is the thruster really waterproof

No, but it isn't designed to be. Just flush the motors with fresh water after a dive to keep them from corroding. Even if the motors only survive a few dives, they are so cheap to essentially be disposable.

I've been working on a ROV myself with similar 3D printed thrusters using ~$7 quadcopter motors, and if I get 2 - 3 dives per motor, I'm fine with that.

Hello!, I'm building an ASV in Argentina and using a couple of T100 thruster. Looking for a mounting I found you on thingiverse.

What a wanderfull work!!!!!

I'm wondering how much thrust do your thruster get. Could it more thrust that original T100?

That's so cool! Can I ask you what  are your considerations for choosing the BNO055 IMU? I'm doing an autonomous boat but I'm struggling to choose the right IMU and I really need some suggestions :D https://hackaday.io/project/10652-green-powered-sailboat 

Sorry - I missed your question when you asked it. I choose the BNO055 because it did all the fiddly calibration and math to convert the various physical sensors into roll, pitch and yaw. I could have written (stolen) that code myself, but it was nice to pay a few extra bucks and have something else worry about it.

Those sound good. I worry about how long they last in salt water which is why I'm being a cheapskate.

Cool project Tim. I'm interested in doing something similar based on an Actobotics cube frame like yours. Do you think the motors will need gear reduction?   

I chose motors with low kV, which means (apparently) that you get less RPMs and more torque per volt applied. I would go lower than I have, but these ones were low enough and dirt cheap. Of course I have yet to run this thing through a set of proper propulsion tests so I've yet to see who good - or not - a choice these are.

Well the price is right for those motors for sure. I did find some 400kV brushless motors on hobby king for about $40 each. I might try those if these ones don't work out. I'll send you a link to my project page once it has some content. Cheers

You can heat shrink the DC motor then pot it with a 3M potting to prevent it from corroding in salt water. The down side is the DC motor may overheat.

I am really curious how the brushless motors will hold up to saltwater. I would expect the bearings, cores, and shafts to have problems with corrosion.

I'm curious too. I'm thrown very cheap motors on this thing, so it's a cost/time-to-failure tradeoff. I've also considered a few things to paint the motors with which might improve them, but I want to see how things fail before I put stainless steel bearings at this.

Perhaps you could use a rotary seal? This can be a dedicated part or an appropriately sized well greased O-ring. 

Here are some examples below:

http://www.embedded.com/print/4014240

http://www.homebuiltrovs.com/stingerthrusters.html

Usually, the coating on the windings get abraded by sea water and sediment and short circuit. If this doesn't kill the motor then corrosion of the bearings and or shafts will do it in. As Tim said, the cost/time-to-failure consideration is very important here. 

That's interesting, I would have expected the corrosion of the cores to be more of a problem. Now if the problem is just with abrasion, perhaps this can be fixed by keeping sediment out of the windings by adding a small cover for the motors. Or even pot the windings in epoxy.

The bearings could be replaced with corrosion resistant plastic bearings or even just a plastic bushing. It shouldn't be too hard to replace the shaft with something more corrosion resistant. 

The cores could also be an issue now that I think of it. For a motor with an aluminum core, the replacement time would be on the order of weeks if not months. Taking an educated guess, the biggest danger of a badly corroded core is spreading corrosion. This will be one of the things I will experiment with as I have access to the ocean and I can set up some test cells with some aluminum disks to test the corrosion rates for aluminum of that scale. 

Potting in epoxy seems to be the most popular way to go about doing it. Lowers the MTBF of these motors in sea water. Bushings, plastic bearings, or even stainless bearings could also be used to help control corrosion. 

Shaft corrosion is likely not be such a big deal as the bearings and windings. I took it into consideration because it is in direct contact with the bearings and could possibly spread corrosion to the surrounding areas. 

I avoided POE because the cables are substantially heavier and less flexible (more cores). Also, I'm measuring ~6 ohms on my cable, which would still drop 8A with 48V. Might work with lower AWG cables.

Hi Tim,

I am hopefully going to be building one of these soon and am going to try out a power line network adapter for getting the data back up.

I believe this may solve the problem of having a high speed connection to the rov over Ethernet as well as being able to supply the rov with plentiful amounts of power to run any systems you want without a major compromise.  I highly doubt adding a power line converter will weigh more than the battery packs you remove and the cable should be equal in weight to that of a cat5e cable per meter.

I may also attempt using flexible fiber optics with a power main as i have the equipment and it couldn't hurt to try. 

what do you think?

