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Model Aircraft Motor idea

Posted: Thu, 07 May 2009, 17:54
by woody
Plettenberg make a monster 15kW continuous 1.9kg brushed DC motor:
Image
25Nm @ 6000rpm = 15kW continuous, 50Nm @ 6000rpm = 30kW peak.

One idea is to mount 2 or more of these bad boys around the geabox input shaft with or without a clutch, giving a very compact and light motor solution.

These are about $800 each, 50 volt, 300-600 Amps.

You could also do series/parallel switching.

cheers,
Woody

Model Aircraft Motor idea

Posted: Thu, 07 May 2009, 18:40
by Electrocycle
I like it!

I think we've just found the motor of choice for racing electric motorcycles :)

Model Aircraft Motor idea

Posted: Thu, 07 May 2009, 18:55
by Johny
Do they have a controller for it? I couldn't see one on the site.

Model Aircraft Motor idea

Posted: Thu, 07 May 2009, 19:44
by woody
According to my R/C Heli friend, the controllers are available from:

castle creations

pheonix (phoenix?)

and are about the same price as the motors.

These are DC brushed, so an Altrax or Curtis should work fine too, I would think.

cheers,
Woody

Model Aircraft Motor idea

Posted: Thu, 07 May 2009, 20:50
by fuzzy-hair-man
That little thing has more power than my mini's original 998 engine! I'd guess it's less than 1/20 the size possibly 1/30th the weight!!! it all seems rather strange... Image

Put a 200W sticker on it and put that in your bicycle Image Image It's sounds like the same size as 200W and 500W motors which makes me wonder how they get so much power into such a little package OR what corners they had to cut and how long it might last...

How are you supposed to bolt it down? 50Nm is a fair amount of torque and I'm not seeing any really solid mountings on the motor?

Model Aircraft Motor idea

Posted: Thu, 07 May 2009, 22:14
by Thalass
That'd make a great gokart motor! Nifty.

Model Aircraft Motor idea

Posted: Thu, 07 May 2009, 22:54
by lithbattboss
I have always liked the Hacker motors also from Germany. Hacker powered model aircraft win more world championships than any other brand of motor.
My all time favourite (because it is a bit quirky) is the biggest motor they ever made called the C50 quad. It combines 4 powerful brushless DC motors all driving one common drive shaft. Sort of like a "4 cylinder electric motor" if you can call it that. Unfortunately I think Hacker stopped making these so the only ones left are those in hobby shops such as this one in London-

http://www.westlondonmodels.com/product ... -C50-Quad/

Its high cost due to its unusual design probably made it unaffordable for most modellers which is why Hacker no longer manufacture them.

Model Aircraft Motor idea

Posted: Fri, 08 May 2009, 00:24
by Richo
woody wrote: 25Nm @ 6000rpm = 15kW continuous, 50Nm @ 6000rpm = 30kW peak.
Woody


Where did you get these values from? link pls
Pitty the RC industry doesn't test the motor like everyone else.

It's one of the biggest and the price is according.
Like PC CPU's the fastest/newest is always exponentially more costly.
You could do it cheaper with smaller motors.
The HXT 7kW are USD$150

For example if you wanted 100kW one possible config would be 5 in a ring and 3 in a row.
With the motors up against each other (not recommended) in a ring thre is still is enough room for a 30-35mm shaft throguh the centre.
15 motors would be $2250 but may get bulk discount. Image

The RC controllers are pretty weak.
Motors this size are usually used for flying RC planes/heli's
Props have a low start torque.
And so the controllers don't have much current protection as a result.
Unlike eV applications which have high start torque.
Common problem in eV conversions with RC controllers is smoked controller.

Obviously some ppl will be happy because it is sub 50V Image
Means probably need 160Ah+ cells - which there are plenty of...

If the setup is using individual controllers for each motor then if one fails then the car still may run ok.
Issues with wiring the motors together for one controller is that they must have all the rotors aligned they won't work like together like induction motors.
If they get out of alignment bad things will happen.


Being quite small and light I think they are perfect for bike/scooter conversion.

Image

Model Aircraft Motor idea

Posted: Fri, 08 May 2009, 04:40
by weber
fuzzy-hair-man wrote: ... makes me wonder how they get so much power into such a little package OR what corners they had to cut and how long it might last...

How are you supposed to bolt it down? 50Nm is a fair amount of torque and I'm not seeing any really solid mountings on the motor?

The mounting is a disk at the back end of it with four M5 tapped holes. This disk is attached to the shaft. The shaft doesn't turn. The front surface and the whole outside cylinder turns. The prop mounts to the front with six M5 screws.

It's 20 poles running at 6300 rpm. A 2-pole running at 6000 rpm would be 100 Hz, so a 20-pole at 6300 rpm is 1050 Hz. It's a bit like transformers. The higher the frequency, the smaller and lighter they can be for the same power throughput. If you can transfer a fixed amount of energy per cycle then one way to get more throughput is to have more cycles per second, but to avoid insane rotational speeds you have to increase the number of poles. But higher frequencies demand different magnetic materials and litz wire and such things to minimise the frequency-related losses.

