Two motors? From X4

Is it possible to run two motors (vertical configuration, one above the other) with two battery packs without overheating? Looking for a light thermal kit, just to get to 1200-1500’AGL. I have no issues launching with my atom 80 so I suspect two engines will work, thrust wise.

Thrust wise 2 motors would be okay. On the other hand if you are using this to climb 1200’+ you might need the 4 motors to have the required efficiency.

I tried a proof of concept a couple of years ago but lacked the skills, time and money to follow through.

This guy did it, but not with OpenPPG equipment:

100% will work. Don’t have an Open PPG but follow this forum closely as I’ve been working ~5 years on two electric powered hang glider units. One is a single motor setup and the other is a twin motor. Both use only 2 batteries 12s setup, the twin weighs 15.5lbs with batteries (14ah) and the single motor weighs 22lbs with batteries and uses (25ah) HV batteries.

I would use 2 x Tattu HV 25ah batteries and 100amp ESCs (80amp esc won’t cut it). I would target pulling at least 165 amps at 4.35 v per cell or 8600 watts. Should give you a 300-400 fpm climb depending on wing, climb will drop to 100-200 fpm as voltage sags but you should be able to reach 1000-1200 on one charge. That assumes your wing performs equal to or better than a WW Falcon 3. Not sure what cruise speed is with para glider but with HG slowest airspeed for high performance glider is around 26mph so 22x10 props don’t work. I would go with 22x12 or maybe 23x12. If you go with bigger props you may want to limit watts through Arduino.

Video of ehelp (single motor) here: also all files are open sourced, link in video description.

Video of XTM5500 (twin motor) here: This uses smaller Mad M6C18 motors though I have the M10’s on hand but don’t like the bigger diameter from a drag perspective. This setup pulls about 120amps (5500 watts) but doesn’t have enough power to climb, just enough to maintain with a Laminar Z9.

Also I came up with a design for a 2 motor setup in line with you goal, see sketch below.

If you have a carbon fiber I beam extend off your back by about 14inch you could have 2 booms that would swing out with motors on the end. By using a single blade prop with counter weights the whole setup could retract into the streamlined harness behind the pilot once in the air. A linear servo would actuate the arms getting pulled back into place. I think the hardest part to this design is getting the props to stop at the right place so everything can fold in. Not an impossible task but you can’t use the hobby wing ESCs, will likely need to go to VESC (if they can handle ERPM) or mechanical system.

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That XTM5500 looks awesome. That some nice engineering and construction.

I do believe you’re overthinking the twin folder though. I had thought about this when I was brainstorming a setup for something like a Sandlin Goat or Carbon Dragon. On the fuselage/boom you attach swiveling arms - they only need to be as long as 1/2 the prop (+1" or more to ensure clearance), so a 36" propeller only needs 19-20" of arm length.

The props are mounted away from the boom. The arms when extended are restrained by wire or cord (like spectra) and the cord is drawn back by shock cord to avoid snagging. To extend the arms, simply start increasing the throttle. To fold, just let off the throttle - the wind and the shock-cord will tuck the system back in.

For a hang glider, you might want to have a manual deployment process to avoid any asymmetric deployment since there’s no rudder to compensate for a temporary imbalance. You should be able to do that with a low profile wire in the front.

I don’t think it’s going to matter a whole lot where the props stop since, to the wind, they’ll be fully feathered. You can go crazy chasing that extra 5% getting them stopped in the optimal spot but at least you’ll be 95% there.

Your design with the motors folding back instead of forward is much simpler. It would add 1/2 the prop diameter to the total length the unit extends off your back compared to folding forward with a single blade prop but is so much less complex. Also with a 22-23in prop unit would only be 23-24in off back assuming a small buffer. I wouldnt use bunge and spectra though, I would use springs and a 3 bar linkage so nothing can ever get caught in props.

Another option is to skip having the motor boom arms fold and use a folding prop and add fairings to the boom arms and a nose cone to the motor (similar to the XTM5500).

With a Hang Glider folding booms isn’t a great option, the arms need to hang about 8-12in below keel and need to have an adjustable angle to get thrust line dialed in, a folding boom would make this very complex. It would also move 3lbs about 12in aft when folded and have an effect on CG, which on the XTM5500 is currently perfectly balanced.

Haven’t posted update yet on XTM5500 but it works well just need to dial in specifically increase thrust to give climb of 200-300fpm.

Every design decision, particularly in the flying world, is a compromise so the consideration of that design was to specifically get away from having to use a folding prop and allow a wider range of prop options while reducing the cost of a feathering mechanism.

I think the thrust angle adjustments could be made without too much issue. A similar mechanism as you have with the XTM5500 could be used. It’s the height of the thrustline that would be the tricky one. With the XTM5500 it looks like you have variable “droop” on the arms. If you were to use folding arms the droop mechanism would need to be outboard of the hinge, so that the propellers would still fold perpendicular to the plane of the keel. It would likely mean that more of the frontal area of the arms is presented to the apparently wind while folded.

