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eneloop aa nimh pack current discharge?


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#1 scruffynerfherder

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Posted 22 June 2017 - 07:03 PM

Hello I am wondering if any of you knew the current discharge or an eneloop aa nimh "pack". I said "pack" because what I am referring to 6-8 eneloop nimh AA batteries in a pack configuration.

I am trying to get my stryfe to consistently fire atleast 100 fps, without using a lipo pack, and preferably without using a giant rc car 6 sub c cell nimh pack if possible, which I think leaves me with a "pack" made up of eneloop nimh AA cells, or using efest imr batteries which I don't think have the current discharge needed for any non-stock nerf 130 motors (except maybe using them in parallel? Not sure)

Will 6 eneloop nimh AA's in series (~7.2 volts) be able to discharge more current than 2 efest imr's in series (~7.4 volts)? What would be the current discharge be for both setups?

Basically I am wanting to improve my stryfe utilizing the factory battery tray (with or without an expanded battery door....and without using a lipo pack....which would either be 2-4 efest imr's & dummy cells, or 6-8 eneloop nimh AA's in a pack configuration, or possibly some imr's in a series + parellel configuration of some sort) but really need some help and suggestions on a power supply that fits my needs (no lipo and can fit in stock tray, even if it requires expanded door/cover) and also has the voltage and current discharge needed for popular 130 sized motors used in nerf applications, which has been extremely hard for me to do...

So does anyone know the current discharge ability of 6 eneloop nimh aa's in series in a "pack" configuration? 8 eneloop aa's?

Anyone know the current discharge ability or 2 imr and 2 dummy cells in series? 3 imr and 1 dummy? Imr in 2s2p configuration?

I am also still trying to decide between "2s voltage" and "3s voltage" as I am not sure if I can get within the needed current discharge rating while hitting the needed voltage using aa nimh or 14500 imr. I need a lot of help :)

Edited by scruffynerfherder, 22 June 2017 - 07:07 PM.

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#2 shandsgator8

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Posted 22 June 2017 - 08:09 PM

http://nerfhaven.com...tryfe/?p=350442


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#3 scruffynerfherder

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Posted 23 June 2017 - 09:43 AM

Your "2s voltage" nimh pack has the current/amperage to run a "3s motor" effectively?
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#4 shandsgator8

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Posted 23 June 2017 - 10:51 AM

Your "2s voltage" nimh pack has the current/amperage to run a "3s motor" effectively?

 

Of course! And it's certainly better than IMRs.

 

People push high end LiPo packs and those batteries are certainly good for a MTB Rhino'd Stryfe, but what really matters is whether the batteries can support sustained current draws. Those "stall" currents only last for a few fractions of a second while the flywheels rev up and in between shots, you don't need those fancy LiPo packs to ensure your flywheels can accelerate back to full speed quickly. So why do people recommend high end LiPos? I have a few theories.

 

First, LiPos are far more finicky and dangerous than NiMH and NiCd (nickel based) batteries. If you pull too much current (within reason) from a nickel based battery you know what you get? A battery that is too hot to touch and a reduced battery life. You do that with a LiPo, and you have a ruined battery pack or fire. So when you work work LiPos your margin for error is far less than with nickel batteries.

 

Second, ignorance. People will follow the instructions of another without understanding why a certain recommendation is given. 

 

Third, spec-whoring. This is related to ignorance, but someone will want to use the biggest, coolest, neatest part even if it's unnecessary so that they can tell themselves they have the "best." There's nothing wrong with this and I'm guilty of that too with some of the things I build or buy, so I'm not knocking it.

 

Example: people recommending 14 or 16 gauge wire for rewired Stryfes or other flywheel blasters. Totally not necessary. A nice r/c hobby quality 18 or 20 gauge wire will do just fine and produce no noticeable drop in performance compared to thicker wire. The bonus is that it's much easier to work with. Am I saying a 20 gauge wire performs exactly the same as a 16 gauge wire, all else being equal? No, of course not, but generally, you're not going to notice a difference in your MTB Rhino'd Stryfe.

 

My 6 cell AA Eneloop powered MTB Rhino Stryfe shoots 100+ FPS darts (Gen 3 Koosh) in sub-zero temperatures with 20 gauge wire and Micro Deans connectors. Also, after about 4 hours or so of constant running, my 2000mah Eneloops cells still have about 70% of their rated capacity still left. It's performance is lightyears ahead of a stock Stryfe (obviously). If I used 16 gauge wire and Deans Ultra plugs with a 2s high end 3000mah LiPo that can handle 80C current draws would I get better performance? I assume so, but I doubt it would be more than slightly noticeable, if it's even noticeable at all.

