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Apr 13, 2020, 06:38 PM
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Profile F-35 Tricopter


Reviving this old project during quarantine. I built the airframe 6 years back but didn't have the software know-how to realistically make it fly through transition, so I set it aside until I knew I could make it fly the way it was meant to. This is also a simple VTOL platform for me to test some transition mixes for other projects I have planned over the summer as part of my thesis work

The basic idea is just a tricopter with a lift fan and two pusher motors mounted on the flaps which can actuate down into the vertical position. I think hiding the pusher motors on the wing airhogs style makes for a nice look as compared to other configurations I've seen with vertical lift motors extending out on booms or whatnot. The lift fan tilts for yaw in hover, and elevons/differential thrust for full control in forward flight.

The airframe is made from 9mm EPP and 10mm poplar spars with some 3mm carbon for reinforcing the foam in key areas.

Power system:
- 3x lumenier 2350kv 2206 motors
- lumenier 4-in-1 35a esc (I really like how responsive the lumenier escs are)
- Gemfan 5045x3 props
- 1800mah 4s Lipo

AUW: ~850 grams
WS: 32"
Length: 44"

I'm waiting on my teensy 4.0 to come in the mail so I can load it up with the flight control code and get her flying in the next week. Stay tuned


EDIT: Version 2 (much smaller and highly agile) here:

Super-Maneuverable RC VTOL F-35 Parkjet (7 min 17 sec)


Working on plans and flight control code!

First version videos:

RC VTOL F-35 Full Transition Flight (1 min 59 sec)


RC VTOL F-35 Low Altitude Transitions (1 min 22 sec)


RC VTOL F-35 Takes Off From Truck (1 min 41 sec)
Last edited by rcjetflyer2; Oct 23, 2020 at 01:35 PM.
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Apr 19, 2020, 03:02 PM
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v22chap's Avatar
pretty simple and cool looking little F - 35 ,,, keep at it !!
Apr 19, 2020, 08:19 PM
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I've got her flying! No outdoor video yet, but here's a hover test indoors while I was tuning gains:

F-35 initial hop (0 min 29 sec)


Running cascaded PID with angle on the outer and rate on the inner loop--still needs some fine tuning but flies fine as it is. I did some half-transitions outdoors today with the motors/flaps deflected at 45 degrees and it flies really well. Then I put it into forward flight mode and did a lap around the front yard just as a parkjet. No full transitions yet, but the airframe and software are ready for it. Just waiting on a time when I have a camera man! Stay tuned
Apr 20, 2020, 12:08 AM
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Some pics of the electronics under the hood:

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Close up of the teensy-based flight controller I'm running; flight control code is my own:

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May 02, 2020, 07:03 PM
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Added some paint and took her for a spin! Still some flight controller tuning to do, but this is the first full flight with complete transitions:

RC VTOL F-35 Full Transition Flight (1 min 59 sec)
May 02, 2020, 08:18 PM
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britinoz's Avatar
Congratulations .That does look very promising.
Happy Landings
Chris...
May 02, 2020, 08:26 PM
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v22chap's Avatar
Congrats ,,, looks very good .. Keep working on it and keep us posted
Good luck on further test
May 03, 2020, 01:37 PM
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Looks great! Do you think the pitch down is from the flaps that the rear motors are mounted on causing a pitching moment as speed increases?
May 03, 2020, 03:54 PM
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Quote:
Originally Posted by elmtree
Looks great! Do you think the pitch down is from the flaps that the rear motors are mounted on causing a pitching moment as speed increases?
There's currently a hard cutoff of the front lift fan when transitioning from the intermediate mode to forward flight, so when that cuts off, the rear motors force the nose down for a second while they get actuated up into the forward flight configuration. I'm coding up my solution as we speak! Stay tuned
May 04, 2020, 12:21 PM
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Looking good rcjetflyer2!

Are you writing code from scratch for your flight controller?
May 04, 2020, 07:30 PM
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Originally Posted by leadfeather
Looking good rcjetflyer2!

Are you writing code from scratch for your flight controller?
Haha thanks! Your EPP F35 back in the day inspired this one! Haven't been able to find your youtube lately, everything alright?

Yea, code is from scratch. Started out on an arduino nano then moved over to a teensy 4.0 (600MHz clock speed vs. 16MHz ). Here's an early flight on a frankenquad with the nano:
Arduino-based Multirotor Flight Controller - Test Flight (0 min 30 sec)


Originally I wrote the FC code for an autonomous quad project for a Vertical Flight Society competition, unfortunately the forum this year was cancelled so we couldn't compete in person. They still awarded prizes based on paper and video submissions, and turns out we won:
VFS MAV Student Challenge - Gate 2 Autonomous Entry (5 min 24 sec)


Something like ~15 lines of code to modify the original quadrotor code for this F-35.
May 05, 2020, 08:39 PM
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Looking forward to seeing how the Teensy 4.0 coding develops!

I have some ideas to share on the F-35 if you are interested.
May 06, 2020, 01:51 PM
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Quote:
Originally Posted by leadfeather
Looking forward to seeing how the Teensy 4.0 coding develops!

I have some ideas to share on the F-35 if you are interested.
Do tell!
May 06, 2020, 09:32 PM
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I'm not suggesting you change your design at all; I thought it would be fun to talk about some other control/power/arrangements that could be used on a similar build to yours.

The one arrangement I had in mind was based in part on the F-22 in the video below. The dual prop in slot blowing over the control surfaces should give great pitch, yaw and roll control... even at zero forward air speed. Now add counter-rotating lift fans for hovering lift and you should have a workable VTOL craft. Note that there is no switch over of yaw and roll inputs to outputs required with this arrangement; pitch yaw and roll controls are the same in hover and forward flight. This gets the weight and forces due to the thrust motors as in your arrangement off the servos and hinges. It does add one more motor for lifting however.

In hover, just enough thrust power to give good control authority, and enough reverse thrust from the lift fan(s) to counter the control thrust.

The lift motors could be coaxial or nearly coaxial and pull air through a control cut out as you have done, or they could be separated across the cg as AJ Wood did in his Harrier some years ago. His harrier had 6 fans/motors. With the blown control surface arrangement I think two motors could be eliminated.


Can your jet do this? (15 min 57 sec)
Last edited by leadfeather; May 06, 2020 at 09:55 PM.
May 07, 2020, 03:26 PM
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Interesting idea, the flaps could also be actuated downward for more downward thrust in hover, and continue their operation for roll... though this would couple yaw and roll which might defeat the purpose.


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