very small generator

[gwhy!]

What do you guys think about running a small out runner with a rc gas motor to use as a genny on a e-bike would it be worth the effort ( extended range of batterys ), I know nothing about rc gas engines to be fair and dont know if they would have to be run at high revs to get the power out which then will make it a bit noisy also can they run for long periods and what sort of fuel consumption do they achieve. Any thoughts

 

[seanreit]

Depends on the Rc engine, the real small ones run on Methanol and castor oil mix and are loud and inefficient two strokes. They do have four stroke that run on same fuel less loud more power but will use a gallon of fuel in an hour easily. The bigger Rc engines are almost identical to wheed whacker engines or other small lawn care engines. Almost always two stroke and run on petrol and oil mix. More can be read at rcuniverse.com search for small engine conversions etc. May have been done, they are a resourceful bunch at that forum.

 

[Drunkskunk]

Super high output, super light weight, and the motors meant for the RC trucks have enough fins to be run at Ebike speeds without melting.
But they burn a special fuel that runs $30 a gallon and are about as efficient as any pure race technology would be. Not at all.

For the same size and weight of generator and fuel, you could go 5 times as far by getting one of those gas bike motor kits and driving the wheel directly with the motor.

 

[Seriousknot]

Ryobi has a 34cc four stroke weedwacker now. Youtube has videos where the rc guys modify them for increased power and rpm. Very light. Also, Rotapower has a very small 10kw generator utilizing a Wankel engine of their own design, this is intended for electric hybrid cars. They also developed a Wankel rotary engine for Weedwacker use. Extremely light and about 2.5 hp. You can see pictures by Googling Rotapower + Flickr.

 

[dogman dan]

As I've said before on this subject, just carrying about 30 pounds of pingbattery or equivilant, and some good chargers works best at this point.

Toting my 100 lb 800 watt honda generator is no solution. The next best off the shelf thing is the current honda, EU 1000 generator that weighs about 50 pounds. But to beat carrying a second battery the weight(including a lot of fuel) would have to be really really light to beat 15 more pounds of lifepo4.

But supposing you could make your own lighther generator, say 20 pounds, 4 stroke, and quiet, that put out 400-500 watts you'd have a bike able to ride till your butt ached bad.

Personally, I find riding two pingbatteries till they cut off such a challenge I rarely want more after that, having traveled 60-80 miles. But I could charge a few hours, and make a 100 mile day of it. Even out here in the west, 60 mile range gets you to the next avaliable outlet. Wallmart usually has one out front, for one. And city parks are a good place to look.

 

[gwhy!]

I was just looking at it as a means of making non-ev-believers happy, When ever I am talking to someone about my bikes or ev's in general there main concern is range, if a very small/quiet genny could be sorted out that increases the range by 2 or 3 this will go a long way to help the cause and get non-ev-believers , believing. its easy to demo the power of ev's and very easy to show people that they can do every thing that a gv does but then they always make a face when you tell them that it needs to be charged maybe every day. I think to really get peoples attention the range needs to be the same as the gas equivalent, now we all know on this forum that that isn't necessary but I can also see where the non-ev-believers are coming from.

 

[dogman dan]

I agree with that idea. I just don't have near the skills to build a lightweight generator, and the current ones avaliable are a bit too big for typical bikes, but maybe ok for something larger, like a pedicab built for that kind of weight.

But to just strap onto a normal bike, 30 pounds of battery or any cargo is about the max comfort level, and two 48v 15 ah lifepo4's takes you further than most folks butts can stand. I've really enjoyed having that kind of range when I want it, but mostly just carry one, and have about 25 mile range carrying 15 pounds.

One really appealing thing about the generator idea is to be able to just look for a cup of gas instead of a plug, or ride in places with no plugs at all for more than 60-80 miles. Something in the 10 pound range would be great, and carry 5 more pounds of gas. Small enough, it could just make a low purring sound that doesn't annoy. Even if it just put out normal charger amps, say 100 watts, it would still extend range, and charge you anywhere. Riding hypermile style, your draw may be only 200 watts, so that 25 mile range ping would double.

 

[REdiculous]

I'd love to see someone do it. Be the first and try and spend as little money as possible so that when you get it working I can copy it.

 

[gwhy!]

I was just looking around on the net for 4 stroker rc engines and there are quite a few, the smallest i found was a 8cc and it weighs in at under a kilo ( dry ), I wonder if this could be coupled with a small light outrunner which will also be under a kilo I think that maybe a whole setup could weigh less that 3 kilo's (7lbs), but then there is the whole question about noise and heat if its running all the time. Could be a interesting little project, I may have to start looking around for one of these small engines to play with.