 

From my research, what really makes a difference is the darts and flywheels, as they affect the accuracy and precision of your shooting the most.


Edited by shandsgator8, 23 June 2017 - 10:57 AM.

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#5 Meaker VI

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Posted 23 June 2017 - 11:22 AM

 
Of course! And it's certainly better than IMRs.
 
People push high end LiPo packs and those batteries are certainly good for a MTB Rhino'd Stryfe, but what really matters is whether the batteries can support sustained current draws. Those "stall" currents only last for a few fractions of a second while the flywheels rev up and in between shots...


I'm interested in going to an enloop-style setup for ease of charging and battery care, but I've got a question that I haven't found a good answer to that you might know.

The Lipo packs peopl use usually have current ratings in the 10-50 amp range. The AA enloops appear to have them in the 2-4 amp range. Without doing a *massive* parallel pack, how do they compensate? Are the stats wrong? Sounds like you're getting decent performance, what's the deal?

Can you link batteries and a charger you'd use? Do you build packs or keep them as AA format in cell-holders?
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#6 scruffynerfherder

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Posted 23 June 2017 - 12:24 PM

Wouldn't "2s motors" like meishel 2.0 perform better at 7.2 volts than "3s motors" on 7.2 volts?

If not, what is the upside of running 3s motors on 7.2 volts over 2s motors?
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#7 shandsgator8

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Posted 23 June 2017 - 02:04 PM

Wouldn't "2s motors" like meishel 2.0 perform better at 7.2 volts than "3s motors" on 7.2 volts?

If not, what is the upside of running 3s motors on 7.2 volts over 2s motors?

 

I know nothing about meishel motors.

 

As for running 7.2v (or a 2s equivalent pack) on a "3s" motor, like MTB Rhinos, I don't know of any advantage besides not having flywheels run so fast that they shoot darts that are highly inaccurate.  When I planned my MTB Rhino'd Stryfe, I intended to run it off an 8 cell AA pack. I tested it on 6, 7 and 8 cells and noticed that I got only marginally reduced range on 6 cells (as opposed to 8), yet the precision (groupings) of my darts were much better on 6 cells than 8.


Edited by shandsgator8, 23 June 2017 - 02:07 PM.

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#8 shandsgator8

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Posted 23 June 2017 - 03:04 PM

I'm interested in going to an enloop-style setup for ease of charging and battery care, but I've got a question that I haven't found a good answer to that you might know.

The Lipo packs peopl use usually have current ratings in the 10-50 amp range. The AA enloops appear to have them in the 2-4 amp range. Without doing a *massive* parallel pack, how do they compensate? Are the stats wrong? Sounds like you're getting decent performance, what's the deal?

Can you link batteries and a charger you'd use? Do you build packs or keep them as AA format in cell-holders?

 

There's more to picking a battery than it can "handle" a certain number of amps. It's not like a battery pack will work a certain way up to a certain current draw, then suddenly stop working - it's more of a continuum of gradually decreasing performance as the current draw increases. That's why discharge curves from a battery analyzer (such as the CBA IV; I have the CBA III and love it, but I don't have the time to analyze loose cells or packs right now) are so important. The discharge curve I referenced in an earlier post in this thread is really helpful because you can see how the voltage sags as the current increases.

 

So to answer your question, when you compare a "10-50" amp draw 2s LiPo to a 6 cell AA Eneloop self-made pack, it's not like LiPo pack will appear to be much more powerful or more durable. First of all, a pair of MTB Rhinos is not pulling as much current as you think. I don't have the specs handy, but I know the stall current per motor is about 8 amps. So the most your're going to need from your battery pack is 16 amps and that's only for a split second when the flywheels start up. When the motors are running between shots, the current will be far less, probably under 8 amps for both motors (my guesstimate).

 

Second of all, Eneloops can handle more than 2-4 amps. Sure, you'll get voltage sag (see the reference chart for exact numbers), but that doesn't mean they won't work. I wouldn't push Eneloops past about 10 amps, continuous, though. And don't forget that you're not running your batteries at full tilt all the time. Most matches end after 5-20 minutes (in my experience) and during that time, you're not running your flywheels at full speed (or shooting) that whole time. So even if you were pushing your Eneloops too hard (which in our case would only reduce their life from 1,000 or so cycles to a few hundred, which is still a long life), the pack has plenty of down time to cool off. And even if your game lasts much longer (like HVz), again, you're not revving your flywheels continuously. 

