually fun to watch this phenomenon. OTOH, I also wonder if that would make for weird dynamics during more aggressive maneuvers. If it became noticeable I'd have to probably post mount the GPS above the packs to get it closer to the CG.

Nice old school style.

I’d be afraid that I’d decapitate myself with something that large.

I feel ya'! If I'm within 10' of it when I takeoff my body tends to slightly lean away from it... as if that would make me any safer lol! It's about to get even worse. This weekend I'll probably be ready for the first hops with a more modern rebuild using the parts from this rig. It's going on a tarot ironman 650 frame and getting 13" CF props. It's getting a gopro sized 2axis brushless gimbal (old school rctimer), 45A 4in1, second fpv cam w/ switcher, and a servo release mechanism. That gimbal with cam alone is going to make the props turn more. This one may get me to lean back enough on takeoff to do some limbo, LOL! I also have 14" CF props coming on the slow boat. With 14" props, the swath of hazard grows to just shy of 44" wide. So I may need to practice my 80's action flick dive to the side moves. Anyhow, I'll post more about the rebuild after I get it working... it has become quite the project requiring lots of CAD, printing, and even some cnc work.

[edit: Gave decapitation more thought... when I get this thing out in a large area I'm actually curious to see if it rips, lol. The new frame is so complex I'd be afraid freestyling it would make a bunch of screws come loose lol. These big rigs do tend to loosen screws 10x more than their smaller cousins. That said, fear hasn't stopped me from trying similar shenanigans in the past... just a matter of time hehe.]

I’d love to hear how that that thing sounds in the air. Might be hard to get a good recording on a microphone though.

I'll see what I can do about posting some video of it flying on yt. I spoiled my kids with AT2020 mics, which I'm sure they'd be more than happy to let me borrow to record sound. I like the growl big copters make... almost as impressive as the sound of a 450 or larger CP heli.

Secondeded. I would love to see this fly as well.