Build Blog for OpenROV #358 (aka "Little Boy Blue") - Post 1


#1


Hello Everyone!

My name is Leslie Bush -- I'm an Industrial Design student at Georgia Tech in Atlanta. I've been following OpenROV since about November 2012 after coming across their campaign page on Kickstarter. I’m happy to say I’ve finally acquired an OpenROV kit, and am absolutely ecstatic to build it. The final result will be on display at the Atlanta Mini Maker Faire in October.

A little about me: as an Industrial Designer/Product Designer, I am involved in the development of mass-produced products -- from raw idea to prototype to assembly line. Industrial Design creates physical solutions to intangible human needs. Just think -- why are people so attracted to the vehicles, robots, and planes? I believe it’s because they expand human potential, as well as satisfy our needs to innovate, inspire, and explore.

One major thing that attracted me to OpenROV is the technological sophistication behind controlling the robot -- piloting it is like something from a sci-fi movie or Japanese anime! Interestingly enough, science fiction plays a major role in influencing real-world technological developments. With collective knowledge from the entire OpenROV community, we have the potential to be apart of a modern robotics revolution.

I plan to blog my experience going through the version 2.4 tutorials, and will capture any successes, failures, or tutorial improvements I have along the way in order to make the build process more accessible for newbies such as myself. Hopefully this will get more citizen explorers excited and ready to build!

Stay tuned for Post 2: Internal Structure Assembly


Leslie


Build Blog for OpenROV #358 (aka "Little Boy Blue") - Post 2
Build Blog for OpenROV #358 (aka "Little Boy Blue") - Post 3
Build Blog for OpenROV #358 (aka "Little Boy Blue") - Post 5
#2

Hello Everyone!

In this post I'm focusing on Step 4: Assembly of the Inner Structure responsible for supporting the thrusters, and Step 5: Assembly of the Acrylic End caps for the e-Chassis. In preparation to work through the video tutorials, I decided to buy all the additional materials I’ll need ahead of time (see http://wiki.openrov.com/index.php/What%27s_in_the_OpenROV_Kit).

Honestly, anytime I've asked for assistance at Home Depot, it's not only wasted my time, but also caused me to lose some faith in humanity. So, I'm compiling a list of brands for products not included in the kit you can ask for specifically & pick up at your local store (Lowes, Ace Hardware, Harbor Freight, etc. may not carry these exact brands). Hopefully your shopping experience will be less psychologically-damaging than mine, heh.

Assembly of the internal structure went swimmingly. Colin's video does a great job of explaining how to use the acrylic cement applicator properly, and takes you step by step through the build process – It's pretty much like snapping legos together.

When going into endcap assembly I forgot to purchase a tabletop vice, so here's how to secure the syringes with tape...

Not the most elegant solution, but it got the job done. Try to secure the syringe with vertical strips of tape so it doesn't wiggle up and down with the direction of your sawing. If you have the money to spare, I’d highly recommend investing in a small tabletop vice, as mentioned in the tutorials. Adding a piece of tape around the 0.13mL line also makes it easier to see where you're sawing, as well as to help keep your cutting square.


I previously used Tap Plastics Acrylic Cement to assemble the inner structure, but ran out and tried to find some more on my shopping trip. It was impossible to find acrylic cement at Home Depot – I ended up going to Hobby Lobby and purchasing Flex-i-File's Touch-N-Flow in the meantime. It claims to work on various plastics including acrylics, so why not. I wasn't expecting such a fast set time with this solvent! I screwed up the first end cap I made. Thank goodness the kit comes with extras.

Something strange happened when gluing the syringe to the end caps: I began to see some very small cracks along the edges of the acrylic (pic isn't the best). I also noticed the same on my OpenROV outer shell. I'm not sure if these superficial cracks could lead to material failures in the long run.


Do any of you guys know what's going on? Let me know in the comments below!


#3

Leslie,

What a great post! It's really cool to see what people are getting from our instructions and what things we may want to add to our next tutorial for assembling 2.5. Photos of the "not included in kit" items are great!

