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Alula Electric Conversion

Converting a discus launched glider to electric power.

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I'm getting too old to toss this glider. My right elbow is shot from abuse as a young adult. It's better to have an electric motor provide the thrust.

I bought an Alula a few years ago. It was everything that Dream Flight said it would be, but my old damaged elbow joints did not tolerate the process of throwing the Alula repeatedly.

The Alula is a DLG (discus launched glider) from DreamFlight. I bought the Alula early on -- thinking that I could handle the stress of the launch on my old bones. It did not work out. After a couple of tosses my right arm was saying, "Don't do this again...it hurts a lot." 

I found a website that provided information to convert the Alula to electric flight -- http://www.jivaro-models.org/alula_trek_electro/page_alula_trek_electro.html. Unfortunately, it's in French, but thanks to Google I could translate it into an understandable english version. I could not get ahold of most of the components called out by the French website. So I set about to find the necessary components available to US citizens. Still, I recommend that you review the French website -- it is a very good explanation of the conversion process.

The Alula Reference Starting Point:

The Alula ships with a heavy NiMH battery and suggests that you use a 7g receiver.  The total AUW for these components is over 40g:

Finding Components:

HobbyKing doesn't have the motor called out by the French website. I waited a few months and then gave up and ordered an equivalent motor from Heads Up Hobbies (which is now going out of buisiness). The HobbyKing motor had a built-in prop-saver, so in order to provide an equivilant capability I added a prop-saver add-on for the motor that allowed for an equivilent solution. Here's what I eventually settled upon for my electrified conversion:I discovered that many of the recommended components are either out-of-stock or unavailable here in the USA. Hobby King was out-of-stock on the motor and ESC, so I went looking for alternatives.

I proceeded to substitute components for what I could get here. This is what I used:

  1. Turnigy NanoTech 300mAh 2S Lipo  = 17g (the same as the French site)
  2. 1510 2200kV brushless motorprop saver = 19g 
  3. Emax 6A ESC = 5g (shortened wires)
  4. FrSky R9 mini receiver = 1.1g
  5. 5.5x3.3 folding prop = 3.5g (same as French site)
  6. Miscellaneous = 2g (motor mount, motor cover, etc.)

Total weight: 47.6g

The links provided are tenuous, so I will provide descriptions that will help you find an equivalent, if you wish to pursue this.

The motor: 

  • KV:2200 
  • Dimension:19mm x 23mm (excluding shaft) 
  • Weight:16.1g/0.57oz (not including connectors) 
  • Diameter of shaft:2mm 
  • Length of front shaft:8mm 
  • Resistance:0.52 
  • Max efficiency currency:2A to 6A,>70% 
  • Max working currency:8.5A 
  • IO:0.5A/10V 
  • Prop recommendation: 
  • 3S/10V, GWS 5030HD, 16500RPM, 5.5A, thrust 272g/9.6 oz. 
  • 2S/7V, GWS 7035HD, 10150RPM, 5.6A, thrust 215g/7.6 oz. 
  • ESC:10A 
  • Battery :2~3s LiPo or 6~10s NiMH

The ESC:

  • EMAX BLHeli-6A
  • Continuous Current - 6A
  • Burst Current - 10A
  • Battery - 1-2S LiPo
  • Dimensions: 22x13x5.5mm
  • Weight - 6g
  • BEC - Linear, 5V/0.8A

The Battery:

Turnigy 2S (7.4V) LiPo, 300mAh/35C rating, 17g, JST connector with JST/HS balance connector. I believe there are better alternatives now. There is another Turnigy 2S 300mAh/70C LiPo that only weighs 18.2g -- a small weight increase for much better power capability. Also, with the popularity of the Whoop class of drone and the new Toothpick class, there are now 300-400mAh 2S LiPo batteries that might outshine the Turnigy stuff.

The Conversion:

I just followed the directions of the website that I referenced above. There are some areas where I deviated:

  1. The motor/prop saver are longer, so the motor mount must be set back further. Therefore, I increased the motor mount template by scaling the image on the printer (see files.)
  2. I used a small sheet of FR4 circuit board for the motor mount. I...
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alula_trek_elec_04.pdf

Template for the motor mount.

Adobe Portable Document Format - 69.65 kB - 08/02/2019 at 21:54

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  • Upgrading to XT30 Connectors

    Bud Bennett08/13/2019 at 18:03 0 comments

    After flying the Alula with the battery's JST connectors I noticed quite a lot of sag when applying throttle. I measured the weight of the JST connectors (and wire) as 1g -- which was approximately the same as a pair of XT30 connectors. 

    I also measured the contact resistance of the JST vs. XT30:

    JST: 350mΩ

    XT30: < 1mΩ

    So I replaced the JST connectors on the ESC and Batteries with XT30. In order to balance the slightly heavier XT30 connectors I added some packing tape to the vertical stabilizer. This was a good thing since the tail was taking a beating when landing on any hard surface.

    It turns out that the total added weight of the XT30 connectors is about 1.5g; less than 1% of the total Alula weight.

    Performance Improvements:

    I noticed that Amber stopped squawking about the battery voltage dropping below 7.5V when I applied the throttle. Flight times increased slightly, from 7 minutes to 7.5 minutes. Good enough.

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Tom Nardi wrote 08/03/2019 at 04:30 point

Fantastic write-up. Impressive how stock-looking the final result is.

  Are you sure? yes | no

Bud Bennett wrote 08/04/2019 at 23:49 point

Thanks, I can’t take credit for the aesthetics. There was a YouTube video of a conversion that required installing the motors behind the spar and cutting a large opening for the non-folding prop. Needless to say I did not follow that approach. 

  Are you sure? yes | no

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