I completed the maiden flight of my Ranger EX 757-3 today, with mixed results.  The flying weight today was 6lbs, using a standard rule of thumb, the power requirements would be 450 - 600W.  The supplied 3715/1000KV outrunner brushless motor only provides 300W.

The GOOD:

  • Initial parameter selection flew the aircraft safely and successfully in Manual and FBWA! 
  • The build was good (no bits flew off)!
  • All the systems checked out
    • Pixhawk
    • GPS/Compass
    • Power monitor
    • LIDARlite V3
    • Airspeed sensor
  • Modes checked
    • FBWA
    • Manual - now have a good trim

The Mediocre:

  • Under powered, with the current motor and 6lbs flying weight takeoff and climb out were sluggish
    • Batteries 2 x 5100mah 3S 8C batteries in parallel - which should deliver 40A each 
    • 40A ESC
    • 25A motor (~300W)
    • Looking to upgraded the motor to 450W plus and may need 60A ESC for 600W motor

Views: 983

Comment by Johnatan on February 11, 2017 at 2:39am

Nice!

Any photos from the internal setup?

Comment by Marc Halcomb on February 11, 2017 at 8:53am

Forward equipment bay:

  • Pixhawk - on vibration mount
  • 3DR telemetry transmitter starboard side
  • Pixhawk power module port side
  • 2 x 5100mah 3S 8C LiPo battery packs
  • Digital L2C airspeed sensor
  • FrSky RC receiver/telemetry transceiver 

Not visible:

  • LIDARlite V3 - bottom of airframe
  • 40A ESC - port side below wing saddle 
Comment by Marc Dornan on February 11, 2017 at 11:06am

Try 6S and a Tiger MN4012-9 with a Tiger 80A ESC. Bit pricey I know. I have one in this spec that I purchased lightly used from a person who had multiple rangers. I have yet to fly it but I have seen it fly well on a Vector but I am adding a Pixhawk 2 to it. 

Better still -- ask on this thread. This is where you need to be. https://www.rcgroups.com/forums/showthread.php?2141115-The-Ranger-E...

Comment by Ben Owen on February 13, 2017 at 8:09am

I flew my Ranger last weekend. Woefully underpowered with stock setup on 3s. Unfortunatly my flight had an abrupt ending. I love the idea of the platform but have yet to ever feel comfortable with it in the air.

Comment by Marc Halcomb on February 13, 2017 at 1:03pm
Sorry to hear your flight ended abruptly. Hopefully the damage is repairable? The stock motor is underpowered for my 6 lbs takeoff weight, I have ordered a 500w motor to replace the stock 300w.

Once the airframe made a cruising altitude it flew very stable and landing soft but positive.

The original post has a plot of power vs airspeed/altitude
Comment by Ben Owen on February 13, 2017 at 1:34pm

From initial inspection it should be repairable. I figured it was the voltage issue not the motor. I'll have to look around and see what motor I can find. Thanks for your calculations. Maybe next time with a better motor my results will be better. Make sure you keep us up to date on your progress.

Comment by Marc Halcomb on February 17, 2017 at 6:35pm

I was finally able to complete the 2nd flight of my Ranger EX 757-3.  My expectations were high, the results were less than impressive.  After installation of a 450W motor, I expected to the current in the 40A range (Burst) for takeoff, followed by 34A (Continuous)  at full throttle.  I expected a considerable boost in performance from the maiden flight, but as you can see I am running at 25A full throttle, and from the right-hand plot only 12A in FBWA.

As a result, I only had slightly better performance for the 2nd flight.  Fortunately, my dodgy takeoff was followed by very stable albeit underpowered FBWA circuits around the field, followed by a nice landing.

  1. The underpowered FBWA mode, was an oversight on my part "THR_MAX" was set to 75% (the default)
  2. Still have not figured out why the new motor is limited to 25A, same as the 300W motor.
    1. I did reset the throttle input settings for the ESC with the new motor, no change?
    2. The battery pack is 2 @ 5100mah 8C's in parallel.  I expect the pack to deliver 40A each battery for a total of 80A's from the pack.
    3. I am tempted to try another ESC, maybe 60A's but that's just a shot in the dark!
  3. Airspeed and rate of climb were ok, but I really expect more from the 450W motor, really need to sort out the power issue before the next flight
  4. Also need to sort out the "roll trim", still has a steady starboard roll in manual mode with the trim full port.
Comment by Ben Owen on February 18, 2017 at 3:34pm
Once I tried to take off in stable mode with throttle limited to 75 percent. She never made out off the ground. It's easy to miss a parameter when there are so many to look at.
Comment by Marc Halcomb on February 20, 2017 at 9:46pm

Ben, besides the "stable mode" takeoff attempt with the 75% throttle limit, do you usually use one of the stability modes for takeoff? eg FBWA, FBWB, STABILIZE ... 

Comment by Ben Owen on February 22, 2017 at 1:30pm

I tried stability takeoff with the higher max throttle and it worked well. I don't think I have enough stick time to use the word usually. I mainly keep it in stability to ensure when it crashes it crashes gear down. Because of the under powered motor I never have ventured to the fbwa, b, rth, loiter or any other mode where I surrender throttle control.

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