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Electric Paramotor...with a Generator???


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Something I have been thing about lately and may very well do, if I can figure out the particulars...I wanted to somehow acquire  a used paramotor frame on a trike and use a 2000W generator to provide a direct A/C current to a 80kv brushless motor. Seeing as how the power supplied from teh generator is 120v, I am not sure if I need to "step-down" the voltage, since the motor is rated at 70v, using a step-down device (power supply) or if I can just use a heavy duty ESC to do this for me, along with a servo to meter the power and thus the speed to the motor. Any thoughts on how I could accomplish this or is it even possible? I am looking to extend the flight time by mounting a "super-quiet" or some other variety of generator to the paramotor frame rather than a standard gas engine, or batteries in the case of an elec motor,  to power the prop. Is there some kind of "supply and demand" law I am violating or some other reason people resort to using batteries in this sort of an application rather than a generator?

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My machine is rated at a little over 21 kw.

Level flight (for me) is somewhere around 65% of that, so 13.6 kw.

Current battery technology gives you around 30 minutes flight for 20 kg battery.

So:

1. Flying with a battery. A 2 kw generator will provide only 15% of power needed. So during the time taken for the battery to run down will add enough back for another 4.5 minutes. A bigger battery would be a lot lighter than having the generator on board as well.

2. Without a battery. You need at bigger than a 14 kw generator and it will weigh lots more than just having the petrol engine/prop.

The point is, hybrid vehicles are aimed at economy and not weight saving. They are very heavy.

 

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Well, originally, to increase flight times. However, I spoke to a mechanical engineer who works for a large aerial vehicle company who told me that I would not be able to generate enough amperage using a generator (one that is small enough to fit on your paramotor trike), so I guess I would have to use batteries. I am not as excited about that though, so I probably will stick to gas engines for now.

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Flylight at Sywell near Northampton have experimented with these hybrids in conjunction with engineering boffins at Cambridge university for many years with at least 2 different 3 axis efficient microlights. They can get the aircraft flying but the performance is never much more than marginal.

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  • 1 year later...

you should check out a guy on youtube called robert murray smith, he's a proper mad scientist type of bloke that makes batteries and does all sorts of other fun chemistry type stuff, he built a graphene battery for an electric moped out of a stack of printer paper, dropping the much heavier OEM battery for something that's a fair bit lighter albeit a bit bulkier, gives a little glimpse of what battery tech in the coming years will be like, far lighter, more energy density etc, ideal for use in the air where weight is a premium.

 

 

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  • 1 month later...
On 21/02/2018 at 18:18, Chance Waite said:

Something I have been thing about lately and may very well do, if I can figure out the particulars...I wanted to somehow acquire  a used paramotor frame on a trike and use a 2000W generator to provide a direct A/C current to a 80kv brushless motor. Seeing as how the power supplied from teh generator is 120v, I am not sure if I need to "step-down" the voltage, since the motor is rated at 70v, using a step-down device (power supply) or if I can just use a heavy duty ESC to do this for me, along with a servo to meter the power and thus the speed to the motor. Any thoughts on how I could accomplish this or is it even possible? I am looking to extend the flight time by mounting a "super-quiet" or some other variety of generator to the paramotor frame rather than a standard gas engine, or batteries in the case of an elec motor,  to power the prop. Is there some kind of "supply and demand" law I am violating or some other reason people resort to using batteries in this sort of an application rather than a generator?

 

Sounds heavy and inefficient out of the gate, I didn't see any focus on these issues (mass and power efficiency).  The most efficient route if you decide to use an internal combustion engine is:

[engine] -> [propeller]

Compare that to what you're proposing:

[generator] -> [dc-dc] -> [inverter] -> [motor] -> [propeller]

I've done some high level ideation to realistically design a traditionally configured electric PPG with 2 hours of flight time and reserve power.  You would need ~200 lbs of lithium batteries, so foot launch is out of the question it would need to be wheel launch. 

