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A Traxxas 5407 TRX 3.3 engine used in RC cars makes 1.42 horsepower, weighs 305 grams, and fits in the palm of your hand. This is 1hp per 0.46 pounds of engine

by 93po 4y ago

A Traxxas 5407 TRX 3.3 engine used in RC cars makes 1.42 horsepower, weighs 305 grams, and fits in the palm of your hand. This is 1hp per 0.46 pounds of engine weight, nearly three times better than the camry engine. Granted an RC engine runs on a mixture of fuel and nitromethane, and doesn't have any reasonable durability compare to a Camry engine. But it also only costs $200.

seabird 4y ago
You can't just make the Traxxas 18x bigger and get linear performance improvement. Trying to compare power/weight between engines with radically different weight constraints is silly.
- syrrim 4y ago
  If you had 18 such engines it would get you precisely 18x the performance, at precisely 18x the weight.
  - aidenn0 4y ago
    And precisely 1/18 the MTBF
    - pas 4y ago
      but it fails gracefully, right? (only one engine fails at a time) it's like RAID, great until the RAID card itself fails
      - aidenn0 4y ago
        It's probably most like losing power in a single cylinder; the effects vary from engine to engine.
        jacquesm 4y ago
        They tend to seize and when they do and you gang them they'll likely break stuff in the other ones unless you add a freewheel or some other luxury like that.
    - 93po 4y ago
      In a way, sure. Often when a car engine fails people just replace it. If you were to replace all 18 when the first one failed, the same way you would with a regular car engine, it's not 1/18 the MTBF. And if it was just 1 failing prematurely and you replaced only that one, you also see that same dynamic with car engines when a single component of it fails that's worth fixing.
  - Retric 4y ago
    No, because you would need to add structural elements, some way of combining power output, and cooling if you’re aiming for a similar form factor.
    - deleted 4y ago
      [deleted]
  - seabird 4y ago
    That's why there's all sorts of widely produced performance vehicles with multiple independent engines!
- 93po 4y ago
  Ok, a Kawasaki H2R engine makes 326 horsepower and weighs about 160 pounds running regular fuel. That's almost identical to the Traxxas - 1hp for 0.49 pounds.
  - seabird 4y ago
    That engine is 4x heavier and supercharged. You're not comparing apples to apples.
    - 93po 4y ago
      my point is that this ratio exists both much smaller and also somewhat larger. it makes sense this same ratio would be possible in the middle of the two as well. also diesels have super/turbo chargers all the time on production engines, why is that cheating?
cjbgkagh 4y ago
I've read about a lot of people complaining about the difficulty of getting the mixture right, perhaps that might be a show stopper for a UAV that must reliably work unattended for a long time. Though the military should also be able to get such mixtures down to a science - so I don't know.
kortex 4y ago
> Granted an RC engine runs on a mixture of fuel and nitromethane That's a huge difference. The main limiting factor in engine power is mass air flow, not fuel. Engines are as much air pumps as they are containers for extracting expansion from explosions. Nitromethane provides extra oxidizer in liquid form, putting nitro engines in some ways closer to rocket engines in terms of power-to-weight ratio.
m463 4y ago
I'm not familiar with that engine, but I remember having little glow-plug engines and they didn't even have piston rings. (and were not efficient)

by 93po 4y ago

seabird 4y ago

You can't just make the Traxxas 18x bigger and get linear performance improvement. Trying to compare power/weight between engines with radically different weight constraints is silly.

syrrim 4y ago
If you had 18 such engines it would get you precisely 18x the performance, at precisely 18x the weight.
- aidenn0 4y ago
  And precisely 1/18 the MTBF
  - pas 4y ago
    but it fails gracefully, right? (only one engine fails at a time) it's like RAID, great until the RAID card itself fails
    - aidenn0 4y ago
      It's probably most like losing power in a single cylinder; the effects vary from engine to engine.
      - jacquesm 4y ago
        They tend to seize and when they do and you gang them they'll likely break stuff in the other ones unless you add a freewheel or some other luxury like that.
  - 93po 4y ago
    In a way, sure. Often when a car engine fails people just replace it. If you were to replace all 18 when the first one failed, the same way you would with a regular car engine, it's not 1/18 the MTBF. And if it was just 1 failing prematurely and you replaced only that one, you also see that same dynamic with car engines when a single component of it fails that's worth fixing.
- Retric 4y ago
  No, because you would need to add structural elements, some way of combining power output, and cooling if you’re aiming for a similar form factor.
  - deleted 4y ago
    [deleted]
- seabird 4y ago
  That's why there's all sorts of widely produced performance vehicles with multiple independent engines!
93po 4y ago
Ok, a Kawasaki H2R engine makes 326 horsepower and weighs about 160 pounds running regular fuel. That's almost identical to the Traxxas - 1hp for 0.49 pounds.
- seabird 4y ago
  That engine is 4x heavier and supercharged. You're not comparing apples to apples.
  - 93po 4y ago
    my point is that this ratio exists both much smaller and also somewhat larger. it makes sense this same ratio would be possible in the middle of the two as well. also diesels have super/turbo chargers all the time on production engines, why is that cheating?

cjbgkagh 4y ago

I've read about a lot of people complaining about the difficulty of getting the mixture right, perhaps that might be a show stopper for a UAV that must reliably work unattended for a long time. Though the military should also be able to get such mixtures down to a science - so I don't know.

kortex 4y ago

> Granted an RC engine runs on a mixture of fuel and nitromethane That's a huge difference. The main limiting factor in engine power is mass air flow, not fuel. Engines are as much air pumps as they are containers for extracting expansion from explosions. Nitromethane provides extra oxidizer in liquid form, putting nitro engines in some ways closer to rocket engines in terms of power-to-weight ratio.

m463 4y ago

I'm not familiar with that engine, but I remember having little glow-plug engines and they didn't even have piston rings. (and were not efficient)