RE the microcracks that form along acrylic glue joints: yeah- we've noticed those too. At first I thought they had something to do with strain from the tightly-fitting syringe, but then I noticed that they form even with nothing that would introduce strain (e.g. no syringe). I'm still trying to figure this phenomena out and will let you know if I learn anything new. Strange, right?!

E


#4

Hi Eric, I'm happy you're enjoying the posts!

I think I found the problem: the acrylic is cracking due to internal stresses that come from being heated up during the laser-cutting process. Applying glue to the edges releases tension, causing those tiny cracks to appear. I also didn't realize acrylic can be manufactured via casting or extrusion -- the extruded acrylic contains more internal stresses due to being pressed through rollers. Similar to how metal needs to be annealed, some internet sources suggest warming up the acrylic in the oven (lol) or lowering the PPI when laser-cutting. Interesting!

Sources:

http://www.artifacturestudios.com/archives/317/

http://www.sawmillcreek.org/showthread.php?51176-Having-problem-gluing-laser-cut-acrylic-parts


#5

Hey Everyone!

Today's blog will be covering Step 6: Assembling the Battery Packs, and Step 7: Assembling and Waterproofing the Thrusters. This was a day of blunders, blisters and mistakes. Nothing too big, thankfully. Read on.

Step 6: Assembling the Battery Packs


It's been a couple years since I've had to solder, so I needed a quick refresher before working on the battery terminals. If you've never soldered before, I highly recommend these two YouTube videos for a primer on the proper technique: http://youtu.be/BLfXXRfRIzY & http://youtu.be/I_NU2ruzyc4. The second video also discusses using flux when soldering which prevents oxidation of the wire being worked on, among other things.

Once reacquainted with this technique, I soldered the 18 gauge wire to the button and spring terminals. Having a helping hands tool with alligator clips to hold parts being soldered makes things so much easier – do buy one.


**Note: I know this sounds obvious for anyone with common sense – and after several years of being in a hands-on field I should know better – but don't solder with shorts on...especially on a drafting table that slants downwards. That handy-dandy liquid-hot metal has the tendency to roll off the table and onto one's lap. That is all.


The War Zone.

I secured the terminals to the acrylic circles using hot glue, then attached the spring terminal to one end of the battery tube. I accidentally made wire loops on both the button and spring terminals, but reheating the glue with the tip of my glue gun to remove and reposition the wire on the spring terminals was a simple fix.


Whoops.

Next came cutting a small hole in each black rubber end-cap to feed the battery terminal wires through. I completely massacred these end-caps with my Xacto knife – ended up applying too much force when cutting through the rubber, making the opening slits too long. Is there a simpler way to do this? I might have to go back and make sure those slits are sealed up with epoxy, so as not to spring a leak when underwater.


Like the tutorial states, use the batteries as a guide to getting the correct wire lengths to push through the battery tubes. I also found having the batteries in the tube helped to keep the spring terminal cap level when hot gluing.


Use the batteries as a guide to help you determine the appropriate amount of wire to string through the tube.

For adhering the rubber end-caps, I purchased Loctite Instant Mix Epoxy, which comes with two self-mixing applicators. One thing to note is the 5-minute set time for the epoxy – once it hardens the applicator nozzle becomes unusable. I suggest preparing both battery tubes so you can epoxy them at the same time.


Feeding the wire through the end-cap now filled with epoxy. Let sit vertically when done.

Step 7: Assembling & Waterproofing the Thrusters

Use a very small Flathead screwdriver or razor blade to pry off the snap ring from the motor. Be careful not to stab into the wires when cutting and removing the heat shrink tubing. I found cutting with the blade pointed upwards helped. Or, you can make multiple passes on the tube, cutting slightly deeper each time. Don't be afraid to give the heat shrink a small tug to peel the rest off. The remaining motor dis-assembly and attachment of new wire was smooth sailing.


(Left) Using an Xacto with the blade up to cut through the pre-existing heat shrink. (Right) Peeling off the heat shrink.