 

[Seriousknot]

The Rotapac Gen Set (rotary engine) weighs in at 40lbs, it is designed for Hybrid cars and puts out a whopping 10kw!!
http://www.flickr.com/photos/37449250@N03/sets/72157617096984972/detail/
Their 2.8 hp rotary engine weighs 4 lbs and is designed for weedwackers. Take a 4 lb engine and mate it to a high amp alternator that is rewired for the voltage your charger requires and voila!! you have a very small, light and compact solution. The only problem is getting your hands on one of their 2.8 hp engines as they have not gone into mass production. Nitto in Japan makes a very nice 20cc rotary engine for helicopters and airplanes, but they cost near $2000.00. I personally have a collection of antique Wankel rotaries.... the smallest is 110cc and weighs 15 lbs and makes about 7-8 hp with only 2 (count them) 2 moving parts, and no oil in crankcase. http://www.youtube.com/watch?v=8Mi-cC1mEAM
If someone had say some skills with solid modeling and access to a cnc, a smaller version of this engine maybe 24.5 cc, could be produced rather easily using sealing technology learned by racing Mazda rotaries. A high performance 49cc twin rotor version could be produced using the same rotors and housings and might be extremely marketable. Hmmm................Or the Wankel could be incorporated into a wheel, aka hubmotor this might be the ultimate parallel hybrid. X5 Frontie with Regen and Micro Wankel rear with Human assist pedaling. Imagine when you show this to your local news channel.

 

[gwhy!]

Or maybe get way from gas power all together, what about compressed air 8) now that would be really cool, just pull upto a gas station and use the compressed air line to top your air tank or maybe even use those small co2 inserts that are used for pumping up your flat tire. Uhmm I need to a bit of looking around to see how these compressed air engines work,max rpm and how long they can run per volume of air.

 

[Jeremy Harris]

I looked at this idea about a year or so ago and concluded that it was definitely possible to build a small and reasonably quiet light weight four stroke generator.

The engines I was looking at were the Honda GX25 and GX35 four stroke strimmer (weedwhacker in US-speak) motors. These are nice and light (2.9kg for the 25cc and 3.46kg for the 35cc), reasonably powerful (720 watts for the 25cc and 1000 watts for the 35cc) and they run at a high enough rpm to run a big outrunner directly, with no belts etc.

They are also reasonably cheap to buy, as you can sometimes get them on eBay. Being complete units, with fuel tank, fuel system and oil tank etc all built in they are relatively straightforward to use for other purposes. The only downside I could see was that they have a built in centrifugal clutch on the end of the crank, which needs a bit of work to hook up to a motor shaft.

Jeremy

 

[Seriousknot]

Some of the small Honda's are even electric start, 115vac I think. It is possible that the starter might work with the dc voltage of the battery pack with some modification. Those little 4 strokes are high compression and hence can be very hard to pull start.

 

[GrayKard]

Get one of those modular weed eater motors that allow you to change attachments. One minute you are cutting the grass or trimming the trees, the next you plug it onto your bike and run down to the store for beer. :lol:

 

[gwhy!]

I looked at this idea about a year or so ago and concluded that it was definitely possible to build a small and reasonably quiet light weight four stroke generator.

The engines I was looking at were the Honda GX25 and GX35 four stroke strimmer (weedwhacker in US-speak) motors. These are nice and light (2.9kg for the 25cc and 3.46kg for the 35cc), reasonably powerful (720 watts for the 25cc and 1000 watts for the 35cc) and they run at a high enough rpm to run a big outrunner directly, with no belts etc.

They are also reasonably cheap to buy, as you can sometimes get them on eBay. Being complete units, with fuel tank, fuel system and oil tank etc all built in they are relatively straightforward to use for other purposes. The only downside I could see was that they have a built in centrifugal clutch on the end of the crank, which needs a bit of work to hook up to a motor shaft.

Jeremy

That could be a very good cheap way of sorting out a small genny , perhaps a 25cc at just under 3kg and a outrunner at around 1kg and a bit of electronics and its sorted at under 5kg, I think this will be over kill on the power output but will be able to make a huge difference in range, maybe a much better application for this sort of power output would be for use on a lightweight motorcycle. Jeremy have you ever looked at compressed air engines ? any thoughts?.
Electric start would be nice but it should not be to much to run something from the electric motor to start the gas motor rather than doubling up on motors and adding weight.

 

[coln72]

We use those little Hondas to power our pedal/petrol trikes. With pedal assistance and smart useage, it is possible to get 24hours out of 3 litres of fuel.

They are great little engines and not that hard to modify to directly drive a shaft as we do not run clutches. Only issue I have had is a bent crank after the flywheel let go......

 

[REdiculous]

Air engines usually suck pretty bad. I've seen a small Tesla turbine mated to an RC motor..it worked better than most, imo. The problem is the volume/pressure it takes to do useful work..those air cylinders don't hold much for their size and weight.

The same problem has kept MDI from really getting anywhere with its air car. Despite massive carbon fiber air tanks and an aluminum frame (iirc), the range still sucks. Their engine should be better than most too, I'd think.

If you want to try air then maybe look into Tesla turbines..it should be better than starting w/ an inefficient air tool. later

 

[amberwolf]

I think to get really useful work out of a modest-sized air tank, you'd need to compress it to liquid state. Then vent the heat from the motor to the output lines and valves to keep them from freezing.

 

[electraflyit]

Whow!!!!!

Maybe our first 'ebike' hybrid coming up.....

eddie

 

[newbiebiker]

any hybrid bikes development ?

