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I've often wondered why there isn't some small turbogenerator, or internal combustion based module for dropping into existing drone platforms to replace large l

I've often wondered why there isn't some small turbogenerator, or internal combustion based module for dropping into existing drone platforms to replace large lithium ion-packs, especially for long duration flights. Heck, even a fuel cell would be far better energy/weight ratio, wouldn't it? And since they would be single or few use, you don't have to worry about poisoning the electrodes anywhere near as much.

Retric 2y ago
There are ICE powered drones, but they aren’t strictly better. Batteries do a lot of things very well such as ramping up and down power output drastically with sub second response times. This allows quadcopter to be very simple mechanically making them scale down really well into a tiny package someone can carry several of them without significant issue. As a bonus tiny drones can be reasonably quiet and cheap.
SCUSKU 2y ago
This startup Radiant is working on portable nuclear reactors, one application being forward operating bases [1]. After watching that video I’m really hoping they succeed both for military purposes but also for civilian municipalities! [1] - https://www.youtube.com/watch?v=LTgS7tOOzsE https://www.youtube.com/watch?v=LTgS7tOOzsE
- niemandhier 2y ago
  Bringing fissionable material near any conflict seems like a bad idea, and a signal on par with positioning nuclear power heads. Aircraft carriers probably are exempt, since intentionally blowing one up as a dirty bomb amounts to a mass suicide attack.
CHY872 2y ago
Battery efficiency is _broadly_ linear; 10kg will give you 100x the capacity of 0.1kg of batteries. This isn't the case with generators. Under 5kg of batteries, engines basically can't compete. The smallest viable petrol engines (you want engines made in large quantities) are around 4kg and need fuel, and so you end up in a situation in which 4kg of engine and 1kg of fuel is as useful as 5kg of batteries (for motors of that size), but every subsequent 1kg of fuel is then also as useful as 5kg of batteries. But you can't really drop this down much, as a 1kg engine is much less useful than 1kg of batteries, and a drone with 5kg of batteries is really a very large drone. Drones are additionally typically very small and light, with mass at an absolute premium. A typical quadcopter will weigh under a kilogram and have maybe 200g of batteries for 20-30 minutes endurance. A drone with a 2.5m wingspan will typically have room for maybe 1-2kg of extra payload, and an engine will not fit into the battery slot. Furthermore, they are extremely sensitive to weight balance issues. This is to say, once you're in the world where you want chemical fuel, you might as well design a drone for it, rather than trying to retrofit. The mass of retrofitting will mess up your prior drone design, and petrol changes the dynamics of what you're trying to do enough that you might as well just do it all differently. Essentially, if you're making a 1-10kg drone, you want battery. If you're making a 10-20kg drone, you might want battery, you might want petrol. Above 20kg, you probably want petrol.
- BobbyJo 2y ago
  Os that due to some thermodynamic scaling trade off or just a matter of fault tolerance (i.e. we cant machine them well enough at that scale to be as efficient)?
  - CHY872 2y ago
    Probably a few factors. 1. Scaling. You want to reap the rewards of someone else investing billions, and while billions of ICE engines are built every year, most of them are much bigger than 50cc. 2. Tolerances, as you say. I know for example that jet engines have low efficiency at small sizes due to efficiency being driven by the gaps between certain rotating parts, which are relatively larger. 3. Certain parts that need miniaturisation are more expensive on smaller engines. For example, a 50cc would typically have a carburettor, a bigger engine fuel injection. A fuel injector would be significantly larger per unit. 4. Some parts are just harder to miniaturise. For example, small turbochargers have to work harder and at much higher RPMs to achieve the same boost due to area scaling quadratically with diameter.
Qwertious 2y ago
Fuel cells are ultimately just fancy batteries, they could electrolyze their output water when they "recharge". But in practice, our cars are all lithium BEVs, not FCEVs. There are some hydrogen forklifts, whose niche is that they're used 24/7 and hydrogen refills are faster than recharging batteries, but ultimately fuel cells make no sense at car-scale or below.
Havoc 2y ago
Bigger RC helicopters and RC planes are often fuel powered >internal combustion Thing with this is that now you need: a) Fuel tank plus a pump b) A combustion chamber c) Gears or a way to mechanically regulate fuel flow ...of which b and c probably need to be metal. For light & small drones you're not necessarily winning here on weight
bilsbie 2y ago
What’s going on with fuel cells? It seems like they’re never considered for anything. What am I missing?
- nine_k 2y ago
  Bringing hydrogen to the front lines is hard. Liquid-based fuel cells are not nearly as energy-dense.
  - bilsbie 2y ago
    Why can’t we load them with water and run them in reverse to make hydrogen and charge them.