The change in CG is definitely a concern with a hang glider since they’re much more sensitive in pitch, which wasn’t nearly as much a concern in a conventional tail fixed wing. As long as you remain in the stable range, trimming CG further forward on launch/land isn’t necessarily a bad thing. You could always compensate by having the batteries move when the arms move so the net change is zero - but that would add a whole lot of complexity.

You make some good points. On the XTM it has variable droop for the arms and variable mount points to angle thrust line further down, so folding arms would be very complex. Also i cut CCW and CW wood props on my cnc router so they fit into my folding hub ![20200723_105427|500x500] so lots of cheap prop options (upload://sqv5ua85a2Wri2ByPy603OtWokp.jpeg). I made the folding hubs out of 7075 Au on my cnc mill and included balancing holes, and added a quick release to the mounts so they pop off for fast break down. With respect to moving CG thats a major pain about a 30-40min job to move hang point and want to be able to choose to fly with or without power unit and make no other changes to glider. The revised XTM version i’m working on is much more streamlined and has fixed arms that hold the boom at about 10in below the keel with a straight boom so the angle can be changed by a single linear servo. The motor arms also have quick disconnects.

Just noticed pic didn’t attach. Quick release is new addition.

Thanks for all the info everyone. Interesting stuff for sure. My plan was to use two of the motors from my x4 with just two batteries. Apparently I need to do a lot of research as electrics isn’t my strong suit.

You should be able to use 2 motors, 2 ESCs and 2 batteries from the x4, at 160amps you would be pulling 7c on the 22mah bonkas. I would personally upgrade to 100amp ESCs so at 80amps its 80% of ESC rating and would go with HV 25mah batteries. This would provide longer run time, more thrust and not be up against specs. Also if you skip folding or feathering props, retractable CF beam it should be a really easy build.

I wouldn’t go with 25mah batteries as they might get you 5 seconds of cruising. I would probably go with 25Ah batteries. Lol

Ha. Good catch. Was referring to these:

Hi, I am interested in building an electric foot launch powered hand gliding unit similar to your e-help. I looked at the your files (thanks for open sourcing your design) and I am wondering if it is better to use MAD M30 at 14S or MAD M40 at 24S. Which option will give me more efficiency and more flight time if I use a total of 4 Bonka batteries.

The bigger prop and fewer number of props will almost always be more efficient. So if you want max efficiency, go with the 43kv M40 or even 40kv M50(doesn’t cost much more). The one downside is that you would be working with much higher voltages. So make sure you really know what your doing or have help from someone who knows what they are doing.

Hey, I was just reading this thread and saw you also got M40 for your own electric paramotor. There are 2 versions of this motor 43kv and 50kv. Which one is better to drive a 125 cm prop. How many batteries do you use and what is your setup? Thank you!

nice2care - PM me if you want to have a call to discuss. In the meantime below is some additional info.

For an ehelp (hang glider unit) both the M30 and M40 will work. I’m selling the prototype in the video to a buddy at the end of the season and have already purchased a M30 100kv for my next revision which will incorporate a lot of other changes. With that mentioned, I think the M40 is overkill and you will need to get a custom wound motor from MAD. Reidar typically uses a 34x12 prop with a 110 or 105 kv rewound hobby king motor. I’m using a 36x14 prop and upgrading to a folding hub which would increase to 37". I wouldn’t go much bigger than that as pfactor will kick in. I have an old LD explorer (mosquito clone) and it was very unpleasant to fly with the big prop, the prop will also hang lower and likely be in grass during launch even with skid to keep it from hitting the ground. If you go with 14s the 100kv M20 or M30 will work without being rewound as you can just go to a smaller prop, you’ll need to figure out what works. On my Hobby Wing 200amp ESC the over current protection often kicks in at 162 amps on the ground when running consistently and sometime in air but not as often so you may want to upgrade to a 250-300amp ESC. However at 14s you’ll get more watts from lower amps so the Hobby wing ESC may still work, don’t know if they are watt sensitive or just current limiting. Motor limits for the M20 is 175 amps and M30 is 195amps don’t recall the watt limits but they are definitely power (watt) limited.

I would recommend starting with the following:

What what thrust are you looking to get? Are you going for more power or less weight? What rpm do you want to swing the prop at? Do you have any battery limitations?

Not sure what nice2care is looking for. However my goal was lowest weight and one climb to 1,500ft. Which I basically achieved with 22lb all in weight and 2 battery system (got to 1,200 ft / 20min flight time). Below is table with test stand data and flight notes from that setup on Falcon 3. The thrust gauge wasn’t working for the MAD 20 motor tests. My conclusion is 8k-9k watts should be target power requirement assuming efficiency isn’t that much different for various setups which I wouldn’t expect.