 

[MrDude_1]

I agree with that idea. I just don't have near the skills to build a lightweight generator, and the current ones avaliable are a bit too big for typical bikes, but maybe ok for something larger, like a pedicab built for that kind of weight.

But to just strap onto a normal bike, 30 pounds of battery or any cargo is about the max comfort level, and two 48v 15 ah lifepo4's takes you further than most folks butts can stand. I've really enjoyed having that kind of range when I want it, but mostly just carry one, and have about 25 mile range carrying 15 pounds.

One really appealing thing about the generator idea is to be able to just look for a cup of gas instead of a plug, or ride in places with no plugs at all for more than 60-80 miles. Something in the 10 pound range would be great, and carry 5 more pounds of gas. Small enough, it could just make a low purring sound that doesn't annoy. Even if it just put out normal charger amps, say 100 watts, it would still extend range, and charge you anywhere. Riding hypermile style, your draw may be only 200 watts, so that 25 mile range ping would double.

slightly off topic, but this caught me off guard. Is 100 watts really considered to be "normal charger output"??
My home/work chargers are 1300watts... I limit it there so I dont draw too much on a shared circuit. My baby charger is 500watts... Is 100 really the norm?? because that means it would be 12+ hours to charge my pack from empty.


going off my bike.... at 66v its 20 amps... but hauling down the road, I can easily pull more than that. 40a for example. if I sustain a 40a draw, with a generator making 20amps, I am only increasing my range 50% until I am empty... and thats with a "huge" 1300 watt generator.


I dont see any generator working unless you're going slow bicycle speeds AND pedaling.... and at that point the range is limited to your fitness level anyway.

 

[Hillhater]

^^^if you are going backcountry and want self support! you would not be planning to burn 3kW + for long.
The plan is to reduce weight and minimise power requirements.
There are plenty of generator units in the 800-1200 W range, but they are all significantly heavier than the devices being sought here.

 

[Jil]

Hi,

7 years later, I reopen this subject !
Technology has evolved since then. 1 liter of gasoline is 10 kWh. Even with 25% efficiency in a motor, it is still 2.5 kWh, equivalent to ~10 kg of good lithium cells.

—> Do you think it could make sense, for long and remote ebike trips, to carry a tiny gas generator and 2 liters of fuel, to be able to recharge anywhere ? Let’s say in the 200-300 watts range (enough to charge a 1 kWh battery in 3 to 5 hours).
If yes, do you have models in mind ?

Or finally a generator is so heavy (I have not found any below 10 kg) that it still better to carry the equivalent weight of batteries ?

 

[DogDipstick]

Or finally a generator is so heavy (I have not found any below 10 kg) that it still better to carry the equivalent weight of batteries ?

We do this on RC helicopters all the time. They run a belt to a brush-less outruner motor off the main shaft: to power all the electronics ad charge the flight control battery for extended ( 30 min plus) flights. Both Nitro engines and Gasser engines. (nitro-methanol two stroke engines, and weed eater engines). All up, the heli is about 12-15lbs, so it has to be light. Entire system under 1 lb.

The downside, is noise and dealing with two stroke fuel... . I know at least someone here has tried it at least once. I remember reading about it here on endless sphere somewhere.

I know one long time flyer who has been building them for years. Raja. You can buy a turnkey system from him.

https://www.rc-thoughts.com/2017/06/how-to-charge-rx-pack-during-flight/

Here are a few pics of typical setups. Here you can see the muffler in the lower pic.

 

[dogman dan]

Because few need such a small amount of remote power, nobody is making the 200w continuous generator I thought would be cool. Something in the 15 pound range. Just enough to run a 48v 3 amps charger would be cool, even though noisy. The little harbor freight generator is still pretty heavy to lug around, but works fine if you carry it to a camp in your car.

Unfortunately, similar wattage solar panel is still pretty big, needing a trailer about 2 feet wide by 8 foot long to carry it around. But again, you could carry it in your car to a camp spot. Or it could be an option to camp for a few days, to fill up a very large battery while camped. Carry a stack of 2'x2' panels to charge enough to get out of the boonies to a plug. Those flexy panels are amazing light.

I never got finished on my solar bed trailer project, tow bike burned in the fire, then leftover insurance money bought me a camp trailer. I just ended up doing the big generator thing up in the mountains, and put the solar on the trailer roof.

Still kind of best to carry 1.5 to 2kw of battery, and two satiators to charge them. Two batteries takes me as far as my ass can stand the saddle time, if you ride slow enough. But you have to reserve enough power to get back to a plug, if you head out into the sticks.

But, with a good sturdy tow bike, and a stable two wheeled trailer, you could still carry the little harbor freight 700 w generator around. Then power a 500w charger with it. Its jut hard to do with typical bike stuff, like tippy bob trailers. my bed trailer was able to stand 300 pound loading, but the bike could not tow that load up mountains. The point is, you can make trailers strong enough to carry a heavy generator around.

Make it a delta trike towing a sturdy two wheel trailer, and you could easily haul the 30 pound generators around. You could also put motors on the trailer. I made mine from 20" bmx forks, so two hub motors on the trailer would be possible. Pretty soon though, it gets to be, get a 125 scooter if you run that much generator.