 

As for the cells I use, I use the white 2,000mah Eneloop AA cells you can get from Amazon. As long as you buy them from a reputable seller, you're getting good cells (generation 3 or later). I'd avoid the black Eneloops Pros since they have higher internal resistance. Yes, the Pros have more capacity, but 2,000mah is more than enough for a day's worth of Nerfing so there's no need to boost capacity by 25% at the expense of higher internal resistance, i.e. less ability to handle higher current draws.

 

As for my charger, I use a peak charger that can handle a various number of nickel cells. I use this:

 

http://www.electrifl...d/gpmm3152.html

 

It's been discontinued and there are other options out there. You need to have an external power supply to use it; I use a CPU power supply.

 

I also build my own packs. Do not use a battery holder like you'd get from Radio Shack. Those things are very inefficient and could melt in our application. I wouldn't use those holders if I needed to pull more than a few hundred mah from my cells. 


Edited by shandsgator8, 23 June 2017 - 03:07 PM.

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#9 Meaker VI

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Posted 23 June 2017 - 03:55 PM

 

I know nothing about meishel motors.

 

As for running 7.2v (or a 2s equivalent pack) on a "3s" motor, like MTB Rhinos, I don't know of any advantage besides not having flywheels run so fast that they shoot darts that are highly inaccurate.  When I planned my MTB Rhino'd Stryfe, I intended to run it off an 8 cell AA pack. I tested it on 6, 7 and 8 cells and noticed that I got only marginally reduced range on 6 cells (as opposed to 8), yet the precision (groupings) of my darts were much better on 6 cells than 8.

 

Meishel Motors

 

Re: Other post:

 

Thanks for the charger links, it's tough to figure out what works/doesn't in the crazy diverse world of hobby RC power systems.

 

My read on current vs. voltage was that you can pull whatever current (within reason; always within reason though that's never really explained and I feel it could be important when we're talking about drawing potentially 25x the given rating) you want out, but that it just diminishes your runtime. As you say, runtime isn't really that long in our case, so NBD, but it is my main concern.

 

How do you build packs? Solder wire and heatshrink, probably, but do you have good examples of how it'd be done?


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#10 shandsgator8

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Posted 23 June 2017 - 04:14 PM

 

Meishel Motors

 

Re: Other post:

 

Thanks for the charger links, it's tough to figure out what works/doesn't in the crazy diverse world of hobby RC power systems.

 

My read on current vs. voltage was that you can pull whatever current (within reason; always within reason though that's never really explained and I feel it could be important when we're talking about drawing potentially 25x the given rating) you want out, but that it just diminishes your runtime. As you say, runtime isn't really that long in our case, so NBD, but it is my main concern.

 

How do you build packs? Solder wire and heatshrink, probably, but do you have good examples of how it'd be done?

 

I suppose your way of wording it is correct, or at least in the ballpark. Yes, as long as the batteries can handle it, they will provide whatever current the motors need. If the motors are asking for more current than the cells can handle, they will fail. How they fail depends on the type of cells you use and the speed at which the "overdraw in current" takes place. If it's gradual, you simply diminish the overall life of the cells. If it's fast, you risk fire (at least in lithium cells), meltdown or leakage. I've destroyed nickel based cells (on accident and including Eneloops) by accidentally shorting them out and they didn't catch fire, only got really hot.

 

As for building your own packs, doing a search on youtube should give you plenty of info. But yes, heatshrink, solder and r/c quality wire and plugs will get it done. You'll need a powerful-enough soldering iron, though. I recommend at least 40W when building battery packs. Hakko and Weller are great solder iron brands.


Edited by shandsgator8, 23 June 2017 - 04:15 PM.

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#11 Meaker VI

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Posted 23 June 2017 - 04:44 PM

If it's fast, you risk fire (at least in lithium cells).

 

I'm pretty sure this is why most people will recommend possibly over-specc'd batteries. It's better to spend an extra $1-2 and get a battery that is way to big than to save the cash and burn your blaster up. My pack is like 1000 mah 25-35 C for a total of 25-25 amps continuous,  way more than the burst rating of the rhino's I'm using.

 

I'll need to spend some time looking at this stuff. Sounds like soldering batteries is something I might be able to do, if my iron is up to it.


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#12 scruffynerfherder

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Posted 23 June 2017 - 05:52 PM

Do you happen to know the "c rating" or current/amperage availability of your 7.2v 6 eneloop aa pack?

