Installing New WTC

[Parallax]

I purchased a new WTC from R&R Model Engineering last year, and its finally time to install this guy. It is a 500x80mm pump unit. It will be going into my 1/96 Thor's Permit. I would very much like to get this guy running before the SubComEast meet on Oct. 20th, but I am running into a few issues I could really use some advice on.


1. How to index and secure the cylinder into the boat. The subdriver I had before used an index pin to locate the wtc, and then I used Velcro straps to hold it in place. The index pin is not an option for this WTC. I was thinking about epoxying a pin in the rear WTC cap, and modifying the bulkhead at the rear that they would index into. Then in the front drill a shallow hole into the foward cap, and install a bulkhead that I could slide a retaining pin through into the forward cap hole. However this WTC is a veryyy tight fit and I don't know if I have enough room to add a bulkhead. (I will also need to trim the existing saddles to an 80mm inner diamter to fit in).




2. The exit points for the servo pushrods are very high in the WTC and use 1/16" rods so I am concerned about both flexing as well as how to fit into such a small space.

3. The output shaft does not have an index to add a universal joint or dogbone set up, and also it is going to be very close to the existing rear bulkhead. So I need to figure out how to connect the output to the prop shaft.


And this is just the mechanical side! I need to get rolling on the electronics as well

On a fun note, the old dogbone interface and collar had been installed with regular metal grub screws so they were completely rusted on. Yours truly got the brilliant idea after stripping out the heads, that he would use a torch to get them off while the shaft was still on the boat. Disaster was narrowly avoided when I realized that was a really stupid idea right as the torch got to work. Luckily the prop was held in with a stainless grub screw so I was able to take the prop off, and then remove the shaft and get the old parts off.

[JWLaRue]

Mike,

I would remove the rear bulkhead entirely. In it's place put either a small bulkhead or a pin in front of the dive module. This would provide something for the module to 'push' against while moving forward. If you only use a rear bulkhead, the module would likely creep forward resulting in the dog bone separating and the stern planes being out of adjustment.

-Jeff

p.s. drop me a line if you'd like to get together before the 20th to work on your boat.

[Ralph --- SSBN 598]

I have never used pins to hold the wtc in place.

I do make plastic blocks that are glued in to the hull on the keel line.
1 goes in front and 1 goes behind the wtc once I fine the location I want.
The blocks are usually about 1/4" wide, 3/4" long and tall enough to get 1/4" on to the end caps.
The front block has a slight taper to it to push the wtc tiht against the back block.

Lift the wtc cylinder up at either end by 1/4" and the wtc is free to move in either direction.
No holes drilled in to the wtc or caps for pins.
Wtc held down with velcro strap mid cylinder.

I have never had a cylinder rotate in my boat but if it did, I would add 2 blocks to the front end cap to index the hull block.
Takes me about 10 minutes to shape and glue the blocks in place.

[salmon]

As you are seeing there are many ways to skin a cat (as horrible as the saying is [I like cats]), looking at what you have, All the above suggestions work. I have David Merriman's Sub-Driver, but I also have Big Dave's, Will Oudmayer's, and my own WTC (there are other's but that is not important).
Looking at your picture, there is something dark.

Is that attached to the bulkhead?
If so, you have a built in pin, build a wall on each side to prevent rotating.
If you still need a pin, the rear bulkhead could have a small hole that does not go deep, but can accept a 1/16" pin from the bulkhead already there. The removal process would be lift the front over the small block you need to install and pull the cylinder forward, disengaging the small pin. Does that make sense, never sure if I am being clear as mud or not.
Peace,
Tom

[subdude]

Mike,

Tom has it nailed. The "dark thing" sticking out is the water inlet to the pump. Put a small, low bulkhead right behind the cylinder, with a notch in for that inlet tube to rest in to prevent the cyl from rotating. Take a look at the build article for the R&R Seawolf conversion in the June issue, it's quite clear there. Add another small restraint as Ralph has described in the front of the cyl and job done!

[Parallax]

Thank you everyone for all of the quick responses,
Jeff I am taking all of the advice and got started last night, by taking out the old bulkhead, clearing out a lot of the old stuff that no longer serves a purpose. I'll def drop you a line asap to set up a time to meet. I just ordered a bunch of new electronics for the WTC, so I should prob plan for after they arrive.

Ralph I like the small bulkhead idea, so I am going to do that with a Velcro strap. Tom I was worried that the plastic inlet might be to weak to use as an index, but it sounds like Jim has had no problem with it so I'll use that.
Jim thank you so much for the build guide. That makes life on this so much easier, I wish I had read it sooner! And I would have never realized about cutting the lead on the second speed control.

The only real issues are that my WTC did not come with the Drive shaft coupling, and I need to fashion a similar bulkhead set up for the dive planes. I am hesitating to replace the bulkhead that has the forward bearing for the shaft, for alignment reasons, but it prob needs to go as I need the space for the dogbone set up and dive plane assembly.