Edited by steelmesh
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On 21/02/2018 at 23:18, Chance Waite said:

Something I have been thing about lately and may very well do, if I can figure out the particulars...I wanted to somehow acquire  a used paramotor frame on a trike and use a 2000W generator to provide a direct A/C current to a 80kv brushless motor. Seeing as how the power supplied from teh generator is 120v, I am not sure if I need to "step-down" the voltage, since the motor is rated at 70v, using a step-down device (power supply) or if I can just use a heavy duty ESC to do this for me, along with a servo to meter the power and thus the speed to the motor. Any thoughts on how I could accomplish this or is it even possible? I am looking to extend the flight time by mounting a "super-quiet" or some other variety of generator to the paramotor frame rather than a standard gas engine, or batteries in the case of an elec motor,  to power the prop. Is there some kind of "supply and demand" law I am violating or some other reason people resort to using batteries in this sort of an application rather than a generator?

The best way to approach this would be to get a small paramotor engine  (belt driven with clutch) and convert the propeller drive pully to a brushless electric motor  then you  could then run this as a hybrid , you could use that motor as a 3phase generator, for charging when you run the engine ( charging would have to be closely controlled or you would overload the engine). 

When the engine is stationery, the centrifugal clutch would disconnect and you could use the motor or you would be able to to use them together as well.  There would be quite a bit of electronic's and separate controllers involved to control and switch everything 

Alternator is around 75% efficient 

Motors is around 80 - 90%max efficiency if you are lucky 

Current draw at 72V   ,  13 kW =185amps

Heat, loss, bearings, electronics, batteries, charging,  etc will add even more losses

Hope this make sense, this is how they are integrating drone engines/motors. They use the motors to help with take-off. 

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23 hours ago, noddyc said:

The best way to approach this would be to get a small paramotor engine  (belt driven with clutch) and convert the propeller drive pully to a brushless electric motor  then you  could then run this as a hybrid , you could use that motor as a 3phase generator, for charging when you run the engine ( charging would have to be closely controlled or you would overload the engine). 

When the engine is stationery, the centrifugal clutch would disconnect and you could use the motor or you would be able to to use them together as well.  There would be quite a bit of electronic's and separate controllers involved to control and switch everything 

Alternator is around 75% efficient 

Motors is around 80 - 90%max efficiency if you are lucky 

Current draw at 72V   ,  13 kW =185amps

Heat, loss, bearings, electronics, batteries, charging,  etc will add even more losses

Hope this make sense, this is how they are integrating drone engines/motors. They use the motors to help with take-off. 

Just trying to understand your proposed transmission layout.  Are you thinking that a motor/generator could be in parallel with the propeller, where the combustion engine could directly transfer torque to both the propeller and the motor/generator?  Then the clutch would allow the motor/gen to drive the propeller with the engine off.  Sounds like the way to go if I assumed right.

In general how will you address problems with the power-to-weight ratio when going to a hybrid?  Long range full electric and hybrids are totally realistic if you wheel launch, but it sounds like no one cares about wheel launch electrics and only want long range foot launch electric paramotors.  

What is the maximum foot launch paramotor weight limit that is within reason?  30 kg?  Tesla battery cells have an energy density is about 0.25 kWh/kg.  Running 10kW continuous for 2.5 hours is about 25 kWh of energy.  25 kWh / 0.25 kWh/kg = 100 kg + [enclosure] kg + [bms] kg + [copper wire] kg + [contactor/fuse] kg + [reserve cell capacity] kg + [forgot about that] kg.  This doesn't consider losses so range would be lower or battery weight increases.

It's depressing I agree.

I think this has been evaluted by 100's of engineers.  They'll need to know a few characteristics to design against such as: 1) Maximum weight, 2) Minimum flight time, 3) Minimum climb rate.  These things will have a significant impact on hardware component selection.  Right now I think characteristic #1 is the deal breaker.

Edited by steelmesh
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 Steelmesh

I would use the propellor hub/pully assembly , use a brushless motor, redesign it and cut grooves on the outside of the motor to run the drive belt over it - use the motor body as my redrive pully.