Last thing I want is to deliver enough voltage but not deliver the current/amps needed and overdrawing the batteries, like I would most likely do with imr's
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#13 shandsgator8

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Posted 23 June 2017 - 06:02 PM

Do you happen to know the "c rating" or current/amperage availability of your 7.2v 6 eneloop aa pack?

Last thing I want is to deliver enough voltage but not deliver the current/amps needed and overdrawing the batteries, like I would most likely do with imr's

 

There is no "C" rating because like I said before there is no "cut off" unless the battery pack has some built in safety mechanism and most don't. And I have no idea how LiPo manufacturers decide what their "C" rating should be. I mean, what's the cutoff for deciding the battery pack can't handle a given current? The temperature of the pack rises 5 degrees within 60 seconds? 120 seconds? How about 15 degrees in 2 minutes? Or maybe it's that the cells will catch fire within 90 second? Or to be more serious, maybe it's a certain amount of of voltage sag under load? If they don't tell us, who knows? I'm not aware of some industry standard, but if there is one, someone can feel free to enlighten me.

 

As for your limiting the current but not the voltage, you're going to have to deal with some sort of regulation or fancy bit of electronics that I know nothing about. I suppose some cells will have some sort of safety shut off, where the cells will self-shut down if you pull too much current from them, but I understand those trustfire/IMR cells with that sort of protection (assuming it exists) will constantly shut down if you pull more than a few amps from them.


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#14 shandsgator8

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Posted 23 June 2017 - 06:05 PM

 

I'm pretty sure this is why most people will recommend possibly over-specc'd batteries. It's better to spend an extra $1-2 and get a battery that is way to big than to save the cash and burn your blaster up. My pack is like 1000 mah 25-35 C for a total of 25-25 amps continuous,  way more than the burst rating of the rhino's I'm using.

 

I'll need to spend some time looking at this stuff. Sounds like soldering batteries is something I might be able to do, if my iron is up to it.

 

If you have a 1,000mah LiPo that's rated for 30C and you pull 35 amps worth of current from it, it's not like it will spontaneous explode or catch fire like you just reached critical mass with fissionable material and started a runaway nuclear reaction. You probably have at least a few seconds before anything really bad will happen; you might damage your pack, though.


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#15 shandsgator8

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Posted 23 June 2017 - 06:08 PM

 

I'm pretty sure this is why most people will recommend possibly over-specc'd batteries. It's better to spend an extra $1-2 and get a battery that is way to big than to save the cash and burn your blaster up. My pack is like 1000 mah 25-35 C for a total of 25-25 amps continuous,  way more than the burst rating of the rhino's I'm using.

 

I'll need to spend some time looking at this stuff. Sounds like soldering batteries is something I might be able to do, if my iron is up to it.

 

You should. It's well worth the internet deep dive as knowing how to solder is very useful for a variety of hobbies. I learned how to do it years ago when I was into R/C cars. I've used it with my other hobbies, including video games, Nerf and other R/C vehicles (boats, subs, helis, etc.)


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#16 scruffynerfherder

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Posted 23 June 2017 - 06:14 PM

Only reason I ask about current/amperage is due to always reading that imr batteries can't supply enough current/amps to run any 130 motor (besides stock) effectively, causing slow spin up of flywheels which I want to avoid which is why I'm looking for options besides imr (and lipo packs) but I'm not sure 6 eneloop aa's can deliver enough current leading me to think ill need to use big r/c sub-c nimh packs...
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#17 shandsgator8

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Posted 23 June 2017 - 06:24 PM

Only reason I ask about current/amperage is due to always reading that imr batteries can't supply enough current/amps to run any 130 motor (besides stock) effectively, causing slow spin up of flywheels which I want to avoid which is why I'm looking for options besides imr (and lipo packs) but I'm not sure 6 eneloop aa's can deliver enough current leading me to think ill need to use big r/c sub-c nimh packs...

 

I use Eneloops and get perfect performance with MTB Rhinos. Will you get "better" performance with SC NiMH packs than a AA Eneloop pack? Probably, but will it be noticeable? I doubt it (I couldn't tell the difference when I compared the two types of packs) and even if you can tell the difference, it won't be much. If it's that important to you, by all means, use SC packs.


Edited by shandsgator8, 23 June 2017 - 06:24 PM.

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#18 scruffynerfherder

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Posted 23 June 2017 - 07:59 PM

I'm def not trying to put down your setup, or say you are wrong in anyway. Its just that on my quest to try to find a power supply for a 2s motor setup that fits in stock location (aside from lipo, including setups that require an expanded battery tray: 2-3 imr, 4,6,8 nimh aa) I've been told multiple times it will not provide the current or amps needed to run correctly without overdrawing the batteries and just looking for clarification and suggestions.

