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Old Feb 11, 2013, 01:07 PM
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Originally Posted by Thomas B View Post
Sorry, I missed your post.

With my motor mod, I am actually flying it on the stock battery and no extra ballast. I do think it is just a hair tail heavy. I have also flown it with a dime stuck in the nose and that worked well, also.

Eventual plan is to make a Y-harness so I can run two stock batteries in parallel, with the second one installed in the aft cockpit area, under the canopy.

Flew the little ASK indoors Saturday evening, at a large full court gym at a middle school. Did well there, but I would no try anyplace smaller. Was a big hit with the other indoor guys.
No issues Thomas!

Today, I finally maidened my twin mot ASK-21 with the stock battery. Used another battery as a dummy weight in the front to balance and got the exact c.g.
The climb was not wonders, but could get to a nice height of around 40-50meters (~150ft). It was cold (~0C) and quite windy (10kph ~ 6mph with gusts).

I had one PROBLEM though...... After a very short time (~3mins) I could hear the motors pulsing, sounded like a Low Voltage Cut-off warning. I know they have such a thing in the ESCs for bigger planes, not sure about the UM receiver+ESCs. This was strange as I later, I put the same battries in my PZ PoleCat UM and was able to fly for another 3-4 mins. Therefore, I am sure that the batteries had enough charge.

I am still wondering, what is the reason for the pulsation.
It is something else with the ESC?
Is it there a current limit?
Is the voltage under the current load lower?
It is difficult to imagine that the 2 small motors could over load the system.
How critical is this issue?

Any helpful comment are welcome, it may correct me from doing something harm to the system.

Best Regards,
Viren
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Old Feb 11, 2013, 01:15 PM
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Pics of my twin motor mod.
I ordered 2 MSRx Heli Tail Motors.
I decided to used the tail carbon fibre rod to mount the two motors.
Used a small piece of plywood to hold it to the wing securing with one screw.

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Old Feb 11, 2013, 02:02 PM
Way to many airplanes!
Canada, QC
Joined Oct 2009
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Originally Posted by rc_virens View Post
No issues Thomas!

Today, I finally maidened my twin mot ASK-21 with the stock battery. Used another battery as a dummy weight in the front to balance and got the exact c.g.
The climb was not wonders, but could get to a nice height of around 40-50meters (~150ft). It was cold (~0C) and quite windy (10kph ~ 6mph with gusts).

I had one PROBLEM though...... After a very short time (~3mins) I could hear the motors pulsing, sounded like a Low Voltage Cut-off warning. I know they have such a thing in the ESCs for bigger planes, not sure about the UM receiver+ESCs. This was strange as I later, I put the same battries in my PZ PoleCat UM and was able to fly for another 3-4 mins. Therefore, I am sure that the batteries had enough charge.

I am still wondering, what is the reason for the pulsation.
It is something else with the ESC?
Is it there a current limit?
Is the voltage under the current load lower?
It is difficult to imagine that the 2 small motors could over load the system.
How critical is this issue?

Any helpful comment are welcome, it may correct me from doing something harm to the system.

Best Regards,
Viren
Simple, pulsation is a way to indicate that you have a low voltage on your battery. The load on your ASK-21 is much more than the Polecat (Two motors and one extra servo). The temperature was near freezing so the battery was probably getting cold as well, particularly if you were gliding a lot (letting the battery cool down A LOT). Those two facts caused the low battery pulsing warning. Once you get back home, or put the battery in your pocket, after the battery got warm again, the voltage went up. When you used it in your Polecat, the voltage was high enough to avoid LVC pulsing. And since you used the motor all the time (no gliding) the battery was always warm (no time to cool off).
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Old Feb 11, 2013, 02:48 PM
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I am still wondering, what is the reason for the pulsation

