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wright100
09-09-2009, 03:08 AM
Hey Guys,

I am working on a project for school to build an extremely efficient vehicle for a competition. To drive this car we are hoping to use a little brushless motor. What would be your guys' reccommendation for the most efficient brushless motor out on the market today? It would have to be somewhere in the 300 to 500 watt range most likely. Thanks for any help.

Nate

Larry3215
09-09-2009, 04:52 AM
In general, inrunner motors are a good bit more efficient than outrunners.

Also, in general, you get what you pay for especially when it comes to efficiency, so your going to want a name brand motor. Avoid the junk from Hobby City/King.

Anything from Neu motors will be very hard to beet but other top contenders - in no particular order - would be:
Hacker
Kontronic
Pletenberg
Lehner

Also, if efficiency is one of the main goals dont skimp on the size of the motor.

In other words, you might find a motor that is say 6 ounces in weight and has a paek power handling capability of 500 watts and your wanting to run at close to 500 watts.

You will get more efficiency from the system if you choose a larger motor and run it at well below its maximum power level.

Id say the average motor has a peak efficiency around 1/4 to 1/3 of its peak power handling level.

So if your going to be running between 300 and 500 watts Id look for a motor that can handle 1500 to 2000 watts peak.

In the Neu line that would be one of the 1515 series inrunners or maybe even the next size up.

Neu also offers some very efficient gearboxes if you need to reduce the shaft speed.

Here is the Neu site.

http://www.neumotors.com/Site/Motors.html

You can order them through Castle Creations web site.

http://www.castlecreations.com/products/neumotors/nm.html

wright100
09-09-2009, 05:00 AM
Thankyou for getting back to me on this. This is the second time I've heard about Neu motors. Their reputation is apparently very good. I am planning on calling them tomorrow to get more information about their motors. I'm hoping they can provide me with graphs on efficiency based on output power. They claimed to have dyno data on their website, but after looking at a few I'm fairly sure they have the same graph up for every motor. Which threw a few questions in my mind about the brand, but recommendations trump websites.

Your comment about the peak efficiency being at 1/3 to 1/4 of the peak power handling surprises me. I thought that the highest efficiency would be when the motor is run close to its maxium continous operating point. Do you know why they are more efficient at 1/3 to 1/4? I'm just curious now. This is a good thing for us because we need a small amount of power to keep the car going at a constant speed but there are hills that we need to climb as well, which will require significantly more power. So oversizing the motor would be advantageous to have the extra kick of power in reserve if needed.



Nate

CHELLIE
09-09-2009, 05:07 AM
Hey Guys,

I am working on a project for school to build an extremely efficient vehicle for a competition. To drive this car we are hoping to use a little brushless motor. What would be your guys' reccommendation for the most efficient brushless motor out on the market today? It would have to be somewhere in the 300 to 500 watt range most likely. Thanks for any help.

Nate

Hi, Is the car going to carry a person, or just its own weight, how big will the car be, what type of batteries will you be using Lipos, a123, ni cad, etc, what is your spending limit/budget, how soon does the car have to be done, where will the car be tested at and under what conditions,

CHELLIE
09-09-2009, 05:14 AM
If you need A123 cells, here are some new cells for $17.96 each, The A123 cells may be the best way to go, check with Larry3215 on that, http://www.hobbypartz.com/a123-systems-2300mah-3-3v-lithium-ion.html

CHELLIE
09-09-2009, 05:21 AM
they have some motors built into a wheel already, 500 and 600 Watts, I dont know how efficient they are, something to take a look at anyway :) LOL

http://video.google.com/videosearch?hl=en&source=hp&q=electric+bike+motor&um=1&ie=UTF-8&ei=3iynSpLnBpSsswPfxeS_BQ&sa=X&oi=video_result_group&ct=title&resnum=4#

Larry3215
09-09-2009, 06:41 AM
Thankyou for getting back to me on this. This is the second time I've heard about Neu motors. Their reputation is apparently very good. I am planning on calling them tomorrow to get more information about their motors. I'm hoping they can provide me with graphs on efficiency based on output power. They claimed to have dyno data on their website, but after looking at a few I'm fairly sure they have the same graph up for every motor. Which threw a few questions in my mind about the brand, but recommendations trump websites.

Your comment about the peak efficiency being at 1/3 to 1/4 of the peak power handling surprises me. I thought that the highest efficiency would be when the motor is run close to its maxium continous operating point. Do you know why they are more efficient at 1/3 to 1/4? I'm just curious now. This is a good thing for us because we need a small amount of power to keep the car going at a constant speed but there are hills that we need to climb as well, which will require significantly more power. So oversizing the motor would be advantageous to have the extra kick of power in reserve if needed.



Nate

Steve has a numbers of dyno graphs but he doesnt have one for each motor.

