8600w Outrunner vs 2000w Inrunner w/ 25:1 Gearbox?

[socalfusions]

http://hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=14427

Vs.

http://www.thesuperkids.com/20wabmcbrpoe.html

If using these motors with a 25:1 planetary gearbox which would be a better choice? From what I've read brushless outrunner motors can achieve similar tasks because the motor doesn't know what its powering, however it also appears that inrunners are more capable of moving more weight and are better suited for high torque, low rpm scenarios.

These were two of the more powerful brushless motors in their class that were around the same price. Is one of them a clear cut winner if using them with a 25:1 gearbox?

[Miles]

Why not start by stating what your needs are?

Leaving aside the myths regarding the merits of inrunners vs outrunners... I thought the BMC motor was an outrunner, too?

[socalfusions]

Why not start by stating what your needs are?

Leaving aside the myths regarding the merits of inrunners vs outrunners... I thought the BMC motor was an outrunner, too?

I was theorycrafting if it would power a very large ornithopter hence the 25:1 gearbox

[Thud]

however it also appears that inrunners are more capable of moving more weight and are better suited for high torque, low rpm scenarios.

please link to your source for that information.
it is in total contradiction to everything Ive learned.

[socalfusions]

however it also appears that inrunners are more capable of moving more weight and are better suited for high torque, low rpm scenarios.

please link to your source for that information.
it is in total contradiction to everything Ive learned.

It appears I was mistaken, I thought inrunners were made for scooter/bike uses and were required to move large diameter tires while moving the weight of the rider as well while outrunners were generally used on rc aircraft to spin small props at high rpm. Any thoughts on the original topic?

[Miles]

Outrunners have the advantage of a larger airgap radius for a given overall diameter. This is because a PM rotor take up less space than the stator. For a comparison of inrunners vs outrunners see: http://endless-sphere.com/forums/viewto ... 85#p302385

Direct drive hub motors are outrunners.

The BMC motor you posted the link to is an outrunner. If you take the outer casing off, it's probably a similar size to the Turnigy.

As we don't have a proper specification for the BMC (just a load of marketing drivel), it's difficult to compare them. The Turnigy seems to be optimised to run faster and so will have greater power to weight ratio.

[socalfusions]

Outrunners have the advantage of a larger airgap radius for a given overall diameter. This is because a PM rotor take up less space than the stator. For a comparison of inrunners vs outrunners see: viewtopic.php?p=302385#p302385

Direct drive hub motors are outrunners.

The BMC motor you posted the link to is an outrunner. If you take the outer casing off, it's probably a similar size to the Turnigy.

As we don't have a proper specification for the BMC (just a load of marketing drivel), it's difficult to compare them. The Turnigy seems to be optimised to run faster and so will have greater power to weight ratio.

Thank you for the links and info, would any inrunner motor be considered brushed? The one thing I'm most confused about is that the Turnigy motor says it can support aircraft up to 35 lbs while I've read that 1000w ebike motors (half the wattage of the bmc motor) can move 200 lbs, although I've seen plenty of videos with the turnigy 80-100 moving ebike at very high speeds. Is this due to the different pole count in these two motors? I'm not sure what weight those values hold seeing as how aircraft and ebikes are quite different. These two motors also have large watt differences to which I'm assuming is what you meant by the Turnigy being able to run faster and having a greater power to weight ratio.

How does one go about choosing a motor for such an application as mine taking into consideration cost and difficulty? I've read that choosing an rc brushless motor will require a bit more work since you need to add hall sensors etc, while the scooter/ebike variant motors are already sensored.

[LegendLength]

Moving an aircraft requires a different amount of power than moving a bike, so I imagine that's why those values are different.

I was interested a few years ago in electric, human-sized ornithopters. I did some rough calculations on minimum power requirements if you want me to dig them up. Pretty sure a 10 kW (continuous) motor would do it from memory.

Hard part of course is working out the drive mechanism. My initial desire was to use electric motors as an assist for the pilots arms while flapping the wings. But I quickly realized motors don't like to be started and stopped twice per second! I even looked at linear motors ( http://en.wikipedia.org/wiki/Linear_motor ) but they seem quite heavy and not strong for side-loads.

You should post details of your research if you get time. There's an aircraft sub-form here I think.

[socalfusions]

Moving an aircraft requires a different amount of power than moving a bike, so I imagine that's why those values are different.

I was interested a few years ago in electric, human-sized ornithopters. I did some rough calculations on minimum power requirements if you want me to dig them up. Pretty sure a 10 kW (continuous) motor would do it from memory.

Hard part of course is working out the drive mechanism. My initial desire was to use electric motors as an assist for the pilots arms while flapping the wings. But I quickly realized motors don't like to be started and stopped twice per second! I even looked at linear motors ( http://en.wikipedia.org/wiki/Linear_motor ) but they seem quite heavy and not strong for side-loads.

You should post details of your research if you get time. There's an aircraft sub-form here I think.

I would greatly appreciate you digging up that information ;D 10 kW sounds very reasonable and doable. When you say drive mechanism are you referring to the gear reduction needed to provide the slow flapping motions? I was very curious to how a persons arms could interact with the motor in the fashion that you stated, their has been a guy by the name of Jarnos Smeets that is really the only person whos done any real work on this type of mechanism although it was unsuccessful (the majority of viewers also doubt its authenticity mainly from the camera pan down and different textures after the camera comes back up), here's a link to his actual test flight the device he created that utilizes his arms to flap the wings via android bluetooth and wii controllers:

[LegendLength]

Wow that video is amazing if true, I'll be following its progress.

