Project: 5" Ducted prop's (WIP)

[Kevin_Erik]

Disclaimer: This project isn’t for those unwilling to try new things and / or potentially risk their Tri-Copter in the process.

Ducted Tri-Copter Mini

5″ Duct, Top View

5″ Duct, Bottom View

Ducts can be sourced from http://www.fliteclub.com.au/product/mini-prop-duct-set-of-4/

Note It’s possible to E-mail “Luke” directly via [email protected]

Props Used Racekraft 5045 Bullnose, Tri-blade (Blue).

Battery Used Nano-tech 1800mah 35-70C.

Overall Weight 729 Grams.

Individual Ducts Weigh 35-36 Grams each.

First flight https://www.twitch.tv/videos/174886060
First flight was a bit rough being that a new tail calibration was needed. Also be aware that the prop clearance with respect to the ducts is < 1 mm. This can lead to the prop contacting the duct in some situations. However, as the Tri flys more this becomes less of a problem as the ducts and props self-fit.

Second flight https://www.twitch.tv/videos/174886209
Second flight was much much smoother and lasted almost 06:30 seconds. The flight time is about the same as without the ducts. Please note, that I’m seeing a bit of Roll to the right but this is the same as without the ducts. Unsure exactly what’s causing this so any advice here would be appreciated. (hint, hint) Also be aware that during the bench top Tail-tune that the overall yaw of the tail is restricted by the Duct’s supports coming into contact with the servo. Hopefully this can be resolved via an update to the Ducts at some point.

Please be aware that the duct fit is a bit rough and requires a bit of modification. After all these ducts were originally intended for use with a Quadcopter. Case in point, the bolt holes on the RS2205-2300kv motor is not uniform. One direction they’re 19 mm apart and from another they’re 16 mm. Then add the fact that the 3D print can be a little rough in some of the finer areas. Getting the bolts to thread through while keep the motor axle off the carbon arms can be a bit challenging. I ended up using a silicon pad between the duct and the carbon arms to ensure the spacing was good. It’s basicly a kitchen drawer stop that has self adhesive on one side. In a way this provides a bit of dampening for the arms so long as the bolts are not over torqued.

RS2205-2300kv Motor Dimensions

Note Cli dump is attached.

Cheers!

Kevin & Erik

Attachments:

1. CLI-Dump.txt

[Kevin_Erik]

Yesterday we sanded and painted the ducts. While this does make them smoother (better air flow) it does add about 3-5 grams to the weight of each duct. Had we realized that, we would’ve left them unpainted.

[Kevin_Erik]

Today we did four flights total with 1800mah (both 35C and 45C) batteries. First two flights were great when Tri was really hauling ass and making some nice turns. (roll is still an issue)

Some things of note:
-At high angles of attack (> 60) the Tri quickly gains altitude despite the throttle being under 30-40% at the time. We’re thinking that the ducts are acting like wings so it pretty much turns into an airplane at that point.

-During our third flight, the yaw control got sloppier and sloppier. Brought it down for a landing and everything “looked” ok. However we forgot to ensure that the tail-duct was level before powering up and it’s possible that this may have caused some of the issues seen in the video below.

iPhone video https://www.twitch.tv/videos/175427405
FPV of same flight https://www.twitch.tv/videos/175432491

Wondering if the servo has been damaged as we do hear a bit of chittering when on the bench for a tail-tune. Either way it’s clear that the tail duct spars don’t leave enough room for the servo to yaw properly. This is despite setting up artificial limits during the bench tail tune. (Setting the yaw left / right limits to be shorter)

[Kevin_Erik]

Just completed a tail-tune without all of the spastic chittering. Had the prop and duct removed, while trimming it to the full limits. Wondering if the proximity of the servo-cable to the main battery negative-terminal is causing some issues too. (Was previously just over the neg-battering solder pad)

[noir522]

Hey Im liking this project. You know your gonna get some nay sayer, just keep going. I wonder how it would do with the emax 2600kv motors (since its pushing 5 inch props it should be possible ). If you ever get that Terje made 3d printed racing canopy then this would look like a serious vicious predator.

Also looks very much like Davids tricopter gold pendent.

Attachments:

1. 

   DSC0105_preview_featured.jpg
   

[Kevin_Erik]

@Noir522 We’ve the camera-mount and landing-pads due for delivery in the next few days. Depending on how those turn out, we may opt for the canopy too. Now as for the naysayers, it’s not important really as this is a “fun” project. To be honest it’s cool as hell just to see it fly. Passerbys stare in disbelief wondering what’s keeping it flying! (props are hard to see and not very loud)

Beyond that, just wish we could get the yaw / roll issues under control as the Ducts can really help performance if designed / installed well. IMO the 5″ ducts are just a bit too heavy for the size of the rotors. Maybe a 6″ would be better suited as the effect from the duct / propeller interaction would be greater. (Higher efficiency and lift per watt of power)

Note: With the 2600kv motor, It’s possible this would end up overheating the motors due to the weight and torque involved.

