Recommendations for 2000 watt RC motor

[katou]

Hi all, I've read most of the posts on this site, but I haven't seen many recommendations for smaller RC motors. I've seen a few lower wattage projects using Turnigy motors, one with Scorpion, and a couple HXT.

I am aiming at a design wattage of 1000-2000 watts in order to keep me pedaling, and to decrease battery size, and keep the cost for the controller low.

Motor will drive front wheel through an internal hub, much like this one by Cargo:

http://endless-sphere.com/forums/viewtopic.php?f=28&t=7874&start

I am looking for good value for the dollar.

Help? My next question will be a pointer to a good primer on battery stuff.

Katou

 

[Miles]

How about this one?

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=7870&Product_Name=TGY_AerodriveXp_SK_Series_63-74_170Kv_/_3250W

 

[Grinhill]

I have two Turnigy SK motors, one is a 50-65 which I ran at about 1100W and a 63-64 which I run at about 1500W.

The larger one stays cool to the touch, the smaller one runs much hotter.

If you are going to run it hard, e.g. uphill grades, you are better off with the larger one.

The usual warnings apply, magnets can come loose and bearings can get noisy. You get what you pay for.

 

[katou]

I checked out all three of those motors. It looks like the magnets and the bearings are the weak spots.

That being said, they are very inexpensive.

Would it be possible to find one with a sealed can? I would prefer that for weather-proofing of the drive unit.

Katou

 

[Miles]

http://www.astroflight.com/index.php?main_page=product_info&cPath=20&products_id=122

 

[katou]

Ah yes, the Astro. Nice motor. Is there another one a little lower wattage? That one's a monster. It is sealed though, which is good.


Katou

 

[Miles]

There's this one: http://www.astroflight.com/index.php?main_page=product_info&cPath=4&products_id=82

Something in between would be better...

 

[MitchJi]

Hi Miles,

Would this be a good choice for his purpose?:
http://www.xeramotors.com/index.php...&category_id=1&option=com_virtuemart&Itemid=1

 

[Miles]

Hi Mitch,

Yes, if Katou will accept an outrunner.

 

[liveforphysics]

When it comes to picking a size of an RC motor, bigger generally has many more benifits than smaller.

Bigger motors with thicker shaft diameters and bigger bearings are better suited towards side loads (like a belt or chain drive).

They also have more area for cooling, and often operate in lower RPM ranges, which makes setting up the gearing drive ratio much easier. Anytime you are able to get your reduction completed in a single stage, and that stage also serves as the power transfer connection to the drive wheel, you are minimizing drivetrain system loss, and lowering system complexity, which should in-turn increase reliability.

Large low RPM RC motors are best suited towards use on an E-bike. Even if you only plan to feed a 4kw capable motor 2kw, it's still going to provide you with a better motor and drive solution to oversize the motor.

Best Wishes,
-Luke

 

[Miles]

Anytime you are able to get your reduction completed in a single stage, and that stage also serves as the power transfer connection to the drive wheel, you are minimizing drivetrain system loss, and lowering system complexity, which should in-turn increase reliability.

Yes, absolutely. The advantages of using a smaller motor are weight and cost - but you have to include the weight and cost of the additional reduction needed, too... The disadvantage is increased loss/maintenance per reduction stage. So make the most of every stage!

If you use a small motor and reduce it with 3 stages to crank speed and then gear it up again to nominal wheel speed and then modify it again through a hub gear or CVT, that adds up to a heck of a lot of drivetrain losses.....

 

[ron van sommeren]

When it comes to picking a size of an RC motor, bigger generally has many more benifits than smaller...

Bigger motor will operate nearer to it's point of highest efficiency.

Prettig weekend Ron

 

[Miles]

Bigger motor will operate nearer to it's point of highest efficiency.

I think that needs some qualification, Ron :wink:

 

[Sam_Q]

I also have one of these:

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=7870&Product_Name=TGY_AerodriveXp_SK_Series_63-74_170Kv_/_3250W

I have not used it yet though. As far as I know though its rated at 3250W at 37V, so run on a 6 cell pack it will put out 1950W. Which is exactly what I have in mind myself.

From what I am reading the problem with the magnets seperating is due to overheating issues, so I am thinking that running at only 6 cells instead of 10 will pretty much avoid all that.

 

[Miles]

I read on RC Groups that they're using a different adhesive now, so maybe there'll be fewer problems.....

 

[katou]

Assuming that the motor housing on both outrunner and inrunner is sealed, and also assuming that the rpm/v is the same, what is the difference?

I've read articles on the difference structurally between the two types, but in practice what does it matter? I find similar motors in either flavour.

Katou

ps. I get the whole "buy big, run small" idea, and I am not averse to spending 200$ on a motor. I'd just like to avoid it if possible

 

[12p3phPMDC]

The shell of the outrunner spinning is much harder to seal vs. an inrunner, IMO.

 

[Miles]

Assuming that the motor housing on both outrunner and inrunner is sealed, and also assuming that the rpm/v is the same, what is the difference?

