Go Back   RCCrawler Forums > RCCrawler General Tech > Electronics
Loading

Notices

Thread: 3s and trottle end points?

Reply
 
LinkBack Thread Tools Display Modes
Old 06-08-2011, 01:35 PM   #1
Quarry Creeper
 
Join Date: Nov 2010
Location: land of no rocks
Posts: 438
Default 3s and trottle end points?

This seems like a silly question for me but I am asking anyways. Would turning the end points down on the trottle with a 3s battery to the point the power is close to a 2s give me more run time since I am not stressing the battery as much?
toka100 is offline   Reply With Quote
Sponsored Links
Old 06-08-2011, 02:16 PM   #2
I wanna be Dave
 
Join Date: Jul 2005
Location: North Idaho
Posts: 3,647
Default

Its more about how hard you are squeezing the trigger.

Turning the EPA all the way down would end up making your rig run in reverse.
Greatscott is offline   Reply With Quote
Old 06-08-2011, 03:58 PM   #3
Quarry Creeper
 
Join Date: Nov 2010
Location: land of no rocks
Posts: 438
Default

Don't know about the reverse thing. Ok say with my slash with my m11. I have the endpoints set at 124% out of 140%. Brake/reverse is set at 78%. When I let my kids or someone else drive it I'm not sure off I turn the trottle endpoints down to 65%. Goes slow enough they won't loose control along with breaking something.

I know it works but was wondering about run time increasing using a 3s turned down.
toka100 is offline   Reply With Quote
Old 06-08-2011, 05:00 PM   #4
PapaGriz Yo
 
Grizzly4x4's Avatar
 
Join Date: Apr 2004
Location: In the garage building the wife a crawler
Posts: 13,137
Default

So if you turn down the endpoints with the 3S so that it runs as fast as the 2S, the motor will be drawing the same amps from each battery.
If both batteries have the same mAh and C rating then pulling the same amps will give you the same runtime.

Last edited by Grizzly4x4; 06-08-2011 at 05:06 PM.
Grizzly4x4 is offline   Reply With Quote
Old 06-08-2011, 05:57 PM   #5
Suck it up!
 
Duuuuuuuude's Avatar
 
Join Date: Mar 2008
Location: Arkansas
Posts: 11,652
Default

Quote:
Originally Posted by Grizzly4x4 View Post
So if you turn down the endpoints with the 3S so that it runs as fast as the 2S, the motor will be drawing the same amps from each battery.
If both batteries have the same mAh and C rating then pulling the same amps will give you the same runtime.
I'd have to disagree. Having more voltage should give you better run times if the amp load is the same as it would be on a pack of lesser voltage.
Duuuuuuuude is offline   Reply With Quote
Old 06-08-2011, 07:01 PM   #6
PapaGriz Yo
 
Grizzly4x4's Avatar
 
Join Date: Apr 2004
Location: In the garage building the wife a crawler
Posts: 13,137
Default

Quote:
Originally Posted by Duuuuuuuude View Post
I'd have to disagree. Having more voltage should give you better run times if the amp load is the same as it would be on a pack of lesser voltage.
But for a motor to run a given speed the ESC provides a voltage, the voltage of the pack shouldn't matter right?

Running the 7.4V battery at 3/4 throttle, the ESC provides say 5.55V.
To run the car the same speed with the endpoints turned down, the ESC will still be providing 5.55V even with an 11.1V battery.

voltage (V) = amps (I) x resistance (R) or I = V/R
If the voltage to the motor is the same and the resistance through the system is the same; then the current draw (amps) is the same.

If the capacity of both batteries is the same then drawing the same amps will give you the same run time.

I'm open to being proven wrong. This is how I visualize it but I could certainly be missing something.
Grizzly4x4 is offline   Reply With Quote
Old 06-08-2011, 09:07 PM   #7
Suck it up!
 
Duuuuuuuude's Avatar
 
Join Date: Mar 2008
Location: Arkansas
Posts: 11,652
Default

Quote:
Originally Posted by Grizzly4x4 View Post
voltage (V) = amps (I) x resistance (R) or I = V/R
Didn't anyone ever tell you that you aren't allowed to state mathmatical equations when I'm talking out of my ass?

