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Old Jul 30, 2012, 07:26 AM
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Originally Posted by thwaitm View Post
It's a 4mm shaft - much bigger than V120D02S
thanks for the reply! looks like its definitely not what I am looking for.
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Old Jul 31, 2012, 07:42 PM
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EMAX ES08MD Servos - First Impressions

Haven't installed the EMAX ES08MD digital metal gear servos into my 4F200 yet. Time just hasn't been on the 4F200's side partly due to waiting for one of my Futaba S3154 servos to be replaced and waiting three weeks recently for the ES08 servos to arrive. And then I've plainly been busy with other more important non RC tasks.

But I did have time on the bench to hook these servos up to the stock ESC, stock 2612 receiver and stock 2603 transmitter. The EMAX ES08MD servos work fine with the stock electronics and do not require any reversing or require the receiver to be oriented 180 degrees. So this is good news.

Also I disassembled the casing on one of the servos just out of curiosity. I must say, the quality of the soldering is not up to par compared to the Futaba S3154 servos. The EMAX servos still work fine - this is just a comparison of the guts between the two. The ES08MD servos are 100% metal gears so that is a plus.

That's all for now on the servos.
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Old Jul 31, 2012, 10:47 PM
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Onyx 2S 7.4V 2000mah 25C Lipo and Battery Calculations

Another adventure of mine is finding a different brand of 2S battery. One that is better performing, will fit under the canopy and is priced under $30.

What I have been using is Gens Ace 2S 7.4V 1550mah 25C batteries ($9.60 at xheli.com). The Gens Ace have been very comparable to the stock 4F200 battery - maybe just slightly better.

Visiting the LHS
Just recently I stopped by my LHS looking to find a better performing 2S battery for the 4F200 that will fit. At first the guy, John, mentioned he didn't have anything better than the stock that would fit my helicopter. All he had that would fit was a 2S 1300mah 20C ThunderPower battery. But then he instantly looked up (doing calculations in his mind) and said, "oh but wait, you're going to love this." John showed me a Duratrax Onyx 2S 7.4V 2000mah 25C lipo. This is a soft case lipo and already has a deans connector on it; a minor plus for me since I run with deans on all my batteries. This battery is actually designed for Traxxas cars.

Enough said. I bought one at my LHS on the spot for $24.95 to try. Why not. I have to see it for myself.
The Battery
Duratrax Onyx 2S 7.4V 2000mah 25C Soft Case Lipo
Available at Tower Hobbies for $14.95
http://www3.towerhobbies.com/cgi-bin...&I=LXCABW&P=SM

Please note this battery will not fit on the stock 4F200 battery tray unless you modify it like I have. This battery barely fits under the canopy with my moded battery tray. My battery tray mod is here: http://www.rcgroups.com/forums/showp...postcount=1861
Seeing is Believing
Feeling is also believing. Performance? Unquestionable difference. I am impressed. The pitch pumps - very improved. So I asked myself how can this be? The Gens Ace are 25C and these are 25C. From what I have read, the 25C refers to a batteries discharge rate. And doesn't more capacity just equate to more flight time?
Revisiting the LHS (with questions)
So I visited the LHS and met John again to have an intelligent conversation into lipo batteries. John does know plenty more than I do about RC. And I walked away with some new found knowledge, a few notes, and a few math calculations to add to my tool kit.

John suspects the Gens Ace are over rated where as the Duratrax Onyx brand are more accurate in their ratings.

What I learned is the 25C does not determine the max discharge rate alone. The capacity (mah) together with the discharge rate (C) will define a batteries max current output.
The Battery Calculations
  1. Determine a batteries constant discharge rate.
    (mah * discharge rate C) / 1000 = constant discharge rate amps

  2. Determine max flight time based on amperage draw (motor, receivers and servos).
    ( (mah / 1000) / draw amps) * 60 = total flight time in minutes
The Battery Calculations Applied
Let's apply these calaculations against some batteries and compare the results. Please note I've data logged the main motor draw at 17 amps using a CC ICE 50A ESC. Keeping it simple, let's figure in only the motor.
  • Stock 2S 7.4V 1500mah 20C lipo
    Constanst discharge rate (1500 * 20C) / 1000 = 30 amps
    Max flight time ( ( 1500 / 1000) / 17amps ) * 60 = 5.29 minutes

  • Gens Ace 2S 7.4V 1550mah 25C lipo
    Constanst discharge rate (1550 * 25C) / 1000 = 38.75 amps
    Max flight time ( ( 1550 / 1000) / 17amps ) * 60 = 5.47 minutes

  • Duratrax Onyx 2S 7.4V 2000mah 25C lipo
    Constanst discharge rate (2000 * 25C) / 1000 = 50 amps
    Max flight time ( ( 2000 / 1000) / 17amps ) * 60 = 7.06 minutes
DISCLAIMER: Actual results will vary. There are a many dynamic factors which are not figured into these calculations. To name a few factors: battery weight, type of blades, mechanical setup, wind conditions, amperage draw from receiver/servos.
Conclusion
There are indeed a variety of batteries out there that you can try. Add these calculations to your tool kit. Use them to assist with your next battery purchase. Hopefull they can save you time and money upfront in instead of doing it the speculatively trial-and-error method, which in most cases can cause you more time, grief, frustration and money. The stock battery can be used as a reference point. You should already know how the stock battery feels in flight.

