RC Electric Off-Road Trucks, Buggies, Truggies and more Discuss electric RC off-road, buggies & trucks here. Also discuss brushless motors, speed controllers aka ESC's, brushed motors, etc

2s 30c or 3s 25c lipo?

Reply
Old 05-20-2010, 10:56 AM
  #1
traxxas85
Thread Starter
 
Join Date: Dec 2009
Location: GREELEY, CO
Posts: 49
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default 2s 30c or 3s 25c lipo?

ok so i am about to buy a traxxas slash with a sidewinder 4600 combo and some RPM stuff. first of all should i run hard case 2s 30c 5200mah lipo or 3s 25c 5800 lipo? im looking for some good low end punch and lots of run time im leaning toward the 3s but does 5c make a huge on the punch? it also has 600 more mah but costs twice as much. also how do i set the lvc thanks! and i think im gonna but the hobbyking 2.4ghz radio does anyone have any experience with it? is it good? thanks guys!
traxxas85 is offline  
Reply With Quote
Old 05-20-2010, 11:08 AM
  #2
Slo-V Flyer
 
Slo-V Flyer's Avatar
 
Join Date: Feb 2006
Location: Arlington, TX
Posts: 3,344
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: 2s 30c or 3s 25c lipo?

The LVC should be set default from the factory for auto lipo.... however I'd hook it up to the Castle link if you have it, or check the instructions on how to program that for auto lipo.

Both can give you the same run time, depending on your gearing, or the 3S lipo can give you more run time if you gear it low.

With that said, the 4600 kv motor is plenty fast on 2s lipo (I run a 2700 kv) so you may fine you get ~25 minutes of run time with the 2s, geared perhaps 18/90 or similar. On the other hand gear down a couple or 4 odd teeth on the pinion and use 3s lipo and you will be able to increase your runtime more. By gearing down with the 3s lipo you reduce the amp draw, but retain some speed. This way you still get good performance, while reducing heat and increase run time.
Slo-V Flyer is offline  
Reply With Quote
Old 05-20-2010, 11:12 AM
  #3
traxxas85
Thread Starter
 
Join Date: Dec 2009
Location: GREELEY, CO
Posts: 49
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: 2s 30c or 3s 25c lipo?

so should i go with 2 2s packs? could i still get some seriously fun wheelies and bashing out of it? or how much more run time could i get like you said if i geared down the 3s? thanks.
traxxas85 is offline  
Reply With Quote
Old 05-20-2010, 11:36 AM
  #4
samguan
 
Join Date: Sep 2008
Location: Toronto, ON, CANADA
Posts: 1,853
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: 2s 30c or 3s 25c lipo?

From personal experience, you should go with 3S if you want crazy speed, wheelie on demand.
samguan is offline  
Reply With Quote
Old 05-20-2010, 11:37 AM
  #5
Slo-V Flyer
 
Slo-V Flyer's Avatar
 
Join Date: Feb 2006
Location: Arlington, TX
Posts: 3,344
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: 2s 30c or 3s 25c lipo?

Given that the packs are almost similar in capacity ~5000 mah, theoretically you can get 50% more runtime with the 3s pack, by gearing down to keep the same top speed you would have with the 2s. This gear down again, would reduce the load on the motor and therefore things would run cooler and reduce current required to keep it going.

As for getting 2 2s packs, I'd say you get 1 2s and 1 3s lipo. You could wheelie with the 4600 on 2s, but you'll just be able to do it waaay more easily with the 3s.

Personally, I run 2s and 3s lipos in the Slash the the 2700 kv motor. I crash more horribly with the 3s and less with the 2s. Other than more speed and insane power with 3s, I don't mind either battery.
Slo-V Flyer is offline  
Reply With Quote
Old 05-20-2010, 11:42 AM
  #6
traxxas85
Thread Starter
 
Join Date: Dec 2009
Location: GREELEY, CO
Posts: 49
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: 2s 30c or 3s 25c lipo?

yeah thanks i think thats what im gonna do i will have pics up of the slash soon anything else i should do to it for durability?
traxxas85 is offline  
Reply With Quote
Old 05-20-2010, 11:45 AM
  #7
Slo-V Flyer
 
Slo-V Flyer's Avatar
 
Join Date: Feb 2006
Location: Arlington, TX
Posts: 3,344
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: 2s 30c or 3s 25c lipo?

Mine is bone stock and I've had it for a year, crashed it into a pole head on at 25 mph, landed upside down, sideways, rolled and tumbled for yards and yards, and I have to say it's one tough bastige. Not one real broken or upgraded part running brushless from day 1. The only issue is the Traxxas rear bumper/wheelie bar mount, it does get damaged over time, but it's a simple design and light weight, and I can replace the bumper with the wheelie setup so I can ride wheelies better, and always go back to the stock bumper.
Slo-V Flyer is offline  
Reply With Quote
Old 05-20-2010, 11:47 AM
  #8
samguan
 
Join Date: Sep 2008
Location: Toronto, ON, CANADA
Posts: 1,853
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: 2s 30c or 3s 25c lipo?