After some semi-careful consideration, I've come to the conclusion that you are correct. When you regulate voltage you typically do it through resistance, so even though the motor itself would be pulling a set amount in either case, the esc (which is basically a variable voltage regulator) would have to scale back the output voltage via internal resistance, which would drain the larger voltage pack in a similar time frame.
Duuuuuuuude is offline   Reply With Quote
Old 06-09-2011, 07:52 AM   #8
Rock Stacker
 
Join Date: Apr 2011
Location: Upper Peninsula, MI
Posts: 64
Default

If you want to take advantage of a higher voltage setup you really need to be gearing down and/or running a lower kv motor. Lowering the endpoint isn't a very good way to moderate speed and power.
simplechamp is offline   Reply With Quote
Old 06-09-2011, 08:41 AM   #9
Quarry Creeper
 
Join Date: Apr 2011
Location: United States
Posts: 226
Default

I don't know any of the math for this but I know when I went from 3s 1300 to 4s 850 I didnt lose any run time........I think he is more concerned with the performance when other people drive it. If you set your endpoints early for the throttle then of course it wont be as fast. Also you could play with your throttle curve if you have an adjustable one in your esc.
PowerCrazy is offline   Reply With Quote
Old 06-09-2011, 09:31 AM   #10
PapaGriz Yo
 
Grizzly4x4's Avatar
 
Join Date: Apr 2004
Location: In the garage building the wife a crawler
Posts: 13,137
Default

Quote:
Originally Posted by Duuuuuuuude View Post
Didn't anyone ever tell you that you aren't allowed to state mathmatical equations when I'm talking out of my ass?
Grizzly4x4 is offline   Reply With Quote
Old 06-09-2011, 10:17 AM   #11
Quarry Creeper
 
Join Date: Nov 2006
Location: Longmont
Posts: 313
Default

The ESC doesn't exactly vary the voltage to control the speed of the motor. Imagine the ESC as a switch turning the full battery voltage on and off several thousand times per second. The amount of on time versus off time is varied to control the speed of the motor. This is called pulse width modulation.

I believe that the OP will gain some run time by using a higher voltage and turning the endpoints down. Will it be a noticable amount? I'm not sure.

read this for more info:

http://homepages.which.net/~paul.hil...llersBody.html

Last edited by toybuilder; 06-09-2011 at 10:23 AM.
toybuilder is offline   Reply With Quote
Old 06-09-2011, 11:06 AM   #12
PapaGriz Yo
 
Grizzly4x4's Avatar
 
Join Date: Apr 2004
Location: In the garage building the wife a crawler
Posts: 13,137
Default

Quote:
Originally Posted by toybuilder View Post
The ESC doesn't exactly vary the voltage to control the speed of the motor. Imagine the ESC as a switch turning the full battery voltage on and off several thousand times per second. The amount of on time versus off time is varied to control the speed of the motor. This is called pulse width modulation.

I believe that the OP will gain some run time by using a higher voltage and turning the endpoints down. Will it be a noticable amount? I'm not sure.

read this for more info:

http://homepages.which.net/~paul.hil...llersBody.html
Ahhhh, see I was afraid I was missing something. Given that information I would agree with you.

Besides, I'd be crazy to argue with anyone who knows electronics as well as you do. Thanks for the information Clint.
Grizzly4x4 is offline   Reply With Quote
Old 06-09-2011, 11:53 AM   #13
Quarry Creeper
 
Join Date: Nov 2006
Location: Longmont
Posts: 313
Default

Quote:
Originally Posted by Grizzly4x4 View Post
Ahhhh, see I was afraid I was missing something. Given that information I would agree with you.

Besides, I'd be crazy to argue with anyone who knows electronics as well as you do. Thanks for the information Clint.
Thanks, Chris. Maybe the real expert, JRH, will chime in here with some more info/explanation.

The RMS (root mean squared) voltage at the motor likely never reaches full battery voltage except at full throttle, because the motor is a large inductor and takes time to charge, but you still have the full battery voltage trying to charge the motor during the ESCs on time.

So with the same load on the motor and higher voltage doing the work, you *should*, according to ohms law, see less current draw at the battery. This is definitely a simplified view of things and there are other variables to consider. Overall, I doubt that with such a small increase in voltage any extra run time would be noticable.

Maybe the OP could do some impirical testing and let us know the results.

Also, the speed control would need to be calibrated with maximum endpoints, and then they would need to be reduced to see any reduction in power at full throttle.

Last edited by toybuilder; 06-09-2011 at 02:19 PM.
toybuilder is offline   Reply With Quote
Reply



Thread Tools
Display Modes

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
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -6. The time now is 01:39 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Content Relevant URLs by vBSEO ©2011, Crawlability, Inc.
Copyright 2004-2014 RCCrawler.com