And yes. It would be engineered within a hairsbreadth of its life. i.e. for ultra light weight, not long life or robustness. You'd want to seriously derate it for use in an EV.
[Edit: spelling]

Model Aircraft Motor idea

Posted: Fri, 08 May 2009, 05:26
by weber
OK. Didn't get it quite right. Individual prop blades mount to the back of the can, while the centre fairing mounts to the front. But I got it right that the shaft is stationary and mounted by the disk at the back that the wires come out one side of, while the can rotates. Here's a photo.

Image

Model Aircraft Motor idea

Posted: Fri, 08 May 2009, 05:40
by Gow864
Twin RC motor powered BMX!! There are quite a few people using RC motors for bikes quite successfully. The linked thread has a twin motored BMX bike, I think that these motors (Astroflight 3210) can put out 3kw each. A nice piece of engineering at least.

Gow.

Model Aircraft Motor idea

Posted: Fri, 08 May 2009, 06:02
by Squiggles
Hub motors for a 4wd go-kart?

Model Aircraft Motor idea

Posted: Fri, 08 May 2009, 06:22
by Thalass
That's alot like a hub motor design. I remember from my work stuff that electrically powered gyroscopes, which need the mass as far from the centre as possible. These gyros have the stator on the inside of the rotor, and to me that would be an ideal form for an EV wheel motor. Where you replace the axle/brake/hub with the motor stator, and the wheel itself would be pretty close to a regular steel wheel. Cheaper to make than a wheel with the motor intergrated into it. :P

Model Aircraft Motor idea

Posted: Fri, 08 May 2009, 17:37
by fuzzy-hair-man
weber wrote:
It's 20 poles running at 6300 rpm. A 2-pole running at 6000 rpm would be 100 Hz, so a 20-pole at 6300 rpm is 1050 Hz. It's a bit like transformers. The higher the frequency, the smaller and lighter they can be for the same power throughput. If you can transfer a fixed amount of energy per cycle then one way to get more throughput is to have more cycles per second, but to avoid insane rotational speeds you have to increase the number of poles. But higher frequencies demand different magnetic materials and litz wire and such things to minimise the frequency-related losses.

And yes. It would be engineered within a hairsbreadth of its life. i.e. for ultra light weight, not long life or robustness. You'd want to seriously derate it for use in an EV.
[Edit: spelling]

Great answer Thanks!! Image I thought they must have been using the aircraft's airflow to cool the motor the picture you posted shows how, with very little weight it wouldn't take long for heat to build up to problematic levels I guess, so I suspect you'd have to provide some pretty serious cooling fans for applications where it's not going to get a lot of airflow all the time.

If we can get lighter motors etc using motors with a large number of poles and higher frequencies why are we looking at 2 and 4 pole motors? (AC case and I might be mixing AC and DC where they don't mix Image) is the really high frequency also really inefficient or does it cost too much to realise high efficiency for motors and controllers of the size required for EVs. Or finally have they done it already and I just don't know? I gathered some of the hub motors were many poled but I thought that was because of their high torque but generally low RPM requirement and they were still being fed power at a similar frequency.

Model Aircraft Motor idea

Posted: Fri, 08 May 2009, 17:50
by Johny
fuzzy-hair-man wrote:If we can get lighter motors etc using motors with a large number of poles and higher frequencies why are we looking at 2 and 4 pole motors?
It's not a stupid question. 2 and 4 pole ACIMs are cheap to make, rotate at around the right speed for industrial applications, and are readily available for those reasons. Higher frequencies at high power require different magnetic material that apparently gets more expensive.
There would be controller implications for higher frequencies as well.

Model Aircraft Motor idea

Posted: Fri, 08 May 2009, 17:55
by Squiggles
A series of random notes:
If only I had not disposed of my AC & DC machines text books!!

It seems that with VVVF drives they talk about frequencies in the order of 250hz. For a 6 pole motor that would be 5000rpm.

In my past employment we used what is known as "Audio Frequency Control" to control street lights & off peak water. Coincidentally this ran at 1050hz. Significantly the 1050hz was created with a motor-generator set where a 3phase 415VAC 50hz motor with star-delta starting would drive a similarly sized 1050hz generator. The coded 1050hz is "injected" onto the power grid. The point of saying all this is that 1050hz is probably not a "high" frequency in electrical machine terms but you can hear it.

I think with appropriate resources a 12 pole motor capable of 500hz operation could be made. I think that it would have better torque characteristics then a 4 pole, not sure you can save weight though as the rotor and copper in the windings and the magnetic components would still need to be of similar mass.

Weight saving is basically down to Aluminium frame instead of steel and possibly the use of higher grade magnetic materials.

Model Aircraft Motor idea

Posted: Fri, 08 May 2009, 21:57
by Tritium_James
The problem with running a motor that has iron in it (ie, nearly everything except an ironless BLDC) at higher frequencies like 500Hz or more is that you need very thin laminations in your iron or you get huge eddy current losses. This is hard to make and therefore expensive.

You also need fine wire sizes, to avoid eddy currents in the wire itself, which means using Litz wire, which means a lousy packing density. You'd probably halve or 1/3 the amount of actual copper wound into the slots in the motor, the rest of it is insulation between all the fine strands. So your resistance losses go up.

Model Aircraft Motor idea

Posted: Mon, 11 May 2009, 15:36
by Hatchet
Can use it for electric swamp buggy or hovercraft?!