Working with the solder and liquid electrical tape really revealed my lack of finesse for tasks requiring fine-motor skills. Basically working with the liquid electrical tape reminded me of when I paint my nails: failure of epic proportions requiring massive clean-up. The supplied brush is pretty huge – application with a small paintbrush would be more precise.


Terrible.

Good soldering technique is crucial – don't leave on too much solder when attaching the wires to the motor. Doing that required me to use a larger heat shrink tube, causing a tighter fit when shrink-wrapping all 3 wires together. I had one large tube tear on me when heated. I don't have a heat gun, so I quickly and lightly rubbed the soldering iron along the length of the tube in order for it to contract. The last procedure in Step 7, Propeller Assembly, was straight-forward and easy.


(Left) Heat Shrink tore due to too much tension from the wires squeezed inside. (Right) Applied a new one.

I'll end this post with a quick question: what exactly needs to be sprayed with silicone? The tutorial stated to spray the inner and outer part of the motor. Should all surfaces be coated?


#6

Greetings Citizen Explorers!


As mentioned in my last post several months ago, my blogging and building has gotten behind due to school commitments, so I’ll be playing catch up for a bit. If you need a quick reminder on my progress, just check out my previous posts below:


Post 1: Introduction

Post 2: Assembly of Inner Structure and End caps

Post 3: Assembly of Battery Packs and Thrusters

Post 4: Little Boy Blue Goes to the Atlanta Mini Maker Faire


Just to speed things up I’ll be highlighting the parts of the build I've had the most difficulty with:

(1) Step 8: Topside Tether Adapter

(2) Step 9: Potting the wire pass-throughs in the end caps...I’m woman enough to admit I messed this up two times, haha.

(3) Steps 11-13: Setting up the cape and software (which I will tackle in the next post).


And with that, let’s get started!



Step 8: Topside Tether Adapter


I realized I left a couple tools out of my list on Post 2 (link) - one being flush cutters. You can get a pair for about $8. BUY THESE. Don’t be clumsy like me and try to snip off connectors with an oversized tool, or you risk damaging other internal components. (http://www.adafruit.com/products/152)


The 22-gauge hookup wire can be purchased online here I managed to get some by buying double-stranded electrical wire from Home Depot and remove the internal wires. Or you can do it the easier way and buy some 22 gauge hookup wire from an electronics store or an online vendor like Adafruit Industries; they’re maker-friendly and have an awesome intro to electronics tutorial section.


Due to my unfamiliarity with handling delicate electronics, I frequently forget that touching the board could potentially cause static electricity to short out the board. Grasping the sides of the breadboard instead of touching things all willy-nilly like me should prevent this.



Step 9: Potting the wire pass-throughs in the end caps.


This step requires setting up the bundle of wires in a taught fashion so the pass-through hole in the acrylic end caps can be sealed shut with epoxy and hot glue. Anything that cantilevers over your table and end cap can be used to tie a string to the wire bundle and keep it vertical. I happened to have a music stand lying around so I adjusted the top of the stand until it hung over the table.



Trouble arose when it came time to apply the epoxy: the tutorial videos clearly and frequently stressed the importance of properly labeling all wires to their respective electronics, as well as to ensure the labels are visible after the wires are pulled through the end cap. Well, I forgot that important detail, and a couple labels got trapped - preventing me from knowing what wires belonged to what. I had to cut off the end cap and start over. Thankfully my college has several laser cutters so I was able to make new acrylic pieces.



My second attempt had better labeling, but I was overzealous with the hot glue along the outside of the end cap pass-through. The excess glue prevented the acrylic tube from properly sealing when connected to the end cap. I also had to re-solder new wire to extend the old wires, which was messy patchwork on my part; I plan to use butt splices next time around to ensure a neat and reliable connection between wires.



On a semi-related note, I saw these waterproof wire nuts at Home Depot. In the event of a leak within the e-chassis, these could be a good alternative to soldering together and coating the ESC wire bundles with liquid electrical tape.


That’s all for now! Blog Post #6 will cover cape and software shenanigans.


Leslie