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Steve Colman02/11/2014 17:36:26
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Another beautiful weekend of flying but with a conundrum.

Went to fly my Calmato which has become my warm up model . I flew it last weekend with exactly the same components with no problem. So, with all prepared, freshly charged lipo inserted and normal checks before committing to flight off we go to the strip.

Upon take off the model barely had enough power to stay in the air so I executed a very low level circuit and just managed to land on the strip with no damage.

Back in the pits a battery check proved inconclusive showing about 12.3v overall with some variation in each cell but nothing out of the ordinary. So, a while later, I tried the model again with another fully charged lipo. Suffice to say, the flight was basically a repeat of the first with another cheek clenching emergency landing.

A club mate wryly commented that both landings were my best in a while but I digress.

In the pits again, I and a friend ran up the motor to full throttle and after a few secs the motor began to slow markedly as if the lipo was flat. One of the two lipo's is begining to show signs of age but the other is relatively new and well looked after.

Club mates suspect the ESC but....well I'm not so sure; it either works or doesn't work like most other electronics. I just did a quick check of the two lipos before posting and both still show 12.3v with the 3 individual cells within reasonable limits.

The only other suspect is the motor of course, which could be on its last legs I suppose.

Any bright ides anyone?

The model is a Kyosho Calmato ST (1.3m) with stock motor. Turnigy Trust 55A ESC; Turnigy 3S 4000mah lipo.

Steve.

Steve Hargreaves - Moderator02/11/2014 17:42:46
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Are you sure the Lipos were fully charged? You wouldn't be the first person to try & fly a model with a nearly flat Lipo he "thought" he'd charged up the day before.....embarrassed The 12.3V reading would tend to disprove that however.

Like you I would doubt the ESC...they tend to work or not...low power problems are rare....I would also doubt the motor....I suppose its possible that it has overheated & damaged the magnets but again I doubt it.

I guess the best course is to try substituting parts & seeing what happens.....I'd charge up the batteries again though...just in casedont know

Lindsay Todd02/11/2014 17:47:59
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I not sure what fixing the prop adaptor is but it might be worth check you have not got it slipping on the shaft of the motor when loaded and would explain an initial level of thrust and then a slow unloading if it is a clamp on adaptor so might just need tightening.

Edited By Lindsay Todd on 02/11/2014 17:48:42

GrahamWh02/11/2014 17:51:47
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I suggest you check the power down setting on the esc. If the trigger voltage is too high (say 3.5 v per cell rather than 3.2v) it may put the esc into low power mode too early. An old battery may give too much voltage drop at high current and trigger this. I have found with some of the many Turnigies I have bought that they are sometimes best treated as being of half the said C value.

Biggles' Elder Brother - Moderator02/11/2014 17:59:48
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Mmm, interesting. Well let's look at the possibilities:

1. The uncharged Lipo is definite possibility - as Steve says its easy to do. So definitely worth a recharge and a check.

2. Duff charger? Could be - saying they are charged when they are not? Did you notice how much went in when you charged them? Might be an idea to discheage them then charge up again and note how much they take.

3. Lyndsay's suggestion of a lose prop is also a definite possibility. Do you have a rev-counter to see what you are getting?

4. Is it possible that you have accidentally reprogrammed the throttle setting on the ESC so you are only getting half throttle even though the stick is fully forward? This can happen if you inadvertantly connected the power battery with the throttle stick part forward, then pulled it back sharply?

5. Could the prop be damaged? Flexing?

6. Is anything getting hot? Any poor connections etc?

BEB

Stuphedd02/11/2014 18:09:52
721 forum posts
376 photos

dry(ish ) joint on the esc , seen it many times !!

starts well and power decays as the joint get hot and the resistance increases and power then drops off

cheers

Tim Hooper02/11/2014 20:39:12
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Dry joint on the ESC to motor connectors?

We've been flying one of these Calmatos for years without a problem.

tim

Steve Colman02/11/2014 22:00:28
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Thanks for the replies.

I'm convinced it's not the batteries, both were balanced charged yesterday afternoon/evening. I did check the prop adapter for secureness at the field yesterday too.

I am leaning towards the efficacy of the joints on the ESC connectors. The positioning of the ESC in the model is such that connecting and disconnecting the lipo is a bit awkward and perhaps the joints are becoming weak as a result.

I will remove the ESC and check out all the soldered joints over the week and re-solder if any look untoward. I will also look at improving the installation too to minimise any undue stress.

Steve.

Bob Cotsford02/11/2014 22:09:38
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Have you tried it on a wattmeter? It might give you a pointer whether it's excess current draw, high resistance or low battery voltage under normal load

Chris Bott - Moderator02/11/2014 22:16:10
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Steve does the ESC get hot? Many will cut back power if they overheat. Then of course they cool down and test out fine later.

Martin Harris02/11/2014 22:22:49
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Talking of hot, a useful diagnostic technique would be to run up the motor under load and feel the soldered joints immediately after shutting down (disconnect the battery first for safety) - any high resistance joint will get hot.

Steve Colman02/11/2014 22:28:51
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I didn't have the wattmeter with me at the field otherwise I would have done a test. The ESC has been fine all summer in ambient temps in the low to mid 30's and functioned as normal a week ago.

Steve.

kc03/11/2014 13:06:12
6636 forum posts
173 photos

I have had this happen! Turned out to be the shaft was loose in the motor ( seemed like the prop adaptor but wasn't). The test is to see if holding the prop then try to rotate the motor outer part. If it moves then the screws have become loose or something similar.

YakMad03/11/2014 14:57:18
518 forum posts

Or the motor shaft could be spinning on the bearings, look for heating marks on the shaft or hold the motor can and see if its possible to turn the prop by hand as kc suggested. I had a few Eflite motors do this due to poor quality bearings, I solved it by applying Loctite Stud and Bearing lock between the shaft and bearing, you wiould need to take the motor apart to do this.

Pete B - Moderator03/11/2014 20:14:44
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I wouldn't gainsay any of the other suggestions here but those symptoms, to me, indicate tiring LiPos. If you can check the internal resistance of each cell, I'd hazard a guess that they'll be around the 250+ mOhm mark.

They seem to charge normally and a no-load voltage reading shows no problem but subject them to a load and the output just collapses....

Pete

Delta Foxtrot03/11/2014 20:22:36
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I agree with Pete that this fits well with tired LiPos. I had exactly the same symptoms last winter when my well used LiPos reached the end of their useful life. A new batch of LiPos and flight performance was restored.

Delta Foxtrot03/11/2014 20:24:02
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You could test them with a wattmeter under load and see how much voltage drop you get with power on.

Danny Fenton03/11/2014 20:54:44
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Well if we are voting I would go for throttle travel reduction. Either via Tx or innadvertant esc programming
Cheers
Danny
Simon Chaddock03/11/2014 22:29:56
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Steve

You really must run it up with a watt meter in line.

If the LiPos are 'tired' it will show a distinct voltage and a corresponding current drop as the motor slows.

If its a bad ESC connection, an ESC 'slowdown' due to over heating or a slipping motor it will show a current drop but with a slight voltage rise.

Steve Colman04/11/2014 07:30:22
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797 forum posts
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Many thanks for all the ideas gents.

I have a couple of hours free today to investigate the problem.

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