Final note, if you decide to get one of these Duratrax Onyx lipos, I would recommend you get just one and try it out. Reason I mention this is because I am using the AR7200BX receiver on my 4F200 and I actually had to enable the tail pre-compensation feature in the receiver, otherwise the tail would blow out a bit with hard pitch pumps. Tail pre-compensation on the AR7200BX is simlar to REVO-MIX in the 2801 pro transmitter. I also suspect that I have my tail belt too tight again... just a suspicion.
p.s. If you find anything incorrect with the calculations, feel free to share your feedback in a constructive manner right here in this thread. After all, the wisdom of the crowd is greater than any one person.

-razorblade
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Old Jul 31, 2012, 10:52 PM
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Looks cool, but crash damage on that thing is going to be a major PITA. Getting three main and tail rotor blades to run smoothly is going to be tough...initially and after every crash. More aerodynamic drag? More weight? More cost/complexity? No actual proven performance over a two bladed main/tail heli? No thanks...
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Old Jul 31, 2012, 11:32 PM
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Quote:
Originally Posted by razorblade View Post
Another adventure of mine is finding a different brand of 2S battery. One that is better performing, will fit under the canopy and is priced under $30.
[*]Stock 2S 7.4V 1500mah 20C lipo
Constanst discharge rate (1500 * 20C) / 1000 = 30 amps
Max flight time ( ( 1500 / 1000) / 17amps ) * 60 = 5.29 minutes

[*]Gens Ace 2S 7.4V 1550mah 25C lipo
Constanst discharge rate (1550 * 25C) / 1000 = 38.75 amps
Max flight time ( ( 1550 / 1000) / 17amps ) * 60 = 5.47 minutes

[*]Duratrax Onyx 2S 7.4V 2000mah 25C lipo
Constanst discharge rate (2000 * 25C) / 1000 = 50 amps
Max flight time ( ( 2000 / 1000) / 17amps ) * 60 = 7.06 minutes


-razorblade
Your equations show that a larger Amp Hr. battery gives you a longer flight time. That's to be expected.
It doesn't tie in the discharge rate in the Max flight time equations.
You assume that the current draw is the same for each battery. You have to tie in the weight delta in each flight time equation. The increased weight will probably increase the assumed 17 Amp draw.
Your off to a good start, but the Flight time equation needs more work.
Anyway it's good food for thought.
Thanks for putting it out there.
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Old Aug 01, 2012, 12:20 AM
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I don't know how many times i have to say it. Most batteries, even good ones. Are not accurately rated. In fact there is no regulatory anything saying "Wait, they lied about their capacity and discharge rate and should be held accountable!" Nope, they just wright whatever they want on a nice wrapper and hope you don't notice the difference.


I will be using Turnigy packs myself from now on. They have performed well for me on my v450 and v120 size. Especially where finding a higher discharge rate on 1S packs has been hard. These are nice for me because they come with the XT60 connector that i use already installed. Both of these should be decently rated, maybe not accurate but better than most.

I think these should fit the 4f200 battery tray without modification too. If not a small modification like Razorblade's is not hard. I just have not gotten around to ordering them yet.

20-30C discharge 1600 mAh pack:
http://www.hobbyking.com/hobbyking/s...Lipo_Pack.html


40-80C discharge 2200 mAh pack:
http://www.hobbyking.com/hobbyking/s...6_models_.html
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Old Aug 01, 2012, 12:28 AM
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Quote:
Originally Posted by clearprop88 View Post
Your equations show that a larger Amp Hr. battery gives you a longer flight time. That's to be expected.
It doesn't tie in the discharge rate in the Max flight time equations.
You assume that the current draw is the same for each battery. You have to tie in the weight delta in each flight time equation. The increased weight will probably increase the assumed 17 Amp draw.
Your off to a good start, but the Flight time equation needs more work.
Anyway it's good food for thought.
Thanks for putting it out there.
Yes. Your observation is correct. The Duratrax Onyx battery does weight 8 grams more than the Gens Ace I have been using. But this is not a bad thing for the 4F200 since it is tail heavy anyway. I figured a while back that the perfect weight up front for best COG is 125 grams. One thing I still need to do is log some more data using the CC ICE 50A ESC because I currently have no idea what motor amperage draw is when using the Onyx battery. The log was full when I plugged in the Onyx battery and day light was coming to an end. Another side effect of having the ICE 50A ESC on the heli (in order to do logging) is it weights 66.5 grams all by itself.

So amperage draw from the motor when using the Duratrax Onyx battery is to come... stay tuned.

