e-calc using cheap DJI parts - RC Groups
Shop our Airplanes Products Drone Products Sales
Thread Tools
Nov 01, 2017, 03:48 PM
Registered User
Discussion

e-calc using cheap DJI parts


here's my config. for a FW450 converted to 500/550 size 8 rotor Quad configuration. and an AUW or 2000 grams..
Amdroix long arms

using 8 cheapo 2212 motors

single 5000mah 4cell pack

30 amp esc

dji 9x4.7 props

I'm getting a respectable 3.5:1 power :weight

running cool motors 44C

flight time 12 minutes at hover


considering the price of these motors and cheap esc's this is a decent power config for lifting a gimbal and 4K camera , add a $45 NAZA light with hacked firmware to FC , this is perfect if your on a ghetto buget.

Any thoughts
Last edited by moonraker007; Nov 02, 2017 at 02:19 PM.
Sign up now
to remove ads between posts
Nov 01, 2017, 07:10 PM
Registered User
Your AUW seems light. What frame are you using?
Nov 01, 2017, 08:53 PM
Registered User
its a fw450 with the carbon fiber tube rails with H3-3d gimbal and Amdroix Aluminum arms , with the gimbal and fpv gear add about 200 grams
Nov 02, 2017, 05:09 AM
Registered User
The estimation is right, 2000 grams is when frame AND payload are less than 800 grams, which is doable.

However, 550 is not big enough to accommodate 8 props of 9" size, please check this claim with a bit of math.
8*9=72" the props circle circumference => diameter = 72/PI = 23 " = 58 cm without any prop clearance !
So you need a 650 frame, or mount the props on two levels, on top and bellow arms, to allow tips overlapping.
No worry too much about tips clearance, is another MR myth that propagates from mouth to mouth, without being verified by anyone.
Those who do it are surprised to find that even 1/4 of prop overlapping has no perceivable effect.
Nov 02, 2017, 06:21 AM
222 km/hr Parkjet flyer
solentlife's Avatar
I'm using DJI motors / props on an SK450 frame .....

The motors are exact fit and the DJI P3 props perfect.

https://www.rcgroups.com/forums/show...-Turnigy-SK450

Betaflight F3 FC
4 x ESC
4 DJI motors from dead P3S
Cheap Hobby King FPV camera / VTX combo
GPS module
3S LiPo (capable of 4S if required)
PWM to PPM encoder
FrSky 8ch Rx

In fact the most expensive part is the Goggles !!

The FPV camera is so small - I can mount direct to servo arm for pan function, controlled direct from an unused AUX ch and rotary knob on TX - no need for gimbal.

The only item the F3 drops out on - Compass ... so no autonomous / RTH functions. But for a cheap starter build ... ??

Nigel
Nov 02, 2017, 11:26 AM
Registered User
Quote:
Originally Posted by moonraker007
its a fw450 with the carbon fiber tube rails with H3-3d gimbal and Amdroix Aluminum arms , with the gimbal and fpv gear add about 200 grams
Your original post said 550 size and 8 rotor quad. Do you have arms extended to 550? Is this a coaxial setup?
Nov 02, 2017, 01:47 PM
Registered User
yes long Amdroix arms co axe with cheap 2212s, but i have to recheck my weight I forgot to add the extra 4 escs, my model is a bit porky and I have excessive electronics and landing gear onboard, I'll clean it up and shave the weight down more, I'm aiming for 1750 grams
Last edited by moonraker007; Nov 02, 2017 at 02:12 PM.
Nov 02, 2017, 02:11 PM
Registered User
Quote:
Originally Posted by renatoa
The estimation is right, 2000 grams is when frame AND payload are less than 800 grams, which is doable.