If you use the power calculator he has it will tell you the efficiency of any given setup. The problem in your case is its designed for props.

You can however, play with it and you will see that at very low power levels the efficiency is bad as well as at the extreme hi end. Choose a motor and battery then change the prop size to change the load on the motor and you will see what I mean.

Also, generally speaking, higher voltage setups tend to be more efficient than low voltage setups.

If you give the guys at Neu the details on your setup Im sure they can make a good recommendation.

The peak power handling for our little motors is limited by how well the motor can dissipate the waist heat. Its physical size/mass is usually the determining factor along with the air flow available for cooling.

If your motor is operating at say 90% efficiency, then at 500 watts power its wasting 50 watts as heat.

50 watts is a lot of heat to get rid of.

If your motor is only 80% efficient then it needs to dissipate 100 watts of heat.

100 watts is a WHOLE LOT OF HEAT to get rid of :)

As to why electric motors peak that low, that same thing applies to many mechanical and electrical systems.

At the extremes, friction and heat build up and begin to rob the system of efficiency.

In our case, wire temps increase which increases resistance. More resistance means more electrical energy converted to heat.

The other major factor is magnetic saturation. The metal in the stators get saturated magentically and begin to generate more and more heat instead of magnetic flux as power level goes up. Plus other things which are more exotic and beyond my understanding :)

ron_van_sommeren
09-09-2009, 09:45 AM
Most efficient motor:
http://www.csiro.au/resources/pf11g.html

As others already wrote, more information about the vehicle for narrowing things down would be very useful Nate.
What kind of school? What level?

Torque?
Do you want direct drive or geared?
How efficient? Percentage?
Budget?
Duration of ride? Seconds, minutes, hours?
Weight issues?
Longevity/sturdiness?
Sensored or sensorless?
Any thoughts about controller(s)?

Trust a forum to complicate things more :D

Also read/search/ask also these e-bike forum on
www.yahoogroups.com/groups/wsc (World Solar Challenge)
www.endless-sphere.com (e-bikes)

Converting car-alternators
http://www.rcgroups.com/forums/showthread.php?t=905411

The most efficient RC motor is a self-wound one, because you get more copper in the motor than a factory. Kits:
www.innov8tivedesigns.com

Motor_rewinding_101
http://www.gobrushless.com
-> knowledge base
-> basic overview (1-5)

Tips and tricks, checks and tests, may keep you from frying yer ESC and/or controller:
http://www.rcgroups.com/forums/showthread.php?t=240993
http://www.wattflyer.com/forums/showthread.php?t=35216

Vriendelijke groeten ;) Ron

wright100
09-09-2009, 03:29 PM
I appreciate all the input I'm getting here. I'm going to try and answer some of the questions.

Right now we are in the design/research phases so I don't have all the answers at this momment, but they will be coming in the near future.

I am a Senior Electrical Engineering Student at Cedarville University. Here is a link to the a website that will give you information about the car.
There are some pictures of the car that give a better idea of what I'm talking about. The car has extremely low rolling resistance, without a person in it I can push it with one finger. With a person it probably takes 2 or 3. At last years competition we powered it with a 50 CC engine from a lawn mower and that could get it going to 30 MPH or faster. We try not to go really fast because the cars have small problems with rolling.

(I can't post links) Look at my follow up post for the links.



To answer your questions Ron:
-We don't know the exact required Torque yet. There is a mechanical team that should be getting us that information in the next week or so.
-The preference is without gears, however we can use gears
-We are funded by the university so we don't exactly have a budget. However I'm not sure if I could swing the $12000 motor by the department head.
-The duration of the race is approximately 36 minutes. We will race than stop for a short time then race again.
-The car with a 130 lb driver weighs about 300-350 lbs.
-I believe sensored is prefered, but I think we could swing sensorless if we need to.
-We have a Computer Engineer working with us to design the controller. I think he's going to buy a controller that is programmable.
-Energy storage in the car is probably going to be a bay of ultra-capacitors.
-We are going to implement regenerative braking to reduce loses due to drag by keeping the car's speed down. This could be done with the same motor that drives the car or possibly a different one.

The project is supposed to be done by the end of March.

I'm not sure if I answered all the questions (I have class now). Be sure that I'm looking at all the responses and linking things for my other team members to look at too.

Nate

wright100
09-09-2009, 03:30 PM
The site of my school team:
http://cusupermileage.blogspot.com/

Shell Eco Marathon (1st competition)
http://www.shell.com/home/content/eco-marathon-en/welcome_global.html

SAE SuperMileage (2nd Competition)
http://students.sae.org/competitions/supermileage/

DKNguyen
09-10-2009, 02:07 AM
Your comment about the peak efficiency being at 1/3 to 1/4 of the peak power handling surprises me. I thought that the highest efficiency would be when the motor is run close to its maxium continous operating point. Do you know why they are more efficient at 1/3 to 1/4? I'm just curious now. This is a good thing for us because we need a small amount of power to keep the car going at a constant speed but there are hills that we need to climb as well, which will require significantly more power. So oversizing the motor would be advantageous to have the extra kick of power in reserve if needed.



