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Author Topic: Puffer Wiggle  (Read 5794 times)

ianb

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Puffer Wiggle
« on: August 26, 2009, 01:02:53 PM »

Well, my Mountfleet Puffer had her first test session at the pond recently. She took a lot of ballast, 2 SLA batteries midships and about 2 lb of large bolts in front of the mast.

The Puffer is very stable and the waterline is about 1 inch below the deck level. The prop is well immersed and she is not trimmed down at the bow.

I tried to set up the rudder servo for a straight hands off run at full throttle and couldn't do it. The stern twitched randomly left and right. Brought her in and checked for play in the rudder linkage, none found: I use the helicopter ball links. Changed the servo, no change in the behavior. No wind was blowing on the test day.

Rudder control is very positive at any speed and the turning circle is good. I sail alone and the receiver is SPCM so that it shuts everything down if the signal is corrupted or lost. The same equipment works just fine on my other models.

So, I am stumped. Any ideas as to what may be causing this?

Ian
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Martin [Admin]

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Re: Puffer Wiggle
« Reply #1 on: August 26, 2009, 02:09:23 PM »

Have you done the usual range checks?
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ianb

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Re: Puffer Wiggle
« Reply #2 on: August 26, 2009, 02:49:07 PM »

Yes. Tx and Rx both working as they should. The Puffer antenna runs up to the top of the mast, so reception is excellent. Antenna is well clear of any other wires and the motor is suppressed. The problem occurs at both close range and at a distance, so I think that the radio link is good.

With the SPCM radio the throttle is set to center stick if there is any loss of signal ie failsafe position.

Ian
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FullLeatherJacket

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Re: Puffer Wiggle
« Reply #3 on: August 26, 2009, 02:53:55 PM »

Ian
It sounds like RF interference is being generated somewhere inside the model. Check for metal to metal joints rubbing against each other. Also twist the two motor wires together along their length between the ESC and the motor.
FLJ
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ianb

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Re: Puffer Wiggle
« Reply #4 on: August 26, 2009, 03:24:40 PM »

FLJ,

Good point. I'll check that aspect of possible internal RF out tomorrow. Its 11:15PM here.

The motor wiring is all paired inside that spiral wrap, and there are no loops or excess wire. The Rx is mounted in the forward part of the hatch opening with the antenna going up the mast. No other wiring up there.

The twitching had a period of 5 to 10 seconds - go straight for 5 to 10 seconds, twitch left or right,go straight for 5 to 10 seconds but on a slightly different heading and so on. Didn't notice any change in the prop wash or in the steam engine sound.

Thank you
Ian
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Shipmate60

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Re: Puffer Wiggle
« Reply #5 on: August 26, 2009, 03:46:41 PM »

What motor is in her and is it suppressed?

Bob
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Re: Puffer Wiggle
« Reply #6 on: August 26, 2009, 06:13:36 PM »

Yes. Tx and Rx both working as they should. The Puffer antenna runs up to the top of the mast, so reception is excellent. Antenna is well clear of any other wires and the motor is suppressed. The problem occurs at both close range and at a distance, so I think that the radio link is good.

With the SPCM radio the throttle is set to center stick if there is any loss of signal ie failsafe position.

Ian
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OMK

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Re: Puffer Wiggle
« Reply #7 on: August 26, 2009, 06:47:40 PM »

I had the exact same symptoms on one of mine. All wiring/range testing/linkages were fine. Not sure if this could be relevant, but the problem went away when I stuck a smaller rudder in there. Fuelled with that knowledge I re-installed the larger rudder and swapped out the servo for another (beefier) one. That too cured the problem.
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ianb

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Re: Puffer Wiggle
« Reply #8 on: August 28, 2009, 11:07:42 AM »

Well, an update seems called for.

I tried the puffer out again today. First I disconnected the rudder servo receiver connection and clamped the tiller arm. Then I disconnected everything else except for the ESC and set her to cross the pond. 3 to 5 seconds a little twitch left, then a twitch left again, then a twitch right, and so on. All this was at full throttle, I didn't try part throttle.

I think that PMK may be on to something as I have found that the rudder is very sensitive around center, so have had to put in about 50% exponential on the D/R in order to make it less sensitive, yet give me full throw when needed. Maybe my rudder is too big (don't fancy changing it at this stage) but I can consider putting in a beefier servo.
Full throw is about 45 degrees L and R, is that about right?

Or maybe I'll just have to live with it!

If I get it solved Mayhem will be the first to know.

Thanks to everybody.

Ian
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FullLeatherJacket

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Re: Puffer Wiggle
« Reply #9 on: August 28, 2009, 12:12:52 PM »

Ian
Are you saying that the rudder linkage and servo were totally disabled for your test? If so then the problem has to be some sort of motor-speed glitch which is causing a prop-steering effect, as there don't appear to be any other forces which could be in play.
I have to say that the rudder movement you have seems excessive, especially for an unbalanced rudder which is so large anyway.
FLJ
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Colin Bishop

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Re: Puffer Wiggle
« Reply #10 on: August 28, 2009, 12:45:20 PM »

It may be possible that the hull is hydrostatically slightly unstable and that the waterflow over the short hull at certain speeds can cause it to veer from one side to the other. As the rudder, even if not operating, is effectively part of the hull then changing its size may well have an effect.

