Author Topic: 4cell and 5cell interchangeable once ESC is programmed for voltage? (Read 2757 times)

Mike Scholtes · « **on:** September 28, 2013, 12:44:06 PM »

This may be a dumb question and doubtless has been answered before but ...

My setup is EFlite 25 (newest version 1150KV), 4cell 3200mah batteries, ICE 50 ESC, Hubin FM9 timer, plane full size Legacy 62 oz. The ESC is programmed using the Castle 3.27 firmware for 14.8 volts 4cell batts. I also have 5cell 3000mah batts. Can the 5cell be swapped in place of the 4cell without reprogramming the ESC, or at all? And, is there any advantage to 4c vs 5c in this setup?

John Cralley · « **Reply #1 on:** September 28, 2013, 01:05:36 PM »

You don't want to use a 5S battery with that motor unless you are looking for an RPM way above what we usually use for control line!!!
In fact, you probably could use a 3S battery as the KV is a bit high for a 4S battery.

Bob Hunt · « **Reply #2 on:** September 28, 2013, 01:22:25 PM »

Hi Mike:

Why are you using a motor with a KV rating that high? I've been running (along with many, many others) an E-Flite Power 25 with a KV rating of 870. I think you have a ducted fan motor there...

Later - Bob Hunt

Dean Pappas · « **Reply #3 on:** September 28, 2013, 01:45:30 PM »

Hi Mike,
I think the 1150 KV version is the one intended for RC electric pylon racing.
It's not for us, and as Bob says, you'd almost want to drop down to 3S. You don't!
Can you get that motor swapped for the standard E25 with the 870 KV?

Let's figure it this way ... the governor is gonna run the "internal throttle" at somewhere between 75% and 95% depending on state of charge, air and battery temnp, battery age and such.
So let's work with 75%. That's the number I use. Some folks go as high as 85%, but I like having the voltage headroom.
Now let's say we have a 4S battery and that runs at 4 X 3.7V (fresh) or 14.8V. 75% of that is 11.1V.
Drop 1V for copper losses in the motor (just a swag) and we have 10.1V left.
Multiply that times KV and we have either ~ 9000 RPM (the "good" E25) or 11,500 RPM with the pylon motor.
That's the RPM setpoint you must use in order to get the governor biased sensibly. There's some leeway but that's basically it.
You don't want to spin the prop at 11,500, I'll bet. Somewhere in the mid 9000's is right and that's why you need a 4S battery and a ~900 KV motor.
Alternatively you could find a similar sized motor with a 700 ~750 Kv and use a 5S battery.
For a 62 ouncer, both options are attractive.

Regards,
Dean

Mike Scholtes · « **Reply #4 on:** September 28, 2013, 01:51:02 PM »

Thanks everybody. I had a feeling something was screwy here. The prior motor in this model was an AXi 2826-10 at 920 kv, and the whole system was very happy till I got a prop strike, stalled the motor, and melted the Phoenix 45. The motor was toast too. SO, swapped to the very popular E25 not knowing, as it turns out, there are different versions of it. Ugh. Anybody need an electric pylon motor?

phil c · « **Reply #5 on:** September 30, 2013, 06:58:07 PM »

You could do like most people do when running higher rpm glow engines. Go to a lower pitch prop. Lots of people run LA engines at 10,500-11,000 rpm with 4 in pitch. Not sure how many suitable 4 in. pitch props there are for a 1100kv motor.

Dean Pappas · « **Reply #6 on:** October 01, 2013, 08:28:26 PM »

Hi All,
Some outrunners start to have resonance issues as they near 12,000 RPM.
Been there, done that and we refused the T-shirt ... right, Bob?

Dean P.

Mike Scholtes · « **Reply #7 on:** October 01, 2013, 10:52:26 PM »

Nah, it's worse than I thought ... motor is actually 1250kv. Is there electric pylon racing in my future??

Solved the problem for now by swapping (mount is interchangeable) an OS 3825 750kv, which should work fine. Will ask Santa for an E-25 later. The OS has a cooling fan on the front like Plettys. Rear mount only. 14 poles, 12 winds, 5mm shaft. No info on bearings.

Mike Scholtes · « **Reply #8 on:** October 01, 2013, 10:54:37 PM »

Oh, and now that I solved THAT problem, is there any advantage to 5C vs 4C if both are suitable for the KV of the motor and prop rpm is set by the Hubin timer? Assume batts in 3000-3200 mah range.

John Cralley · « **Reply #9 on:** October 02, 2013, 06:08:34 AM »

Quote from: Mike Scholtes on October 01, 2013, 10:54:37 PM

Oh, and now that I solved THAT problem, is there any advantage to 5C vs 4C if both are suitable for the KV of the motor and prop rpm is set by the Hubin timer? Assume batts in 3000-3200 mah range.