However, 550 is not big enough to accommodate 8 props of 9" size, please check this claim with a bit of math.
8*9=72" the props circle circumference => diameter = 72/PI = 23 " = 58 cm without any prop clearance !
So you need a 650 frame, or mount the props on two levels, on top and bellow arms, to allow tips overlapping.
No worry too much about tips clearance, is another MR myth that propagates from mouth to mouth, without being verified by anyone.
Those who do it are surprised to find that even 1/4 of prop overlapping has no perceivable effect.
coaxe quad with amdroid arms
Nov 02, 2017, 02:23 PM
Registered User
ok, in this case increase props and use different props on top and bottom, higher pitch on bottom
I would go with 10-11x3.8 on top and 9-10x4.7-5.5 on bottom.
Nov 03, 2017, 10:43 AM
Registered User
Quote:
Originally Posted by renatoa
ok, in this case increase props and use different props on top and bottom, higher pitch on bottom
I would go with 10-11x3.8 on top and 9-10x4.7-5.5 on bottom.
wonderful idea sir!
Nov 03, 2017, 01:20 PM
Registered User
Quote:
Originally Posted by moonraker007
yes long Amdroix arms co axe with cheap 2212s, but i have to recheck my weight I forgot to add the extra 4 escs, my model is a bit porky and I have excessive electronics and landing gear onboard, I'll clean it up and shave the weight down more, I'm aiming for 1750 grams
I would be surprised if you can get it close to 2000 g. I would expect more like 2350 or so. You will still have plenty enough power to handle this load.
You may have to add additional parts to mount the second set of motors underneath the arms. You will need long CF tubes and structure to mount the gimbal and camera out in front of the props. The lower set will be the problem. You will need the battery mounted farther to the back to balance the gimbal/camera, so again more structure.
Some folks have had problems with the aluminum Aimdroix arms transmitting too much motor vibrations. This may be worse with two sets of motors on each arm running at different speeds.
Anyway good luck with your build. I look forward to seeing your progress.
Last edited by syotr; Nov 03, 2017 at 01:25 PM.
Nov 06, 2017, 03:31 AM
Registered User
Different props top and bottom is mandatory in a coax setup.
The lower prop must suck the air pushed from the top, thus a higher speed of air column, more RPM and bigger pitch needed on bottom.
Otherwise the bottom disks will just freewheel, or worse, become a brake for the top layer !
Nov 06, 2017, 04:58 AM
222 km/hr Parkjet flyer
solentlife's Avatar
Quote:
Originally Posted by renatoa
Different props top and bottom is mandatory in a coax setup.
The lower prop must suck the air pushed from the top, thus a higher speed of air column, more RPM and bigger pitch needed on bottom.
Otherwise the bottom disks will just freewheel, or worse, become a brake for the top layer !
??

I don't argue your logic ... but as an owner of various Co-Ax helis etc. - the top and bottom blades are same.

The bottom blades benefit from an already speeded up air flow, reducing losses on them. It effectively creates a virtual pitch increase of the lower props.

Nigel
Nov 06, 2017, 07:37 AM
Registered User
Heli works significantly different than MC, both props are same RPM, but could have different pitch, and the pitch is variable during flight.
The final goal probably is the same, to avoid the bottom disk act as a brake for the upper disk.
Nov 06, 2017, 08:24 AM
222 km/hr Parkjet flyer
solentlife's Avatar
Quote:
Originally Posted by renatoa
Heli works significantly different than MC, both props are same RPM, but could have different pitch, and the pitch is variable during flight.
The final goal probably is the same, to avoid the bottom disk act as a brake for the upper disk.
Sorry we'll leave it there ... we agree to disagree.

Nigel


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion App for the airplanes (CG calc., power setup e.t.c) ShurikMur Electric Plane Talk 5 Sep 28, 2017 01:30 PM
Discussion E-calc question bob93447 Power Systems 3 Mar 04, 2017 10:23 PM
Discussion Pizza Trays Plane... aka the Very Easy Plane V.E.P. built with cheap F939 parts RC Lover san Foamies (Scratchbuilt) 2 Feb 07, 2017 05:50 AM
Discussion E calc calculations vs real world ? sagomon Glow to Electric Conversions 17 Jul 30, 2016 04:55 PM
Discussion e-Calc and rotor pitch calculation STUCARIUS Scratchbuilt Multirotor Drones 1 Apr 26, 2016 11:29 AM