Page 4 of 14
Re: My "MINIRAY" Rov.
Posted: Jan 18th, 2015, 12:44 pm
by olegodo
Yes, I also remember you could also fit a "anti siphon tube" inside the tank that would help prevent the liquid co2 coming out and in to the paintball gun.
But I would really rather use compressed air tanks over co2 for this.
Re: My "MINIRAY" Rov.
Posted: Jan 19th, 2015, 3:11 am
by bigbadbob
Good call on the expansion tank steve.
I'll look into it.
My cylinders are disposable so I couldn't put an anti syphon tube in unless i went with re-fillable bottle. and if i went that route i'd use nitrogen as i have a plentiful supply, as far as I know nitrogen doesnt suffer the same freezing problem.
Goog suggestions guys. cheers for the input.
Re: My "MINIRAY" Rov.
Posted: Jan 19th, 2015, 10:01 am
by bigbadbob
I've been having a good think about my oposing piston tank, here's the theory....
On the surface- the pistons are fully out at either end of the cylinder, pressure in the hull is 0psig and pressure in the tank between the pistons is 0psig. and of course water pressure is 0psig.
(psig= pressure referenced to air pressure)
To dive- I pull a slight vaccuum in the tank (this pressurises the hull slightly) just enough to get the pistons moving inwards towards each other and draw in enough water to reduce the displacement of the ROV, which will start to sink.
As it sinks, the water pressure increases and the tank pressure increases accordingly, the air in the tank will compess slightly and allow the pistons to move further in which decreases the displacement further until I reach my design depth of 10m/33ft.
Water pressure is then 14.7psig, tank pressure is also 14.7psig as the pistons move to balance the pressures.
Hull pressure is a few psig.
When i want to surface, I pump air from the hull into the tank enough to raise it's pressure above 14.7psig, the pistons move out and displace water from the cylinder so the rov starts to rise.
My intended pump has a maximum pressure of 1 bar or 14.7psi above hull pressure so my depth is limited to 10m by the pump.
This may turn out to be a bit deeper depending on how much air i have to pump into the hull to get the ROV to dive and how much i have to pump back into the tank to get it to rise.
So... That's the theory, now to build it and see what really happens in practice.
Comments welcome, even if just to say don't be so stupid, it'll never fly.
![Laughing :lol:](./images/smilies/icon_lol.gif)
Re: My "MINIRAY" Rov.
Posted: Jan 21st, 2015, 4:35 pm
by bigbadbob
I found a regulator today that should suit my needs-
Looks like i'll be able to change the outlet fitting and remove/blank off the gauge and knob to lighten things up.
I've allready made an adapter for 60g bottle to this regulators 16g threads. although i have some 16g bottles which hold 8 litres of co2 which should be enough for a dive.
This way i can go deeper by pressurising the hull at depths> 10m and also have an emergency surfacing system.
I may need a relief valve to blow off excessive hull pressure as I surface.
I'd better not come up too quick or MiniRay might get the bends.
![Laughing :lol:](./images/smilies/icon_lol.gif)
Re: My "MINIRAY" Rov.
Posted: Jan 21st, 2015, 5:38 pm
by a_shorething
ha ha. Explosive decompression!!!
You'll be surfacing like one of those nuclear subs that practically come out of the water when they come up!
![Smile :)](./images/smilies/icon_e_smile.gif)
Re: My "MINIRAY" Rov.
Posted: Jan 22nd, 2015, 7:11 am
by bigbadbob
The more i think about combining the two systems, the more it makes sense.
If I have the co2 or N2 bottle and regulator slung under the vehicle and a pressure relief valve in the hull I can keep the hull pressure say 1 bar above seawater pressure at all times.
As well as keeping water out, this 1 bar will also assist the pump for surfacing from depth.
I'm getting impatient waiting for parts to arrive in the post now.
Hopefully the pump won't need solenoid valves as I'm short of space in the hull.
Putting the pressure relief valve in the lowest point of the hull will also mean I can purge any water that does creep in just by blowing a bit of ballast.
Or even have the leak sensor hooked up to the pump to blow automatically.
![Very Happy :D](./images/smilies/icon_e_biggrin.gif)
Re: My "MINIRAY" Rov.
Posted: Jan 28th, 2015, 1:31 pm
by bigbadbob
Well... I made the two cylinders, 4 pistons etc and got the pump...
The pump turned out to be a one way diaphragm type and not capable of overcoming the friction of the pistons and if i make the pistons any looser they leak....
So.. back to the drawing board, maybe a bigger pump or more likely a re-think.
Got to move house again so it'll have to wait. boo hoo.
Re: My "MINIRAY" Rov.
Posted: Oct 4th, 2016, 5:30 pm
by bigbadbob
Well... two house moves later and I finally have a garage, a shed, a new lathe and a play room. yay!
The Mrs got a new prosthetic so was getting around better but was then told her cancer is back, in her lungs this time.
As you can imagine, I havn't had much time for ROV building but have given up on variable ballast and got another 19w pond pump to run as a vertical thruster using a 50mm Robbe prop.
I cut a 36mm hole vertically down through my hull and cemented in a piece of 32mm bore, solvent weld, ABS waste pipe so it's sealed the hull again. I've mounted the pond pump motor in there and will run the cable in through a gland.
Soon be time for more pressure testing when life allows.
I'll finish it one day.
Re: My "MINIRAY" Rov.
Posted: Oct 15th, 2016, 6:05 pm
by bigbadbob
And it works!!!!!!!
the MiniRay Mk2 has done it's first dive to the bottom of a barrell.
Vertical thruster works well with temporary ballast hanging off the bottom, will make something more permanent soon.
Compass displays fine on the HUD (head up display) and I can initiate a compass calibration using a cheap IR remote control.
Leak sensor also displays on the HUD.
Ignore the HUD code I posted above, it doesn't work, pm me if you want the code to program a minim osd to display gy26 compass etc.
![Image](http://i88.photobucket.com/albums/k180/bigbadbob76/ROV_mk2_zpschpjbjny.jpg)
Re: My "MINIRAY" Rov.
Posted: Oct 23rd, 2016, 6:13 am
by bigbadbob
I've now added a depth sensor which displays on the HUD. that took a bit of code fiddling but I got there in the end.
I'm an electronics engineer not a software engineer so I get a bit lost in code sometimes but it's a good feeling whe you stop swearing and start cheering.
update.... My rov saw it's first fish today!!!!!!
it survived a 12ft dip in the sea without leaking, and was going good until it's battery went flat.
Note to self- order new batteries. reckon i'll get away with 18v for the 12v thrusters, by the time the volts drop over the umbilical it won't be far off 12v anyway.