Hi All,
I am sure that many of you have heard of the OpenROV Project which involves building your own ROV from a kit. I am an experienced model builder with plenty of experience and a reasonably equipped workshop, but I was a little taken aback at the complexity of assembling the OpenROV from their kit of parts. It seemed to me to be a high school to college level project requiring a small team of experienced modelers to successfully put the OpenROV together though I could be wrong.
It appeared to me that there were a number of critical assembly requirements that had to be performed spot on as there was no going back to realign or reseal once the assembly was completed. Therefore I have been looking around to see if there might be an easier way to design and build a ROV similar to the OpenROV without having to perform some of the critical assemblies required to complete the OpenROV.
One area of the OpenROV design that I took exception to was the thrusters. They were not going to last very long when immersed in seawater due to the exposed bearings and stator/armature. To me this was a kind of deal breaker as to the questionable lifespan of these thrusters. I know that commercial thrusters are not cheap (think Seabotics or CrustCrawler) and the OpenROV project was just trying to overcome the high price of commercial thrusters with their homebrew design. Still the unknown lifespan of the OpenROV design did not leave me with a warm feeling to say the least.
Then came along Blue Robotics and their T100 Thruster KickStarter Project Link. Their design approach looks good and they have actually tested and characterized prototypes of the thrusters they will deliver to the pledgers. With the addition of the in-thruster water cooled ESC this design becomes very attractive in that it reduces the number of wire penetrations in the Water Tight Compartment (WTC).
Great! Now we have a source of reasonably priced thrusters so what is next? Well, that is where you, the ArduBoat members, come in.
Let's start thinking about the WTC, navigation controller, communication, power, ballast, buoyancy, etc. and attempt to come up with a reasonably priced ROV that the average ArduBoat member might want to consider building.
Regards,
TCIII AVD
Replies
Tom,
Okay. Sounds good.
Thanks for sharing the ROV-Suite link. I haven't seen that one before.
-Rusty
Tom,
It is great to use excess pieces, but be careful to have any open end sealed in the epoxy. If you don't the water will leak in under pressure. Using a heat shrink tubing which has adhesive applied on the inside makes a better seal, but still should have the inboard end sealed in the epoxy.
A comment on cables. Over the years we have found that cables for ROV's should have an outer jacket of polyurethane, rubber, or polyethylene. We found that PVC jacketed cables have micropores that are formed when the jacket is extruded over the cable. We have had many instances, where the water has got in through these micropores and hosed right up the cable, ruining it. I have 100's of feet of PVC jacketed RG59 for video that have all failed by this mechanism.
Ken
@Ken,
Thanks for the insights, much appreciated.
The end of the cable jacket in the cable penetrator counter bore is sealed with CA that is cured with Kicker. Then both the exterior counter bore and interior shaft (WTC side) of the cable penetrator are sealed with marine grade epoxy.
The jacket of the Thruster power cable is a very thick urethane (1/32" thick?) that is very dense and will definitely not degrade.
Regards,
Tom C AVD
Hi All,
I spent most of today completing the routing of the Thruster power and control cables.
It turned out that I needed 3/8" dia cable clamps, which I was fresh out of, to position the power and control cables to the ROV chassis so I was off to my local Home Depot. While I was there I also purchased #6 x 1/2" ss button head sheet metal screws to attach the cable clamps to the chassis.
Once I had routed and clamped the cables into position to my satisfaction, I adjusted each cable for a little slack and marked it with my trusty Sharpie marker where it entered its respective hole in the 10 hole End Cap. I then pulled each cable out and made sure that the marked length of both the right and left horizontal Thruster power and control cables were close to the same as the wiring route for each horizontal Thruster is the same. I then did the same for the and right and left vertical Thruster power and control cables. Once I was satisfied that the power and control cable marked lengths were virtually the same, I began planning how I would remove each Thruster and pot each Thruster's power and control cables in its respective cable penetrator.
More to come.
Regards,
Tom C AVD
Hi All,
Today I attached a 10 hole End Cap to the rear of each WTC and then mounted the two WTCs in their Support Cradles in the ROV Chassis.
I then proceeded to determine the best routing of the Thruster power and control cables that would minimize any interference with water flow through the Thrusters.