I used to run Mamba Max 4600KV and I broke couple of these:



Just make sure you don't tighten the slipper too much or else eventually you will break the pin on the input shaft running 3s.
samguan is offline  
Reply With Quote
Old 05-20-2010, 11:48 AM
  #9
traxxas85
Thread Starter
 
Join Date: Dec 2009
Location: GREELEY, CO
Posts: 49
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: 2s 30c or 3s 25c lipo?

thats really good to know and should i be worried about the previous owner said the heat sink fell of and he is gonna put it back on with double sided tape heat conducting pad.
traxxas85 is offline  
Reply With Quote
Old 05-20-2010, 11:50 AM
  #10
samguan
 
Join Date: Sep 2008
Location: Toronto, ON, CANADA
Posts: 1,853
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: 2s 30c or 3s 25c lipo?


Quote:
ORIGINAL: traxxas85

thats really good to know and should i be worried about the previous owner said the heat sink fell of and he is gonna put it back on with double sided tape heat conducting pad.
If you are worry, remove the heat sink and go to your local computer shop and buy some thermal paste. Apply some paste and then put the heat sink on it. Then tie it down with zip tie.
samguan is offline  
Reply With Quote
Old 05-20-2010, 11:51 AM
  #11
traxxas85
Thread Starter
 
Join Date: Dec 2009
Location: GREELEY, CO
Posts: 49
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: 2s 30c or 3s 25c lipo?

im not worried i was just wondering if this is ok.
traxxas85 is offline  
Reply With Quote
Old 05-20-2010, 11:52 AM
  #12
samguan
 
Join Date: Sep 2008
Location: Toronto, ON, CANADA
Posts: 1,853
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: 2s 30c or 3s 25c lipo?


Quote:
ORIGINAL: traxxas85

im not worried i was just wondering if this is ok.
You should be ok, but just watch the temperature when you are running 3s.;
samguan is offline  
Reply With Quote
Old 05-20-2010, 11:57 AM
  #13
traxxas85
Thread Starter
 
Join Date: Dec 2009
Location: GREELEY, CO
Posts: 49
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: 2s 30c or 3s 25c lipo?

what would be good gearing in grass and stuff?
traxxas85 is offline  
Reply With Quote
Old 05-20-2010, 12:15 PM
  #14
Slo-V Flyer
 
Slo-V Flyer's Avatar
 
Join Date: Feb 2006
Location: Arlington, TX
Posts: 3,344
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: 2s 30c or 3s 25c lipo?

With the 4600 motor on 3S lipo, I'd try 15t pinion and stock spur. If that stays cool with 3S than you're good for 2S lipo and a couple teeth higher on grass too.
Slo-V Flyer is offline  
Reply With Quote
Old 05-20-2010, 12:20 PM
  #15
traxxas85
Thread Starter
 
Join Date: Dec 2009
Location: GREELEY, CO
Posts: 49
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: 2s 30c or 3s 25c lipo?

with a 90t spur how would a 19t pinion do?
traxxas85 is offline  
Reply With Quote
Old 05-20-2010, 12:44 PM
  #16
traxxas85
Thread Starter
 
Join Date: Dec 2009
Location: GREELEY, CO
Posts: 49
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: 2s 30c or 3s 25c lipo?

and for 3s will i need a battery tray expansion kit?
traxxas85 is offline  
Reply With Quote
Old 05-20-2010, 01:34 PM
  #17
Brainanator
 
Brainanator's Avatar
 
Join Date: Jun 2009
Location: Great Falls, MT
Posts: 2,482
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: 2s 30c or 3s 25c lipo?

with 3s you'll have heat problems... http://www.youtube.com/watch?v=c-6H0vp5HbM 2S lipo will wheelie, and youll break alot less. you might still have heat probs though
Brainanator is offline  
Reply With Quote
Old 05-20-2010, 07:57 PM
  #18
dmowery
 
Join Date: Apr 2010
Location: Andover, MN
Posts: 169
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: 2s 30c or 3s 25c lipo?