The actual power requirements for a flapping-winged aircraft are obviously difficult to work out because it depends on the efficiency of the craft (i.e. "sink rate"). But a way to take a simple view is to look at the efficiency of existing hang gliders and work from there as a best case scenario:

From http://www.ornithopter.org/forum/showthread.php?t=429:

The best sink rate I could find for an existing hang glider was about 0.8 m/s at 8 m/s (17 mph). The glider was the Condor which is a large learning glider and travels very slowly.

This means the pilot would be effectively lifting their own weight 3 feet every second, which is about 1 kW. For human power you need about half that or less, otherwise it's too much for a non-athlete.

So in other words if you wanted to power a hang glider with a propeller, you'd need a 1 kW motor. That assumes the motor is 100% efficient, as well as the controller, wiring harness and propeller. Of course in real life motors are more likely going to be 90% efficient, controllers 95 perhaps and the propulsion is around 80% using a good propeller.

You'd multiply all those efficiencies together and get a value of like 0.90 * 0.95 * 0.80 = 0.68 . That means the whole system's efficiency is 68% . So to get 1 kW at the wing tips you'd need to feed it that 32% extra that gets wasted by the system which would be 1.32 kW input power for level flight (i.e. no climbing ability).

These figures are all rough of course and using the best case scenario of a well designed glider. But it's just to demonstrate a way of working through the numbers to help get a feel for the absolute minimum power requirements. For an ornithopter I feel the propulsion will be quite inefficient compared to a glider (I reckon only 50% at best) and the weight will be large. So if I had a gun to my head I'd choose at least a 10 kW motor.

[socalfusions]

Wow that video is amazing if true, I'll be following its progress.

The actual power requirements for a flapping-winged aircraft are obviously difficult to work out because it depends on the efficiency of the craft (i.e. "sink rate"). But a way to take a simple view is to look at the efficiency of existing hang gliders and work from there as a best case scenario:

From http://www.ornithopter.org/forum/showthread.php?t=429:

The best sink rate I could find for an existing hang glider was about 0.8 m/s at 8 m/s (17 mph). The glider was the Condor which is a large learning glider and travels very slowly.

This means the pilot would be effectively lifting their own weight 3 feet every second, which is about 1 kW. For human power you need about half that or less, otherwise it's too much for a non-athlete.

So in other words if you wanted to power a hang glider with a propeller, you'd need a 1 kW motor. That assumes the motor is 100% efficient, as well as the controller, wiring harness and propeller. Of course in real life motors are more likely going to be 90% efficient, controllers 95 perhaps and the propulsion is around 80% using a good propeller.

You'd multiply all those efficiencies together and get a value of like 0.90 * 0.95 * 0.80 = 0.68 . That means the whole system's efficiency is 68% . So to get 1 kW at the wing tips you'd need to feed it that 32% extra that gets wasted by the system which would be 1.32 kW input power for level flight (i.e. no climbing ability).

These figures are all rough of course and using the best case scenario of a well designed glider. But it's just to demonstrate a way of working through the numbers to help get a feel for the absolute minimum power requirements. For an ornithopter I feel the propulsion will be quite inefficient compared to a glider (I reckon only 50% at best) and the weight will be large. So if I had a gun to my head I'd choose at least a 10 kW motor.

Jarnos has 13 videos in total on his youtube account showing the process of building his mechanism, they are definitely worth a look. I feel that your estimate on a 10kW motor is promising seeing as how Jarnos design only used two 2kW brushless motors. That makes sense that a lot of the power would be wasted due to all of the moving components that take place with flapping wings, it almost seems as though you have to increase the flap rate exponentially as the weight increases to generate enough thrust and lift. Another interesting thing is the drive that Jarnos used on his setup, which was a wiggle drive created by a gentleman by the name of Kjell Dahlberg. This hasn't been widely used on ornithopters and even when it has, it was hard to tell if it could perform as well as conventional crank drive ornithopters.

Wiggle Drive



Wiggle Drive Ornithopter

[Bjorntsc]

Read the comments on YouTube. It was just a hoax, he admitted it was fake...
Combination: shit, I wish it was real.

[bzhwindtalker]

It was a really good hoax, they even used real-fake camera shake and youtube-level quality to make it look belivable. We all want to fly, rigth?

[circuit]

You won't be able to use that turnigy in any kind of EV. It has very low inductivity and will kill any bicycle/motorcycle motor controller.

[zappy]

You won't be able to use that turnigy in any kind of EV. It has very low inductivity and will kill any bicycle/motorcycle motor controller.

Hi Circuit, this is a ridiculous thread but what you stated is not correct. I just want to stop mis information about current controllers not being up to the job of running these low inductance motors. This motor can be driven reliably using an 8KW kelly controller(under $500) with fast firmware installed, halls and Berties brilliant timing adjuster. This constant mis information is retarding progress to more energy dense powertrains.

Zappy

[toolman2]

You won't be able to use that turnigy in any kind of EV. It has very low inductivity and will kill any bicycle/motorcycle motor controller.

haveing a bike in the shed using this very motor, and the kelly being 100% reliable for the last 6 months of daily use, i can safely say you are not correct.

also theres a dude in the US dale kramer (kilone or similar username) who is the designer of the lazair plane, and he used 2 of these very motors 10kw each to fly him off the water with floats, im all up for new ideas but id maby ovoid the flapping and use a prop..