Progress on The Sir Frankie Crisp.....in LOCKDOWN!!! (cont'd)

[Ben Brigham]

Hi coryhenry,
You know, that's a damn good idea. The evolution of the sub's guts left this WTC at the center of the bulkhead, with less and less inside it over time. Once I got the two Sub10 ESCs which are immersible, I shortened the WTC down to being only able to fit the one servo. But in all this redesigning, the "legacy" WTC had more to do with what it was mounted to and what was mounted to it rather than keeping stuff dry, which is a pretty silly reason to have a WTC. I should find a find a way to just seal, or "pot," the one servo. Might free up some critical space in the process. Thanks for the excellent suggestion!

[Ben Brigham]

Okay, after the day in the testing tank, I generated a to-do list. Yes, it was a long list.


“Overall Too Heavy” and “Statically Unstable (in Pitch)”:
Still working on this task but I made good progress. In a way, the two issues are related, and ought to both be solved with more buoyant foam placed high in the bow & stern, and less weight forward. It may be necessary to add a little weight low in the aft compartment but we’ll see how it goes.



I sectioned off the last area in the bow with cardboard & plastic, & poured some “mix & pour” foam into it. The “after” picture is sort of deceivingly tidy. In reality the process looked more like this:


What happened is that I had mixed proportions expecting the chemistry to behave more or less the way it had before. But over time (let's say months) the reactivity understandably goes down. My previous experience with an older batch caused me to overmix the new batch, So yeah, that was fun.
Still have the aft foam section to do. Hopefully this will address the pitching-aft problem.


The "overall heavy" won't be as messy to address. I bought a set of stubbier & lighter 12v lead acid batteries. Each of them about half as heavy as the regular size. My thought is to put a stubby one in the very front (there are two slots for batteries) and a regular size one behind it. So that'd be a savings of 2 lbs, and far forward, so I'm feeling good about that solution. If it still needs lightening and/or if the sub still pitches forward too much then I can just use two stubbies.

"WTC Leak":


The lesson here is to always stick with the same WTC source, because not all manufacturers will make the exact same tube, and not all WTC bulkheads will be the same either. Simply ordering a "WTC3.5" will be no guarantee the bulkhead will fit, nor will the O-ring necessarily match either. I had muscled the old bulkhead into a newer tube and it seemed to work fine for a while, but it popped when I wasn't looking and flooded the dry space once in the water. Fortunately by that time the only thing left in the dry space was one servo.
Then (here) on the SCR Forums, CoryHenry recommended simply "waterproofing" the servo and do away with the WTC entirely. In all my experience I'd never heard of doing such a thing. I knew it worked with some battery designs, but a servo? And as luck would have it, Bob Martin had a video covering the procedure. Seems to work perfectly so far.



Farewell, old bulkhead. May your notorious TC-85 stink live on forever

So now I have a slimmer design, the servo now lives on the ballast tank side of the bulkhead. No need to 'linearize' the pushrod movement to get through a waterproof housing. So much less to worry about!

"Valve Spring Too Weak":
This is probably going to require some trial'n'error tinkering. The ballast tank drain valve wasn't quite sealing perfectly. It was aligned fine, just not burly enough I guess.


So I installed a spring that's double the number of coils, presumably for double the sealability. We'll see what happens there.

"Aft Drains Too Slow":
The free-flooded area aft didn't have almost any functional limber holes, as it turns out. I'm such a moron. The ones I had originally drilled got covered by the motor dry space, and I'd never gotten around to drilling new ones. So I knocked that job out in an afternoon. Again, Bob Martin had a useful video on the procedure which I more or less followed. Hot-glue proved to be the perfect lay-up material in my case, holding the brass guides in place while lifting up cleanly afterwards.



"Thrust Reversed"
I must've flipped the polarity to those motors back & forth about six times! during this whole build. Once it was in the water, sure enough, forward was reverse and vice versa. Embarrassing but an easy fix.

So there's one final mix & pour foam session remaining to do, and then I'll be able to try everything out in the apartment's submarine testing tank a second time. Stay tuned. I'll post a video like last time.