Hi tim,

I have been looking into a few of the home plug adapters. I even found one that has two ethernet ports on one end, and one on the other. This configuration would be perfectly suited for my application and actually cut the number of wires on the tether in half or even by 4. http://www.amazon.com/TP-LINK-TL-PA4026-KIT-Powerline-Starter/dp/B010Q29KRK/ref=pd_sim_147_3?ie=UTF8&dpID=31c2eAWH75L&dpSrc=sims&preST=_AC_UL160_SR160,160_&refRID=08P7ZDW1FYRFQJ8XJADM

I need the pair of cables for an IP camera, as using one of those is cheaper and easier to pan/tilt. I also require one for the Arduino that runs this entire mess of wires and lights, all of this all has to be done in a tight space and no ethernet switch is even small enough to fit. I believe this model should be hackable, but potentially harder to hack. This pair also communicates far faster than I need them too so updates to a full HD Video streaming system is possible in the future. 

As an Aside, I have just created a Hackaday page for the Luna I project which can be found at https://hackaday.io/project/9523-luna-i-rov

-MrCullDog

Why not Power-over-ethernet? With ~48V you do not have too much loss in the transmission.

I explored POE as an easy solution to the issue of getting power down, However, The power level required for even 3 thrusters is almost 60 amps at 11v. There is no way to transmit this much power down over POE. I plan to scale this design up to a much larger ROV which could require power measured in kW. In this case. A transformer to step the voltage down from a high voltage to a lower voltage and a AC-DC converter to manage the conversion to usable power is the way to go. The issue with this is that it simply isn't practical for small ROVs. I believe that Lipo batteries are the best way to run the ROV. Although I am open to new solutions to this problem. 

@MrCullDog

So basically you could just charge the batteries slowly over PoE and extend the range. Your average power consumption will be less than 660W. At least you can power the electronics, even if the batteries are down.

In really big ROVs the go the other way with the transformers: They step the voltage up for the transmission. To about 1kV for the electronics supply and about 3kV/3Ph for the 100kW Main motor which drives the hydraulics. The whole cable is several cm thick and terminates in the transformer box. I don't know if they have a battery for the electronics. The motor is mains only.

You could still use a high voltage approach, possibly with an 1:1 isolation transformer from the mains, a rectifier - even with power factor correction, if you want and go down with ~350VDC. Assuming 230V mains, but half of it (USA mains) is probably sufficient. So you save the AC/PFC section of a switch mode converter in your ROV.

@Martin I have heard of 3kV 2 or 3-Phase 400hz AC at low current being used as the supply for most ROV systems. I believe that you can get large scale generators to supply exactly that. Using mains voltage is an option its the equipment required up top and on the ROV are likely slightly bulky for what I am attempting to build ( I will explore my options with that). In fact, It may actually be quite easy to run both mains voltage and ethernet with the Home-plug interface. For the scaled up design, I will design HV circuitry to deliver the correct power to the Motors and electronics. I don't know that this vehicle will ever be built. But it has been interesting to design it and has helped with design decisions on the smaller vehicle.  

At this point. Lipo Batteries seem to be the best thing to use. In the future It will be possible to add POE/mains To run at least the electronics in the event of a power loss. This way I should be able to locate it and retrieve it fairly easily. 

@MrCullDog: I don' know, if I would call 3*11A exactly "low current" :-) But that was for sure a mains frequency 3Ph motor, powering the hydraulic pump. In that case the power came probably from the generators in the support ship. You do not need or want 400Hz there (losses in 5km transmission cable and the motor itself). 400Hz are often in use in aircraft for lighter transformers and for high speed motors (>3000rpm), but a hydraulic pump normally is not made for that high speed.

Of course there are many different designs.

Perhaps it is possible to use the PoE approach with a higher DC  voltage. The ETH-magnetics are often rated for 1500VAC for 1 min. I would expect them to take 200 or 300VDC common mode voltage for longer time. But I dont know, how much current they can take.

@Martin

 http://www.deeptechoilservices.com/pdf/Quantum_9.pdf This document details some of the superficial details of an ROV used in the real world. Surprisingly, It uses "normal" 3-Phase power at somewhere around 380V @ 475kva. I honestly have no clue now that I look again where I got the number 3kv @ 400hz ( Will do more research) Potentially, they are using that to power topside equipment which converts it to usable power. The reason for this confusion may be that technical details for these machines are very difficult to nail down, as they are often proprietary and protected under NDA's and special agreements. Although ~300v over POE like circuitry sounds risky,  I will experiment with the limits of CAT-5e cabling and POE cabling as removing the pair of batteries from the ROV would certainly be a nice thing to do. 

Hi tim,

 I have yet to assemble my own ROV. I am in the phase of gathering parts and finalizing designs at the moment and plan to release some initial documentation this week with everything going open source once the project is fully underway. I will send a link when I have it ready. 

