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X450-01 quadcopter (10/11/2013 build)

*** DRAFT ***

Introduction

This article is a collection of build notes for my X450 quadcopter project. The size is 450mm diagonal between motor shafts.

Fig 1:

Key elements of the configuration are:

The mass of the fully populated quad is ~1200g.

Design review

Drive system

Fig 3:

 

Fig 2 shows the characteristics for the 1147 SF propeller. The green dots are for an operating point of 1170g thrust for each propeller at 9.0V (WOT on a flat battery), and the indicated motor power is 118W at is 6560RPM. The efficiency scale (eta or η) is optimistic as the model does not properly take into account the efficiency impact of PWM operation where shorter pulses of higher current create more winding loss than the DC equivalent current.

At hover (3630RPM), input power is 24W/motor, total current at 11V should be around 9A

Nevertheless, input power for 4 motors on 9V should be a little above 100W, 10A has been allowed in battery endurance planning.

Power consumption was measured with the fully populated X450 (though with no additional payload) at 7.5A and 760g in the hovering state. Indicated motor/ESC efficiency is (16.8*4)/(7.5*12)=67/90=75%.

More current is required to climb vertically, but the quad should climb at a modest rate at that current with modest lateral velocity (due to increased lift because of the lateral movement).

At 8.3V, the motor should achieve about 6,310RPM and about 375g of thrust which would accommodate a payload of perhaps 750g with reduced performance. Under these conditions, motor output power would be about 40W each, DC current about 6A each or 24A in total (10C) and motor dissipation around 20W each. Overall, operation at that power is well within the limit of the battery current, mission time is dramatically reduced.

The motors are capable of 8,000RPM with these propellers on 11V, for maximum input power of 120W each, 44A (18C) in total, total thrust of 2400g.

Implementation

The following are notes on the construction. Some issues were noted during initial build, some a little later.

Flight controller

 

Fig 5:

Fig 4 shows the output ports used.

Fig 4:
 

Fig 4 shows the flight controller.

Fig 5:
 

Fig 5 shows the flight controller connections

 

Table 1: Receiver connections
Channel Use FC pin Tx Comment
1 Throttle THR Thr  
2 Roll ROLL Ail  
3 Pitch PITCH Ele  
4 Yaw YAW Rud  
5 Aux1 AUX1 THR  
6 Mode AUX2 3POS  
7 Discovery beeper NC AIL  
8 Spare NC GEA Vibration capture

Table 1 shows the receiver connections.

Table 2: ESC connections
FC pin Motor Comment
1 Right front  
2 Left rear  
3 Left front  
4 Right rear  

Table 2 shows the ESC connections.

Table 3: Bluetooth connections
Bluetooth pin FC pin Comment
Vcc GND  
Gnd 5V  
Rx RX1  
Tx TX0  

Table 3 shows the Bluetooth connections.

 

Propellers

The quad uses nominally 11"x4.5" slow two bladed fly propellers. These are available from a range of sources, and initially the cheap ABS plastic ones have been used.

Propeller mounting

The motors included propeller mounts with collets to suit the 5mm plain shafts. Propellers needed to be reamed out to M8 to suit the adapters, adapter nuts are (non-ISO) 14mm AF.

Power distribution

Power distribution is a Hobbyking distribution board with XT60 connector for the battery and four way 3.5mm connectors for the ESCs.

Receiver

Fig 2:

Figs 2 shows the FrSKY V8FR-II HV receiver receiver.

ESC

Hobbywing Skywalker 40A / BLHeli 11.1.

It delivers better drive system efficiency, and faster / finer resolution control.

Motor

The motors are Turnigy Turnigy D3530-14 1100kv Brushless Motor, specifications:

Battery: 2~4 Cell /7.4~14.8V
RPM: 1100kv
Max current: 22A
No load current: 1.6A
Max power: 315W
Internal resistance: 0.077 ohm
Weight: 73g (including connectors)
Diameter of shaft: 5mm
Dimensions: 35x30m
Prop size: 7.4V/12x6 14.8V/8x4
Max thrust: 1100g

 

 

Measurements

Drive system

Fig 6:
 

Fig 6 shows a static test of the ESC + motor on a 20s sweep from 0% to 100% servo input on a regulated power supply at 12.6V. There was 0.48A current drawn by the four ESCs and FC with the motor OFF, so 0.48A needs to be deducted from the figures in the graph, and about 6W from the power graph.

Expected hovering rpm is around 5,700, actual current consumption was 2.9-0.48=2.42A.

The rpm and current did not sag at full power (>86% servo input) which is good, poorer motors will sag as the winding heats up though current at 13A is 62% of rated maximum, and more importantly, I^2 is only 38% of that at maximum rated current. There was some speed instability though at full power caused by frame vibration and turbulence in the test setup.

The servo signal is a linear ramp of 0 to 100% over 20s, so 5%/s. The ESC range is 1170 to 1860, which is 17% to 86% of the input signal. The rpm response curve is not exactly linear, but not too bad.

Crash damage

Crash damage has mostly been to the propellers which seem reasonably robust... but they are breakable.

The plastic legs are easily broken, especially the landing feed.

A couple of spare frames were purchased to provide spares. 

Further experiments:

 

Links / References

Changes

Version Date Description
1.01 10/11/2013 Initial.
1.02    
1.03    
1.04    
1.05    

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