There is the issue of propeller synchronization which will be heard on large propeller airplanes perhaps this was what you heard ...out of synch props
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Old Feb 11, 2013, 03:14 PM
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Originally Posted by RealGambler View Post
Simple, pulsation is a way to indicate that you have a low voltage on your battery. The load on your ASK-21 is much more than the Polecat (Two motors and one extra servo). The temperature was near freezing so the battery was probably getting cold as well, particularly if you were gliding a lot (letting the battery cool down A LOT). Those two facts caused the low battery pulsing warning. Once you get back home, or put the battery in your pocket, after the battery got warm again, the voltage went up. When you used it in your Polecat, the voltage was high enough to avoid LVC pulsing. And since you used the motor all the time (no gliding) the battery was always warm (no time to cool off).
Thanks for you reply.
I hardly did any gliding. On the contrary I was flying full throttle most of the time...... But, I agree with you on cold being one of the reasons. I Also think that the 2 small motors were not working at their best efficiency at high spin rates and cold temps. May be they aren't so efficient and thus draw more current.This in addition with cold batteries may be the reason of Low Voltage.
.......will report once I have tested it in warm conditions.
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Old Feb 11, 2013, 03:18 PM
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Originally Posted by tlar633 View Post
I am still wondering, what is the reason for the pulsation

There is the issue of propeller synchronization which will be heard on large propeller airplanes perhaps this was what you heard ...out of synch props
Brilliant idea, but I don't think this was the case.
The pulsation was not all the time but only after couple of minutes. Plus, the pulse frequency was too low compared to the spin rate.
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Old Feb 11, 2013, 05:01 PM
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Originally Posted by tlar633 View Post
I am still wondering, what is the reason for the pulsation

There is the issue of propeller synchronization which will be heard on large propeller airplanes perhaps this was what you heard ...out of synch props
It's called LVC. The motors pulse when the voltage sags below a certain point to let you know that you should have landed awhile ago. Flying to LVC kills your LiPos. But the battery's internal resistance goes way up when cell temp drops below +40 F, so the voltage sags a lot earlier when flying in cold wx than it does when flying at +50 F or higher.

Joel
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Old Feb 13, 2013, 08:17 AM
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powder springs georgia
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I finally got the parts for the finishing of my cradle to get the glider up..I have wired it and tested the switches...all is working...cked. cg with it attached to the bird. The release seems to work...I decided not to put a parachute on it...It is so light that I do not think it will hurt it on a fall...All thats left is the final test..it is to messy today but soon. I ran the motor up and am not sure if it has enough power..but will find out soon... My biggest worry is it will not release I will just have to fly it to the ground...If it works it will be really nice to just launch and fly...I am putting a long orange ribbion on the cradle to recover it later...
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Old Feb 13, 2013, 04:11 PM
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Originally Posted by sanman55 View Post
I finally got the parts for the finishing of my cradle to get the glider up..I have wired it and tested the switches...all is working...cked. cg with it attached to the bird. The release seems to work...I decided not to put a parachute on it...It is so light that I do not think it will hurt it on a fall...All thats left is the final test..it is to messy today but soon. I ran the motor up and am not sure if it has enough power..but will find out soon... My biggest worry is it will not release I will just have to fly it to the ground...If it works it will be really nice to just launch and fly...I am putting a long orange ribbion on the cradle to recover it later...
Nice work so far.
Your worry is justified. Seems like you are using the onboard tow release hook to attach/release the cradle. the release servo is weak. So if the cradle weight plus aero load during flight pulls hard on the release pin, the friction is higher than the servo force and it may not release.
I had a similar cradle for piggybacking my ASK (photos in post #1467) and once I had the problem that it didn't release. Both the planes crashed from 50ft.
Be careful and all the best.
regards,
Viren
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Old Feb 13, 2013, 07:08 PM
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Originally Posted by rc_virens View Post
Thanks for you reply.
I hardly did any gliding. On the contrary I was flying full throttle most of the time...... But, I agree with you on cold being one of the reasons. I Also think that the 2 small motors were not working at their best efficiency at high spin rates and cold temps. May be they aren't so efficient and thus draw more current.This in addition with cold batteries may be the reason of Low Voltage.
.......will report once I have tested it in warm conditions.
It has to do with the cold effect on the batteries much more than the cold effect on the motors.