Cheers!

Kevin & Erik

[Kevin_Erik]

Made quite a few changes last night to the YAW PID’s and filters.
Note: Original values are in parentheses.

# diff
# Triflight 0.7 Beta 2 / RCEXPLORERF3 3.1.7 Jun  4 2017 / 13:39:27 (1698ba5)
name Kevin & Erik's M
servo 5 1260 1600 1440 40 40 100 -1
aux 0 0 0 1800 2100
aux 1 28 2 925 1300
aux 2 1 2 1700 2100
aux 3 2 2 1300 1700
aux 4 31 1 1800 2100
set min_check = 1010
set max_check = 1980
set min_throttle = 1100
set max_throttle = 1900
set 3d_deadband_throttle = 10
set auto_disarm_delay = 3
set small_angle = 30
set align_board_pitch = 180
set gyro_sync_denom = 2
set deadband = 10
set yaw_deadband = 10
set servo_lowpass_hz = 300  (400)
set servo_lowpass = ON  (off)
set tri_tail_motor_thrustfactor = 46
set tri_tail_servo_speed = 588
set tri_motor_acc_yaw_correction = 16
set failsafe_delay = 5
set failsafe_off_delay = 5
set failsafe_throttle = 1100
set failsafe_throttle_low_delay = 5
set failsafe_procedure = AUTO-LAND
set acc_hardware = MPU6000  (auto)
set accz_deadband = 50  (40)
set pid_process_denom = 1
profile 0
set yaw_accel_limit =  8.000  (10)
set yaw_lowpass = 100  (0)
set p_pitch = 43
set i_pitch = 30
set d_pitch = 26
set p_roll = 49
set i_roll = 30
set d_roll = 48
set p_yaw = 100  (170)
set i_yaw = 20   (45)
set d_yaw = 60   (45)
set p_level = 55  (50)
set i_level = 55  (50)
set level_limit = 60  (55)
set rc_rate = 75
set rc_rate_yaw = 75
set roll_srate = 75
set pitch_srate = 75
set yaw_srate = 75

This morning we had a wonderful 2 1/2 flights without tail twitch!

However the 1/2 flight ended in the Tricopter sideswiping a pole. While the Tri looks fine (motors spin up, gyros, FC, camera etc), we did bend one prop slightly (replaced) and apparently have no action from the servo except when the Tri is first powered on.

Note: Servo response during flight felt a little delayed and sluggish. Will have to bump the rates up slowly.

Cheers!

Kevin & Erik

[Kevin_Erik]

So we’ve released the servo from the motor mount, and powered up the Tri. When tail-tune is enabled, servo spins clockwise for a few seconds then stops. Thinking that we may have a wiring / cable issue of sorts.
Beyond this, servo appears to be unresponsive to tail-tune commands from TX.

Edit: Replacement servo on order as we found a wire that looks nicked. Strongly suspect that servo electronics were also damaged during impact.

[GAntonjo]

[Kevin_Erik]

@GAntonjo Well yeah… saw that video a while back. Ducts work great and even provide lift in situations where the attack angle is pretty extreme. Along the same lines, the ducts self-stabilize the craft due to the lift generated over the ducts lip trying to balance out.

Two drawbacks thus far
-Current duct design limits the Yaw range available without coming into contact with the servo. It’s most likely why I wasn’t able to avoid the utility pole, just couldn’t turn fast enough. When I’m able, I plan on making a revised version of the duct that’s more tricopter “Yaw” friendly. (Most likely a 3-spoke design)

-Weight is a big issue when each duct is 35-40 grams each. When I redo the design I’ll look into alternative materials and mfr-processes to see if any improvements can be made.

Cheers!

Kevin

[Kevin_Erik]

3D printed landing gear and camera mounts should be here either today of tomorrow!

[Kevin_Erik]

More info on ducted propeller characteristics: https://www.youtube.com/watch?v=0stl1U9evzU

Q-Tip props: https://www.youtube.com/watch?v=pJEQ4xKFUi4

[Kevin_Erik]

Finished the first draft of the 5″ Duct for the Tricopter-Mini, one that I hope is a little more servo friendly than the ones I am currently using.

Please be aware that I haven’t printed this yet so I’ve no idea if there are any bugs. (STI file is attached, compressed into rar to meet file size requirements)

Cheers!

Kevin & Erik

Attachments:

1. 5-Inch-Duct-for-Tricopter-Mini.rar

[Kevin_Erik]

Made a few updates to smooth things out more. See version 2.0 below.

Cheers

Kevin & Erik

Attachments:

1. 5-Inch-Duct-for-Tricopter-Mini-V2.0.rar

[Kevin_Erik]

Having a prototype printed out in PETG. Should see it early next week. (Will post pics)

Kevin

[Author]

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