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Zoom › Motor/speed-controler sagging!
05-02-2005 09:35 PM  12 years agoPost 1
BigGuyInLA

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Los Angeles, CA

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I have a EF brushless motor, CC Phoenix 25 controller, 4 HS-56's. My shogun rotor is running at 1800 rpm, and it will hover for a few seconds and then the motor sags and loses rpm and won't even hover. It seems that the battery/speed-controller is losing power (current limiting?) randomly after only a few seconds of flight. Any ideas or help would be appreciated...

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05-02-2005 10:09 PM  12 years agoPost 2
leslie

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Hollis, NH - USA

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Hi BigGuy,

What battery are you running?

What pinion (number of teeth) are you running on your motor?

What is the KV rating of your EF motor?

I'm not an expert, I've had my Zoom for several weeks, but flying great, spent a year learning on my hummingbird FP.... 1800 rpm seems low.


I suspect when you answer the three questions above, you will get a ton of help, this board is great for helping people out.

Cheers,
Leslie

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05-02-2005 10:53 PM  12 years agoPost 3
BigGuyInLA

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Los Angeles, CA

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What I'm running...

I'm running the EF lipo 11.1v 1600mah battery, the EF brushless motor which comes with a 10T pinion, and I don't know KV rating of the EF brushless...

What rotor rpm are people running on the Shogun?

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05-02-2005 11:18 PM  12 years agoPost 4
leslie

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Hi BigGuy,

It seems most people are running aroun 2200 to 2300 ish.

I checked out EF motors and found this:
http://www.hobbypeople.net/gallery/165370.asp

the motor appears to be a 3600KV motor, which is fine, 10Tooth pinion is fine

----------------------------------------------------------------------------------------------
the math (albiet rough)

3600KV * 11.1 Volts (batt) = 39960 (rpm max)

132 Tooth Main (check it some are 140?) / 10 (pinion) = 13.2 ratio

39960/13.2 = 3027 *.8 (motor efficiency) = 2421 (approx rpm)

**** good
____________________________________________________


the specs look fine. your setup sounds solid.

Are your pitch settings correct, what are they? I'm assuming the battery is correctly charged etc., etc.

If your pitch settings are whacked, i.e. too much pitch at too low rpm you could be stalling (bogging) the motor.

Others, please chime in!!

Cheers,
Leslie

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05-03-2005 01:15 AM  12 years agoPost 5
dada

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Try changing batteries to a much higher discharge rated packs. If the discharge rate isn't high enough you'll dump the pack quick and overheat the cells too. Look for the constant discharge not the maximum burst discharge. Since bursts discharges are like for about 20 sec max. Nice for accellerations but doesn't help for general flights/hovers.

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05-04-2005 12:39 AM  12 years agoPost 6
rcnut2

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Canada

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Hmmm…, I think your battery pack cannot deliver. I’m getting around 17 to 18A draw from my Himax on a 3S pack for a head speed of 2100RPM. I’m in agreement with “dada” in changing to a different battery pack. Even if the EF could deliver a 10C discharge, that only gets you 16A continuous but I suspect it’s probably only 8C rated. I would try first before buying a new battery pack to moving down to a 9T pinion. Using Leslie’s math, you can still achieve 2180RPM at 80% efficiency. This would drop your current draw a little and keep the motor and controller a little cooler. My 2 cents worth.

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05-04-2005 02:02 AM  12 years agoPost 7
leslie

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Hollis, NH - USA

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Hi,

Just to check the not so obvious, before changing batteries and causeing undo expense. Is your pitch setup correct, by the instructions?

You might have too much pitch a lower rpm causing a stall situation. I'm not familiar with the battery you are running, but based on mah rating I would think a 1600mah lipo would get you more time.

dada, and rcnut2 your thoughts? Shouldn't this setup run longer??

I'm running TP1320's 3cell and get 12- 16 minutes, granted the discharge rate might be higher but this is an order of magnitude off.

thougths?

leslie

ps: to credit the math, check the century board, zoom did the math

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05-04-2005 02:31 AM  12 years agoPost 8
BigGuyInLA

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Los Angeles, CA

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Battery power sagging?

According to the EF website, this 3-cell lipo battery is rated at 7C discharge. I have a second EF battery of the same type, so I'm going to swap batteries and run a test to see if it behaves differently.

Leslie, about the pitch setup, I'm not sure what you mean. I spool up to the set rpm with the collective pitch set neutral (mid-point on throttle, which has the rotor pitch at zero degrees). Then, when I increase the collective pitch to the point where the Shogun starts to hover, the rpm will stay at the set rpm for a few seconds, then suddenly sag to a lower rpm.

After hearing the comments here about the battery maybe not being able to handler the current, I'm thinking that's a good thing to check...

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05-04-2005 06:03 AM  12 years agoPost 9
dada

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hmmmm...it all depends on what his headspeed is. All I know is that with lower headspeed you need greater pitch in order to create lift and vice versa. However, given that increased pitch also increases drag, it's better to decrease the pitch and increase the headspeed. So in that matter I'd say decreasing the pitch by about 1 at the top of the collective should help a little.