The same effect occurs sometimes on full size yachts which are short and beamy as well.

Colin
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derekwarner

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Re: Puffer Wiggle
« Reply #11 on: August 28, 2009, 01:28:21 PM »

My need the three person test  %%  

1) sit the puffer on a sheet of glass
2) person 1 .....holds the rudder firmly
3) person 2 .....gently holds the hull
4) person 3 .....gently actuates the RC...in fwd & astern + port & stdb
5) person 2 .....whilst gently holding the hull.......accepts the rudder servo movement to allow the rotation mass of the hull
6) persons 1+2 ...... stay ship bound whilst person 3 takes the R/C tx further >>>>>>>>>>>>>>>>>>away
7) simply testing & visually watching the R/C rudder function out of the water ....without load or pressure will confirm ZILCH

However the 'restricted' tests at close range should visually define the conditions/actions & hence the source of the R/C glitch  O0 ...................however this may only partially resolve points offered by others.........  :o Derek
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dreadnought72

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Re: Puffer Wiggle
« Reply #12 on: August 28, 2009, 01:50:19 PM »

I'm leaning towards Colin's suggestion. A hull speed which results in twitches.

Andy
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snowwolflair

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Re: Puffer Wiggle
« Reply #13 on: August 28, 2009, 03:03:11 PM »

Is it an old servo, if so is its centre point on the feedback pot wearing out?  Old problem you dont often see these days, but your symptoms match.
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Colin Bishop

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Re: Puffer Wiggle
« Reply #14 on: August 28, 2009, 05:20:27 PM »

I think Ian said he disconnected the rudder servo and clamped the tiller arm and it still happens in which case it isn't anything to do with the rudder servo.

Colin
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Martin [Admin]

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Re: Puffer Wiggle
« Reply #15 on: August 28, 2009, 05:28:03 PM »


Any chance of a picture of you rudder set-up Ian?
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ianb

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Re: Puffer Wiggle
« Reply #16 on: August 29, 2009, 03:37:51 AM »

Here's some pictures of the rudder set-up. Hope they are easy to see.

Thank you for your comments FLJ, I too wondered about the possibility that the radio and/or the ESC was glitching. Because the twitch was to both the left and right at random, it seemed to me that an intermittent cut or loss of power would always cause the twitch to be in the same direction. Maybe I was incorrect in this assumption.

I have cut back the rudder servo travel to about 70% of full which gives me a swing of about 30 degrees. Haven't tested it in the water yet.

All up weight is 13 kg, maybe too heavy?

Really appreciate all the interest in my problem.

Ian

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Martin [Admin]

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Re: Puffer Wiggle
« Reply #17 on: August 29, 2009, 03:43:10 AM »

Lovely neat installation!
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ianb

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Re: Puffer Wiggle
« Reply #18 on: August 29, 2009, 03:47:59 AM »

Sorry, screwed up the pictures. I'll try again.

Ian





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ianb

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Re: Puffer Wiggle
« Reply #19 on: August 29, 2009, 03:53:53 AM »

Thank you for the kind words, Martin.

What are you doing up at this time in the morning????

Ian
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Martin [Admin]

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Re: Puffer Wiggle
« Reply #20 on: August 29, 2009, 05:22:59 AM »

Always loking after the interests of all my Mayhem friends... and I'm also slightly mad.....  %%

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OMK

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Re: Puffer Wiggle
« Reply #21 on: August 29, 2009, 06:55:10 AM »

Da Boss: Be careful though because you can get some real weird comments from some real weird folk if you post in the small hours of the morning.

Janb: Pardon me if this sounds blatantly obvious, but have you tried any of what Derek Warner has suggested yet? Namely, how does it behave when it's not in the water?
Furthermore, take a bow for the neat electrical installation, but how is the wiring beneath the deck? Do you have sufficient distance between the clean wires and the dirty ones? By that I mean are your servo wires and receiver wires well separated from those on the ESC and the motor?
Silly question, I know, but we're all shooting in the dark here.
For what it's worth, it seems that your hull/ship design may not be the cause of the problem after all, which may point to one of electrical interference.

<edit>

By the way... Yep - 45-deg's either side of neutral sounds about right.
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OMK

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Re: Puffer Wiggle
« Reply #22 on: August 29, 2009, 07:08:16 AM »

One other thing.......

This too may sound a bit cheesy, but I just noticed that the linkage on the servo horn seems a tad close to the actual body of the servo. Do you suppose it may be causing it to bind or snag?

Hmm... on seconds thoughts, perhaps not, else you would have noticed by now, right?
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ianb

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Re: Puffer Wiggle
« Reply #23 on: August 29, 2009, 08:28:18 AM »

PMK

Thank you for your comments.

I have all the power cables on the port side and all the signal cables on the starboard.

No, the linkage does not bind on the servo, A good point though, which I have now checked again.

Next weekend, weather permitting, I hope to have a chance to try out what Derek Warner has suggested.

Will keep you posted.

Still stumped, as usual.

Ian
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OMK

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Re: Puffer Wiggle
« Reply #24 on: August 29, 2009, 09:49:59 AM »

Well, that's about as far as my fault-finding knowledge with this particular teaser goes. Sorry I couldn't be of any help.
Keep posting though. Hopefully you will get there in the end. I for one would love to know what the cause of the problem could be.

Hope your weather stays better than ours.
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