[nostalgk]

This. I recently worked with a company that produces drones among other things, and spoke with the head of research there.

More or less, they said they had given up on putting money into drone R&D until battery technology caught up, as they had plenty of ideas that they believed in but were unfeasible due to battery life.

[libria]

As RC vehicles {car|helicopter|plane} get larger they reach a certain mass where liquid fuel - usually a petroleum - is preferable to battery. Why is this not an alternative for drones?

[desdiv]

It's been done, but it's expensive. Not many people can drop $30,000 on a drone: https://www.bhphotovideo.com/c/product/1416171-REG/walkera_q...

[cameldrv]

It's hardly $30k to buy a gas drone. You can buy a Cox .049 engine for $50 or so.

You're looking at a fixed wing aircraft though with one of those. What's made the quadcopter drone possible is the high torque and instantaneous throttle response of small electric motors, combined with fast control electronics. The conventional way to fly a small helicopter is just like a full sized helicopter, with a main rotor and a mechanical swash plate.

With the right control electronics, these can easily be made into drones, but people tend to not like them as much anymore because they're mechanically complex and finicky. The electric motors are simple, and when one goes bad you just drop in a new one.

[twic]

Could you couple one of those engines to a generator, and use that to power the electric motors? You'd need a battery or supercapacitor to handle change in throttle demand that outpaces generator response too.

[jsjohnst]

Weight is the limiting factor. Try to find a generator that can output up to 400amps at 25V (what my big drone draws) and yet weighs less than five pounds including fuel.

I think that’s a more impossible goal than increasing power density in batteries is.

[danmaz74]

400 ampere??

[scotty79]

https://youtu.be/7zMPodObo-Y

This guy tries to make gasoline powered generator for large drone.

[yardie]

Thermal to mechanical to electrical to mechanical. That’s a lot of energy conversions and with each conversion you lose a lot of efficiencies.

[m-ee]

Controls are more complicated if you're not using electric motors where a microcontroller can easily adjust the RPM. Someones already linked a hybrid drone with a gas powered generator but it's not cheap. In high volume it could probably come down a lot but I don't know how much demand there is for it.

[bluescrn]

The electric motors used can change the speed of 4+ independent propellers extremely quickly.

This is hard to do with petrol engines, without costing a lot of extra weight or mechanical complexity, in a system where any single failure means a crash

[scotty79]

I wonder if there's some simple variable transmission that could be electronically controlled to deliver power from the motor to the propellers in highly controlled fashion.

[ahartmetz]

A generator and four motors. Efficiency would probably be around 70%. It's about 90% in diesel-electric locomotives where more weight and money is spent on efficient conversion hardware.

[scotty79]

That adds weight of 4 beefy electric motors to the system.

There's differential based continous variable transmission that varies according to resistive torque on a control shaft: https://makezine.com/2012/08/10/lego-continuously-variable-t...

This might enable electronic control witout using any motors just one simple coil per propeller. Energy generated through this way of control could be stored to power onboard devices.

[fma]

I've watched people fly RC airplane and helicopters with gas engines. They still exist, and there are air fields for them. I've seen them since the 90s as a kid. They aren't expensive but, are bigger and require an actual landing and takeoff area.

https://www.hobbytown.com/gas-rc-airplanes/c7574

[TylerE]

Those aren’t usually gas, but rather a nitromethane mix, runs off glow plugs (saves all the issues of timing, spark plus, distributors...)

[terravion]

Indeed this has been done since WWI. https://www.warhistoryonline.com/military-vehicle-news/short...

[libria]

Let me rephrase: why would companies consider battery life a limit when liquid fuel is a viable way forward for range, time-aloft or size?

[s1artibartfast]

Repeating my post above:

Given the line of sight limitation for drones, gas power does not add much value. Batteries are usually sufficient to map/photograph the area within range of the operator. Given this legal limitation, it is often more economical to hire a small plane like a Cessna with an avionics package and a 400 mi range.

[guelo]

Nobody wants to risk the liability and noise of a flying lawnmower.

[buran]

And then use it for what?

They exist, but they are expensive. https://www.youtube.com/watch?v=wS0Hr2lw604

[colechristensen]

It certainly has been done, and on small drones too.