I trimmed the existing saddles down, so now the cylinder fits very nicely in the hull (even if a bit tight bow to stern). I will add the velcro strap to the center, and I will need to relocate the weights up front to add the small bulkhead.


I also carved out the sail so I can fit the air inlet.


The battery that came with the WTC is an odd 95 mm form factor for a 7.4v ni-mh battery but I wanted to get another one with more then 1600 mah. An 11v is a problem as I looked up the specs on the motor and it nearly doubles its rpm to 12000.

[Ralph --- SSBN 598]

Regarding the motor rpm.

With all but 1 boat, I have to adjust the output at the Tx to slow the rpm down.
My Tx setting is down to 30% for 3 boats and down to 20% for 1 boat.
This allows me to use most of the movement on the Tx stick.
Still this is too fast and I run my boats at about 1/4 throttle and less.
It is noice to have the extra speed to get out of trouble on occasion.

I find it easier to adjust at the Tx than at the motor in the cylinder.
--------------
3 of my boats use 12v batteries.
The speed controllers steps down the voltage and are used to power the Rx.
No wires from batteries directly to Rx.

I learned this the hard way.
I had 2 speed controllers in the boat.
Main motor and ballast motor.
And I had a direct wire from the battery.
Well this produces a lot of problems.
TOo many battery supplied wires.
I was told to disconnect all but the main motor Rx whic feeds the Rx with power.
All my issues went away.

[Parallax]

Hi Ralph,
Have you ever had any problems with motors being damaged from running at the very low end of their rpm range? I had always thought that if the motor is running at close to the stall speed you could cause a lot of heat damage to it, as well as forcing the electrical system to run at a higher amp to overcome stall? I'm not remotely an expert on electrical so if it I can adjust with just the TX that is great news.

Also anyone have suggestions on what type of plastic to use for the new bulkheads? I have a lot of acrylic lying around but my gut tells me that is to brittle to use.

[bob_eissler]

I'd stick with 7.4 v since that is what came with the wtc. Ought to be able to find a suitable battery on Amazon or Hobbyking. Subs don't work hard enough at slow speeds to cause damage to the motor. Acrylic, plexiglas or built up epoxy will work for bulkheads. Just scuff up the acrylic and add some drill holes for the epoxy to get a good grip on.

[Ralph --- SSBN 598]

I am not at all an RC electronics guy.
I listen to those who know aqbout such things.

About motors and stall rpm.
I have used motors that turned out to be high rpm types and did have problems getting them to run slowly.
I had motors that I could program down to 20% which was still too fsat.
THen I trimmed the Tx down to 30% then down to 20%.
This helped but still I only had about 1/4 throttle before the motor was too fast.

After buying an ENgel's Akula II I learned about piston ballast systems and I learned abuot Endel's motor and speed controller for submarines.
I still have to program the Tx down to about 30% but I Can watch the propeller turn at slow speed.
I see no cogging at all. I can count the revoutions of the propeller.
I have been using this motor and speed control in my subs.
Even rebuild electronics tray to accomidate this parts.

I have 2 other boats which do not have the piston or Engel's motor/speed controller.
These are small boats and I use very small motor with an attached gear box which if I remember correctly are about 6:1 gear boxes.
This keeps the motor rmp in mid range and the propeller turning slowly.

I have not experienced hot motors or speed controllers.

The motors I use now.
I will have to look to see if they are the 300 or 400 type.
I will get that info tomorrow when in the shop.
Happen to have one of those motors on the work bench project now.

https://engel-modellbau.eu/shop/en/Electric-Motors/E-Motors-Brushless/

I also use the use the Sub Commander ESC.
But there athers that will do as well.
I have a couple of those on the work bench as well.
Don't know the maker or model but I am sure I can get that info off the parts.

[JWLaRue]

Have you ever had any problems with motors being damaged from running at the very low end of their rpm range? I had always thought that if the motor is running at close to the stall speed you could cause a lot of heat damage to it, as well as forcing the electrical system to run at a higher amp to overcome stall? I'm not remotely an expert on electrical so if it I can adjust with just the TX that is great news.

Mike,

Running a motor very slowly (low RPM) won't hurt at all. This is not the same as stalling, which would be the condition if the motor armature was prevented from rotating while current is being applied.

Also, don't over-think the need to adjust the transmitter end point for the ESC. At least not at this point. Let's first see how the boat runs at various throttle levels and then, if necessary, look at making an adjustment.

Also anyone have suggestions on what type of plastic to use for the new bulkheads? I have a lot of acrylic lying around but my gut tells me that is to brittle to use.

Acrylic will be fine. There is not going to be a lot of stress placed on the forward bulkhead and virtually none on the aft one.

-Jeff

[Ralph --- SSBN 598]

The motors I have in 3 boats is the Engel's
C35-30-300 brushless

1/72 Skipjack.
1/96 Akula II
and now the 1/72 Gato turning 2 propellers with 1 motor and a 3 gear gear box.
Gear box is 1 in and 2 out at a 1 to 1 ratio.