UFO Mass-Thrust Trade Off Studies Spring 2016

/in , /by

Written and posted by: Luis Valdivia (Project Manager)

Table of contents:

  • Introduction
  • Formula
  • Tests
    • 1291g
    • 1391g
    • 1504g
  • Conclusion
  • References

 

Introduction:

This document highlights the importance of weight for the UFO abducted quadcopter. Each EDF delivers a maximum thrust of 650g. Running all 4 motors should be able to lift the quadcopter, if the aircraft is not over weight capacity.

 

Formula:

In a hobbyking forum, we found a formula used to determine the allowed weight for certain thrust values carried by the motors.

 

Thrust per edf = (Weight of aircraft * 2)/Number of fans being used

We can turn the formula around and solve for the maximum weight allowed on the UFO abducted.

 

Weight of aircraft = (Thrust per edf * Number of fans used)/2

 

In our case we will have an allowable weight of:

Weight of aircraft = (650 g* 4 EDFs)/2 =1,300g

 

Tests:

Our first test, we attached the 3d printed legs we intended as a replacement of the original landing legs.(also included the battery, 4 EDFs, 4 ESCs,  multiwii flight controller, wireless receiver, lipo low voltage indicator and support attachments for the frame) . The weight of the vehicle for this test was 1291g (9g below our limit).

 

The video can be seen here

 

Our second test, we attached the ducts to hold the servo motors and also included the battery, 4 EDFs, 4 ESCs, 4 pairs of 3d printed legs, a multiwii 328p flight controller, wireless receiver, lipo low voltage indicator and support attachments for the frame. The weight of the vehicle for this test was 1391g (91g above our limit).

 

The video can be seen here

 

For our third and final test, we attached the servo motors (x4) and also included the battery, 4 EDFs, 4 ESCs, 4 pairs of 3d printed legs, 4 ducts to hold the servo motors, a multiwii 328p flight controller, wireless receiver, lipo low voltage indicator and support attachments for the frame. The weight of the vehicle for this test was 1504g (204g above our limit).

The video can be seen here

Conclusion:

 

As a conclusion, we determined the thrust vectoring control for stability would not be possible with the current set up we have. Possible solutions: replace current set up with stronger fans, tilt current EDFs to vector thrust, and finally side fan(s) similar to a helicopter. Table 1.1 demonstrates the necessary thrust per EDF (assuming 4 EDFs are being used) to lift our vehicle. Strictly, anything above 1300g WILL NOT LIFT.

 

Weigt of vehicle (g) Thrust per EDF (g)
1291 645.5
1391 695.5
1504 752

Table 1.1 Above demonstrates relation between mass and required thrust, for liftoff. 

References:

  1. http://www.hobbyking.com/hobbyking/forum/forum_posts.asp?TID=38561