R/C Tech Forums

Go Back   R/C Tech Forums > General Forums > Electric On-Road

Reply
 
Thread Tools Search this Thread
Old 05-07-2013, 06:07 AM   #1
Tech Master
 
Join Date: Nov 2012
Posts: 1,122
Trader Rating: 13 (100%+)
Default What do the numbers on the motors mean? Also batteries?

I see some people with numbers on their batteries, what and how do people measure to get thes numbers and what do they mean?
Also I see on some websites ( EAM motors) that they measure the strength of the rotor, resistance of the stator and shim the rotor.. What and how can I do these things to know what the numbers on any motor purchased from some other company that doesn't do it for me
JOE SI is offline   Reply With Quote
Old 05-07-2013, 09:05 AM   #2
Tech Regular
 
Timbo99's Avatar
 
Join Date: Mar 2010
Location: Melbourne AUSTRALIA
Posts: 385
Trader Rating: 14 (94%+)
Send a message via ICQ to Timbo99 Send a message via AIM to Timbo99 Send a message via MSN to Timbo99 Send a message via Skype™ to Timbo99
Smile Email

Hi,
I'd send an email to the company asking the questions you want answered.
Cheers
Tim
__________________
Serpent ERYX/S411 Le#189,#024,TE/Airtronics/MuchMore FLETA 4/Ryan Dezign-
"The finest RC paintwork in Australia"/LEESPEED/Ame T-Shox/THiNK Carbon.
"If at first you don't succeed,.....tell'em it's the "Beta" 1.0 version"
Timbo99 is offline   Reply With Quote
Old 05-07-2013, 09:20 AM   #3
Tech Master
 
locked's Avatar
 
Join Date: Mar 2010
Location: Toronto
Posts: 1,758
Trader Rating: 1 (100%+)
Default

EA checks all the stuff he sells. The rotor numbers are a gauss measurement (magnetism). He also dynos each motor. Most places do not do any of this.

You won't regret buying anything from EAM. You'll never get a lemon from him. Great guy, top notch products.
locked is offline   Reply With Quote
Old 05-07-2013, 09:42 AM   #4
Tech Lord
 
wingracer's Avatar
 
Join Date: Nov 2007
Posts: 12,861
Trader Rating: 24 (100%+)
Default

All perhaps true but fails to answer any of his questions.

I'll give it a shot starting with batteries:

There are all sorts of numbers thrown around with batteries like mah, C rate, etc. But for our purposes, there are three numbers that matter when testing to determine performance. They are:

1. Discharge time.
2. Average voltage.
3. Internal resistance.

Now to acquire these numbers under conditions suitable for our application requires a charger/discharger that can provide them at high discharge rates similar to what we draw on the track. So you will need at least a 25 amp discharge, 30 or 35 might be even better and keep track of all these numbers during the process to display usefull overall numbers. An example of such a charger would be Competition Electronics (Turbo 35, GFX, etc).

Now what you do is put a pack on the charger, set it to a cycle mode and hit start. It will charge the pack, then discharge it. You can adjust most of the parameters such as charge rate (5amp or 6amp or 10 amp, whatever you like), discharge rate (20 amp, 30 amp, etc.) cutoff voltage (the voltage at which the charger will stop discharging) etc. Once the charger finishes its cycle, it will display some numbers for you based on the performance of the pack.

1. Discharge time. This is how long it took the pack's voltage to drop down to the cutoff voltage point. Basically it's the pack's capacity. This number used to be critical back in the day but with modern LiPos having more capacity than we need, it is a bit less important.

2. Average voltage. This is an average of the voltage the pack was putting out under the load while discharging. This is a very critical number as the higher it is, the faster your car will be (on average) over the course of a run.

3. Internal resistance. This is usually calculated based on the performance of the pack. It is the resistance of the pack itself. There is equipment to physically measure this but if you can get all the other numbers, it isn't really needed. Lower numbers are better than higher numbers but average voltage gives you an idea of it since high resistance packs will usually have lower average voltage as well (though not always).

These numbers can give you some idea of which pack is better than another. Beware though as they can be misleading. I will talk about that later.

I will talk about motors later.
__________________
Sean. Certified speed crazed mowron.
Team Shepherd USA
www.ashfordhobby.com

Last edited by wingracer; 05-07-2013 at 09:57 AM.
wingracer is online now   Reply With Quote
Old 05-07-2013, 04:47 PM   #5
Tech Master
 
Join Date: Nov 2012
Posts: 1,122
Trader Rating: 13 (100%+)
Default

Quote:
Originally Posted by wingracer View Post
All perhaps true but fails to answer any of his questions.

I'll give it a shot starting with batteries:

There are all sorts of numbers thrown around with batteries like mah, C rate, etc. But for our purposes, there are three numbers that matter when testing to determine performance. They are:

1. Discharge time.
2. Average voltage.
3. Internal resistance.

Now to acquire these numbers under conditions suitable for our application requires a charger/discharger that can provide them at high discharge rates similar to what we draw on the track. So you will need at least a 25 amp discharge, 30 or 35 might be even better and keep track of all these numbers during the process to display usefull overall numbers. An example of such a charger would be Competition Electronics (Turbo 35, GFX, etc).

Now what you do is put a pack on the charger, set it to a cycle mode and hit start. It will charge the pack, then discharge it. You can adjust most of the parameters such as charge rate (5amp or 6amp or 10 amp, whatever you like), discharge rate (20 amp, 30 amp, etc.) cutoff voltage (the voltage at which the charger will stop discharging) etc. Once the charger finishes its cycle, it will display some numbers for you based on the performance of the pack.

1. Discharge time. This is how long it took the pack's voltage to drop down to the cutoff voltage point. Basically it's the pack's capacity. This number used to be critical back in the day but with modern LiPos having more capacity than we need, it is a bit less important.