That would be 5S vs 4S but we know what you mean.

Glad you have the KV sorted out!!

Doug Moon · « **Reply #10 on:** October 02, 2013, 06:35:12 AM »

Quote from: Dean Pappas on September 28, 2013, 01:45:30 PM

Hi Mike,
I think the 1150 KV version is the one intended for RC electric pylon racing.
It's not for us, and as Bob says, you'd almost want to drop down to 3S. You don't!
Can you get that motor swapped for the standard E25 with the 870 KV?

Let's figure it this way ... the governor is gonna run the "internal throttle" at somewhere between 75% and 95% depending on state of charge, air and battery temnp, battery age and such.
So let's work with 75%. That's the number I use. Some folks go as high as 85%, but I like having the voltage headroom.
Now let's say we have a 4S battery and that runs at 4 X 3.7V (fresh) or 14.8V. 75% of that is 11.1V.
Drop 1V for copper losses in the motor (just a swag) and we have 10.1V left.
Multiply that times KV and we have either ~ 9000 RPM (the "good" E25) or 11,500 RPM with the pylon motor.
That's the RPM setpoint you must use in order to get the governor biased sensibly. There's some leeway but that's basically it.
You don't want to spin the prop at 11,500, I'll bet. Somewhere in the mid 9000's is right and that's why you need a 4S battery and a ~900 KV motor.
Alternatively you could find a similar sized motor with a 700 ~750 Kv and use a 5S battery.
For a 62 ouncer, both options are attractive.

Regards,
Dean

Thank you for this explanation.

Dean Pappas · « **Reply #11 on:** October 02, 2013, 10:17:06 AM »

Quote from: Mike Scholtes on October 01, 2013, 10:54:37 PM

Oh, and now that I solved THAT problem, is there any advantage to 5C vs 4C if both are suitable for the KV of the motor and prop rpm is set by the Hubin timer? Assume batts in 3000-3200 mah range.

hi Mike,
So let's assume you'll adjust the pitch to get the desired lap times at the appropriate "75% of volts times KV" RPM setting ...
The 5S setup will achieve this at lower current and higher RPM than the 4S setup.
The motor will run a little cooler on 5S, and you may enjoy 2% more efficiency as a result of that reduced heating. Then again the slightly higher RPM will make the prop losses a tiny bit worse. i'll bet it's a wash.
The real issue is battery capacity.
Batteries come in discrete cpacities: in other words, you can't buy a 2375 mAh battery if that's all you need. There are 2200's and 2500's, for example.
It all comes down to battery weight.
A 4S 3300 is probably adequate, just as a 5S 2500 will be. These two packs are likely to weigh close to the same.
The 5S 2500 actually has about 6% little less energy capacity than the 4S 3300, but depending on the brand of battery and price you pay, there could be a 2 or 3 ounce difference in weight.
If you spend enough time comparison shopping, that weight difference could go either way!
Do you have a charger that maxes out at 4S or something bigger?
Are you planning to stick with 750 KV motors? Go 5S.
There isn't a single answer. I hope that helped.
Regards,
Dean

John Rist · « **Reply #12 on:** October 02, 2013, 12:51:09 PM »

I hate to sound like a stuck record but the KR timer and a cheep speed controller would have protected the whole system during a prop strike.

Mike Scholtes · « **Reply #13 on:** October 02, 2013, 05:32:47 PM »

Thanks again, and especially Dean. I had the OS 750KV sitting around unused so this was an opportunity to try it. Seems well made. The math tells me I need to haul out my Zippy 5S 3000 batteries and order some more. My charger will handle up to at least 6S so no problem with that. My intention is to get the E25 into the next model and stick with 4S batteries for the next little while, but for now I will be a 5S guy.

I have heard Keith's simple timer is not susceptible to cooking when the prop is stopped as in a noseover (my case), a nice advantage, but I already have several Hubin timers and the small computer to adjust it at the field. The solution seems to be to fly better. And rotate wing mounted gear a little more forward.

Igor Burger · « **Reply #14 on:** October 03, 2013, 05:52:02 AM »

Quote from: Dean Pappas on October 02, 2013, 10:17:06 AM

The motor will run a little cooler on 5S, and you may enjoy 2% more efficiency as a result of that reduced heating.

