Hello.
How long will a DT-750 last underwater in salt water? Wouldent it short out and burn? Is this something you reccomand me to use?
Will "potting" the copper windings be a smart move to make it work perfect under water? Or anyone got a smart idea to make my rov operate in salt water down to 50 meters ?
Making a thruster from a DT-750
Re: Making a thruster from a DT-750
Toffe, corrosion of bearings, magnets and stator iron more of a concern than the windings shorting out. Where the windings connect to the 3 wires could possibly be insulated. Running ROV in fresh water after salt use and spraying in some WD40, CRC66 or similar would prolong the motor's life. Either design the ROV so motors can be replaced easily at the water, and have spare motors handy, or go for an oil-filled thruster design. Unless you find some sort of shaft adaptor, this motor is no good for oil-filled because a shaft seal will not work with the threaded shaft. Unfortunate because the DT 750 looks very good as an ROV motor in other respects. In any case, by the time you messed around pulling the motor apart to insulate any exposed joints etc, you could be well on the way to having made an oil-filled thruster. A lathe helps, but is by no means essential.
Ross
Ross
Re: Making a thruster from a DT-750
I'm sorry that I have to ask but how would i build this "oil filled" ? Are there any designs on this? Tips ideas? I'm no "inventer" nor engineer myself. 
Re: Making a thruster from a DT-750
Do not need to be an engineer, but just a little bit inventive. By saying oil-filled I really mean pressure-compensated - that is the term used in the commercial ROV industry. Lots on it on the internet if you search those terms. Briefly though, because this should really be on a new or existing forum topic, I will try to describe.
As far as we ROVers are concerned, oil is incompressible. So by filling your motor housing with oil, thus taking out as much air as possible, the pressure inside stays the same as the pressure outside, irrespective of depth. Considering there will still be a small amount of air inside (difficult to remove all air completely), you need to have some part of your motor housing flexible, so the pressure at depth compresses that rather than the rigid walls of your housing.
So take a bit of PVC or other rigid tube, close off one end with a cap, drill a hole in the cap smaller than the seal for the shaft to stick out. Then securely mount the motor inside the tube, put the seal over the shaft and glue it to the end cap. Drill 3 holes in the tube for the motor wires to go through, and glue these too. Polyurethane glue/sealant works OK. To the open end of the tube you attach some very flexible tubing, use more glue or a hose-clamp, then fill the whole lot with mineral oil, and plug the end of this flexible tube. Put the propeller on and there you have a pressure compensated thruster. That's the general idea at least. Search this forum, openrov or the internet in general to find suitable oil. Make sure that the glue you use is strong enough to hold the seal on when you squeeze the flexible tube a bit. For seals just search shaft seal and the shaft diameter you end up using.
Regarding electrics and oil: Should there be a problem with the motor overheating or arcing (sparks) be aware that most of the oils suitable for this sort of use are flammable and could also even expand and blow out of the enclosure when overheated. Some would say that because the housing is full of oil, with no air, fire is not possible. BUT, should some oil leak out and air get in, the potential for fire, explosion and/or burns is present. Use common sense, and work in a tidy fire-resistant workshop, not in an office or indoor space. Oil can be a bit messy anyway.
Hope that gets you started.
Ross
As far as we ROVers are concerned, oil is incompressible. So by filling your motor housing with oil, thus taking out as much air as possible, the pressure inside stays the same as the pressure outside, irrespective of depth. Considering there will still be a small amount of air inside (difficult to remove all air completely), you need to have some part of your motor housing flexible, so the pressure at depth compresses that rather than the rigid walls of your housing.
So take a bit of PVC or other rigid tube, close off one end with a cap, drill a hole in the cap smaller than the seal for the shaft to stick out. Then securely mount the motor inside the tube, put the seal over the shaft and glue it to the end cap. Drill 3 holes in the tube for the motor wires to go through, and glue these too. Polyurethane glue/sealant works OK. To the open end of the tube you attach some very flexible tubing, use more glue or a hose-clamp, then fill the whole lot with mineral oil, and plug the end of this flexible tube. Put the propeller on and there you have a pressure compensated thruster. That's the general idea at least. Search this forum, openrov or the internet in general to find suitable oil. Make sure that the glue you use is strong enough to hold the seal on when you squeeze the flexible tube a bit. For seals just search shaft seal and the shaft diameter you end up using.
