Please help noobie on Motor/Battery selection for E-Revo
 

I've just started a Revo conversion using the Tekno kit. I am new again to RC(been about 15years) and will only be bashing (at least to start). So I'm looking for decent speed, long run times, and decent handling. No wheelies and no land speed records needed. Eventually I'd like to go to a track, but there are only 2 anywhere close to me. I will be locking the trans into second gear on the eRevo. I will be running a center diff with both mechanical brakes. (similar to Finnster's original conversion) and I plan on getting the MMM.

So I've been looking at these motors:
Medusa 60mm 1600kv on 5s
Medusa 60mm 2000kv on 4s
Feigao 8XL 2084kv on 4s
Feigao 9XL 1853kv on 4s

I've kinda been leaning towards the 1600kv Medusa, cuz it seems like theres a trend to go lower kv and higher voltage. My concern with the 1600kv is BrianG's calculator (awesome BTW!!!) says it will only be running 28,000 rpm on 5s and i think the Medusas are rated at 60k. Will i be losing a lot of efficiency and power running it at such a low RPM?

As far as batteries go, the more i read, the more confused i get. I understand the more volts I run, the more power i should get. And i thought the more mAH I had would give me longer run times. But now theres this 'C' rating which i cant get my head around. How does the C rating effect power, run time, etc and how do all three inter-relate and effect each other?

A couple of the batteries Ive been looking at are:
TrueRC 4S 8000mAh 10C
Polyquest 5S 4500mAh 30C
ZippyH 4S 5000mAh 20C
ZippyH 5S 5000mAh 20C

Thanks for any info and advice you can provide. Also, Im open to other suggestions. These are just what my inexperienced researching came up with.

Wow, there's a lot to answer in that post.

I think if you don't want incredible speed, the 2000KV medusa on 4s will probably be a good starting point for you. 5s can get very fast, very quick. 4s is nothing to scoff at. Granted, there's a benefit to going with higher voltage, as the whole system will be more efficient, and you're likely to see better runtimes.

My 9xl Revo is very fast on 4s, and it's much easier to keep the temps down than it is with the 8xl. It will still wheelie like mad. You can tune it modestly to keep help keep it under control, as you said you weren't into that (yet, LOL).

I'd say the MMM should run any of the setups you posted without a problem. So your ESC choice is (hopefully) good.

Batteries..... hrm. lol.

looking at c ratings:

The c rate of a given battery cell, is a measurement of how quickly a battery can discharge its usable capacity. Without over complicating things, we can use a simple formula to determine what sort of constant amp draw a pack can deliver by using it's c rate.

multiply the c rate by the capacity and you will see the amp draw capability of the pack. The true RC pack for example.

10 x 8000 = 80,000.

Now remember, we're talking mA here, so 80,000mA = 80A. So we can see, the truerc 10c 8000mAh pack should deliver 80A constant. When selecting your pack, you must consider what the amperage demands of your setup will be, according to motor / voltage selection.

I'm sure you will have further questions ;). Good luck with your build! I think you've selected an excellent platform to jump in on. A big part of your choices will depend on budget, so it's good to have an idea of what you'd be willing to spend for a solid setup.

Oh yeah, and welcome to the forums! Lot's of great folks around here!
J>

The 1600kv medusa is a little slow for 5s, but it would be much better on 6s- MMM esc will be happy with either, and you can gear those multi-pole motors quite high to get some more speed out of them.

The C raing on batteries is simple, once its explained properly... Basically, the C rating is a multiple of the capacity in mah, and represents the theoretical maximum output of that battery, EG:

20c 5000mah lipo can put out 100amps
10c 4000mah lipo can put out 40amps.

Batteries come with a few C ratings- continuous, sustained, peak/maximum- fairly obvious what they mean.

In general, a BL motor will run at a continous power level, drawing about 10-20amps, but you will see peaks (under acceleration and braking etc) upto 80-120 amps or so, depending on the specific vehicle setup, motor, driving conditoins, weight etc etc.

Depending on budget, a battery that can provide 80amps continuous or more is great for a 1:10 scale MT or similar. Most places give the maximum amp draw of the motor, which makes life easier when choosing batteries.

EDIT: I type too slow...

Thanks for the replies, guys. Its a little clearer now.

What do you think of the Medusa 1600kv on a 6S 4000mAh 25C with the MMM?

Shouldnt that give me decent efficiency and run times while providing a ton of speed & torque and still not getting too hot?

And cant I dial the ESC down until i want/NEED the speed?
I guess it would be better to have it there for when i want it rather than changing the setup.

I don't know anything about Medusa motors, so I can't comment on them, I have more expierence with Feigao's.
My suggestion would be the 9XL on 5s, I like to aim for 35,000 rpms with the motor. With my Revo project I have a Neu 1515/2.5d (1700kv) on 6s lipo.
As far as wheelies go it goes with the territory of running a BL motor, they have a lot of instant torque that a nitro doesnt have...you can try to control it with taller gearing and a CD but I have found helps is a little extra weight in the nose

You can adjust the timing and punch control on the MM and MMM escs- reducing timing will reduce rpms a bit and run the motor cooler (in theory), and increasing punch control should reduce wheelies and starting torque.

Like Neil said, increasing punch control/decreasing start power will help tame wheelies, but will also not work the batteries and ESC as hard, and will translate to slightly increased runtimes...

But smaller smiles...

Bah, what's fun about not being able to steer? Sure, wheelies are fun at first, but they get really old really quick. If ESC settings are done right, you can get a happy medium between wheelies (but only when you want to) and control. Or, I guess another option is to leave the ESC settings at max and just take it easy with your throttle finger.

I would go with the 9XL and 4s lipo combo. To tame wheelie's or get rid of them all together do the following....

Run the 3.3 extended chassis on your revo.
Use high gearing
Use a some what loose slipper clutch setting
Reduce punch or startup on your esc to tame power from a stand still
Use a techno RC eletric clutch on your motor instead of a pinion
Move your battery as far forward as possible

BTW the zippy-H lipo's are nice, the zippy-R lipo's are even nicer for just a few bucks more but they are long & skinny packs so make sure they will fit on your truck. The zippy-H are normal length packs though.

SuicideNeil, up in post #3 you said that the 1600kv Medusa is a little slow for 5s. When i put it in BrianG's calculator I get 29600RPM. The other combination that is getting a lot of recommendations is the 9XL on 4s which works out to 27400RPM.
The calculator shows the Medusa having 1 more mph over the 9XL.

Can you help me understand your statement?
Is it a torque thing? Is it becuz the Medusas are rated at 60k RPM?
If i bump up to 6s on the Medusa I get 35500RPM. Wont that cause a lot more heat or is that going to be more efficient?

Does anyone know the optimum RPM for Medusa V2's?

Thanks

Well, maybe not slow per-say, but higher quality motors can be reved higher, and can definately handle being geared taller. I dont know the efficiency range of the Medusas, but feigaos work best in the 30-35,000rpm range- any faster and they start to run hot (well, hotter than normal at any rate). One way of looking at the Medusa is to say its better to rev them a little higher and then gear down (torque bonus), than to run them slower and try to gear up too much (higher load on the esc). If you get a 6s esc, then the slower medusa will be great on 5 or 6s, and it appears much better quality than the feigaos, for not much extra $$.

What is this? I Googled it, but found nothing.

Try "Tekno RC". http://www.tekno-rc.com/