Retric 2y ago

There are ICE powered drones, but they aren’t strictly better. Batteries do a lot of things very well such as ramping up and down power output drastically with sub second response times. This allows quadcopter to be very simple mechanically making them scale down really well into a tiny package someone can carry several of them without significant issue. As a bonus tiny drones can be reasonably quiet and cheap.

SCUSKU 2y ago

This startup Radiant is working on portable nuclear reactors, one application being forward operating bases [1]. After watching that video I’m really hoping they succeed both for military purposes but also for civilian municipalities! [1] - https://www.youtube.com/watch?v=LTgS7tOOzsE https://www.youtube.com/watch?v=LTgS7tOOzsE

niemandhier 2y ago
Bringing fissionable material near any conflict seems like a bad idea, and a signal on par with positioning nuclear power heads. Aircraft carriers probably are exempt, since intentionally blowing one up as a dirty bomb amounts to a mass suicide attack.

CHY872 2y ago

Battery efficiency is _broadly_ linear; 10kg will give you 100x the capacity of 0.1kg of batteries. This isn't the case with generators. Under 5kg of batteries, engines basically can't compete. The smallest viable petrol engines (you want engines made in large quantities) are around 4kg and need fuel, and so you end up in a situation in which 4kg of engine and 1kg of fuel is as useful as 5kg of batteries (for motors of that size), but every subsequent 1kg of fuel is then also as useful as 5kg of batteries. But you can't really drop this down much, as a 1kg engine is much less useful than 1kg of batteries, and a drone with 5kg of batteries is really a very large drone. Drones are additionally typically very small and light, with mass at an absolute premium. A typical quadcopter will weigh under a kilogram and have maybe 200g of batteries for 20-30 minutes endurance. A drone with a 2.5m wingspan will typically have room for maybe 1-2kg of extra payload, and an engine will not fit into the battery slot. Furthermore, they are extremely sensitive to weight balance issues. This is to say, once you're in the world where you want chemical fuel, you might as well design a drone for it, rather than trying to retrofit. The mass of retrofitting will mess up your prior drone design, and petrol changes the dynamics of what you're trying to do enough that you might as well just do it all differently. Essentially, if you're making a 1-10kg drone, you want battery. If you're making a 10-20kg drone, you might want battery, you might want petrol. Above 20kg, you probably want petrol.

BobbyJo 2y ago
Os that due to some thermodynamic scaling trade off or just a matter of fault tolerance (i.e. we cant machine them well enough at that scale to be as efficient)?
- CHY872 2y ago
  Probably a few factors. 1. Scaling. You want to reap the rewards of someone else investing billions, and while billions of ICE engines are built every year, most of them are much bigger than 50cc. 2. Tolerances, as you say. I know for example that jet engines have low efficiency at small sizes due to efficiency being driven by the gaps between certain rotating parts, which are relatively larger. 3. Certain parts that need miniaturisation are more expensive on smaller engines. For example, a 50cc would typically have a carburettor, a bigger engine fuel injection. A fuel injector would be significantly larger per unit. 4. Some parts are just harder to miniaturise. For example, small turbochargers have to work harder and at much higher RPMs to achieve the same boost due to area scaling quadratically with diameter.

Qwertious 2y ago

Fuel cells are ultimately just fancy batteries, they could electrolyze their output water when they "recharge". But in practice, our cars are all lithium BEVs, not FCEVs. There are some hydrogen forklifts, whose niche is that they're used 24/7 and hydrogen refills are faster than recharging batteries, but ultimately fuel cells make no sense at car-scale or below.

Havoc 2y ago

Bigger RC helicopters and RC planes are often fuel powered >internal combustion Thing with this is that now you need: a) Fuel tank plus a pump b) A combustion chamber c) Gears or a way to mechanically regulate fuel flow ...of which b and c probably need to be metal. For light & small drones you're not necessarily winning here on weight

bilsbie 2y ago

What’s going on with fuel cells? It seems like they’re never considered for anything. What am I missing?

nine_k 2y ago
Bringing hydrogen to the front lines is hard. Liquid-based fuel cells are not nearly as energy-dense.
- bilsbie 2y ago
  Why can’t we load them with water and run them in reverse to make hydrogen and charge them.