These  motors work very well as generators, that is how motorbike alternators are design (3 phases with a 3phase rectifier to get it to DC) 

That makes it very compact.

I was looking into building an electric paramotor and gave up after calculated that I need at least 287  lithium 18650 cells to get to at least 30min of flight time, and make it reliable. 

 

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On 01/11/2019 at 14:31, noddyc said:

 Steelmesh

I would use the propellor hub/pully assembly , use a brushless motor, redesign it and cut grooves on the outside of the motor to run the drive belt over it - use the motor body as my redrive pully.

These  motors work very well as generators, that is how motorbike alternators are design (3 phases with a 3phase rectifier to get it to DC) 

That makes it very compact.

I was looking into building an electric paramotor and gave up after calculated that I need at least 287  lithium 18650 cells to get to at least 30min of flight time, and make it reliable. 

 

That sounds like a clever layout!   Probably shave a little weight off compared to other configurations. 

If someone develops an electric foot launch paramotor with a warranty right now and goes to market, it would be at least $20k and would probably still use off-the-shelf components and would still have an embarassing flight time. Anything cheaper would be some backyard built design that is a project in itself to use, and they probably make you buy your own batteries so they don't have to deal with managing energy storage.

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  • 1 year later...

I have been following this thread and reading it and re-reading it for a week now. Noddyc can you draw a cartoon diagram of your proposal? I am seriously considering building it!

I think in a nutshell (and correct me if Im wrong) the idea of this thread is Chance Waite has this idea of using electric portable generators to replace the paramotors themselves. But the problem I think is that he doesn't realize that paramotors are more efficient than portable generators as they are larger. Rule of thumb for internal combustion engines, the larger the engine the more efficient it is and portable generators are NOT efficient compared to larger motor cycle engines or paramotor engines.

If you examine my attached screenshot of my spreadsheet of our Australian Gentrax portable generators I worked out the most efficient generator as well as it's power density of roughly 125W/kg. It's output is 3.5kW and it's weight 28kg. Compare that to a Flattop paramotor I have been closely researching to be my first paramotor for years now and you will see it has a power density of 800W/kg because it has a full power rating of 20kW and it weighs 25kg. Compare 125W/kg to 800W/kg !! The paramotor is has much much more power density! About 6 times more! While this doesn't prove higher efficiency it does show that the larger paramotor is more power dense. I can't work out the efficiency of a paramotor without the fuel consumption numbers at a specific wattage. And no paramotor website supply this information. Very strange. It's like there is a deliberate technical gap in this sports. So I make educated guesses. I assume that the "flight time" numbers used by the websites assume 50% of max thrust/power. Using this assumption you can see in the second attachment that it shows that the paramotor in general has about only 2-3% more fuel efficiency. So if going by my "educated guess" is correct the main advantage in paramotor is it's higher power density which still means that if the fuel efficiency is still roughly equal, it would mean that paramotors still maintain higher overall efficiency because of it's vastly higher power density.

Your idea Noddyc, is to have a normal paramotor engine (large internal combusion engine) and use it as a generator because then it will be more efficient if it is running at the peak efficiency RPM and torque correct? That will increase it's efficiency as an electric generator and the electricity can be used to power the propealar to boose efficiency. I would think that in such a situation you probably want to have some lithium ion batteries and super-capacitors (with a voltage booster) to act as a buffer. And as you pointed out need to make sure the buffer doesn't get overloaded with voltage when it's full.

Have I understood this thread so far?

What I don't understand is why you would choose to go 3 phase AC? Is that the most efficient configuration as a generator? Also would that same generator be used as a motor? Or would the motor be a seperate device also connected to the propellar? (Is the prop connected to one or two electric motors/generators?