I race them all the time in spec class and use only 2 cell batts and beat the snot out of them as we have 10 cars in a off road heat and just like red neck racin/rubbin they get scratched and total parts breakage for the year has been less than 5 bucks - 3 cell will take some batt box mods and produse some over heat as 2 cell is max they were designed for and no heat problems - yea we change the radios but all else bone stock except the right rear we put a screw in the bumper to keep it from comming out on a hard drop and gouging holes in the expensive carpet -dirt no problem
dmowery is offline  
Reply With Quote
Old 05-28-2010, 07:56 PM
  #19
traxxas85
Thread Starter
 
Join Date: Dec 2009
Location: GREELEY, CO
Posts: 49
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: 2s 30c or 3s 25c lipo?

also i will be getting turnigy lipo what do you guys think of it?
traxxas85 is offline  
Reply With Quote
Old 05-28-2010, 09:03 PM
  #20
Brainanator
 
Brainanator's Avatar
 
Join Date: Jun 2009
Location: Great Falls, MT
Posts: 2,482
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: 2s 30c or 3s 25c lipo?

I have had great luck with all my turnigy lipos (a whopping 2), with my friends there are 5 total, and all work great!
Brainanator is offline  
Reply With Quote
Old 05-28-2010, 09:54 PM
  #21
AdamHeard
 
Join Date: May 2010
Location: San Luis Obispo, CA
Posts: 49
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: 2s 30c or 3s 25c lipo?


Quote:
ORIGINAL: Slo-V Flyer

Given that the packs are almost similar in capacity ~5000 mah, theoretically you can get 50% more runtime with the 3s pack, by gearing down to keep the same top speed you would have with the 2s. This gear down again, would reduce the load on the motor and therefore things would run cooler and reduce current required to keep it going.

As for getting 2 2s packs, I'd say you get 1 2s and 1 3s lipo. You could wheelie with the 4600 on 2s, but you'll just be able to do it waaay more easily with the 3s.

Personally, I run 2s and 3s lipos in the Slash the the 2700 kv motor. I crash more horribly with the 3s and less with the 2s. Other than more speed and insane power with 3s, I don't mind either battery.
This isn't exactly true, your motor's free speed increases linearly with voltage, but the stall current does as well. Power dissipated in the motor is based on the current squared, so it's hard to predict.

Depending on the gearing, it could run cooler, but it could be the other way as well.

AdamHeard is offline  
Reply With Quote
Old 05-29-2010, 02:56 AM
  #22
Slo-V Flyer
 
Slo-V Flyer's Avatar
 
Join Date: Feb 2006
Location: Arlington, TX
Posts: 3,344
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: 2s 30c or 3s 25c lipo?


Quote:
ORIGINAL: AdamHeard


Quote:
ORIGINAL: Slo-V Flyer

Given that the packs are almost similar in capacity ~5000 mah, theoretically you can get 50% more runtime with the 3s pack, by gearing down to keep the same top speed you would have with the 2s. This gear down again, would reduce the load on the motor and therefore things would run cooler and reduce current required to keep it going.

As for getting 2 2s packs, I'd say you get 1 2s and 1 3s lipo. You could wheelie with the 4600 on 2s, but you'll just be able to do it waaay more easily with the 3s.

Personally, I run 2s and 3s lipos in the Slash the the 2700 kv motor. I crash more horribly with the 3s and less with the 2s. Other than more speed and insane power with 3s, I don't mind either battery.
This isn't exactly true, your motor's free speed increases linearly with voltage, but the stall current does as well. Power dissipated in the motor is based on the current squared, so it's hard to predict.

Depending on the gearing, it could run cooler, but it could be the other way as well.


I understand that, I was trying to provide some non-head exploding answer, but I think I can't put it into words. Yes when going up in voltage, assuming you keep the same exact gearing, you also increase the amp draw proportionally. So 50% more voltage, going from 2s 7.4v to 3s 11.1v, will typically result in 50% more amp draw, again, given the same load on the motor (that being your gearing and everything else in the truck being the same, weight, tires, etc).

Usually more voltage does result in increased amp draw and then excessive amp draw results in more heat. That is why proper gear reduction is important in keeping the temps cool (relatively) when going up in voltage. Agreed.

Theoretically, going up double in voltage, from 2s to 4s lipo for example, net's about 4 times the power, not 2 times, as most people might think (including me for a long time). You're getting twice the RPM from twice the voltage feed, sure, but as stated above, you are also potentially increasing amp draw 2 times as much (again, assuming the motor can handle that amperage and convert it to usable torque), put simply you've increased the power output exponentially, not linearly.

/semi-geek stuff.

Slo-V Flyer is offline  
Reply With Quote
Old 05-29-2010, 09:17 AM
  #23
traxxas85
Thread Starter
 
Join Date: Dec 2009
Location: GREELEY, CO
Posts: 49
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: 2s 30c or 3s 25c lipo?

even geared 14/90 or 16/90?
Quote:
ORIGINAL: Brainanator

with 3s you'll have heat problems... http://www.youtube.com/watch?v=c-6H0vp5HbM 2S lipo will wheelie, and youll break alot less. you might still have heat probs though
traxxas85 is offline  
Reply With Quote
Old 05-29-2010, 09:29 AM
  #24
Access
 
Join Date: Mar 2005
Location: , CA
Posts: 4,900
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: 2s 30c or 3s 25c lipo?