I've read articles on the difference structurally between the two types, but in practice what does it matter?

You wouldn't want to seal an outrunner - it needs the air circulation to get rid of heat.

The airgap is at a slightly greater radius on an outrunner - so a bit more torque (for a given case diameter)

 

[12p3phPMDC]

u wouldn't want to seal an outrunner - it needs the air circulation to cool it.

Good point...
What about a protective cover?
A plastic tube with a 1/4" or 6mm gap that could
be connected to an intake air tube.
If you added a fan and a duct, would the cooling
improve?

 

[Miles]

It's getting a bit complicated.....

 

[MitchJi]

Hi,

When it comes to picking a size of an RC motor, bigger generally has many more benifits than smaller.

Bigger motors with thicker shaft diameters and bigger bearings are better suited towards side loads (like a belt or chain drive).

They also have more area for cooling, and often operate in lower RPM ranges, which makes setting up the gearing drive ratio much easier. Anytime you are able to get your reduction completed in a single stage, and that stage also serves as the power transfer connection to the drive wheel, you are minimizing drivetrain system loss, and lowering system complexity, which should in-turn increase reliability.

Large low RPM RC motors are best suited towards use on an E-bike. Even if you only plan to feed a 4kw capable motor 2kw, it's still going to provide you with a better motor and drive solution to oversize the motor.

Yes, absolutely. The advantages of using a smaller motor are weight and cost - but you have to include the weight and cost of the additional reduction needed, too... The disadvantage is increased loss/maintenance per reduction stage. So make the most of every stage!

If you use a small motor and reduce it with 3 stages to crank speed and then gear it up again to nominal wheel speed and then modify it again through a hub gear or CVT, that adds up to a heck of a lot of drivetrain losses.....

Most of the cost advantage can easily be negated by the additional reduction costs required by a smaller higher RPM motor. The 5 turn version of the small Astroflight has a kv of 450 RPM per volt. The 5 turn 3210 is 276 so it requires about 40% less reduction. The smaller motor does cost $175 less but you could easily spend that much for the additional drive parts.

The larger motor weighs 18 oz. more but most of the weight savings will probably be chewed up with additional drive parts.

Your best choice might be a 12 turn 3210 with a kv of 113.

 

[katou]

How do you mount the outrunners? Most of the ones I've seen have a rounded bell on the front. I want a flat front in order to mount the motor to a flat plate.

I see why people are drawn to the big AXI and HXT motors, they're cheap!

 

[liveforphysics]

The shaft can poke out where ever you want on an outrunner motor... On the mounting face side often works best for our applications, or on the rotor/bell side if a person is driving a prop in an RC plane.



If you want it sealed, an Astro 3210 is the absolute smallest motor I would ever recomend to be paired up with trying to move a human on an E-bike.


Bigger motor = less cost to get the system completed, and better reliability once you have it completed.

And like Ron said earlier in this thread, you will be in a better efficiency by under-powering a larger motor than running a smaller motor at max rated power, which will have increased core loss and increased eddy current losses from higher saturation and higher flux density.

 

[MitchJi]

Hi,

I see why people are drawn to the big AXI and HXT motors, they're cheap!

Discussed at length in this thread (first post quoted below):
http://www.endless-sphere.com/forums/viewtopic.php?f=28&t=10416

Cheapo motors..............

K, I may be opening a can of worms here, but I cannot help but start this thread. :?

I am curious as to why there is such popularity [with the E-bike crowd] of these cheapo HXT (and similar) motors? I know they cost less than high end motors, but the list of problems is stagering;

-Magnets coming loose
-Bad windings
-Bad bearings

What else could possibly go wrong with a motor? And these are problems right out of the box!

I mean, come on! Sure you are only paying under $100 rather than $300 or more, but now you need to buy new bearings and install them, rewind the friggin thing, reglue the magnets...............

Maybe I am just more open with spending money (and no, I am not wealthy). But, I cannot understand why these things are so popular. Maybe for someone who is retired and has huge time to put into the motor it may be worth it. But, man, I cannot understand why these motors are so highly defended and recommended by so many people.

Sorry, this has turned into a rant. But, I am getting kind of tired of email after email after email I recieve about HXT and other bargain motor problems. I find it funny that a $600 Ping battery is fine, but heaven forbid anything over $100 is spent on a motor.

Who else finds this strange?

Matt

I do not mean to insult anyone who has bought one of these motors and rewound or repaired it in one way or another. I am just shocked how many people find it perfectly fine to recommend them to anyone and everyone who asks for a decent motor.............

 

[12p3phPMDC]

It's getting a bit complicated.....

Well, I agree that KISS is good....but, these motors were
designed to sit behind a prop where large amounts of air
are being pumped through them.

Maybe a fan mounted on the prop side is good enough...
But, if you had a velomobile with an enclosed fairing you may not
get enough airflow. A NACA duct on the side that routed air through
a tube to the motor is pretty simple...