However, from his description of his problem it sounds like a discharge problem to me. All batteries have the ability to provide a greater burst of energy before dropping to a sustainable level. That's why you see both burst and constant current ratings in the specs of the packs. Here's a simple test to see if it is the battery....

As soon as you get the blades moving start counting and bring it into a hover. Keep counting until the power sags and the heli starts to fall. If it's about 20-30 secs then it is the battery. You've reached the max burst rate of the pack and it's dropping down to the constant rate. Which, at 7c may not be enough amps to power the heli.

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05-04-2005 06:10 AM  12 years agoPost 10
dada

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whoops I forgot to mention what is your exact settings for cc25? Perhaps it could be something as simple as the controller doing it too. Also I've found with the shogun the following items helps with reducing amp draw, and power...

1. gear mesh...too tight and the motor has to work harder...to light and you strip...it's gotta be just right.

2. Pitch setup...For the zoom I've got mine set for about -1/-2 at the bottom and +7 at the top. This gives me about +2 in the middle. Set your pitch mechanically with the collective pitch rod. If you've got that set right then you can run a flat curve and it'll give +/-7 at both ends naturally. Then simply raise the first collective pitch point to give you -1/-2 (about 50%) and it should all be set.

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05-04-2005 05:44 PM  12 years agoPost 11
BigGuyInLA

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Los Angeles, CA

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Pitch?

Whoo! That last part about pitch setup from dada went right over my head... This is my first (non-simulated) helicopter, so I'm still learning all this new stuff. I guess I've got to read up some more on pitch setup.

In the meantime, I got a bunch of things to try out (gear-mesh, new battery, etc.). I really appreciate all of the responses I've received to my questions - lots of good info!

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05-04-2005 10:17 PM  12 years agoPost 12
BigGuyInLA

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Los Angeles, CA

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Governor vs fixed mode...

I think I see part of my misunderstanding of what Leslie and Dada were saying about pitch. I guess most guys run in "fixed" mode, but I set up my Shogun's ESC to run in governor mode. So, I don't think I have an issue with having too great a pitch angle for a given throttle stick position.

My ESC is set up in governor mode, and my transmitter is set up hold the throttle at fixed value no matter what position my transmitter's throttle (collective) stick is at. The ESC's job is to keep the rpms constant no matter what the load. The throttle stick position only controls pitch...

I hope the above makes sense...

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05-04-2005 11:08 PM  12 years agoPost 13
leslie

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Hollis, NH - USA

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Hi BigGuy,

I leaning with dada on this, I'm thinking it's the battery. But I would try setting your ESC to fixed mode to see it there's any difference.

I'm running TP 1320's 3cell, I thought these might be a tad underpowered but I'm getting 12-16 minutes of easy flight time. Mostly hovering, circles, 8's etc.

I thought you might have too much pitch at the throttle level you're running at. You could check with the motor disconnected. It's sounds like you've got a handle on that, so I'm back to the battery.

Let us know how you make out.

Cheers,
Leslie

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05-05-2005 01:46 AM  12 years agoPost 14
BigGuyInLA

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Los Angeles, CA

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Yep, looks like the battery was the problem

I swapped out the battery with another of the same brand - and the problem mostly went away. At the end of about a 10 minute flight, just hovering, the battery was pretty hot - almost too hot to touch. I guess this means I'm pulling too much current from it...

I'll try a higher capacity battery next.

Thanks for all the help you guys...

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05-05-2005 01:56 AM  12 years agoPost 15
leslie

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Hollis, NH - USA

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Hi BigGuy,

You might want to search around this board for pinion sizes. The battery/motor/pinion are very interelated. You might solve this by going to an 8 or tooth pinion. I think the chili pepper motor is 3600kv too, you might see what they are running for a pinion gear size

I'm running a 4200KV motor with an 8t pinion, the motor gets warm,almost hot but not burning to the touch. Neither do the batteries. I'm getting decent power, althougth I'm not flying 3D.

Hot battery, is bad. Hot motor will shorten the life. Balance is key.

Glad you are closing in on it

Cheers,
Lesie

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05-05-2005 02:32 AM  12 years agoPost 16
dada

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Glad you were able to solve your problem. 3 items to invest in to save money in the long run. A tach, watt meter and temp gun.

I believe the chili pepper runs at a 9T...but the EF brushless isn't as efficient as the cp from what I've heard. Anyhow better batteries are the way to go. Try getting a set of the new polyquest 1800 20c packs. They're lightweight and fit into the stock frame nicely.

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05-05-2005 11:55 PM  12 years agoPost 17
dada

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The good ol' paper mesh trick. But that's the first time I heard of someone using a paper towel. Also when you feed out the paper through the other end look at how it feeds out to. If the pinion/gear is warped it won't feed straight through and will come out at a different angle it then it went in.

I was taught that less pitch = less drag. Less Drag = more rpm's or more importantly more effecient motor.

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