May 23, 2016

BB-8

BB-8 was a bit of a reluctant project for me. During the lead up to The Force Awakens I was busy finishing up my R2-D2 and by October I was already starting to work on Mark Watney from The Martian. However, a few components were undergoing runs when the movie came out, and seeing how the project would be a fun engineering challenge I started to work on my own BB-8.

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Much like the R2 Builders Club, a BB-8 builders club started up pretty much right after the first trailer. There was a lot of discussion about the design, and most importantly the development of 3D models of BB-8’s head and side panels. My friend Daniel printed one of the heads and gave it to me as a birthday present. While most builders have been finishing the 3D prints, I found the print to be heavy and prone to pealing, so I decided to mold it and cast a copy in fiberglass. The result is much stronger and less than half the weight of the printed model! The remaining parts were molded and cast in SmoothCast 300. Everything was painted with Krylon paints.

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The ball is two 20 inch diameter, 0.5 inch thick polycarbonate hemispheres purchased from California Quality Plastics. Using a file from the builders club, a drill jig was made using a CNC, allowing pins to be added to the hemispheres so they remain fixed in relation to each other while the droid rolls. Even with the jig, there were a few spots where there was a noticeable edge where the two hemispheres met. While this was easy enough to sand off on the outside, I used strips of cardstock taped to the ball to determine the edge that had to be sanded down on the inside.

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At the time of writing there are two schools of thought concerning how to make the droid move, which I refer to as the hamster and the pendulum or spindle. The hamster is basically a robot that moves around inside the ball causing it to move. This is the same way the Sphero BB-8 moves. The pendulum refers to a droid where the drive mechanism is fixed to one axis and turns by shifting or rotating its weight, which is how the xrobotsUK version 2 and 3 droids work. While the pendulum method provides the best options for assembly and control, it has one serious drawback in that only one ring around the ball ever touches the ground. Considering what the wheels look like on my other robots I opted to go with the hamster method so the ball would wear more evenly as all surfaces will eventually touch the ground.

My CAD skills are a bit rusty and I wanted to minimize the amount of fine machining required, so I started off by locating two gear down motors that could be mounted directly to usable rubber wheels. After several days of looking for options I settled on two NPC 2212 motors with 4” soft rubber wheels. Then using a sketch pad and MDF, I laid out a skeleton for the drive system. This was an iterative process and three mockups were created before I cut the first functional prototype out of birch plywood. On prototype 1 I had the wheels mounted higher on the ball so the batteries and weigh could be suspended between them. While this did allow the ball to move on early test, the contact point of the wheels caused the hemispheres to push out and separate. This problem was eliminated on prototype 2 where I put the wheels as low as possible and the batteries and weight on the outside. Not only did this eliminate the splitting problem, the lower position provided a better “gear” ratio with the ball and helped refine handling.

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Next was attaching the head. The question I get asked the most is, “How does the head stay on?” This is actually the simplest part of the build. 8 magnets, 4 in the head and 4 in the body, keep the head attached. Ball castors are used so the head and the mating plate can move around the ball. The polarities are matched such that the head will always fit on one way.

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With this set up and all the programing I would have to do, I decided that the head would only turn. Leaning would have complicated the stability system and this layout did not allow me to incorporate a counterweight for the head. The mast is built from aluminum channel and components from ServoCity. The motion of the head is controlled with a high torque servo. Since the motion of the head is limited to looking between full left and full right, I can use the head as a reference point for what direction is forward on the droid.

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BB-8 is naturally unstable and wants to rock back and forth. This is bad for a lot of reasons, and difficult to eliminate with the transmitter alone. The solution was to incorporate an Internal Measurement Unit (IMU), an Arduino, and a Proportional, Integral, and Derivative (PID) loop. The IMU provides data about the droids orientation (how much he is leaning) and feeds that into the Arduino, which is basically a small computer. The Arduino takes that data along with the signal from the receiver, and computes how much power to send to the motors. The PID loop is a function that calculates how much power to provide based on position. Eventually I will explain in detail how this works on my A7L page, but most of the stability design was borrowed from xrobots UK. I am not great at programming or control theory, so it took about a week for me to make the droid stable on the drive axis.

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Speaker placement on BB-8 is tricky. The speaker can’t be in the ball because there are no holes in the ball and you would not be able to hear it. This means the speaker needs to be in the head, but the controls need to be in the body. Instead of plugging the WAV trigger directly to an amplifier and speaker like I do with the Dalek and R2, I purchased a Bluetooth transmitter so the sound can be sent to an off the self Bluetooth speaker in the dome. Right now the sounds are recorded from the Sphero BB-8, but as people pull the sounds from the film the files will be upgraded.

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I had to be VERY careful about painting the ball as it will receive more abuse than any other prop I have ever painted. After running test with scrap polycarbonate, I decided to go with Krylon Fusion paint as it is designed to bond to plastic. The ball was sanded down, cleaned 3 times with isopropyl alcohol, then painted with 6 coats of paint and allowed to cure for two days. One of the club members designed graphics for the circles and the club now does runs of them in automotive grade vinyl. The decals were applied, lines drawn with Sharpie, then the entire ball received several layers of Krylon Crystal Clear.

