Scratch built Typhoon advice needed

[Mermod]

Yes I'd love to have a chat with 25yo me about our future back and brain surgeries and point out a large sub might not be ideal in the future :) must be something wrong with me though cause I'm still starting that 66inch Nautilus.

[Subculture]

So many of us have been there with the ‘gotta be a biggun’ desire, some never quit, but most downsize once they realise what a hassle dealing with a big model is.

[Mermod]

I took the plunge yesterday and cut out the big tank I glassed in all those years ago, I'm glad I did as I weighed the sub before and after and it turns out it was 2.2kg! so I think I may have overdone it just a tad :)

I've given up on the piston tanks completely as the cost of re-working them with planetary geared motors and all the work involved was more than I wanted right now so I'm on the hunt for the perfect geared water pump, I can't believe how hard it is to find one that would suit the pressurized system, there are however plenty of diaphragm driven one way pumps, not reversible of course but instead of pumping the water back out could a solenoid be added to let the internal pressure push the water back out?

Thanks' again for all the help.
Phill

[Subculture]

That is essentially how the Eden/Sheerline system works, except they tend to use a centrifugal pump, and the hose is checked by pinching it with a cam controlled by a servo. The same servo is also used to actuate a micro switch which powers the pump when filling the tank. Very simple and inexpensive.

The downside of this system is the tank tends to be large as the system half fills the tank. You also needs to be very diligent with the baffle design to limit sloshing.

[Mermod]

That is essentially how the Eden/Sheerline system works, except they tend to use a centrifugal pump, and the hose is checked by pinching it with a cam controlled by a servo. The same servo is also used to actuate a micro switch which powers the pump when filling the tank. Very simple and inexpensive.

The downside of this system is the tank tends to be large as the system half fills the tank. You also needs to be very diligent with the baffle design to limit sloshing.

That all sounds very cool, I'm seeing a plan come together, a large tank is not problem as I certainly have the room, I'm thinking waterproof junction box in the rear for motors, rear planes and rudder, possibly pump depending on the size of box I find, another box in the bow with servos for bow planes, retracts, bow thruster ESC and stuff and as for battery maybe a big gel cel in the free flood area.

I can go crazy with the baffles as I have plenty of access to acrylic sheet and a laser cutter :)

I would appreciate some guidance/advice on ballast tank size, boat is 1.8m long and weighs 10kg, removable top half weights 2.8kg and the separation is pretty close to the waterline, there is still a section of the top with the rudder area that is permanently attached to the hull that cant be weighed.
I'm hoping a central tank won't cause see sawing but I could be wrong but what size should this tank be? or perhaps two side by side tanks? I don't know and could do with some guidance.

Phill

[Subculture]

Engel Typhoon is about the same size and construction as your boat, that has 1650ml of ballast tank volume split over two 825ml piston tanks. So I'd take that as a ball park and somewhere between there and 2000ml if your laminate is on the chunky side. In general resin rich GRP tends to be around 20% denser than water, but can go higher depending on how glass rich your layup is. Therefore I'd expect your hulls upper half to displace around 2200-2300ml of fresh water, and as the waterline is slightly above the hull break, I'd say that around 2000ml would be about the right, but ultimately an empirical analysis is the only accurate way for a hand laid composite hull.

For 110mm tubing- likely 104mm ID, a tank volume of 4000ml (half filled) gives a tank internal length (less bulkheads) of around 470mm, any baffling inside would have to be additional, making the tank longer still.

Regarding stability, such a long tank part filled is bound to reduce it, baffling will be essential and will help, but can't eliminate it completely. I favour tanks that fill completely with no air bubble. That tends to mean piston tanks, flexible bags, or aspirated fixed tanks.

[Mermod]

All this seems to bring me back to the aspirated tank system, perhaps I should change my thinking, or just go with the sealed tanks just to get moving.

If the long sealed tank will no doubt reduce stability just how much can the APC be relied on to counteract it?

