Watt Meter - WattFlyer RC Electric Flight Forums - Discuss radio control eflight

Power Systems Talk about motors, ESC speed controllers, gear drives, propellers, power system simulators and all power system related topics

Watt Meter

Old 10-24-2007, 03:26 AM
  #1  
celticflyer
Member
Thread Starter
 
Join Date: Aug 2007
Posts: 374
Default Watt Meter

I just purchased an Astro wattmeter. I'm running a Tower-Pro 2408-21
I have a 2 cell 910 mah lipo @ 20c I am pulling 14amps at full throttle. The ESC is 18amps.The prop is a 11/4.7
I also have an 2cell 1800mah That came with the setup on a different plane(no c listed) I haven't measured this one. My question is that if I invest in a 3 cell what can I expect? will I have to backup on the prop size?

John
celticflyer is offline  
Old 10-24-2007, 03:56 AM
  #2  
marchino61
Member
 
Join Date: Apr 2007
Location: Perth, Western Australia
Posts: 261
Default

Originally Posted by celticflyer View Post
I just purchased an Astro wattmeter. I'm running a Tower-Pro 2408-21
I have a 2 cell 910 mah lipo @ 20c I am pulling 14amps at full throttle. The ESC is 18amps.The prop is a 11/4.7
I also have an 2cell 1800mah That came with the setup on a different plane(no c listed) I haven't measured this one. My question is that if I invest in a 3 cell what can I expect? will I have to backup on the prop size?

John
You will definitely have to reduce the prop size. You would probably be drawing more than 20A if you kept the same size prop. You are already overloading the motor as it is only rated at 13A. You would also need to change the ESC.
marchino61 is offline  
Old 10-24-2007, 04:08 AM
  #3  
celticflyer
Member
Thread Starter
 
Join Date: Aug 2007
Posts: 374
Default

OK I just looked it up and Max is 14A . It recommends an 18amp ESC so by going to more volts should increase power so will a smaller prop lesson the load on the motor but increase per formance? Am I thinking right or is their more to it. Would a 9/4 or maybe a 9/6 be a better choice? Wher is a good place to start?

John

http://www.xushobby.com/servlet/Detail?no=21
celticflyer is offline  
Old 10-24-2007, 04:15 AM
  #4  
Dorsal
If it Flies, I love it!
 
Dorsal's Avatar
 
Join Date: Jan 2007
Location: Tracy, California
Posts: 548
Default

Since I = E/R, or R = E/I, the "Resistance" of that setup is 7.4 / 14 = 0.528 Ohms.
So, if you increased E to 11.1 Volts, your new I = 11.0 / 0.528 = 21 Amps, which is too much for that 18A ESC.


(And you thought algebra was a waste of time!)
Dorsal is offline  
Old 10-24-2007, 06:55 AM
  #5  
marchino61
Member
 
Join Date: Apr 2007
Location: Perth, Western Australia
Posts: 261
Default

Originally Posted by celticflyer View Post
OK I just looked it up and Max is 14A . It recommends an 18amp ESC so by going to more volts should increase power so will a smaller prop lesson the load on the motor but increase per formance? Am I thinking right or is their more to it. Would a 9/4 or maybe a 9/6 be a better choice? Wher is a good place to start?

John

http://www.xushobby.com/servlet/Detail?no=21
a 9x6 will probably pull roughly the same current as your 11x4.7 (i.e. about 21W as shown above) - the reason being that although you are reducing the diameter, you are increasing the prop pitch. The 9x6 would give you a higher speed but lower thrust than the 11x4.7.

I would suggest starting with an 8x4 and going up or down from there depending on the results. According to United Hobbies, even with this prop, the motor will draw over 13A:

http://unitedhobbies.com/UNITEDHOBBI...idProduct=4321

This should give you roughly a 50% power increase over your 2S set-up since the current is similar but voltage has increased 50%.

Also note that different makes of prop draw different amounts of current, even in the same prop size. I have noticed that GWS props draw less current than sturdier items - perhaps an indication that they are flexing and hence not cutting through the air as effectively.
marchino61 is offline  
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
supi7
New Product Announcements
2
09-18-2008 05:45 AM
mlamb01
Field Equipment For Sale & WTB
6
06-22-2008 10:51 PM
supi7
Power Systems
2
04-25-2008 09:52 AM
claya2
Batteries & Chargers
6
04-01-2008 09:23 PM
RSS Feed
RCU RSS Feed
27
12-13-2007 06:57 PM

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
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 On


Quick Reply: Watt Meter


Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.

Page generated in 0.08981 seconds with 13 queries