Quote:
ORIGINAL: Slo-V Flyer
Quote:
ORIGINAL: AdamHeard
Quote:
ORIGINAL: Slo-V Flyer
Given that the packs are almost similar in capacity ~5000 mah, theoretically you can get 50% more runtime with the 3s pack, by gearing down to keep the same top speed you would have with the 2s. This gear down again, would reduce the load on the motor and therefore things would run cooler and reduce current required to keep it going.

As for getting 2 2s packs, I'd say you get 1 2s and 1 3s lipo. You could wheelie with the 4600 on 2s, but you'll just be able to do it waaay more easily with the 3s.

Personally, I run 2s and 3s lipos in the Slash the the 2700 kv motor. I crash more horribly with the 3s and less with the 2s. Other than more speed and insane power with 3s, I don't mind either battery.
This isn't exactly true, your motor's free speed increases linearly with voltage, but the stall current does as well. Power dissipated in the motor is based on the current squared, so it's hard to predict.

Depending on the gearing, it could run cooler, but it could be the other way as well.
I understand that, I was trying to provide some non-head exploding answer, but I think I can't put it into words. Yes when going up in voltage, assuming you keep the same exact gearing, you also increase the amp draw proportionally. So 50% more voltage, going from 2s 7.4v to 3s 11.1v, will typically result in 50% more amp draw, again, given the same load on the motor (that being your gearing and everything else in the truck being the same, weight, tires, etc).

Usually more voltage does result in increased amp draw and then excessive amp draw results in more heat. That is why proper gear reduction is important in keeping the temps cool (relatively) when going up in voltage. Agreed.

Theoretically, going up double in voltage, from 2s to 4s lipo for example, net's about 4 times the power, not 2 times, as most people might think (including me for a long time). You're getting twice the RPM from twice the voltage feed, sure, but as stated above, you are also potentially increasing amp draw 2 times as much (again, assuming the motor can handle that amperage and convert it to usable torque), put simply you've increased the power output exponentially, not linearly.

/semi-geek stuff.
Actually both of you are oversimplifying, those things are only true for resistive loads and a motor is not. You get current squared by applying ohm's law and you can only apply ohm's law for a resistive load (voltage goes away b'cos current draw is proportional to voltage for a resistive load).

From a RC standpoint, Amp draw is based more on the level of acceleration of the vehicle than anything else. Modern brushless (sintered rotors and all) and LiPo acceleration being so great, even a 17.5 motor on 2s geared low can pull 100A, it just won't do it for very long. B'cos the setup will max out in speed and it will stop accelerating very quickly. Now you put that 17.5 on 4s or even 6s with the same gearing and it's going to be able to accelerate for much longer, so it will pull that high current for much longer.

If you want to get down to the physics part of it, with the modern gear the best model to apply is energy conversion. Power is energy use over time, electrically it is Volts * Amps and you are converting electrical power to mechanical power (and some heat, vibration, etc. that comes from inefficiency, which stays between 65% to 85% with the modern setups, depending on overall quality and setup).

If you take a setup running off 6V or a setup running off 12V, to get them to accelerate at the same rate, they both have to draw the same amount of power electrically. So the 12V setup can get by drawing half the current that the 6V setup can, efficiencies being equal. The only catch here is that efficiencies aren't equal, everything you do to the setup (like change the gearing or going to a higher voltage) is going to shift the efficiency in one direction or another. But generally you're not going to move the efficiency by more than +/- 10% to 20% unless you start to do real drastic things (like serious overgearing). Efficiency is a big topic in itself and trying to maximize efficiency should be the ultimate goal of a modern setup, especially one designed for high performance.
Access is offline  
Reply With Quote
Old 05-29-2010, 11:09 AM
  #25
Brainanator
 
Brainanator's Avatar
 
Join Date: Jun 2009
Location: Great Falls, MT
Posts: 2,482
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: 2s 30c or 3s 25c lipo?


Quote:
ORIGINAL: traxxas85

even geared 14/90 or 16/90?
Quote:
ORIGINAL: Brainanator

with 3s you'll have heat problems... http://www.youtube.com/watch?v=c-6H0vp5HbM 2S lipo will wheelie, and youll break alot less. you might still have heat probs though
I still have heat probs with 12/86 on 2s. (changing the spur is less drastic than changing the pinion, so 12/86 is lower than 14/90) The heat probs usually arise on asphalt, with there is a lot of traction. But I have to quit running on dirt some times too. I usually have it geared 14-15/86
Brainanator is offline  
Reply With Quote
Reply


Thread Tools
Search this Thread
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 Off



All times are GMT -8. The time now is 07:50 PM.