brenthampton79

I have a traxxas slash with a velineon set up along with the rustler vxl I am currently running tenergy nimh batts ranging from 6 cells to 8 cells, I like the 7 cells in the slash the most and the 6 cells in the rustler for the small track in my back yard. My question is will a 2s lipo have more performance than the 7 cell in the slash? I know that it should have more than the 6 in the vxl, I use lipos in my airplanes (3s 2100mah smaller planes) but haven't made the switch to lipos in the cars yet, I orderd a 20c 3s 5000mah from hobby city for the rustler and my electric plane i'm working on, but I will more than likely use the 3s in the plane most of the time, I want to use lipo's since everyone is saying they are getting longer run times with the cars, can you give me the pro's and cons to the lipo vs nimh, I already know they cost more and that they take longer to charge and all that I am already set up to use lipos with airplanes and charge them soo im mostly curios about performance run times that type of stuff
Thanks
Brent

Jeremy Z

LiPos have higher energy density. More power with less weight. But they are also more fragile and sensitive to proper charging techniques. You know a lot of this stuff from your LiPo experience in planes, I'm sure. You have a charger and balancer, or balancing charger?

A 2S LiPo of the same capacity as a 6c NiMH will of course outperform the NiMH. It may even be on par with the 7c, due to the weight savings and stiff voltage.

One thing to consider is that in the car world, crashes are common and expected. Not so in the plane world. So you should really get a hard case LiPo if you're going to run them in your cars. If you crease or smoosh them, they're no good. Nickel battery packs are much more durable than the non-enclosed LiPos that are so cheap these days.

brenthampton79

Thanks Jeremy

Yes i have the proper charging equipment, I have two equinox balancers that plug into my hobbico accucycle

I am planning about maybe building a hardcase for them since you do end up flipping the trucks and are a lot harder on the pack that way or buying them with the harcase on them

Also I understand c rating mah pretty well i think

My current nimh set up i figure I am getting 40 amps with 8.4 volts of pressure, with a 2s 20c 5000 mah lipo i figure I'll get 100 amps with 7.4 volts of pressure,
Correct me if im wrong but I am guessing the amps will be as important as the voltage when it comes to speed right? thats why i figure that type of lipo will cancel out the increased voltage of a 7 cell nimh
thanks again
Brent

Access

Current (Amps) is always drawn by the load. It's never forced into things. No load means no current; likewise, if your load is drawing only 10 Amps max (ie. you are driving very lightly) you won't recognize any difference between the LiPo or NIMH if they are near the same voltage.

Where the LiPo helps is the current handling capability, when you push the performance of your vehicle, like accelerate hard, brake hard, climb a hill, or try to go fast on rough terrain. You may not see a huge difference in top speed, rather you'll see a difference in this kind of performance.

brenthampton79

access thanks

that helps explain some more then so the lipo will have more acceleration so to speak, like coming out of the corners and punching it then. So do you think the 2s lipo will keep up with the 8.4 nimh?

Mufasa_719

Correct. The punch a lipo puts out is more noticeable than a nimh.

brenthampton79

okay cool thanks everyone I think i'll start switching over to all lipos and probably with 2s and one or two 3s, i figure the 3s is fast but the 2s is probably plenty on a shorter track right?

brenthampton79

Did some more thinking about the amps and all

I guess since you can draw a higher load from the battery on a lipo you can select a higher gear ratio and get enough speed to equal te 8.4 since you can pull the higher load??? Is this right? Is that how traxxas can show that a 7.4 volt lipo can beat a 8.4 nimh?

Traxxas4fun

My Feedback: (3)

lol, im basically wondering the exact same thing. i got a rustler with the 4600 system and im wondering between a 2s lipo or an 8 cell nimh.. i want the most speed. only bashing no racing

FairTax4me

No. You don't want to change your gearing just for a battery. The reason lipos tend to be faster is that they can provide more current to the motor therefore making it spin faster, and have more torque.

I'm not sure what Traxxas said about the difference between lipo speed and nimh speed. But they probably compared a cheap nimh with a good lipo to get that result. A "good" lipo will be able to put out many more amps and much more voltage than most nimhs can even dream of. But a good 8.4v nimh should be able to hold its own against a 7.4v lipo.

This pack will get you far more speed than any 2S lipo. http://www.promatchracing.com/proddetail.php?prod=7480
Gear down some because your motor and ESC will run hotter with the higher voltage.

Access

You can gear up but at some point you start having problems with motor heat.
More current means more torque, but it also means more heat, and it's not linear. Twice the current means 4x the heat, remember (I^2)(R) or Ohm's law as applied to current, resistance, and power.

Brushless motors are best kept below 180F, 200F is the point where most start to suffer damage.

brenthampton79

Okay

fairtax thats what I was thinking about the amps, i know it makes a difference on airplanes and also thanks for the warning about not gearing up and the heat issue, also fairtax im not worried about getting more speed I just want to know if im going to have similar performance,(I like the performance of the 8.4nimh) I have 4 8 cell lipos and have ran a couple of 9 cells in my rustler but it was only good for straight line runs in my opinion again thanks for the advice

Acces also thanks for the warning and the numbers I'll use 180 as my guide then, I am going to get a 2s lipo and try it out my brother has a vxl identical to mine so we'll just get our best 8.4 nimh and run it against the 2s lipo and see which wins

vge

I have a Slash with the VXL system in it and let me tell ya this, with even the smallest 2000mah 11.1 20c batteries it is almost uncontrollable. You really will feel like your flying a plane some times because if a little air gets under it, it will take off and flip. Now when I drop my 4000mah 15c 11.1's in it, it is a little bit easier to control. But still you wont be making any sharp turns. I was really considering pulling my vxl from my slash because it really takes some of the fun out flipping so much.

Mufasa_719

The slash vxl on 2s isnt tooooo bad