The first picture below shows the 10 hole End Caps in their respective WTCs mounted in the ROV Chassis:
WTCs with10 hole End Caps
The next picture shows a mockup of a Thruster power and control cable mounting scheme:
Mockup of WTC End Caps with Thruster Power and Control Cables
The final picture in this group shows the Thruster cable routing from the top of the ROV Chassis:
Top View of Thruster Cable routing
I am trying to keep the Thruster power and control cable routing from becoming a rats nest in the rear of the ROV Chassis. Where there is wire holding up the cables, I will use cable clamps to route and retain the cables in the positions shown in the pictures. I will also add additional cable ties to help confine and route the cables away from the Thruster water flow.
Since this is my first cut at routing the Thruster cables, I am open to suggestions if anyone can spot any obvious flaws in my cable routing scheme. I plan to have long cable pigtails inside the WTCs to allow the battery and navigational trays to be removed from the front ends of the WTCs.
More to come.
Regards,
Tom C AVD
Hi All,
Today I completed the assembly of the four WTC End Caps. Two of the End Caps have no penetrator holes and will be mounted on the front of the WTCs while two of the End Caps have 10 penetrator holes each for the Thruster ESC power and, control cables, and auxiliary power and instrumentation cables. The End Caps with the penetrator holes also have Enclosure Vent Plugs installed to vent trapped air when the End Caps are inserted in the ends of the WTCs and to equalize the pressure in the WTC with the atmosphere when an End Cap needs to be removed. The Blue Robotics WTC assembly document can be found here.
The End Caps consist of a clear Acrylic Plate (with or without cable penetrator holes) that is attached to an O ring Flange which will be inserted into the ends of the WTCs. The Acrylic Plate is attached to the O ring Flange with six M3 x 16 ss machine screws and compresses an O ring, which is mounted in a groove in the face of the O ring Flange, for a watertight seal.
After assembly of the End Caps I installed an Enclosure Vent Plug in each of the 10 hole End Caps. The Enclosure Vent Plug is much like a Cable Penetrator except that it has a dual O ring screw in sealing plug where the Penetrator cable would normally be inserted.
I then temporarily attached the two cable penetrators, that I had previously potted with a 1 meter 6 mm dia power cable and a 1 meter 3.5 dia control cable, to one of the 10 hole End Caps to get an idea of how the Cable Penetrator spacing would look like.
Shown below are a plain solid Acrylic End Cap, a 10 hole End Cap with the Enclosure Vent Plug attached, and finally a 10 hole End Cap with the Enclosure Vent Plug, and the two Cable Penetrators installed:
Forward End Cap with solid Acrylic Plate
Tomorrow I will remount the WTCs in their respective Support Cradles on the ROV chassis Main Cross Brace/WTC support so that I can determine the correct power and control cable lengths for the ESCs. The ESC power cables will go to the rear End Cap on the lower WTC (battery compartment) while the ESC control cables will go to the rear End Cap on the upper WTC (navigation controller compartment). I will also determine the correct length for the power and instrumentation cables that go from the the battery compartment WTC to the navigation controller compartment WTC.
More to come.
Regards,
Tom C AVD
To pressure test the housing for leaks, I recommend you use something like this:
http://www.harborfreight.com/brake-bleeder-and-vacuum-pump-kit-6932...
Hi bigkahuna,
I bought one of the vacuum pumps, that was in your link, today at Harbor Freight.
Since I have a couple of spare blank cable penetrators, I plan to bore out the center of the blank cable penetrator to a diameter that will accommodate one of the adaptors included with the pump and epoxy the adaptor in place in the penetrator.
Then I will run a vacuum check of the battery WTC with the End Plates in place but without the battery tray as I am sure that it will outgas a fair amount and I will spend a long time pumping the WTC down to a stable vacuum.
Regards,
Tom C AVD
Hi bigkahuna,
Thanks for the link, much appreciated.
I will have to take a look at that pressure/vacuum tester.
The price seems right and the local Harbor Freight is only a couple of miles from where I live.
Regards,
Tom C AVD
Tom, What type of epoxy did you use. Nice progress.
Regards,
David R. Boulanger
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