[Ben Brigham]

By the way, I've got plenty of that mix & pour foam left over. If anybody's in the Los Angeles area and is interested in grabbing it, just let me know.
It's the Fibre Glast 2-pound chemistry. Yours free, fcfs.

BB

[Ben Brigham]

Since my last posting I’d gone through a long laundry list of fixes & adjustments to make. The testing tank at the apartment has been really convenient! I can’t believe how many people waste this valuable resource just to swim. What a freak show.



Checking a couple things off the list: Aft limber-hole problem: fixed. Speed-reversal problem: fixed. And by the way, these motors are strong! I haven’t gotten to the point of testing this thing for speed, but I already know I’ll have to go easy on the throttle especially in turns. I don’t want to rip the stern planes off.

In addressing the overall heavy-and-pitch-unstable problem, the combination of battery size reduction (one of the two) and adding foam sections fore and aft did the trick. I have close to ideal freeboard height and it sits nice & trim now. It took a couple of tries though. I was amazed at how sensitive the pitch (backwards) problem could be initiated. During the second tank test it was still consistently resting back on its butt.

https://youtu.be/HiPnY8h2_hk

I estimated that the volume of a typical soda can’s worth of foam (~360cc) would be enough, and it seems to have worked perfectly. “Just stick a can of foam up its ass”; words to live by.







The ballast system still isn’t really cooperating. Some solutions have worked great (waterproofing the servo) other things are suffering from my poor judgment calls (excessive servo throw) and a new issue arose with the seal of the ballast tank roof screw-down cap.

Mid-way through the second tank test, the ballast servo went ‘graunk!’ and stopped responding entirely. Whatever it was sounded mechanical in nature. The servo disc (‘don’t-call-it-a-WTC’) is still in the hull so I haven’t figured it out for certain, but I think it’s my fault. Wait, of COURSE it’s my fault.
The servo’s task is to pull back against the force of the drain valve spring AND the water pressure keeping the valve seated. And I wanted lots of volume going through that bigass valve so I made the servo’s throw range quite large. The servo also pushes against the resistance of three Schrader valves to release propel into the tank, a force that’s also considerable and therefore the throw should be small. The servo is, or was, able to do both these things, at least for a while. But I think I was asking too much of it. Something may have jammed or bound up, and it was too much for the little servo. I’ve got the servo going though maximum distance with minimum strength, and that’s frankly the opposite of what I should do. So I’ll move the pushrod closer to the servo arm’s pivot and tune the whole system better next time I get the chance.

The screw-down cap, it turns out, is disgracefully leaky. The cap & threaded top is from a large kimchee jar, the plastic being a bit soft and not an ideal material but spatially is wide enough for access needs. Now that I’ve installed the acrylic dome piece into this jar-cap relationship, the seal between these three pieces isn’t quite right. Half the time I get it sealed, half the time not at all. So I’m going to rearrange the gaskets & try to put in a thin reinforcement ring to help get that area sealed properly.
The valve itself needs a little improvement too. While the spring strength now appears fine, the rubber gasket does an iffy job of sealing the valve when closed. So I’m going to try a thicker, spongier type of rubber.

https://youtu.be/tuBfI51RUxU

The cool part of using the cap of a kimchee jar was that I just screwed the whole drain valve assembly onto another, identical jar and tested the valve separately in the testing tank. Yay modularity! I should’ve run this kind of test months ago.

Will update as I learn more...

[salmon]

I have found, if you take a long time to post (I am a horrible typer) the links to the images will fail (timeout maybe?) - if you edit the post and re-add your images it works.

[Ben Brigham]

Hi Tom,

Yeah, thanks. I'd gotten hip to that. This seems to be something a little different.
I normally compose all the text in MS Word, then copy-paste it down into the field here and very quickly drop in the images & links. This was the case for the above post, and everything looked great.
Then the next day all the images had died.
So I figured I must have just not noticed or something so I re-posted the whole thing again, quickly adding in the pics and links. Everything looked great. I re-opened the thread a second time just to be safe and everything still looked great, all images were visible. Looked perfect.
Then the next day all the images had died again.
The images are no larger than previous ones, so I don't know what's going on. Have I hit some data limit?