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porpoising problems

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porpoising problems

Postby greenman407 » Mon Dec 03, 2007 2:31 pm

at scale speeds or under my albacore operates at periscope depth ok, a little sensative but ok. if you run any faster it porpoises up and down. the faster you go the worse it gets.you cant keep it from broaching or turning on its nose and heading straight down. could it be that the apc is set too sensative or not sensative enough? or perhaps there is another problem? with the dave merriman wtc-3 theres plenty of power to make this thing rip, but as you see i cant use it. :cry: any takers? thanks mark
Image p.s. did i mention that it is an x-tail?
There are OLD pilots and there are BOLD pilots but there are very few OLD BOLD pilots. MAG
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Postby Chuck Chesney » Tue Dec 04, 2007 9:17 pm

I've been hesitant to offer a comment on your question, since I have zero experience with an X-tail craft, but under almost any other set of circumstnces I would say that you have way too much sensitivity with your control surfaces. The boat is over controlling by a huge margin.
You might try setting the pushrods from the servos to a lower setting so that the control surfaces have less throw to them. If that dosen't help, the APC may be set too sensitive also.
The sub should respond more like a ship and less like an F/A-18.
Chuck

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porpoisig albacore

Postby greenman407 » Tue Dec 04, 2007 10:55 pm

thanks chuck,im going to continue playing with the adjustment of my apc. thanks :)
There are OLD pilots and there are BOLD pilots but there are very few OLD BOLD pilots. MAG
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Postby Davy » Wed Dec 05, 2007 5:09 am

Yes , sounds like too much sensitivity in the APC unit.

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APC control

Postby Mike Dory » Wed Dec 05, 2007 2:01 pm

Mark, Your problem is not unknown of, when it comes to X tails, they are faster to react then a conventional stern arrangment. On your APC you will find a set of 3 female plugs side by side with a jumper wire connecting one set together. Pull the jumper, and move it to the next set of female plugs. (If I recall correctly this was the ones closest to the outside edge of the plastic cover) this should reduce your sensicivity. Should you have continued problems with your APC or the X tail in your boat in general, Get in touch with Skip Asay he designed and built both the APC and Albaore your using. Your not going to find anyone with more knowledge. on the subject matter. The Last time I saw Skip he was still sailing his Albaore. That's a fine looking photo of your boat underwater. Best Wishes, Mike Dory
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albacore porpoising

Postby greenman407 » Wed Dec 05, 2007 9:31 pm

davy, thanks for replying. im going to have to adjust it and try it, adjust it and try it until i get it right. thanks mark
There are OLD pilots and there are BOLD pilots but there are very few OLD BOLD pilots. MAG
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Postby greenman407 » Wed Dec 05, 2007 9:39 pm

mike dory, thanks, actually my apc comes from atomic subs and it has a potentiometer that you adjust. i have adjusted it in the past and found that it had no effect but i think its probably a matter of small adjustments and observe the results as it is very sensitive. thanks :o
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Postby JWLaRue » Wed Dec 05, 2007 10:24 pm

Mark,

....maybe try removing the pitch controller and seeing how the boat behaves....?

-Jeff
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Postby greenman407 » Wed Dec 05, 2007 10:36 pm

now thats an idea. that will be interesting
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Postby aeroengineer1 » Thu Dec 06, 2007 12:39 am

It sounds like there are a few potential problems. Here they are in the order that I would check them in. The first is the sensitivity of the APC. It operates as the multiplier of the signal, and if it gets too high, then it could cause the system to go unstable. The next one could be the speed of the servos. Another big one could be the location of the center of gravity of the boat out of the water. The problem might be that the boat is generally unstable, and the APC is able to make it artificially stable at low speeds, but cannot stabilize it at higher rates of divergence. In this case it might be appropriate to increase the sensitivity of the APC and the servo rate, but it would probably be better to move the cg forward and reballast the boat. You also might want to check that the APC is mounted in the proper plane. If it were cocked to one side, it might be sensing side to side movement and then applying a correction for that, which translates to movement in a different plane.


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Postby Sub culture » Thu Dec 06, 2007 7:03 am

On a side note, recent experiments have shown that electronic x-tail mixers and levellers can sometimes react in strange ways.

My recent experiments with a GWS V-tail mixer and one of my levellers showed that under certain circumstances, the servo movements can become 'bitty' or 'grainy'. I think this may be something to do with pulse timing, both units are using microcontrollers to modify the incoming pulse from the receiver, but it's an interesting phenomenon.

Norbert Bruggen now sells a small leveller designed purposely for x-tail submarines, as it has a built in mixer. Seems elegant and straightforward.

More information here.

(scroll to bottom of page- in German only I'm afraid)

Andy
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Want to dive your boat in crystal clear water? Then you had better Dive-in- http://www.diveintomodelsubmarines.co.uk
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porpoising

Postby greenman407 » Thu Dec 06, 2007 11:03 pm

thanks gents for your suggestions. i will consider everyone of them. as a side note ive always had trouble with a constant jitter of the x-tail. i feel that this is a result of the apc and the mixer fighting it out for control of the sub. this may be an indicater of a hidden lack of cooperation between these two units. in other words they are not working well together. so a few changes are in order. thanks p.s. kinda funny aint it
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Postby greenman407 » Sat Dec 22, 2007 6:24 pm

News flash!!!! An X-tail albacore without an APC is not an option. Today I took it to the lake hoping that setting up various exponential settings on my computer radio would make the difference. It doesnt make any difference. Up , Down , Up , down. Im not going to win the navigation award at Carmel this way. But putting it back in provides another problem.I will post a new topic on it. It will be under the heading computer radio APC mixing problems
There are OLD pilots and there are BOLD pilots but there are very few OLD BOLD pilots. MAG
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Postby greenman407 » Mon Dec 24, 2007 1:27 pm

Good day gents, today I returned to the lake with Albacore in hand.I am so pleased!!!! :D It could not have run better!!! :lol: What I did was to take Skip Asays advice and reinstall the Subtek mixer with a matching Subtek APC. They do work better together without a doubt. I run my subs at a lake that has a shore that is long and straight.Since it is spring fed it is relatively clear. After settling in I set it at a reasonable speed and brought it down to periscope depth. After a couple of adjustments it ran just under the surface for about 150 yards without broaching once! Very very good. I then got brave and increased the speed and was pleasantly surprised that it still continued to track well.It started to move up and down just slightly but the APC was able to keep up with it.I was still at about half throttle and was having to walk fast to keep up with it.This Albacore with a Dave Merriman WTC in it is unbelievably fast. Next time I go I will go even faster until I discover its limits. However back to the problem at hand. The porpoising is gone but the jittering of the planes and the rudders are back. However it doesnt seem to cause any handling problems. Next step is to buy another mixer and see if that solves it. The hardest thing in the world is trying to operate an X-Tail and walk and take video at the same time.Especially with rudder servos reversed.
There are OLD pilots and there are BOLD pilots but there are very few OLD BOLD pilots. MAG
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Albacore Porpoises

Postby Steve Jensen » Thu Dec 27, 2007 6:03 pm

I had the same issues with my Albacore at the last Fun Run of the year;it was very frustrating.

I put it on the shelf in my shop, and it has not done it since.

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