A Skipjack in Ireland

[The Boattrainman]

Hi Guys,

I'm open to correction on this but I think the Engel Uni-pro that drives the Piston Tank has a depth control function (using the 'hall' effect it counts the number of revolutions of one of the cogs).

Also, and this may be a biggie, as Dave pointed out I may be light on volume of the Tank at 500ml (by Dave's calcs I'm short 200ish ml), so this may end up as a partial 'dynamic' diver, flood to conning tower/mast level and drive down under the waves, so depth control my be moot. To be honest, I dunno..............

It'll have to wait till the Tank arrives.


Rob

[He Who Shall Not Be Named]

Hi Guys,

I'm open to correction on this but I think the Engel Uni-pro that drives the Piston Tank has a depth control function (using the 'hall' effect it counts the number of revolutions of one of the cogs).

Also, and this may be a biggie, as Dave pointed out I may be light on volume of the Tank at 500ml (by Dave's calcs I'm short 200ish ml), so this may end up as a partial 'dynamic' diver, flood to conning tower/mast level and drive down under the waves, so depth control my be moot. To be honest, I dunno..............

It'll have to wait till the Tank arrives.


Rob

Don't confuse 'hovering' (deliberate adjustment of ballast water weight to seek the 'ideal' neutral buoyant condition) with 'depth control'. Depth control is either achieved with bow/sail-planes or changing the angle-of-attack of the hull to water flow -- the classic Lake/Holland means of ascending or descending; both means require movement of the vehicle through the fluid.

So, you may not have enough ballast tank for scale operation on the surface. In this case your boat, in surface trim, will have a waterline higher than scale. No biggie. Once you flood-down, you'll be golden. Get the boat near neutral and achieve depth control with either the stern or the sail planes. I prefer to let the angle-keeper do its job of keeping the hull level, and to work the sail-planes for depth control.

Review this video as I explain how I do it.

https://www.youtube.com/results?search_query=city+lake%2C+merriman%2C+skipjack

David

[The Boattrainman]

Roger that David, I'll def look at that option.

Rob

[The Boattrainman]

Final version of schematics as per David's suggestion.




The Boattrainman

[The Boattrainman]

Last picture of the On/Off switch linkage inside the hull (upside down) under the opening hatch.




The Boattrainman

[The Boattrainman]

I replaced the nuts with these 3mm knurled ones on the rods.



The ones at the servo and motor end are glued to the rods (making them 3mm long bolts).





At the forward end, the rods are cut so that they come to the end of the knurled nuts when under maximum compression so I don't have to keep figuring out is the WTC fully sealed. The knurled nuts were a real bargain at less than 2 Euros for 20, and free postage from Hong Kong!

Up next is the Piston Tank from Engel which will arrive this week.

The Boattrainman

[The Boattrainman]

The 500ml Piston Tank is exactly as per the dimensions on the Engel site, so my paper template was accurate.

It came from Engel beautifully packaged and at 175 Euros seems good value to me, it's nicely engineered from good quality components.




The space on the tech rack for the tank is cut using a slitting disc in a mini-drill within the marked lines, initially it looks like it's done with an axe.




The steel wires are now inserted through the entire WTC to add strength, 2mm sides added and a slot for the tank outlet cut.




The tank is trial fitted, the slight overhang of the motor will be useful.




It all fits snugly into the WTC.




The Boattrainman

[The Boattrainman]

This aluminium fitting is made to go under the piston tank motor and also acts to keep the tank centered and in in place.




The Piston Tank is fired up to test the spindle fitting which runs through the holes in the styrene box over the battery.





The forward end of the tank sits up to the drive motor housing with the outlet in it's slot.





A single piece of 3.2mm styrene acts as a top bearer, Engel don't recommend you glue anything to the tank in case the glue/epoxy warps the plastic, so the bearer is held in place with double sided tape. The bearer presses against the upper inside of the WTC, and helps keep an air gap around the motor so it doesn't touch the WTC.

.


This 2mm rod inserted in the WTC shows the cooling gap between motor and WTC.




The tank can't move in any direction as it's compressed on all sides inside the WTC.




That's the tank sorted, there's a lot of cleaning up of the styrene to do, but it fitted without any major problems.


The Boattrainman

[The Boattrainman]

The beauty of this system is that once you pull the tech rack out.......................






........the piston tank clear just lifts off.




The Boattrainman

[He Who Shall Not Be Named]

I normally don't post unless I have something other than praise to put forth. But, I must say: what a well crafted and thought out WTC arrangement you've come up with. I have yet to see a major false move on your part. Your mastery of technique and ahead-thinking planning makes you a most formidable model-builder, sir. I look forward to each post.

David

[greenman407]

Yes, Excellent work, very inspirational.

[The Boattrainman]

Thanks guys.

The WTC build is counter intuitive in that initially you would assume the biggest 'lump' is the Piston Tank and it should be sorted first, and the rest of the electronics built around the installation.

However, there is no room for variations given the limited size of the space, and as the PT is the known quantity thanks to the dimensions on the Engel website (all Engel PTs regardless of capacity are 75mm in diameter), it stands to reason that the spaces for the servos, ESC etc. have to be sorted first. These electronics can be sized to fit the spaces available, micro servos, mini ESC. Also, there was no point acquiring the PT unless the WTC itself can withstand the internal pressure of the compression when it is filled with water.

Finally, if I had done the PT first, I would have to work with a very flimsy tech rack, given most of the centre is removed to fit the thing. I would almost certainly have broken it drilling and sanding the various openings.

Rob

[The Boattrainman]

The sides of the WTC where the tank sits is reinforced with small pieces of brass sheet between the steel rods and plastic sides.





They hold the plastic tight to the steel rods as gluing these together would be hard.




I can position the Main Switch now the PT and the PT switch unit position is fixed. I had to cut the Main Switch housing down a bit and re-site the indicator LED to the front.




The rod to the On/Off switch exits through a small hole to keep it from moving outside the WTC.




The Boattrainman

[Greevesman]

Agreed! A master model maker!

[The Boattrainman]

Sorting out 12V power distribution involves installing a fuse and holder and simple connectors. I'm contradicting myself here as I previously stated that I'm not a fan of fuses in a model sub, but I'll give this one a shot.

A U-shaped piece of styrene is used as a keeper plate, it glues to the side of the main switch housing.




A set of four connectors will distribute positive (+) power using 20 Amp single core jumper wires, they are screwed up tight to the fuse holder to keep it in place against the keeper plate. Wiring between the main switch, fuse and connectors will be mostly hidden but still accessible.




The small tab I left near the piston tank motor holds two connectors that will distribute the negative (-) power.




It's easier to see the fuse holder setting in this shot, no screws or glue needed to keep it in place.





The Boattrainman