Data glove --> throttle control and flight instrument

This is my latetest gadget, a "data glove" controls the eHayabusa and serves also as flight instrument. The OLED display is very bright and clearly visible from a distance. It shows the system status (System off, flight data) and does not disturb the hand movement in any way. Very handy.

Here is a short video of a test run to see how it functions. The system is still modular and can display any information provided: flight time, sensor information, heading etc. It is connected to the Ardunio by a I2C bus which works fine with 1m cable.

New battery position

The belly pack was nice, but has an inconviniency while starting. It changes the harness fit and limits the movement. So I finally decided to put the batteries in the housing. 2 sets of 8000mAh 12s Lipo cells fit perfectly and are secured with a velcro strap.
The batteries weight in total 4 kg so that the overall weight of the eHayabusa is from 4-6kg depending on batteries.

Controller change

I changed the controller from an old Arduino Uno to an Arduino Nano. There is not really a weight problem, but the smaller Nano fits better in the housing.
Here you can see the size difference:

The Arduino Nano controls now also the "data glove" flight instrument.

Heat managment (2)

To activily control the power output due to heat dissipation I installed 2 NTC sensors. One for the motor and one for the ESC. As the heat dissipation is slow, there has to be an offset for the cut-off temperature. I tried several configurations and about 45ºC gives good results for motor and for ESC. The real temperatur of the motor is about 80ºC when the sensors gets to 45ºC.
The motor is than powered down in a cooling mode, not completly shut-off. For about 2 minutes the motor can only run with low RPM and the small propellers realy cool down the motor.
Here is the photo of the motor rod with the ESC and NTC sensors.

Heat management (1)

The heat management of the motor is essential for an effective use of the energy. About 50% of the electric energy is wasted into useless heat. The heating of the motor and components reduces their efficiency and causes more loses (resistance).

There are mainly 3 components which dissipate the heat:

• motor
• ESC
• wires

My strategy is as follows:

• reduce the thinnest wires (ESC to motor) to a minimum
• increase wire diameter from battery to ESC to a maximum 
• have the ESC cooled externally
• have the motor cooled externally

The result is that I changed the battery cable to and placed the ESC on the motor rod. This reduces the wire length from ESC to motor and gives the ESC a cooling from the air flow of the propeller.

I also installed some additional propeller blades to cover the center of the 40" propeller.
The cooling of the motor was really bad before, as the direct driven motor does not get a good air flow from the 30" or 40" propeller.
With the additional 2 small blades (about 10", from a helicopter), I cover just the center of the propeller. Looks cool (and it is) and should give 500g more of thrust :-)
You can see the ESC (red circle) and the additional blades (green circle). The propeller is still well balanced after the change.

RPM measurement

Today I did some RPM measurement to calibrate the throttle control. As I have a Arduino to produce the input signal for the ESC, I can put it easily to any desired value and watch the RPM count from the Hall effect sensor.
I made the measurement with the 40" propeller and here is the result. The input signal varies from 0-179 and the RPM output has the expected curve. The max. RPM for this motor is 5800. At 5400 RPM I measured a thrust of about 13kg which is in accordance with the previous measured valued.
The output signal is now limited to 150 to not exceed this power setting.

Hall sensor for motor RPM

To know the RPM of the motor is a good thing. As the throttle control is done by a Arduino, I can use the RPM value to prevent the motor from overheating and adapt the throttle to different propeller configurations by software.
I made some research how to install a RPM sensor in a model motor. There are basically three posibilities:

• getting a signal right from the 3 wires of the synchronous motor --> that needs some soldering and signal processing
• putting a optical sensor for the propeller RPM --> possible, but too much components for electronics
• Hall effect sensor with magnets glue to the motor --> needs a least 2 additional mangets

I than realized that the motor has yet a lot of magnets inside. There are 40 of them ... so why do not use the Hall efect sensor with them?
This magnets are glued to the inner side of the moving motor housing. I have to get as close as I can to get a good signal. I tried some configurations with a standard Hall effect sensor and it worked.

The Arduino software checks now every 200ms the counts of the magnets and calculates the RPM.
Nice and simple. The value can be used to adapt the ESC signal to control motor speed.
The photo shows the position of the sensor, glued to the motor mounting. You can also see the motor mounting rod, made of carbon fibre. There are some wires left for 2 additional temperature sensors: one for the motor and one for the ESC.