Bell Boeing V-22 Project

Taildragger

Legendary member
Need some inspiration? :p
Here are some pics i got at the reno air races
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tamuct01

Well-known member
A short update:

I took the Osprey out in my yard for some test flights. I'm not sure the reasons why, but the change to the 3-blade rotors has made the previous PID tuning not acceptable. I did many short hover flights in the yard to work up to an acceptable tune in the dRhemFlight VTOL controller I'm using. I did 8-9 flights, recharging batteries as needed and I have a few observations:

1) The spur gear tilt mechanism is probably a lost cause. There is too much backlash in the gear train and I can see each rotor twist as pitch and yaw inputs are made. It got so violent in some of the tests that I'm amazed it didn't break anything.

2) The motor/gear train I'm using is not suitable for a 3-blade rotor. There's a lot of extra mass to swing around and the motor was very hot after even a short 1-2 min flight.

As much as I hate to "start over," I think I need to return to CAD and go to a rack and pinion tilt setup like Rotormast does. I thought about other geartrain systems, but I haven't been able to come up with a workable one other than the rack and pinion. I may also drop the scale forward sweep and dihedral wing to simplify things in the construction.
 

tamuct01

Well-known member
V-22 Osprey Project - Design Changes for v3

It's been a busy end of 2021, and as we start 2022 I'm getting closer to building version 3 of the Osprey wing. The single biggest problem I've faced is the amount of backlash in the direct spur gear drive of the tilt mechanism. It introduces some nasty instability that, left unchecked, would likely destroy the model in flight.

I've investigated other tilt mechanisms, but the one I keep coming back to is the rack and pinion design that Tom Mast uses in his model at Rotormast. His design uses a high-torque digital servo with a small pinion gear driving a rack attached to the rotor nacelle. The servo has been modified with an external potentiometer that's driven by a gear on the translation tube to give positional feedback to the servo. I like this design a lot because 1) It works, and his model is proof, and 2) it requires less torque from the servo and has less backlash.
I ordered the pair of modified servos, potentiometer, and rack from Tom's site and started modeling the new system in CAD. I quickly found a problem, though. The large rotor drive gear would interfere with any rack and pinion system because it's located above the rotation axis. Tom solved this problem by running a 2-stage gear reduction on his model. Instead of directly copying this design, I opted to extend the main rotor shaft and position the main gear below the translation axis. I was able to purchase some solid stainless 5mm shafts to machine my own. I don't have a mill or a lathe, but I do have my grandfather's Emco Unimat Mk.4 mini-lathe/mill that with some work was able to make some accurate holes for the rotor and gear bolts.

In the previous design, I didn't like the external servo linkages for the flaperons. The servo was inaccessible without cutting the wing open, and it didn't look very nice. The V-22 has quite a thick airfoil, so I thought that a 9-gram servo could fit in the wing and drive the flaperons directly. I quickly modeled this up in CAD and found that I could fit a servo in the wing and directly attach it to the flaperon. I designed a servo mount hatch that would bolt into the wing and provide maintenance access without damaging the wing.


A minor change that will likely have larger implications as I move forward is that in the previous model I tried for the scale look with the wing swept forward a few degrees and a few degrees of dihedral. That model also had zero degrees of wing incidence built into the center mounting block. To simplify, I went with a straight wing this time and added 3 degrees of incidence in the mounting block. I'm hoping that in forward flight it should generate a bit more lift from the symmetric airfoil.

In the 3D printing world, there is a new PLA formulation on the market that relies on temperature-activated foaming agents to create a lightweight, but pretty durable structure. Available from Polymaker and eSun, this new PLA-LW is being adopted quickly by 3D printed airplane manufacturers as a replacement for regular PLA and PETG for parts that don't need to be super strong. I purchased a roll of the eSun LW-PLA and started to rethink certain parts in the wing design. Could I use this material as a replacement for shaping balsa stock for leading and trailing edges? Could I use it to print the bulk of the aileron itself? This redesign is giving me a chance to try these out.
From the test prints with ribs and other components, the LW-PLA is 50%+ lighter than the stock PLA. It's certainly not as strong and feels like a plastic-y foam. With a minimal infill, the structures can be quite rigid and light.

As of this writing, I've completed the left wing and rotor assembly and have started printing the right side. I'm waiting on some carbon fiber rod from China that acts as the spar and once I have that I'll start assembly of the right wing. Here's hoping the new design works!

https://aggiehobbies.blogspot.com/2022/01/v-22-osprey-project-design-changes-for.html
 

tamuct01

Well-known member
I finally got everything together and I'm nearing the first flight of the new version 3. This one has a redesigned rotor tilt mechanism similar to Tom Mast's version. I got everything together and all my indoor preflight checks are done. The weather turned cold and windy today, so I'll have to wait until we get a clearer day to fire it up outside. I've got my fingers crossed for this first flight!

