Hi all,
This is my first new tread and it is a build log for my Academy 1/150th scale U-581 (it is a U-Boat Type VIIC). It is an old motorized toy sub that I have converted into an RC sub. I have see a few other people post their threads for it but none had very detailed instructions, I hope to fix that.

First we have the model: It is a motorized 1/150th scale U-Boat Type VIIC (U-581) it can be found in a few places on the net for around $20 (nice and cheap). it is 18inches long with a beam of not quite 2 inches. While simple, it is still a model kit and comes with lots of detail.
it comes with a motor which I replaced with a nearly identical brushed 370 (at 7.4V a little too much power). It already has a rectangular WTC with a gasket that works surprisingly well as long as you get it aligned right.

I used Gorilla Glue to attach two micro servos near the front, this gave me maximum room to bend the push rods as needed. I glued them in a groove on the underside of the upper deck, depending on when the model was maide yours may not have this, Ive seen a few different types. Attaching everything to the top deck worked pretty well.

Below is the initial lay out with a small aircraft ESC (no reverse unfortunately), radio, and NiMH Battery. Motor is also test fitted.

Here you see I have changed the layout, the radio now sits on top of the ESC and the battery now occupies the last third of the WTC. Te motor has been installed and the stuffing box filled with White Lithium Grease. The stuffing box and gasket are part of the kit, it is empty according to the instructions but by drilling a tiny hole in the side of the sub, I was able to use a syringe to fill it and allow for servicing later. The White Lithium Grease also does not appear to harm the plastic.

Now the push rods, I replicated the seals from the instructions for my Dumas Bluefish. Brass push rod with brass tube sleeve glued (or you can solder) on passes through another brass tube lined with White Lithium Grease, and a piece of silicone fuel tubing on the outside end (added later). The size of the engine compartment keeps them out of the way.

I've cut down the arm on the aft dive plane to keep the attachment inside the hull. I've also attached a servo arm to the top of the rudder with a screw (be sure to grease the rudder so it works well.

*Pleas note* Do not glue the aft portion of the deck on yet, it makes things harder, I wound up removing mine al the way up to pool-trials.

With the controls complete it is time to add the engine compartment.

I threaded the cord from the ESC to the motor through a pre-existing hole for the toy version, please note, the engine compartment is open to the WTC. and as you can see I have glued the two together permanently sealing the engine compartment, make sure your done in there. ***DO NOT use Duco cement for this it does not work on this plastic, use regular Model Glue***

Here it is ready for the bathtub test.
She worked great, everything ran but she needed a lot of counterweight later to balance. She took on water in the engine compartment because I used Duco cement instead of model glue and I only discovered that after going to town with the silicone, lots of re-doing, grrr.

The included gasket for the WTC worked well but needed some trimming to keep it away from the push rods and lined up correctly.

I prepared for the test and added a lot of counterweight to get the deck awash. New seal around the engine compartment looks good in the tub. I switched to a Lithium battery as the old NiMH batt I had didn't want to work.

Took it for a test run in the pool before adding the details and paint. First run went well but took on water after a few minutes because the gasket was not seated right. Fixed and tried again, turning is poor (I will adjust the rudder later) went more than fast enough at 1/5th throttle. With that aircraft motor and the silicone tube shaft coupler that was included, any more would damage it. But that's okay, I still had all the power I needed and more.
Handling was significantly better under water, but I had trouble maintaining depth at first. It went nose up and down a few times but I recovered. Seems it takes very little movement to control, on top of that, this kit was designed to dive anyway so the non-moving bow planes are already set slightly down, this means that, if balanced like mine, at cruse speed it will dive by itself and you will actually have to pull up some!

All said, it was a great success, I'm going to make a few adjustments to improve the turning and seals and then fill out the details, whole thing only took about a week.

I posted a video of the second test run on Youtube, sorry for the quality, I forgot to change the resolution on the camera:

Successful Test of RC Submarine (5 min 7 sec)