BB-8

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BB-8

THIS PAGE STARTED PRIOR TO THE BB-8 BUILDER'S CLUB BEING FORMED Lots of it's "old", take a look at http://bb8builders.club for more current info.

BB-8 is a cute little rolling droid we first saw in the first teaser for Episode VII: The Force Awakens. Since then BB-8 has put in other appearances, notably at Star Wars Celebration. For now there's a lot of discussion about how he is constructed.

As with all of the droids on rebeldroids.net, there are multiple ways to have a successful build. This information is compiled from a variety of sources, including the forum discussions. Some information we are fairly certain about, and other bits less so, though unsupported conjecture is hopefully clearly indicated. (Eg: the Holoprojector looks like an Artoo HP, so we're calling it that, but not having seen footage of it in use, for all we know it's a particle beam emitter).

Name

Does "BB-8" mean anything? Bowling Ball 8? Beach Ball? Basketball? Ball Bearing?

Variants

We know of at least 3 versions of BB-8 used in the film

  • CG version is probably the most ubiquitous.
  • Moving stage version that rolled out on stage at Celebration VII
  • Static model/puppet version that was shown at the special exhibition. (It's unclear if it is actually used as a puppet)

Of the 3, the stage version shows us BB-8's range of motion, but with limited detail. The static model has the most detail.

Movements

BB-8 is capable of several interesting movements, as can be seen in the Celebration Stage video.

  • Body is omnidirectional. It can move in any direction at any time
  • Body can spin in place. Unclear if this is intentional, however the body can rotate under the head.
  • Head can dip, usually in the direction of movement, but it can be at other orientations as well.
  • Head can move from side to side, it doesn't have to face the direction of the body movement.
  • Her head can also rotate in place regardless of the vertical or horizontal position.

Sound

Yes, she can talk. Kinda sounds like R2 in a fishbowl or something. You can hear her voice on celebration stage video. She seems to sound more like a human language than Artoo.

Lights

The static model in the exhibition had solid lights that were always lit and did not flicker. The dynamic stage model also has primarily static lights that do not change, however there are two notable exceptions:

1) There's a "vocoder" light under the eye that blinks in time with her speech, as you can see on the video. 2) We see some of the lights in the sphere get occluded and dim or go blank. The working theory is that this isn't intentional, but rather some internal structure within the sphere occludes the lenses.

On the static model, hi-res images clearly show most of the lights as being common LED segments. The one difference is a couple of white lights which seem to have a hexagonal screen filter.

On the dynamic model, the sphere appears to be illuminated internally with lenses for each light.

Head

Unlike Artoo, who's head is egg-shaped, BB-8's head is primarily a hemisphere on top of a short cone, at least on the static model. The transition from the hemisphere to the cylinder is about 1/2way through the orange stripes.

Many of the features of BB-8's head are recognizable from other droids, though the white logic-looking display hasn't yet blinked or changed color.

The two antenna on back are fairly simple shapes, yet look so similar to present-day wifi and other radio antennas it makes one wonder if they were found parts. Of course they're also really simple shapes to machine, but it does make you wonder.

Eye

The eye has a bit of inner detail that can be seen in some of the higher resolution photos. There also appear to be 4 Phillips screw heads that are visible from some angles that appear to be fairly far below the detail.

Vocoder

A simple little light under the eye that's probably going to be one of the more interesting electronic bits. This light brightens and dims in sync with BB-8's voice, as can be seen on the Stage Video. A pulsing meter-like light isn't too hard, but think about that a moment. The sound from the stage voice came through the auditorium speakers (as did Artoos). We know that the old movie droids didn't have voices, but maybe these new ones do. In either event, some sort of synchronization between the droid and the speakers had to have been going on. Either BB-8 was getting level information transmitted to her, or BB-8 was transmitting sound to the auditorium. (Kresty wonders if maybe the servicing photo we have of BB-8 is adding the auditorium mic to her circuit?)

Holoprojector

Like the traditional Astromechs before her, BB-8 has a Holoprojector. (Disclaimer, we haven't seen it work, so maybe it's something else). BB-8's HP is a little sleeker looking than R2's, however the HP on the models is clearly fixed and non-moving. Given that the structure appears to have the ball gimbal thing, it seems likely that it's intended to move, perhaps we'll see that happen on the CG model.