Nate
Peak motor efficiency (as a rule of thumb) is when the motor is loaded down to run at 6/7 to 7/8 of the no-load RPM (or 1/7 to 1/8 of stall torque). Since peak power is at 1/2 no-load RPM or 1/2 stall torque (same thing), it's not much different than saying maximum efficiency is at 1/4 of peak power. But there still is a difference. First of all, it's a lot easier to measure operating RPM than it is to measure output power so it's more practical.

THe second is that the RPM curve is a a sloped line, while the power curve is an upside down parabola, so there are actually two points where power output is 1/4 peak power (obviously for higher efficiency we are talking about the 1/4 peak power point with a higher RPM).

THe third thing is that applying something such a simple rule of thumb to something simpler (like a RPM-torque curve which is just a straight line) is more likely to be accurate than doing the same thing to to something more complicated (the RPM-power curve which is parabolic- it doesn't matter so much that it's parabolic as it matters that it's curved.).

joe90
09-21-2009, 03:22 PM
Wright100

I have selected a neu for its efficiency.
Based on their spread sheet calculator peak efficiency vary much. but in my particular case peak occur around 1200W 43 volts 27A and is around 95% for a neu 1910-2y

It seems affected much by operating voltage and type of winding. in the Neu case.

Chose your motor based on your power need, too big or too small your are off the peak efficiency.

It seem that you must use as much as volts as you can. this reduce the joule losses. it is easier for components simply because there is less Amperes for the same power.

500w is a small motor by rc standarts.
use around 80-90 % of the stated rpm/v it help a lot the 3 phases drive to be more efficient too
Use as big a wire as you can
keep the motor cool to reduce the increase in internal resistance from heat.
just try to implement everything written in good engineering books.

most people in forums dont see the whole picture and tend to focus on one aspect. adivce from here is to be regarded with some perspective.

Chosing the right motor is a balancing act between
operating voltage
power level
usable rpm

you can play with their spreadsheet on neu website.
go to motors select a serie and on right top of the page there is a link

and see what suit you best.

Regards

Michel

wright100
10-09-2009, 03:01 AM
I am really leaning toward neu at the momment. I have been recommended to them by numerous people but I have qualms about how much I trust them. They don't return any emails or phone calls. They seem to be impossible to get ahold of. Has anyone had any reason to doubt the calculator they post on their website?

Nate

Larry3215
10-09-2009, 08:09 AM
The motors are excelent. The calculator will get you in the ball park only. There are too many variables for it to be any other way.

1)The motor itself will have some variation from the stated specs. Even good ones are not all perfect. You can expect at least a few % variation in kV and Ir between motors. With Neu, the variations will be far less than with most any other motor but its still there.
2)Batteries. Battery internal resistance varies a HUGE amount and that will probably be the single largest factor in the uncertainty of the predictions. How well will YOUR packs hold up to the load? No one will know untill you actually test them.
3)Connectors and wiring resistance. How good are you at soldering? Are you using hi quality connectors and large gauge wire? Even a few milli ohms can make a significant difference. A cold solder joint or cheep connectors or small wire can make a large difference at hi power levels.
4)ESC and settings. This is probably the next biggest variable. Are you using a quality esc or a cheep one? What are the settings? Sometimes they cam make a large difference.
5)Instalation. How good is the cooling? Hot components have higher resistance and run less efficiently. Any excess friction anywhere? Extra drag?
6)Measuring equipment? Hobby grade meters can be waaaaaay off. Even the name brand hobby stuff is often not all that accurate but usually close enough for our purposes.

Bottom line is - no way to be 100% sure what YOUR results will be in YOUR particular application with all YOUR accessories and the way YOU installed them and set them up. Just too many variables.

If you luck out and/or are very good in all your choices you will be at the top of the range. Make some bad choices or setup decisions and you could be way down.

The calculator will get you in the ball park. With my setups its usually been reasonably close- within 10% either way. Sometimes its been way off though - maybe 20%-30% off. Sometimes the rpm is very close but the power if off significantly. Sometimes the power is very close but the rpms are off.

I think I heard the Neu guys have been off at the NATs or some other compititions recently. That may be why they havent been answering.

wright100
10-09-2009, 02:16 PM
Hey Larry,

Thanks for the response. It definately builds my confidence in the company that so many people have good things to say about them. I see what you are saying about the specs. A company can only post ratings based on their test setup. Small mistakes on the users part can make a huge difference.

Nate