Phill

[Subculture]

If you have Norbert Bruggens book, there's a formula in there which enables you to calculate the reduction in metacentric height for a part filled ballast tank.

I plugged the numbers for your boat, assumed 22kg overall displacement- same as Engel- and would get worse if the boat was lighter. Bear in mind that the metacentric height for a Typhoon would probably be 15mm if you're lucky.

[Subculture]

Having two tanks half the length improves things quite a bit as you can see. Sadly another issue rears its ugly head if the tank is sealed- ensuring equal volume in each for correct longitudinal trim. The R&R twin pump system side steps this issue by locating the snorkel relief in the horizontal baffle, effectively acting as a limit switch for the pump.

[Mermod]

I'm feeling that re-vamping my piston tanks just might be the best way to go despite being aluminium with "O" ring seals, I'm still glad I removed the watertight compartment as it was waaaay to heavily laid up, a new lighter variant looks to be the way to
Subculture I do like your idea of a planetary gearbox for more efficiency than what I currently have and the MFA ones are easily available here in Aus.
I'm a very visual kinda guy and I found this video on youtube which to me looks great, is around the same diameter and runs an MFA arrangement, only problem is I just cant make out the model number on it, would anyone have any ideas which one it might be?

https://www.youtube.com/watch?v=bTo3akHom6I

Thanks once again, Phill.

[Subculture]

Looks like a 919D, probably running on either an 11:1 or 6:1 ratio plus a further single stage reduction of around 3:1. Once again Norbert Bruggens book has a very acceptable formula for calculating wattage and gear ratios for a given piston tank, just basic Newtonian mechanics.

[Subculture]

Assuming your tanks are 70mm diameter like the Engel units, then something like these on the 1726RPM gearing, with an external 3:1 single stage to clear the spindle would do the job.

https://tinyurl.com/288x2mdw

[Mermod]

Assuming your tanks are 70mm diameter like the Engel units, then something like these on the 1726RPM gearing, with an external 3:1 single stage to clear the spindle would do the job.

https://tinyurl.com/288x2mdw

Yep, 73mm ID, those geared units look really nice, I'll get onto ordering them ASAP, I'm guessing the 385 in the description means the motors a mabuchi 385 or similar, do the Engel units run a 385 or a 540?

Also do you have any good links to suitable gears for the final reduction? I think currently my final gear that is attached to the threaded insert is from a Traxxas Emaxx :)

Phill

[Subculture]

I don’t know what pitch the gears are on the Emaxx. Most car gears in the 1/8-10th scale are usually metric pitched and somewhere in the region of 0.7-1 mod in pitch. You can count the teeth and make a measurement of the external gear diameter to find out from charts what the pitch is assuming it isn’t imprinted on the gear itself.

Engel tanks use both 400 and 500 size motors, depending on the tank. Not sure why they mix and match so much, as a 400 size motor is more than sufficient to drive a 70mm piston, as you only need around 30 watts or so for moderate tank filling times.

Your existing gear train looks decent enough though, if the tanks are pulling a lot of current is that because of friction in the drive, too high revving motors or have you got a bit too much compression on your o-rings?

[Mermod]

Good point, I nipped down the workshop and poked at the large E-maxx gear that surrounds the drive nut and I think it's quite free without being loose so I think the o rings ok, I knew a guy that worked at the local hydraulics place and gave him my tubing and asked him to machine the piston and o ring groove to suit, thought it was safer than my basic machining skills :)

The next group of gears is an old electric flight gear drive for mounting on 540 motors, the small brass gear is a 9mm 14tooth that fits on the drive motor, this meshes with a nylon 25mm approx 30tooth this runs the output shaft where I mount the standard 13T rc car pinion for meshing with the previously mentioned e-maxx gear.
The 540 size motor that runs it all is an EM 407, ill quote the chart all at 12v... no load RPM 13000 Amps .470 AT Maximum Efficiency RPM 11,178 Amps 2.883 Stall Torque 1.543 G-CM

Once again thanks for taking the considerable time to look at my project.

Phill