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tamuct01

Well-known member
It's crazy that it's been 6 months since my last post on this project. It's not dead yet! I've worked up a better way to tune the PID values in dRehmFlight VTOL without having to plug in my laptop each time. After a few tethered flights in the garage, I think I have the values dialed in enough for a free flight in the yard.

However, it's been hot as hell's front porch in Texas and quite windy so that test flight got delayed a bit. It was calm this morning, so I gave it a shot. The rate mode controls feel pretty good, so I'm likely to stick with them. The angle mode rates need some more adjustment as I'm picking up some pretty severe oscillations. Back to the garage for that!

Unfortunately, as I landed the last time the right rotor tore off its mount and struck the wing:
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I feel pretty dumb about this one because I knew this was a failure point. In the previous design, the nacelle rotation shaft extended through the nacelle and was attached on both sides with a 3D printed mount. Because this design has the longer rotor shaft extending below the nacelle shaft, I had to cut the nacelle shaft short and beef up the 3D printed mount that's only attached on one side. Apparently, it wasn't enough and separated at the layer lines as expected. :(

It's back to CAD to see what I can do. There might be just enough inside the nacelle side plate to pin through another shaft. Maybe I can use some carbon fiber tube along with 3D printing to beef it up. I'm not sure yet. Does anyone have a lathe/mill who wants to make a couple of parts for me? :D
 

NickRehm

Member
Oof, glad it happened close to the ground so the damage was relatively isolated. I wrecked my first 450 not by trying to do acrobatics, but by catching the skids on the grass and it slightly tipping over.

Don't have access to cnc anymore, but if you need anything laser cut in nylon or something, let me know. I can borrow the machine at work for quick jobs
 

tamuct01

Well-known member
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tamuct01

Well-known member
The aluminum parts from Aliexpress arrived. I think these will work well. They weigh 14 grams each compared to 4 grams for the plastic parts. The whole craft is over 5 pounds so I'm not going to sweat an extra 20 grams.

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I'm off to CAD to adjust the model to use these. :)
 

Beaver5150

Active member
I thought about trying that on a 9" twin prop platform using a Naze32 in bicopter mode. Getting the transition from vertical to horizontal might have been a challenge.
I don't have much luck setting up the CLI commands for the servo outputs on those drone FC's. I was lucky to get one set up for tricopter once.
I wonder how well a heli FC would work for your application.
 

tamuct01

Well-known member
I thought about trying that on a 9" twin prop platform using a Naze32 in bicopter mode. Getting the transition from vertical to horizontal might have been a challenge.
I don't have much luck setting up the CLI commands for the servo outputs on those drone FC's. I was lucky to get one set up for tricopter once.
I wonder how well a heli FC would work for your application.

I looked into a number of FC options when I started. None have a cyclic-pitch bicopter in their list of supported frames. I started trying to use a F4 FC with Betaflight setup for a plane sending data through an arduino for servo mixing, but the arduino wasn't fast enough. I looked into ArduPilot, but I would have to write the code to support this style of frame. Finally, I discovered Nick's dRehmFlight VTOL project and I had the code up and running in a few hours.
 

tamuct01

Well-known member
I got the new metal rotor mounts and redesigned the rotor plates accordingly. I have also repaired the damaged wing. However, when I assembled everything the tilt servos were not responding. I've disassembled one of them now and the control board was toast. I'm not sure when these got damaged, but I'm guessing that both tilt servos are toast. Fortunately, I have a spare set of Hitec D85MG servos. I can modify these to use the external pots, but it's one setback after another.
 

tamuct01

Well-known member
I successfully modified the extra D85MG servos I had on hand to use the external potentiometer. I had to reprogram them to match the tilt curves of the old servos, but after an hour or so with the dRhemFlight code, my transmitter, servo programmer, and an angle gauge got it sorted out. I think it's ready to resume flight testing.

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tamuct01

Well-known member
Did a test flight today and was picking up quite a bit of vibration from the right rotor. After a moment, one of the ball linkages on the swashplate stripped out of the hole. Fortunately, it was on the ground and it only broke the anti-twist bar on the swashplate. I'm thinking that I'll swap back to the two-blade rotor heads. The 3-blade ones just seem so heavy and the added mass certainly doesn't help the tilt servos any.
 
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