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After giving the clear coat a day to dry, the ball was weathered with acrylic paints from Michael’s. There are A LOT of videos on how to do this, but in a nut shell you paint a little on, wipe it off, and repeat until the droid looks worn.

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While I am happy with the result, the droid still has one issue in that he is not stabilized side to side. I had to finish him as is due to looming deadlines, but this fall I hope to revisit the drive system and add a swinging weight before celebration. Big thank you to Dan Valdez, Cory Pacione, James Bruton, and the BB-8 Builders club as this would not have happened without your help!

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To stay up to date with our other projects, be sure to like out collaborative page 2StoryProps and my personal page A7L Props on Facebook!

For more build pictures, visit the flickr album click here.

Thanks for reading!

-Wayne

September 24, 2015

Jaune Arc's Crocea Mors from RWBY

And now for the final write up in the JNPR prop series, we present the creation of Jaune’s armor, sword, and shield.

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Jaune’s sword was built pretty much the exact same way Pyrrah’s was, in fact they were built at the same time. The sword is made up of layers of MDF and plastic with an ApoxieSculpt tip since this was a one off build. The main difference is the handle on Jaune’s is PVC glued to the MDF blade. After paint, they grip was wrapped in blue vinyl and glued down with Goop.

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The armor started by taking some measurements from our Jaune, to figure out the rough size and curve the armor would need to take. I then sculpted bucks with pink insulation foam. After initial shaping, the foam was coated in ShellShock to make a hard coating that would survive the heat and pressure of vacuum forming. After smoothing with bondo the edges were shaped with ApoxieSculpt. The armor was then pulled from 0.06” styrene.

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The front and back plates attach directly to the hoodie with Velcro. The smaller piece of the shoulder armor is glued to the large piece with eva foam in between to provide the correct offset. More EVA foam was added to hold the shoulders in the correct location. They attach to the shirt using elastic bands and Velcro.

In the show, Jaune’s shield fold up into a sheath for his sword. To replicate this look, the shield was built up using layers of 0.04” styrene. Internal sections were cut out to reduce weight, while a metal rod was glued in the center to keep the assembled shield straight. Two straps were glued to the back and everything was then painted with krylon.

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And that’s it! This was a very demanding project as everyone’s props had to be completed in a 6 week window, but having the whole group going around is a lot of fun and I am very happy with how everyone’s costumes came out.

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As I mentioned in the first post I only made the props and hard components for the team. All the costumes you see in the pictures were made by the individuals wearing them, except for my coat which was made by our Nora. Additionally our group has two of the villains, Cinder and Torchwich, who made their own costumes as well. I think we can all agree they did a phenomenal job and it was a lot of fun working with them.

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Looking forward, I’d like to try and make the main RWBY team’s weapons at some point, but there is a large project I plan to start after Halloween that will take a lot of my time. Be sure to check out Nora’s, Lie Ren’s, and Pyrrah’s write ups and thanks for reading!

To stay up to date with our other projects, click here to follow us on Facebook.

For more build pictures, visit the flickr album click here.

Click here for Nora Valkyrie’s Magnhild!

Click here for Lie Ren’s StormFlowers!

Click here for Pyrrha Nikos' Milo and Akouo!

-Wayne, 2StoryProps

September 21, 2015

Pyrrha Nikos' Milo and Akouo from RWBY

We’ll continue our JNPR write ups with Pyrrha’s sword and shield.

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As with Nora’s hammer, Pyrrha’s weapon transforms in the show into a sword, shield, or rifle. At the request of my friend who portrays the character in our group, we decided to make the sword. The build started once again by obtaining the straight-on references from Monty’s facebook page and scaling it up with the grid method. The blade itself is half inch thick made from two layers of MDF. The rest of the sword was built up using layers of MDF, plastic and plywood.

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Since this would be a one off build (although I wanted to make a mold I did not have the time or resources available) the tip needed to be reinforced, otherwise the MDF would easily snap. The solution I used was to cut the tip off, add a threaded rod, then rebuild it with ApoxieSculpt. The sword was then primed painted, and given vinyl detailing

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For the shield I put our ProtoFormer to use. I started by making a buck out of layers of MDF. Circles were achieved using a homemade compass and carefully cutting them on my scroll saw, then sanding the proper curves in. The details were added with a dremmel engraving tool with small holes drilled all the way through so air could exit during the vacuum forming process. A copy was then pulled using 0.04” styrene. The shield is about 21 inches wide and likely the widest object we can make a pull from.

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The pull was trimmed and then mounted to a plywood back piece using Goop. Before the two were joined a 1 inch cube of pink foam was glued to the center of the board to prevent the shield from collapsing in. The straps are bolted into the board using set nuts. The shield was then painted with Krylon paints and hand brushed acrylic for the details.

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Thanks for reading. Be sure to check out the write ups for Nora and Lie Ren’s weapons and stay tuned as we finish things up with Jaune!

To stay up to date with our other projects, click here to follow us on Facebook.

For more build pictures, visit the flickr album click here.

Click here for Nora Valkyrie’s Magnhild!

Click here for Lie Ren’s StormFlowers!

Click here for Jaune Arc's Crocea Mors!

-Wayne, 2StoryProps