A few things to note about the beads, they are particularly suited for buoyancy (They use Syntactic Foam on the professional ROVs), I don't know much about the sealing properties, but it could possibly work for sealing connectors. For the enclosure itself, Oil compensation is the way to go for deep diving, as oil is non compressible and will prevent the electronics tube from collapsing well above the rated pressure of your tube. The benefit of this it that there is no pressure differential between the inside and outside, so long as you can keep the oil from leaking out (This can be challenging) it will stay sealed. The down side, as you probably know, is that all of your electronics get coated in oil which can be very difficult to remove if you need to make a modification. Taking all of this into consideration, oil is likely the best way to implement all of this. 

The thrusters that I am using are 3D printed Kort nozzles that I found at http://svseeker.com/rov_thrurters.htm. They can generate about 4 pounds of thrust each, but are substantially more expensive than what you have implemented. If you don't have access to a 3D printer the cost is substantially higher.

As for the manipulator, It will very likely be the first to go in the depth test. Professional ROV's use hydraulics to move the joints. But on an ROV this scale, Implementing Hydraulics is not practical. And thus loosing one or two servos is much preferred to having to build a hydraulics system. The servos may continue operating even while flooded with water, But I wouldn't count on this as the inside could begin to corrode and potentially even short as well. I have been thinking about using stepper motors for this as they are brushless motors. However they require more code and are heavy when compared to servos, they also consume much more power, but have greater gripping/lifting force. As always, more research into ROV manipulators is required. 

The only area that I have been struggling with is the tether. Actual neutrally buoyant cable is incredibly expensive to buy and Ethernet cable doesn't really float. So I am really not sure what to use to send signals down and back.

-MrCullDog

For tether, check out the work the OpenROV folks did to get the Homeplug adaptor working - this is what I'm using for comms to the surface (ethernet over 2 small gauge wires). I had originally planned to send power down the tether too (it can live on the same pair of wires as the comms) but I'd have to use too high a voltage or too large gauge wire to make this practical. The OpenROV folks also sell neutrally buoyant kevlar tether (http://store.openrov.com/collections/experimental/products/neutrally-buoyant-tether) but it's rather costly ($5 a meter).

I think, the time the servos will continue to operate when flooded is to be measured in seconds. And "water resistant" servos do not mean in any sense of the word "pressure resistant". So I think the only way to go is to fill them also with oil. At least gears like some lubrication :-) Electrical brushes not so much, so probably you have to find - or make- brushless servos, best with hall effect position encoders. About the buoyancy of the cable: Is it possible to fix plastic floaters in regular distance to the cable? Like the egg shaped things used for fishing nets?

Also - do you have a link to your own ROV work?

Hi there,

Thanks so much for your comments - I really appreciate them. I haven't consider the specific depth this craft can go to yet - I've yet to get it into the water and this is definitely prototype-1. I'm going to be very interested in what depth things fail; the manipulator will be the first to go I'm sure.

Thrusters are an area I'm particularly interested in (hence the ridiculous number of them). The short term goal is for the ROV to be "self balancing" - that is, to not roll/pitch while I drive it around. I have a lot of software to develop yet.

The glass beads sound very interesting as an alternative to filling things with oil. So far I've resisted anything that permanent. 

I'd like to start out by saying this is exceptional work! Looks very professional. I do have a few suggestions for you that I have found building my own ROV:

1. Observe the professional ROV's form Woods Hole, Scripps, Oceaneering, Odyssey, etc, and to see how they configure thrusters, manipulators, etc. A good place to start is with this video. Keep in mind that we have the opportunity to try things that they simply cant. So use these as a place to start but try to come up with your own solutions to a problem as well.  http://oceanexplorer.noaa.gov/okeanos/explorations/ex1302/new_rov_video.html

(they show lots of detail about an ROV that costs an unbelievable amount of money) 

2. Syntactic foam is some amazing stuff. It is well worth the money spent. I am not sure of your target depth, but 3M makes the Glass beads that go into it, and you can get 5 lbs for about $50 here: http://www.aircraftspruce.com/catalog/cmpages/bubbles.php?clickkey=10403 It is the K20 series which should be good to somewhere around 1100 ft. This will be mixed with epoxy to create the rigid foam. I plan to test the ratio established on the website soon and will report the results. 

3. As for my own project. It is relatively simple compared to what you are building. It only occupies about a cubic foot of space and has a 3 thruster layout with no manipulator. It has a T-slotted frame so adding a manipulator later is not difficult. The main reason for this is minimizing passthroughs, which can be a massive headache if you discover that one is leaking. As a final aside I am using this connector to attach the ROV to the tether that runs to the surface vessel. This plug actually goes into the hull through a BlueRobotics through-hull connector to allow it to be quickly disconnected/connected on the surface: http://www.amronintl.com/rmg-4-mp-rmg-series-in-line-rubber-molded-connector-4-male-pins-with-18-in-pigtail-of-18-gauge-so-sjoow-aiw-k-cable-for-kmdsi-helmets.html It is low cost and good to 20,000 PSI. 

You are doing a great job with the engineering and layout of this machine. It is very well executed. Keep up the good work!