Regarding electrics and oil: Should there be a problem with the motor overheating or arcing (sparks) be aware that most of the oils suitable for this sort of use are flammable and could also even expand and blow out of the enclosure when overheated. Some would say that because the housing is full of oil, with no air, fire is not possible. BUT, should some oil leak out and air get in, the potential for fire, explosion and/or burns is present. Use common sense, and work in a tidy fire-resistant workshop, not in an office or indoor space. Oil can be a bit messy anyway.
Hope that gets you started.
Ross
Re: Making a thruster from a DT-750
Slightly more ...... engineered
But a similar concept to the above, below.
http://martin-wareham.blogspot.co.uk/
Martin
But a similar concept to the above, below.
http://martin-wareham.blogspot.co.uk/
Martin
Re: Making a thruster from a DT-750
Love that design on that link, but where do he get that kinda parts to make it? That is my main problem, i could make a lot but there is no parts other than PP pipes easily accessable.
It looks like his parts were made for just that thing?
It looks like his parts were made for just that thing?
Re: Making a thruster from a DT-750
Martin makes those parts himself and operates a commercial business - read his blog and website. Martin - very impressive work overall. I was thinking about making motor controllers myself that would be more suited than than hobby ESCs I'm using now. Impressed.
Toffe, what I suggested earlier is accessible to anyone. You need a cordless drill, a vice (vise), some drill bits and basic hand tools such as hacksaw, files, screwdrivers, pliers, sandpaper etc. I don't know what pipe fittings are available in your country, but here PVC is very common. Be careful using other plastics because some such as PE and PP cannot be glued easily (too "slippery")
Toffe, what I suggested earlier is accessible to anyone. You need a cordless drill, a vice (vise), some drill bits and basic hand tools such as hacksaw, files, screwdrivers, pliers, sandpaper etc. I don't know what pipe fittings are available in your country, but here PVC is very common. Be careful using other plastics because some such as PE and PP cannot be glued easily (too "slippery")
Re: Making a thruster from a DT-750
I've got replacement shafts for the DT-750 making it a fully 4mm shaft instead of threaded. I cant find any shaft seals for 4mm shafts online anywhere? I mean how will it work? Got any links for me?
Re: Making a thruster from a DT-750
Well done! I'll trade you for information on the shaft adapters please Can you supply a link or other description?
Seals: http://modelluboot.de/Zubehoer/Dichtungen.html#WDR
Actually, I got some 4mm shaft seals from a bearing supplier in the UK. Just had a look for the paperwork but cannot find it, and can't remember their name.
Earlier I mentioned drilling 3 holes in the side of the rigid tube to bring the motor wires through. Solder on solid copper wire (=not stranded) first so what goes through the holes is solid, and put sealant around that. If you were to use stranded, oil will leak out between the strands. Put a cable tie around the tube and wires to stop them bending back and forth and snapping off or breaking the sealant.
Can you supply a link or other description?Seals: http://modelluboot.de/Zubehoer/Dichtungen.html#WDR
Actually, I got some 4mm shaft seals from a bearing supplier in the UK. Just had a look for the paperwork but cannot find it, and can't remember their name.
Earlier I mentioned drilling 3 holes in the side of the rigid tube to bring the motor wires through. Solder on solid copper wire (=not stranded) first so what goes through the holes is solid, and put sealant around that. If you were to use stranded, oil will leak out between the strands. Put a cable tie around the tube and wires to stop them bending back and forth and snapping off or breaking the sealant.
Last edited by rossrov on Jun 22nd, 2013, 4:20 pm, edited 1 time in total.
Re: Making a thruster from a DT-750
Last edited by rossrov on Jul 3rd, 2013, 5:12 am, edited 1 time in total.