Assembling questions


#1

I am a newbie and just started the assembling of my OpenROV 2.6
I am concerned about the cementing of the endcaps to make sure they can withstand
the water pressure. Since I would have to get it right on the first try and it would be
difficult to seal it should it leak at 100m. In the instruction video it shows that the cable
entry is sealed with hot glue on the outside and with epoxy on the inside. Would it be
better to use epoxy to seal the cable entry on both ends as it flows better than the hot
glue. Any suggestions. tips or tricks on how I can do this right would be greatly appreciated.


#2

The hot glue is only intended to act as a dam to stop the epoxy flowing out the other side and can be removed once the epoxy has set. Just apply a good amount of hot glue around where the wires exit, then fill the whole feed-through with epoxy from the other side. On the opposite end-cap you can use tape to cover the exit and get a nice clean finish (the tape will peel right off the epoxy once set.

Other tips:

  • Epoxy flows much better when warm, if you have a heat gun you can warm it in the tube, and/or once applied to get it to flow into corners and around wire, this will also help get any bubbles out. If the epoxy is starting to go off and becoming to thick to work, you can apply a little heat to get it to flow again.
  • Make sure you apply the recommended amount of acrylic cement at a minimum. If you use too much, the excess will spill out over the edges and will wind up with fingerprint marks on the acrylic but the bond will still be good, if you use too little you will have a poor bond, so if anything err slightly on the side of too much (the pictures in the guide show the perfect amount).
  • When laminating the end-caps, hold the pressure on for at least 30 seconds or clamp it if you can as if you release the pressure too early any slight warp in the acrylic will drive the bond apart and releasing and re-applying pressure will not result in a great bond (tends to draw air/bubbles into the joint).
  • Don’t rush it, do a dry run for each part (you could even use water to get a better feel for how it will work) inject the cement then place it on the bench check the alignment and then apply pressure.
  • You can leave the paper on the sides not being cemented, I found the best way was to leave it only on the side that you will be setting down on the bench, this way you can easily judge the amount of cement and the bottom side is protected from overspill and kept clean.

#3

thanks so much for the detailed info. I had already cemented the endcaps but it did not come
out that perfect with some airpockets. I just held it together by hand, as seen in the video but
I hope it will make a good watertight bond. If I heat up the epoxy, wont this reduce the working
time until it sets? I also have a question about the motors which I had to disassemble and had
to remove the spring loaded lock washer on the shaft. Do I have to put this washer back on the
shaft which would be very difficult, on final assembly, or is the magnetic force enough to keep
the motor and propeller in place


#4

Warming up the epoxy will just make it less viscous, it is a great way to increase the working time and improve results. If you are doing small fiddly jobs where you mix up a small batch, it really helps as you can just re-warm the epoxy any time it has started going off a bit and is to awkward to work with. I almost never use epoxy at room temp anymore.

As I understand it, for the 3 blade props there is no need to re-install the lock washer, but if you have a two bladed vertical prop it does need to be re-installed.


#5

Thanks so much. I have the 2 bladed vertical thrust prop, so I have to remove the motor to
reinsert the lock washer since I don’t have the tool for it and the hole in the acrylic plastic
is too small to reinstall it. How comes the 2 propellers for forward thrust don’t need it? don’t
they also go into reverse which could pull off the motors. What is the best way to protect
against salt water damage. Is WD40 the right treatment since I will use it only in salt water.
A question about the other endcap that has to cables. Should I use hot glue since it can be
removed later to use it to install any additional or replacement wires.


#6

From what I gather the two blade prop produces significantly more thrust than the three blade ones (they changed to this to improve the dive performance) and can pull the bell off the motor if not secured.

Most people around here recommend using silicone lube spray for the bearings, before and after dives.

I wouldn’t consider using hot glue to pot the end-cap feed through, it is not strong enough and wont bond very well to the acrylic in any case. Add some additional wires for flexibility if you like, I have the four for the IMU plus another 4 spare through my end-cap. If you need to down the track you can always just buy another end cap kit, it is a lot cheaper than replacing all the bits that fail if the salt water makes its way into the e-tube.


#7

You are right, the hotglue is not strong enough, I wonder why the other endcap even has
the cable hole and the video shows sealing it with hot glue. Do you know if there is a way
to get audio input, I like to connect a microphone. When soldering the motor wires to the
connector which shows ESC-1 A B C, ESC-2 A B C and ESC-3 A B C, how to I know
which wire coming from the motor is A B or C since they are not labeled as such?


#8

Heat normally reduces the cure time of epoxy. It does also , with at least some epoxies, make it less viscous, but it shortens working time. I also heat up the epoxy as it helps get air bubbles out, both by thinning and by expanding the air bubbles. If you get it too hot though, it can suddenly cure up and form a skin on you. I use a heat gun, which does not heat evenly obviously. :D.


#9

The order of the motor connections doesn’t really matter too much as all it does is change the direction of rotation which can be reversed through the cockpit, but if like me you are a little pedantic, just solder them in any order, test them and if they are rotating in the opposite direction, swap any two leads for that motor and it will also reverse the direction of rotation.

I presume they opted to keep the end caps the same to reduce the number of unique parts in the kit, that way the end cap pieces are interchangeable. I think the instructions are intending to show the hole in the end cap being plugged with hot glue, to be filled with epoxy.


#10

But the motor has 3 wires so how would I know which 2 to swap. or is this a trial and error
type situation. I try to get everything done correctly, so I don’t have to start troubleshooting
any issues. Do you know if there is a way to connect a microphone, I would like to connect
one to record audio with the video if there is a way to do that.


#11

Thank you for your input, I appreciate it. I just ordered a small hot air gun 100F-500F
adjustable, good for heat shrink and also for heating the epoxy. So I could apply the
epoxy from the mixing nozzle directly into the end cap and then use the heat gun to
warm it up to make it flow better and avoid any bubbles.


#12

On brushless motors to change the direction of rotation you have to swap two of the three wires. Which ones you swap doesn’t matter.
For example you have 3 motor wires labelled A, B and C and you have 3 terminals on the ESC labelled 1, 2 and 3.

Connection for rotation clock wise:

A to 1
B to 2
C to 3

Now to make the motor rotate counter clock wise, you have three options of connection:

A to 2
B to 1
C to 3

A to 1
B to 3
C to 2

A to 3
B to 2
C to 1

All three combinations will make the motor turn counter clock wise. In any case, with a three phased brushless motor you can change the direction of rotation by swapping two wires of your choosing. I hope this clears the matter up a bit.

Good luck with the assembly!
Olaf


#13

Also, there’s a setting to reverse any given motor in OpenROV Cockpit. These settings will get saved with your ROV. This makes it so you don’t have to worry about soldering anything after you get the vehicle running.

~Eric