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.

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.

 

Maiden flight

Today was the big day, the maiden flight of the ascending aid. I choose a small hillsite near Toledo (Magan, Cerro del Aguila) for this first test as the height is only 90m and I had to go back by walking with 15kg of equipment and 4kg of motor/battery.
The wind direction was perfect for this site, north-west with about 5-8 km/h. The test was conducted with the old battery set and the 30" propeller with 10kg thrust.
The ground handling is very easy, the battery pack does not disturb too much. The start procedure is like a normal paraglider. The motor is switched on when airborne to prevent any hazzle with the lines. The motor is also switched of before landing for the same reason.
I flew 2 nearly parallel tracks to compare the sinking speed with and without motor. You can see the details in the track log. The 10kg thrust gives me a ascending rate of about 1m/s. It could not compensate the 1,2 m/s sink rate at this moment, but it would have made the flight much longer if I wished.
Next time I will try the 40" propeller with 15kg thrust. In this configuration, a positve ascending rate should be possible.
Here is the link to the video :

And here the track log:

Arrival of new batteries

Today I received also a new battery pack. The new Turnigy Lipos are 15C rated and weight a little more than the first ones (only 10C). Now I have 6 x 8000mAh 6s batteries. Next test will be conducted to compare the performace of each one. With all batteries I should have a autonomy of about 20min full power. The battery weight is 6kg and the housing motor 2kgs as before. Here a photo of the two battery types:

New BEC

Today I got a new BEC to power the Arduino. The former setup was a smaller BEC rated 6s, which burned down after 5 minutes. Than I installed a 9V battery. with the new beter BEC I do not have to check for the voltage of the 9V battery. as far as there is a 6s 24V LiPo connected, the Arduino has power. Here is the photo of the old and new BEC (old, small one is already junk):

Ground test with video

In this viedo you can the the assembly of the eHayabusa to the standard harness Swing Connect Reverse. The test was conducted with the 30" propeller. Than I tried the 40", which gives >15kg of thrust. But in this configuration the heating of the wires is to much, after 60 seconds I stopped the test. I will install a new software version for the 40" propeller to limit time of full throttle to prevent any overheating.

https://www.youtube.com/watch?v=C8QBHXXR0wA

Physics behind the electrical ascending aid

First of all, what power do I need to keep a paraglider in the air?
From a very simple model, we can estimate the power we need to keep us in the air (without ascending or descending).
If my paraglider has a sink rate of about 1m/s and weights 110kg (weight force: about 1100N), than I need a power P of : P = F x v to keep me in the air.
That means only about 1100W. That is independant of the power source. With an propeller and a efficiency of about 50%, we need 2200W on the propeller to keep us up. Every additional Watt would give me a lift.

Second, what power do I need to get me in the air from ground?
That is far more complicated. The moment with most power consumption is the phase when the paraglider is just behind you at the start. This is the "parachute" moment. The full canopy is open, but not above you, it's behind you and causes a tremendous drag.
The power of the paramotor needs to compensates this drag force and needs to deliver a push force of 500-800N (50-80kg) in a normal condition.
Just for a few seconds, but without this power the canopy will not rise.
As a foot starter you deliver also a lot of power to overcome this drag with your feet. In a trike configuration, the motor has to due all the work and needs even more power.

What is the best canopy?
Normally a reflex canopy is used for paramotors, because it is more stable at higher velocities. But the reflex has a drawback, it has a lower glide ratio as a standard paraglider. The glide ratio defines also the vertical sink speed at a given horizontal speed.
Just an example: the glide ratio of a reflex canopy is half the glide ratio of a normal canopy. That means roughly that the glider has double the sink speed. That means we need to double the power to maintain us in the air.
So the best choice is a standard canopy. We can't fly to fast, but the goal is to reach the next thermic, nothing else.

Picture of prototype

This is the design/prototype of the eHayabusa ascending aid for Swing Connect Reverse harness:

Project description

This a my blog about the project "eHayabusa", a lightweight electric paramotor system ment as ascending aid.

Project philosophy:
The eHayabusa is no "full" electric paramotor for a simple reason: the technology and cost to achieve a full electrical paramotor are not feasible until now.
Nevertheless, an electric ascending aid is possible and economical.
The main difference between an electric paramotor and an ascending aid is the power and the maximum time of power deliverance.
With an ascending aid it is more difficult to make a foot start from even ground, but once in the air, it has nearly the power of an traditional paramotor.
How is it possible that such a low power motor can fly a paraglider? Finally it has only 12kg of thrust. We will come to this point later on.

Project data:

• Weight: basis version only 4kg
• Push force of system: about 120 N 
• Battery capacity: 5 min of full throttle
• Maximum height gain: 150m 
• Assembly time:  < 5min, ready to start
• TOW: <110kg

The design is specially fit to my harness, Swing Connect Reverse, but it's adaptable to nearly all standard harnesses.