As other posted, it is definitely the low voltage causing the motor pulsing. Standard on the uM powered models

I get flights of 4-5 minutes, with part full power and part cruise flight....but my flights on very cold days and/or with a worn battery are less.

The best thing to do is to make that dummy battery do some work and install a parallel harness so you can plug both of the batteries into the circuit. Mine will have that mod shortly.
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Old Feb 13, 2013, 08:29 PM
Way to many airplanes!
Canada, QC
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Quote:
Originally Posted by sanman55 View Post
I finally got the parts for the finishing of my cradle to get the glider up..I have wired it and tested the switches...all is working...cked. cg with it attached to the bird. The release seems to work...I decided not to put a parachute on it...It is so light that I do not think it will hurt it on a fall...All thats left is the final test..it is to messy today but soon. I ran the motor up and am not sure if it has enough power..but will find out soon... My biggest worry is it will not release I will just have to fly it to the ground...If it works it will be really nice to just launch and fly...I am putting a long orange ribbion on the cradle to recover it later...
Not sure how it works? It seem to have it's own battery, so basically, you put the battery in, and the motor/propeller goes full, even after release? Or you have some throttle control? Or when you release, the motor turn off?
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Old Feb 14, 2013, 06:50 AM
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I have 2 switches...one is just an on-off switch and the other a pressure switch..Once the bird is in the cradle I use the on-off switch to start the prop...once released the pressure switch will cut it off...
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Old Feb 14, 2013, 06:52 AM
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Originally Posted by rc_virens View Post
Nice work so far.
Your worry is justified. Seems like you are using the onboard tow release hook to attach/release the cradle. the release servo is weak. So if the cradle weight plus aero load during flight pulls hard on the release pin, the friction is higher than the servo force and it may not release.
I had a similar cradle for piggybacking my ASK (photos in post #1467) and once I had the problem that it didn't release. Both the planes crashed from 50ft.
Be careful and all the best.
regards,
Viren
Thats what I am worried about, any ideas how to fix that???
I read your post and the one for the guy that did it in Australia and his worked fine...I posted this question on that site ..will see what he says....Wost case is I just fly it back down to the ground or the power runs out and glide back.Maybe just roll the plane to release the pressure

I had the plane not release on the tow line this week, but after a 2 trys it finally released...
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Old Feb 14, 2013, 09:50 AM
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after thinking about it some more did some more mods to the cradle to try and release any pressure on hook...I did 3 hand held cradle releases with the prop running and they all released and motor cut off..will try tomorrow at the club...even if it does not work it was fun messing with it and i still have my tow buddy to get me up and going
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Old Feb 14, 2013, 02:59 PM
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Originally Posted by turboparker View Post
It's called LVC. The motors pulse when the voltage sags below a certain point to let you know that you should have landed awhile ago. Flying to LVC kills your LiPos. But the battery's internal resistance goes way up when cell temp drops below +40 F, so the voltage sags a lot earlier when flying in cold wx than it does when flying at +50 F or higher.

Joel
Thanks everyone for comments. I agree with fact that LVC kicks in sooner at low freezing temperatures as compared to when it's warm.
I can also agree that the twin micro motors + asx3 pull more current than the single motor in UM PoleCat.
Last couple of days, I have been experimenting with my twin mot ASK and here are some observations:
This time the LiPos were warm. I used my friends LiPo warming case and they were over 30deg C till just before flying.

First the eflite 150mAh 25C LiPos, LVC after 30seconds. Later I could fly 4mins of PoleCat with them.
Then SLS 150mAh 20C LiPos I could fly the ASK for good 4mins before LVC.
Another LiPo 120mAh 20C decent 3mins of flying LVC.
All batteries are only 10-12 flights old.

I wonder why the eflitte 25C LiPos give up so soon. Is it that for my use lower C Lipos are better for my twin motor ASK. Does it make sense?
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