I am not too keen on creating a propelar that is powered by both Internal Combusion Engine as well as electricity. But I want to try. But as a minimum what I really want is the ability to use the paramotor as a high output electric generator so that when I land on my "base camp" I can use it as an electric generator to supply power to the camp site. At least in the order of a few kW but ideally about 20kW which is about the same power as the mechanical output from combustion.

David

gentrax.png

flattop.png

Edited by David Ong
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Ok I made a fatal error in my above analysis, looks like the generators are indeed much much more efficient than the paramotors which are extremely inefficient. The numbers for the paramotor efficiency had an error in it, I forgot to divide my Wh by the number of litres the engine runs on. The Wh number was reached by multiplying kW output by hours of run time associated with it (presumably half throttle is used to work out run time in hours before fuel tank is dry). 

Anyways after the correction is made Paramotors seem to be only 2-3% efficiency! That means 97% of the energy in the fuel is wasted as heat! Can someone confirm ?

As for the generators their efficiency are much better: they are 10 over times better with an efficiency about 30%. Cars have an efficiency between the two extremes at 20%.

So looks like there is still a use for the generators here! The only advantage of the larger paramotor engines is power density! They can output more power by consuming more fuel faster.

I also had a brief chat with Noddyc privately and got some numbers off him to put in my spreadsheet. All the evidence is in the screenshot below of my spreadsheet.

Can the efficiency of a paramotor be improved by turning it into an electrical generator as well as an engine? Or will this not change the fact that most of the wasted energy is heat?

Also I am wondering if the above 2 mentioned paramotors im using in the screenshots below are 2 or 4 stroke engines and if they use carborator or fuel injection. I am hoping and guessing that they are 2 stroke carbs and that the newer 4 stroke fuel injected ones coming out such as blackhawk Intruder 250 EFI 4 stroke will have much better numbers. So far all I know is that it consumes 4.3L/hr and its max power is 35HP. If we maintain the assumption that all rated fuel burn rates are at 50% power then that would give it an efficiency of 4.62%.

 

David

 

thermal efficiency.png

Edited by David Ong
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I looked at the conundrum a while ago (mainly to solve a "dirive" specific issue so it was purely dc motor driven prop)
It seems you are likely to lose some power, efficiency and gain some weight.

A smaller motor running at constant max power/efficiency needs to supply cruise current (Maybe 5~8kw?) and enough surplus to charge a pack in reasonably short order (2~5kw maybe?) for takeoff power and the occasional boosted climb.

Save "some" weight with a smaller IC motor, gain weight with a large alternator, the DC drive motor, battery/capacitor, etc...

An accumulated 15kw might be ok ish for takeoff power... 20kw+ would be better and you'll need at least couple of minutes at that.
(Small pack (10Ah?) with massive discharge)

I built a 12v generator for my camper years ago using a 100A alternator on a honda GX100 (classic Honda generator engine) and that alternator must have weighed 5kg and would get VERY hot if I pushed it much passed 20A @14.8v (nowhere near the motors 1.5hp potential but its lasted thousands of hours so far... its getting tired now though)

Alternators are simple but very inefficient and my unwillingness to have two large permanent magnet rotors and an inverter (and learn all sorts of new shit) put an end to my exploration... A single permanent magnet rotor that can generate during cruise and boost when you need it would make more sense (would probably need two winding schemes) but that would place me back into long drive shafts and exotic drive coupling so I left the idea there.

I do like the basic principle but it may be an uphill battle to get it to make any practical sense. 

Currently I fly a four stroke (15kw ish) and can get 50mpg in still air... Hard to beat that :) 

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21 hours ago, Blackburn Mark said:

I looked at the conundrum a while ago (mainly to solve a "dirive" specific issue so it was purely dc motor driven prop)
It seems you are likely to lose some power, efficiency and gain some weight.

A smaller motor running at constant max power/efficiency needs to supply cruise current (Maybe 5~8kw?) and enough surplus to charge a pack in reasonably short order (2~5kw maybe?) for takeoff power and the occasional boosted climb.

Save "some" weight with a smaller IC motor, gain weight with a large alternator, the DC drive motor, battery/capacitor, etc...