Battery Weight Comparison:
  • Stock 2S 1500 20C
    85.25 grams
  • Gens Ace 2S 1550mah 25C
    96.75 grams
  • Duratrax Onyx 2S 2000mah 25C
    105 grams
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Old Aug 01, 2012, 12:57 AM
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Just to give an idea. I did the calculation run down using 17 amp motor draw. Its all I have right now to plug in.
Quote:
Originally Posted by IntegrityHndywrk View Post
Constant discharge: 32A
Max Flight Time: 5.64 minutes
Weight: 97 grams
Length: 106 mm

Nope this battery will not fit under stock canopy. Its too long. The Duratrax is 90 mm long and it barely fits under the canopy with a battery tray mod. Maybe the V200D03 canopy is bulkier in the nose?
Quote:
Originally Posted by IntegrityHndywrk View Post
Constant discharge: 88A
Max Flight Time: 7.76 minutes
Weight: 120 grams
Length: 97 mm

I did not see this before on hobbyking. It may fit. This battery looks awesome. The COG will be perfect. Its longer than the Duratrax which is 90 mm long. But you will have to mod the battery tray to get it to fit. Unless the hobbyking is listing the wrong specs.
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Old Aug 01, 2012, 01:07 AM
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Guys,

Since I fired up this battery discussion... again. There's some things I missed to mention.

The ESC plays a factor. What I mean is there's a limit to how much current the motor is allowed to draw. And of course the motor itself.

Worst case is the battery runs cooler and you get more flight time. The weight of the battery is not figured into those basic calculations, among other things. There are some mad scientist heli equations out there. But the basic ones I presented I can do using a simple calculator in less than a minute.

It should be interesting to see what the CC ICE data log shows for motor amperage draw with the Duratrax Onyx battery plugged in.

Also, the perfect weight upfront for best COG is 125 grams.
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Old Aug 01, 2012, 01:23 AM
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Internal resistance

I see you guys are talking battery talk. I might be on the wrong thread but, I have a question.
What amount of internal resistance is considered a good point to stop using a pack, per cell and total pack resistance? I have some 4s 4000 mha 30C that are surging, the internal resistance reads approx 9 milliohms per cell with a total internal resistance of 36 milliohms for the pack. I know lower is better but I don't know how high is too much I need some rule of thumb figures. Thanks for anyone's help.
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Old Aug 01, 2012, 01:29 AM
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Quote:
Originally Posted by razorblade View Post
Guys,

Since I fired up this battery discussion... again. There's some things I missed to mention.

The ESC plays a factor. What I mean is there's a limit to how much current the motor is allowed to draw. And of course the motor itself.

Worst case is the battery runs cooler and you get more flight time. The weight of the battery is not figured into those basic calculations, among other things. There are some mad scientist heli equations out there. But the basic ones I presented I can do using a simple calculator in less than a minute.

It should be interesting to see what the CC ICE data log shows for motor amperage draw with the Duratrax Onyx battery plugged in.

Also, the perfect weight upfront for best COG is 125 grams.
Don't forget you probably have a slightly different weight on your tail with the BX unit, and now with MG servos going in..

I don't understand why those batteries wouldn't fit.. The stock battery is 108mm long.. ? Is it because they are too tall?
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Old Aug 01, 2012, 01:36 AM
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Quote:
Originally Posted by IntegrityHndywrk View Post
I don't know how many times i have to say it. Most batteries, even good ones. Are not accurately rated. In fact there is no regulatory anything saying "Wait, they lied about their capacity and discharge rate and should be held accountable!" Nope, they just wright whatever they want on a nice wrapper and hope you don't notice the difference.
Everyone is saying it. Even John is saying the same thing. Every manufacturer out there is making up there own specs because they can. Now John does carry Turnigy batteries, just not anything that will fit the 4F200 with my battery tray mod.
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Old Aug 01, 2012, 01:39 AM
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Quote:
Originally Posted by bonner View Post
I see you guys are talking battery talk. I might be on the wrong thread but, I have a question.
What amount of internal resistance is considered a good point to stop using a pack, per cell and total pack resistance? I have some 4s 4000 mha 30C that are surging, the internal resistance reads approx 9 milliohms per cell with a total internal resistance of 36 milliohms for the pack. I know lower is better but I don't know how high is too much I need some rule of thumb figures. Thanks for anyone's help.
5-10 milliohms per cell is still very good. Sometimes lipo cells just have crazy issues. But if a pack ever gives you flight anomalies i would discontinue use. What method are you using to check your internal resistance? I would start worrying when it gets above 10 per cell. If it goes above 20 it probably won't power your helicopter properly at all any longer.
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Old Aug 01, 2012, 01:42 AM
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Quote:
Originally Posted by IntegrityHndywrk View Post
Don't forget you probably have a slightly different weight on your tail with the BX unit, and now with MG servos going in..

I don't understand why those batteries wouldn't fit.. The stock battery is 108mm long.. ? Is it because they are too tall?
Nope... the stock battery is 85mm long.

Remember this post? http://www.rcgroups.com/forums/showp...postcount=1689

I do... must be because I did the work.
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Old Aug 01, 2012, 01:47 AM
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Quote:
Originally Posted by IntegrityHndywrk View Post
Don't forget you probably have a slightly different weight on your tail with the BX unit, and now with MG servos going in.
Damn it. Your right. I didn't think about that. Crap so maybe the perfect wait up front is somewhere around 120 grams? Too many damn variables.

What do you figure?
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