2. Average voltage. This is an average of the voltage the pack was putting out under the load while discharging. This is a very critical number as the higher it is, the faster your car will be (on average) over the course of a run.

3. Internal resistance. This is usually calculated based on the performance of the pack. It is the resistance of the pack itself. There is equipment to physically measure this but if you can get all the other numbers, it isn't really needed. Lower numbers are better than higher numbers but average voltage gives you an idea of it since high resistance packs will usually have lower average voltage as well (though not always).

These numbers can give you some idea of which pack is better than another. Beware though as they can be misleading. I will talk about that later.

I will talk about motors later.
Thanks, exactly what I wanted to know
JOE SI is offline   Reply With Quote
Old 05-07-2013, 04:48 PM   #6
Tech Master
 
Join Date: Nov 2012
Posts: 1,122
Trader Rating: 13 (100%+)
Default

Quote:
Originally Posted by locked View Post
EA checks all the stuff he sells. The rotor numbers are a gauss measurement (magnetism). He also dynos each motor. Most places do not do any of this.

You won't regret buying anything from EAM. You'll never get a lemon from him. Great guy, top notch products.
His motors are definitely the Kreme of the cropp
JOE SI is offline   Reply With Quote
Old 05-07-2013, 04:53 PM   #7
Tech Master
 
Join Date: Nov 2012
Posts: 1,122
Trader Rating: 13 (100%+)
Default

Low resistance= good in lipos and motors I'm guessing?
Lower resistance = higher discharge?
Gauss? The bigger the number the better, that's my guess since it would be a stronger magnet?
Wing racer answered the rest
JOE SI is offline   Reply With Quote
Old 05-07-2013, 06:02 PM   #8
Tech Master
 
locked's Avatar
 
Join Date: Mar 2010
Location: Toronto
Posts: 1,758
Trader Rating: 1 (100%+)
Default

Quote:
Originally Posted by JOE SI View Post
Low resistance= good in lipos and motors I'm guessing?
Lower resistance = higher discharge?
Gauss? The bigger the number the better, that's my guess since it would be a stronger magnet?
Wing racer answered the rest
yes sir, all correct
locked is offline   Reply With Quote
Old 05-07-2013, 08:27 PM   #9
Tech Lord
 
wingracer's Avatar
 
Join Date: Nov 2007
Posts: 12,861
Trader Rating: 24 (100%+)
Default

Well, yes and no. I will get to that soon.
__________________
Sean. Certified speed crazed mowron.
Team Shepherd USA
www.ashfordhobby.com
wingracer is online now   Reply With Quote
Old 05-07-2013, 08:43 PM   #10
Tech Lord
 
wingracer's Avatar
 
Join Date: Nov 2007
Posts: 12,861
Trader Rating: 24 (100%+)
Default

OK, lets break this down a bit:

Quote:
Originally Posted by JOE SI View Post
Low resistance= good in lipos and motors I'm guessing?
Lower resistance = higher discharge?
Gauss? The bigger the number the better, that's my guess since it would be a stronger magnet?
Wing racer answered the rest
In batteries, yes lower IR is better but you don't necessarily need to know it as it can be inferred from the average voltage number (which is the important one). The reason low IR is good is that the lower the IR, the more voltage the pack will deliver under heavy load. But by testing under heavy discharge, we get the average voltage under that heavy load so a pack that reads good on the voltage can be inferred to be good on IR as well. Since IR reading is a bit of a mixed bag in terms of accuracy, I don't put as much stock in it.

In motors, yes lower resistance readings are usually better WITHIN THE SAME BRAND OF MOTOR! That bold print part is important. If you have six brand X stators, the one that reads the lowest is probably going to be the fastest. However, if you have one brand x and one brand Y stator, it might or might not be. A different stack design might result in higher resistance numbers but run better.

Rotors and gauss. The bigger the number, the stronger the magnet. Generally it has been my experience that the bigger and stronger the rotor (within the rules of course) the better in most applications but not all. In theory, it is possible to "over magnet" a motor but the only time I find this to be the case is 1s boosted apps such as boosted 1/12th where a smaller and weaker rotor is often quicker.
__________________
Sean. Certified speed crazed mowron.
Team Shepherd USA
www.ashfordhobby.com
wingracer is online now   Reply With Quote
Old 05-07-2013, 09:22 PM   #11
Regional Moderator
 
CarbonJoe's Avatar
 
Join Date: Jul 2006
Posts: 2,661
Default

Rotor sizes and gauss meter readings aren't absolute either. Different brands of gauss meters will produce different numbers, and you can't really compare them between brands, and they also may not measure the same between meters of the same brand. I'm not sure how well the manufacturers calibrate the meters, if at all. There are tolerances on everything electronic.

All that the rotor diameter really determines is the "air gap" to the stator. This distance is usually different between motor designs. In general, the larger the air gap, the higher the RPM/less torque the motor has. This is just like a weaker rotor usually will have less torque/more RPM. The trick is finding the sweet spot (right combination) of rotor and stator for a given motor. That combination may be different for 1s vs. 2s classes.

For example, a weaker, smaller diameter rotor might be great in 1/12 scale, but a stronger, larger rotor may be the ticket for a touring car (assuming the same model of motor).
__________________
*** The Gate - Celebrating 8 years at the same location ***
The difference between genius and stupidity is that genius has its limits. - Albert Einstein
Understeer is when you hit the wall with the front of the car and oversteer is when you hit the wall with the rear of the car
CarbonJoe is offline   Reply With Quote
Reply



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off



All times are GMT -7. It is currently 12:49 PM.


We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
Powered By: vBulletin v3.9.2.1
Privacy Policy | Terms of Use | Advertise Content © 2001-2011 RCTech.net