I really really want a battery setup that fits the stock battery tray (2-3 imr) or fits stock tray with expanded cover/door (6-8 nimh aa) that can supply the amp current needed to run 2s motors (honey badgers, meishel 2.0 etc) without overdrawing my battery setup
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#19 shandsgator8

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Posted 23 June 2017 - 08:03 PM

I'm def not trying to put down your setup, or say you are wrong in anyway. Its just that on my quest to try to find a power supply for a 2s motor setup that fits in stock location (aside from lipo, including setups that require an expanded battery tray: 2-3 imr, 4,6,8 nimh aa) I've been told multiple times it will not provide the current or amps needed to run correctly without overdrawing the batteries and just looking for clarification and suggestions.

I really really want a battery setup that fits the stock battery tray (2-3 imr) or fits stock tray with expanded cover/door (6-8 nimh aa) that can supply the amp current needed to run 2s motors (honey badgers, meishel 2.0 etc) without overdrawing my battery setup

 

Assuming you're running MTB Rhinos or equivalent motors, what you've been told is wrong. If you don't believe me, fine, but my setup works very well and there's no disputing that. If you're curious about using Eneloops with Honeybadgers, I can't say, since I don't use those motors and don't know what their specs are.


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#20 Meaker VI

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Posted 23 June 2017 - 09:40 PM

I really really want a battery setup that fits the stock battery tray (2-3 imr) or fits stock tray with expanded cover/door (6-8 nimh aa) that can supply the amp current needed to run 2s motors (honey badgers, meishel 2.0 etc) without overdrawing my battery setup


It sounds like "overdraw" on a NiMh just means shorter runtime, which isn't a big deal at all since "shorter runtime" in this case still means *hours* of game time. On a Lipo it'd be a big deal to overdraw long term.

Use Rhinos, since that's what he's telling you work well.
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#21 scruffynerfherder

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Posted 23 June 2017 - 11:00 PM

Its not so much that I'm afraid of the outcome of overdrawing the batteries, I just want to be able to supply the amps the motors demand for best performance (I know it sounds funny after saying I don't want lipo)
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#22 Meaker VI

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Posted 23 June 2017 - 11:58 PM

Its not so much that I'm afraid of the outcome of overdrawing the batteries, I just want to be able to supply the amps the motors demand for best performance (I know it sounds funny after saying I don't want lipo)


That's the thing - my understanding is that they battery can supply infinite amps, but it just decreases the runtime. If it's got 2,000 mah (2 amp hours), if you draw 16 amps it'll run for 7 minutes 30 seconds (2 Amp Hours/16 Amps = 0.125 hours * 60 minutes/hour = 7.5 minutes).

 

NiMh just doesn't fail catastrophically if put through high-draw. Lipo has a C rating to say how high that draw can be for that battery, I have no idea how it's determined or what it means for other chemistries.

 

What shandsgator is telling you is that he gets super-stock performance from a AA NiMh pack running Rhinos, IIRC in a stock cage. I do not know if a NiMh is a good choice for a non-stock FWC, wheels, or 180/132 setup, he'd have to step in with that information. My reading indicates that 2s (~6-8v) motors draw more amps to get the same performance as 3s (~10-14v) motors at lower amps (you trade volts with amps to get the same performance), so I'm not sure going to a meishal would be better than undervolting a Rhino.


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#23 shandsgator8

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Posted 24 June 2017 - 04:32 AM

Its not so much that I'm afraid of the outcome of overdrawing the batteries, I just want to be able to supply the amps the motors demand for best performance (I know it sounds funny after saying I don't want lipo)

 

Eneloops can supply the amps for MTB Rhino motors. 


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#24 scruffynerfherder

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Posted 24 June 2017 - 08:28 PM

3s motors on 2s voltage asking for less amps makes a little sense to me now, but wouldn't 2s voltage keep 3s motors from hitting its ideal critical rpm? Just trying to learn.
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#25 shandsgator8

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Posted 24 June 2017 - 08:36 PM

3s motors on 2s voltage asking for less amps makes a little sense to me now, but wouldn't 2s voltage keep 3s motors from hitting its ideal critical rpm? Just trying to learn.

 

Yes, but THAT'S THE WHOLE REASON WHY I RUN 2s voltages - to avoid too high flywheel RPMS, which create inconsistent dart patterns.


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