R/C Tech Forums

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

Reply
 
Thread Tools Search this Thread
Old 07-30-2009, 10:15 AM   #46
Tech Elite
 
seaball's Avatar
R/C Tech Charter Subscriber
 
Join Date: Sep 2001
Posts: 4,303
Trader Rating: 9 (100%+)
Send a message via Yahoo to seaball
Default

ttt!
__________________
*** The Gate II - Home of Mike Wise ***
seaball is offline   Reply With Quote
Old 07-30-2009, 12:27 PM   #47
Super Moderator
 
Cpt.America's Avatar
R/C Tech Elite Subscriber
 
Join Date: Mar 2009
Location: Washington State
Posts: 11,081
Trader Rating: 52 (100%+)
Default

Quote:
Originally Posted by seaball View Post
ttt!
Since the math doesn't seem to tell us all THAT much, why don't we come up with a rule of them for the minimum gauge wire you should run, for any given application? something like:

TC 17.5
16 awg = slight loss in performance
13 awg = no loss in performance
12 awb = no loss in performance

Do it for 17.5, 13.5, 10.5, 4.5 TC, them maybe again for lighter pan cars.
__________________
A big thanks to my sponsors:
- Fantom Racing - www.fantomracing.com -
- Fusion Graphix- www.fusiongraphix.com -
- RCSpecialties -
Cpt.America is offline   Reply With Quote
Old 07-31-2009, 06:33 PM   #48
Tech Adept
 
Join Date: Mar 2009
Location: Metro New York
Posts: 139
Default

In a brush motor the peak mechanical output power (shaft power) is 1/4 the starting electrical power input. Electrical power peaks at zero rpm and goes down exponentially as the rpm and reverse-emf voltage in the motor comes up. The motor absorbs less and less current as the rpm increases, while the terminal voltage drops a bit initially (as Mattnin describes) then comes back up toward battery voltage at higher rpm.

So if you know the battery voltage and peak mechanical power, and assume a brush motor model, you can estimate the starting current very roughly as follows.

Pmpk = 0.25*Vs*Is,

Pmpk - peak shaft power in watts
Vs - open circuit battery voltage
Is - start/stall current drawn at zero rpm

Note: Is = Vs/(Rs + Rm) = Vs/Req

Rs - source resistance in battery, wires, transistors, etc.
Rm - resistance in motoring coils under commutation
Req - equivalent motor circuit resistance

Substitute for Is:

Pmpk = 0.25*(Vs^2/Req)

Step 1 Estimate Req:

Req = 0.25*(Vs^2/Pmpk)

Step 2 Estimate Is:

Is = Vs/Req

(Compare to the transistor AMP rating in the ESC!!! The ESC may self-limit the current to protect the FETs.)

Step 3 Impact of Rs:

When Rs = Rm, half the voltage drops across Rs, and half drops across Rm, thus a reduction of Rs below Rm helps bring up the peak mechanical power Pmpk. In an Ideal Circuit Rs = 0!

This is why low internal Rs LIPO batteries allow for much more powerful motors to be used with high current pass transistors. Higher ampacity wires are necessary to flow the current, so all components are beefed up to improve the State of the Art.
SystemTheory is offline   Reply With Quote
Old 08-03-2009, 07:21 AM   #49
Tech Elite
 
seaball's Avatar
R/C Tech Charter Subscriber
 
Join Date: Sep 2001
Posts: 4,303
Trader Rating: 9 (100%+)
Send a message via Yahoo to seaball
Default

bump.
__________________
*** The Gate II - Home of Mike Wise ***
seaball is offline   Reply With Quote
Old 08-06-2009, 09:01 AM   #50
Tech Elite
 
seaball's Avatar
R/C Tech Charter Subscriber
 
Join Date: Sep 2001
Posts: 4,303
Trader Rating: 9 (100%+)
Send a message via Yahoo to seaball
Default

.
__________________
*** The Gate II - Home of Mike Wise ***
seaball is offline   Reply With Quote
Old 08-06-2009, 09:38 AM   #51
Tech Master
 
chicky03's Avatar
 
Join Date: Mar 2002
Posts: 1,993
Trader Rating: 1 (100%+)
Send a message via AIM to chicky03
Default

__________________
Serpent America, Picco, Desoto Racing, Motiv, J Concepts, Nitro Pro fuel, PT RC Racing Oils, TQ Wire(best wire ever!), BSR tires, Arrowmax, Xceed, Sanwa, Amain Hobbies, MIP, Getcustomized, EZ Customs
chicky03 is offline   Reply With Quote
Old 08-06-2009, 09:46 AM   #52
Tech Master
 
BBSpence's Avatar
 
Join Date: Feb 2002
Location: Northern VA
Posts: 1,731
Trader Rating: 45 (100%+)
Default

I went with 4 gauge, just so I won't keep thinking in my head during a race....is that guy faster than me because his is bigger?

BBSpence is offline   Reply With Quote
Old 08-06-2009, 10:33 AM   #53
Tech Prophet
 
Casper's Avatar
 
Join Date: Aug 2004
Location: Orange, Ca
Posts: 17,764
Trader Rating: 34 (100%+)
Default

Just don't use that in your 12th scale. It will throw off the balance!
__________________
TLR/Losi Team Driver
TLR/Losi | Tekin | DE Racing | Spektrum | Exotek | JBRL | Kolor Koncepts | OC/RC |Sticky Kicks | Imagine It Graphics | Casper-RC.com
TLR 22 4.0 SR, TLR 22T 4.0, TLR 22-4 2.0, Spektrum DX6R

WWW.CASPER-RC.COM TLR and Tekin setups
Casper is offline   Reply With Quote
Old 08-06-2009, 01:30 PM   #54
Tech Addict
 
jt415gz's Avatar
 
Join Date: Mar 2008
Location: The Bay
Posts: 656
Trader Rating: 29 (100%+)
Default

you can seriously hook up a 1000W stereo system in your RC Car with that! ...but, well, it wouldn't go anywhere...
__________________
Thanks,
-jT =]
jt415gz is offline   Reply With Quote
Old 08-07-2009, 06:44 AM   #55
Tech Elite
 
seaball's Avatar
R/C Tech Charter Subscriber
 
Join Date: Sep 2001
Posts: 4,303
Trader Rating: 9 (100%+)
Send a message via Yahoo to seaball
Default

e=mc^2
__________________
*** The Gate II - Home of Mike Wise ***
seaball 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 11:18 AM.


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