An accumulated 15kw might be ok ish for takeoff power... 20kw+ would be better and you'll need at least couple of minutes at that.
(Small pack (10Ah?) with massive discharge)

I built a 12v generator for my camper years ago using a 100A alternator on a honda GX100 (classic Honda generator engine) and that alternator must have weighed 5kg and would get VERY hot if I pushed it much passed 20A @14.8v (nowhere near the motors 1.5hp potential but its lasted thousands of hours so far... its getting tired now though)

Alternators are simple but very inefficient and my unwillingness to have two large permanent magnet rotors and an inverter (and learn all sorts of new shit) put an end to my exploration... A single permanent magnet rotor that can generate during cruise and boost when you need it would make more sense (would probably need two winding schemes) but that would place me back into long drive shafts and exotic drive coupling so I left the idea there.

I do like the basic principle but it may be an uphill battle to get it to make any practical sense. 

Currently I fly a four stroke (15kw ish) and can get 50mpg in still air... Hard to beat that :) 

You can build an induction motor instead of relying on magnets. Btw, what is your fuel burn rate at 15kw? Also is your 4 stroke EFI?

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5 minutes ago, David Ong said:

You can build an induction motor instead of relying on magnets.

Not sure they have the power to weight ratio or efficiency of permanent magnets.

 

8 minutes ago, David Ong said:

Btw, what is your fuel burn rate at 15kw?

No idea... Cant see it being much more than 3 liters per hour but I cant see it lasting very long running flat out for long periods.

 

12 minutes ago, David Ong said:

Also is your 4 stroke EFI?

No
There is an argument that a well tuned carb can give more hp so besides the auto mixture tuning for pressure change, its added complexity and weight start to look like it wont earn its keep on a paramotor.

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Oh man I discovered another error, turns out my oridignal analysis was correct because I didn't keep the energy density for gas constant between tabs. Paramotors are more efficient because they are bigger, they have more power density and energy fuel efficiency. The winner goes to BlackHawk Although it's based on the 60% power assumption for quoted fuel burn rate so it's just iffy. Noddyc's paramotor however we know is 46% well above gas generator efficiencies thus making generators undesirable.

thermal efficiency.png

Edited by David Ong
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Hi

My thoughts.

I would not use the "paramotor " engine for power ,they are not design for that, service intervals would be almost every week depending on use.........

If you look at the Honda gx200  engine that  gets used in the "egg motor projects "and for racing. 

It is designed to run at around 20 percent of full potential  ,at that it will happily run for years, gets used in everything .

If you take the same motor , change piston , conrod,  etc you can get it up to 22hp. At this power output you would have to service /rebuild it almost after "every race " as it gets used at it limits.

This is the same for all aviation. A car engine runs at about 20 percent power while aviation  engines normally  run at 75 to 80 percent power , this is why service is done regularly. 

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The idea to use an electric motor in tandem is not to be able to fly with it ,more to help with take-off. 

If you use an motor as I suggested you could use an 2kw motor and when you use it , you could over load it up to 4-6 kW for 30 seconds with no problem  ,then you are up and it can cool down 

In this time you would empty  all power from the "batteries".

I would use a Brushless 3 phase motor  because  the are compact ,light and efficient (in the monster efi system they use that same idea with a 3phase Brushless motor  for power )

My ppg engine I would use would be a top80/atom 80 size to keep it very small,  charging would be at properly at max 500 watt ( let it charge over an hour to no affect performance)

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On 06/11/2019 at 16:02, steelmesh said:

That sounds like a clever layout!   Probably shave a little weight off compared to other configurations. 

If someone develops an electric foot launch paramotor with a warranty right now and goes to market, it would be at least $20k and would probably still use off-the-shelf components and would still have an embarassing flight time. Anything cheaper would be some backyard built design that is a project in itself to use, and they probably make you buy your own batteries so they don't have to deal with managing energy storage.

 

16193759693017213385577616180631.jpg

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