porpoising problems

[greenman407]

Thanks for posting Steve. Do

Thanks for posting Steve. Do you run with Subtek mixer and apc?And if so do I understand you to say that it has only happened once? Mine has done it the last time, every time since I got it. I think I am ready to call subtek and tell them about it. I can already tell you what he's going to say.

[greenman407]

I called Mikes subworks and

I called Mikes subworks and told them again about the jittering problem and they agreed to send me another one at no charge. Cool! I will install the new mixer in place of the old one and note the results. Itll probably take a couple of weeks. Ill fill you all in at that time. Thanks

[greenman407]

Re: porpoising problems

Alot has happened since my last post , what three years? Anyway the porpoising problem became manageable as I said but recently it got alot worse. After talking with Dave Merriman and Kevin Mcleod it dawned on me. I put the waterproffed servo and bow planes and mechanism in the bow of the boat and I think it pushed it over the edge. The balance point is 3 and 1/2" ahead of the center of the sub, Im going to move it back one inch and see what happens.

[petn7]

Re: porpoising problems

I suffer from similar porpoising problems as well. It's been my observation that more sensitive pitch control and faster servos help deal with the problem, although a better trimmed and balanced submarine would probably be more effective. I'm actually about to swap out a 0.23 second (per 60 degree arc) servo with a 0.09 second (per 60 degree arc) servo. I expect drastic improvements, but who knows.

Keep us updated.

[pirate]

Re: porpoising problems

Greenman,
I was dealing with a jitter problem with my SubTech APC-4 on my Ohio recently too. I tried all kinds of suggestions from grounding wires to insulating servos to gear noise. Then by accident I found the problem. While having the WTC apart I was holding the motor out of the hull looking at it while running and the twitching stopped, Then I dropped it onto the hull by accident between the servo tray and the edge, and it made a huge buzzing sound from vibrating against the two surfaces. The APC servo when hay wire. As soon as I removed the motor the APC servo was fine again.

This led me to the conclusion that the problem was vibration, and the APC was so sensitive that it reacted to the slightest vibration. By insulating my servo tray from the WTC tube by placing styrofoam between any surfaces that touched, and doing the same between the outside of the WTC tube and its supports in the hull, the jitters have gone away.

Hopefully this helps.

Pete

[greenman407]

Re: porpoising problems

Wow! Now there might be something to that! I wonder about mounting the apc on a small piece of styro and see what happens. That should probably be my next move. Thanks!

[greenman407]

Re: porpoising problems

Right now the APC is mounted on a dab of silicone to the servo tray. The silicone itself is rubbery so you would think that ,that would be enough to dampen vibration although the stuff is rather firm when it dries. Perhaps wrapping it first in shrink wrap loosly sized and then foam and then silicone? Some one famous said that neccesity is the mother of invention.

[greenman407]

Re: porpoising problems

Ok, last night I cut some small pieces of foam the size of the APCs and siliconed them down first then siliconed the APCs on top of them. This morning early I got up and tested them and saw no difference at all. I think that I will go by homedepot tonight and see if they sell small rubber washers and install them under the thumb screws that hold the servo tray to the motor bulkheads and see if that will help.

[greenman407]

Re: porpoising problems

Ok , I tried to isolate the servo tray from the motorized endcap by using rubber washers but it still did it. I mounted the APCs on blue foam and then on a foam reciever wrap made to cussion RXs. Still no good. So where are we at? I have three WTCs. I have three pitch controlers. They all show a lot of jittering when you run the motors and thus the gear boxes. Its possible that it will have little or no effect on the sub since the movements are fast and symetrical. In other words the planes will move offcenter to the right and then immediately move back to center and then to the left and return , all in a split second. I dont like it but ......... If the APC was mounted in the front compartment of the 3" WTC that might do it. But to do that I would need a small dia. 10 conductor wire to go through the small conduit. If the motors and drives were in there own WTC by themselves, that might do it.

[pirate]

Re: porpoising problems

Greenman,
I'd say from your recent experiments the vibration cause is probably ruled out. Mine was immediately noticeable. If you were to separate the APC from the tray, as I separated my motor from the tray when mine noticeably stopped twitching, and run the motor then, that would give you a solid answer to whether vibration is the cause or not. You may waste a lot of time and frustration moving the thing all around when you don't have to.

[thor]

Re: porpoising problems

Are the gears in your reduction metal?

[greenman407]

Re: porpoising problems

No , the gears are nylon or some kind of plastic. If you take the APC and hold it slightly above the servo tray but dont let it touch it works fine. But once it touches the foam or the rubber it begins again

[greenman407]

Re: porpoising problems

I love it when a plan comes together! Monday I took her to my sub pond( well its not really mine, you know what I mean). By moving the CG back 1 inch it rides beautifully at all speeds. It could probably stand to go back a little more but I found out what I wanted to know. The reason I say that is, if you just blast on the throttle it will still porpoise badly, but if you start out smooth and easy and increase throttle in a controlled manner it will behave itself which tells me that the APC is doing its job. However once the oscilations start they just get worse. You have to back off on the throttle till they stop and then ease into it again. The Duo-prop retrofit will add a lot more weight in the rear so I will address this issue again at that time and maybe move the CG a little bit more then. As far as the glitching of the planes controlled by the APC , on the work bench it still does it. The next thing that I want to check is , does it do it in the water? Perhaps the water absorbs some of the vibrations and maybe it doesnt do it when its in the water. Either way it doesnt seem to matter to the submarine because its riding just fine. Perhaps I could use the dry space in the front of the 3" WTC for the APC only and put all the other stuff in back and see if that will solve it. Perhaps I will make up two 3 cell NIMH batts.( wired for 7.2 volts) and mount them on the floor of the sub right under the ballast tank, that way I wouldnt have to try to cram sooo many wires thru the conduit that runs from the front dry space to the back one. Possibly........possibly.......