Lower KV on the same armature means also higher resistance, additionally higher rpm also means higher iron loses, if you calculates all over and over, you will see that efficiency of all motor KVs in the same armature with the same copper filling is the same. Means KV does not change the efficiency. (FOR FULL TRHROTTLE)

We use AXI 2826/13 what is modifficication of AXI 2826/12, however /13 has better copper filling, what really improved the efficiency, but the difference is really microscopic. The reason why we use 6 cells with kv=690 is better match of 5" prop with motor KV and battery voltage and yes we run between 10 000 and 12 000 (active timer is set to work in that range). And yes also resonantion frequency is the issue here, however 10 000 is already OVER that frequency for AXI 2826. Before we got info that it is at 13 000, but it was some misunderstanding, it was probabaly for 2820 or without prop or some harmonic or I do not know, we found that resonantion happens somewhere between 9500 and 10000, so it is good to keep well under 9500 or over 10000.

Quote from: Dean Pappas on October 02, 2013, 10:17:06 AM

Then again the slightly higher RPM will make the prop losses a tiny bit worse. i'll bet it's a wash.

That is right, in level flight. But when props goes to higher slippage, low rpm prop will go to regume when larger part of prop blade is sstalled, or working at high AoA with higher drag. Also the lift coefficiet is higher, so induced drag on tips is higher, means low pitch, high rpm prop is better for climbing and better keeps rpm after corners. It is necessary to test what is better. I like props with less then 0.5 P/D

John Cralley · « **Reply #15 on:** October 03, 2013, 09:14:13 AM »

Quote from: Igor Burger on October 03, 2013, 05:52:02 AM

Lower KV on the same armature means also higher resistance, additionally higher rpm also means higher iron loses, if you calculates all over and over, you will see that efficiency of all motor KVs in the same armature with the same copper filling is the same. Means KV does not change the efficiency. (FOR FULL TRHROTTLE)

We use AXI 2826/13 what is modifficication of AXI 2826/12, however /13 has better copper filling, what really improved the efficiency, but the difference is really microscopic. The reason why we use 6 cells with kv=690 is better match of 5" prop with motor KV and battery voltage and yes we run between 10 000 and 12 000 (active timer is set to work in that range). And yes also resonantion frequency is the issue here, however 10 000 is already OVER that frequency for AXI 2826. Before we got info that it is at 13 000, but it was some misunderstanding, it was probabaly for 2820 or without prop or some harmonic or I do not know, we found that resonantion happens somewhere between 9500 and 10000, so it is good to keep well under 9500 or over 10000.
That is right, in level flight. But when props goes to higher slippage, low rpm prop will go to regume when larger part of prop blade is sstalled, or working at high AoA with higher drag. Also the lift coefficiet is higher, so induced drag on tips is higher, means low pitch, high rpm prop is better for climbing and better keeps rpm after corners. It is necessary to test what is better. I like props with less then 0.5 P/D

Thanks Igor, This is good information to know!!! I seem to recall that you are using a three bladed prop and wonder if your 0.5 P/D is referring to a two bladed prop or a three bladed one (or does it even matter?).

Igor Burger · « **Reply #16 on:** October 03, 2013, 09:28:04 AM »

I have 3 blade 11x5 carbon prop with almost flat bottom, so it needs ~11 000rpm.

Author Topic: 4cell and 5cell interchangeable once ESC is programmed for voltage? (Read 2757 times)

Mike Scholtes

4cell and 5cell interchangeable once ESC is programmed for voltage?

John Cralley

Re: 4cell and 5cell interchangeable once ESC is programmed for voltage?

Bob Hunt

Re: 4cell and 5cell interchangeable once ESC is programmed for voltage?

Dean Pappas

Re: 4cell and 5cell interchangeable once ESC is programmed for voltage?

Mike Scholtes

Re: 4cell and 5cell interchangeable once ESC is programmed for voltage?

phil c

Re: 4cell and 5cell interchangeable once ESC is programmed for voltage?

Dean Pappas

Re: 4cell and 5cell interchangeable once ESC is programmed for voltage?

Mike Scholtes

Re: 4cell and 5cell interchangeable once ESC is programmed for voltage?

Mike Scholtes

Re: 4cell and 5cell interchangeable once ESC is programmed for voltage?

John Cralley

Re: 4cell and 5cell interchangeable once ESC is programmed for voltage?

Doug Moon

Re: 4cell and 5cell interchangeable once ESC is programmed for voltage?

Dean Pappas

Re: 4cell and 5cell interchangeable once ESC is programmed for voltage?

John Rist

Re: 4cell and 5cell interchangeable once ESC is programmed for voltage?

Mike Scholtes

Re: 4cell and 5cell interchangeable once ESC is programmed for voltage?

Igor Burger

Re: 4cell and 5cell interchangeable once ESC is programmed for voltage?

John Cralley

Re: 4cell and 5cell interchangeable once ESC is programmed for voltage?

Igor Burger

Re: 4cell and 5cell interchangeable once ESC is programmed for voltage?