Body

The dynamic BB-8 version is a fairly smooth sphere with low detail. The static model has the most detail of the 3 versions we've seen so far.

Her body consists of 6 circular "hatches", which fans currently presume have utility arms or other gizmos contained within them. Each "hatch" is different than the others.

In between each group of 3 hatches are "access plates", a total of eight.

Her sphere is nominally 500mm, however the 3 variations may deviate from that due to construction materials. For American builders, 20" is only slightly bigger and is likely close enough.

Hatches

BB-8 has 6 different round orange hatches on her body. Each of them is unique, so to discuss them in a common language, we've numbered them 1 through 6, like a dice, as see in the following picture: normal_BB-8_Panels~0.png

The generic orange circle and tabs shape is consistent for all 6 hatches, though some have other structures that intrude on the orange ring.

Hatch 4

Hatch 4 has a pattern that sort of looks like an awards ribbon with a few lines through the round part of the ribbon.

One of the most interesting things about Hatch 4 is that the static model was sitting on it in the Exhibition room. So we don't have great views of it's details. And on the moving stage BB-8, there isn't much detail, same as all the other hatches.

Hatch 5

Hatch 5 is painted on the models to look like there's a wear mark where it may swivel open. It's not entirely clear how that might work at this time.

Hatch 6

One of the most fun hatches is Hatch #6. This hatch has bits that look like opening doors, and there are 3 center bars that appear hinged on one end. Additionally one has a shape reminiscent of Artoo's utility arms, so perhaps this hatch contains BB-8's version of utility arms. Things like that and the head Holoprojector that tie into the history from a traditional Astromech are pretty nifty.

Access Panels

So called because we have a photo of someone servicing BB-8 with an access panel removed and his hands inside the droid. These are the 8 triangular panels between the orange hatches. For the most part the access panels are identical, however a few have some hash marks and one has a light on it.

The clasp/rivet looking circles are entirely decorative on the models, however the panels are fastened, it is different than that.

Each access panel has a small rectangular region that looks like a small door for finger access, like to pull off the panel. The door's position is consistent with respect to the edge it's on.

The orientation of the access panels appears somewhat random, however it does seem consistent between the models we've seen so far. Its unclear if a mechanic in the Star Wars Universe would just put whichever panel was closest in each position, or if the mechanic would worry about the orientation of the panel. Perhaps if a panel was removed, the droid serviced, and the panel replaced it would rotate 120 degrees.

Internals

On the static model a couple of the panels are askew. It's unclear why they aren't fitting perfectly in the display. Perhaps those panels allow access to the puppeteering controls?

On the dynamic stage model we have a photo with one of the panels removed. It appears that the panel is a thin sheet with an inner lip that it connects to, similar to pie plates on a typical R2 Builder's Club Artoo unit. The fastening is unclear as well, however in one of the corners of the inner layer there is a rectangular mark that might perhaps be a magnet.

Mechanical Construction

There is some debate about exactly how BB-8 operates, however we have a lot of information from various sources, including Sphero's patent information, a few photos, careful viewing of the video, and similar sources. The current consensus is that the stage droid is very similar to a toy Sphero, with a "hamster" car inside the sphere, and an arm above the hamster that connects the head via magnets. An alternate build method is presented below.

Unlike two wheel toy Sphero, BB-8's hamster is a 3 wheel holonomic drive as demonstrated by the ability of the sphere to move in any direction without prepositioning the hamster. Additional video shows the sphere rotating under the head at one point, clearly the hamster is rotating in the opposite direction at a speed that exceeded the coefficient of friction between the sphere and the carpet.

From the hamster, there's an armature that extends to the top of the sphere. That has a plate with magnets to which the head is attached magnetically, on the other side of the sphere.

The armature has 3 degrees of freedom as demonstrated by the model on stage. There are various mechanical possibilities to provide those 3 degrees of freedom, however the 3 observable motions are:

  1. The head can rotate in place. The simplest way to do that is to rotate the magnetic plate inside the dome
  2. Her head leans forward and back. This could either be on a car and track that follows the curve of the dome, or an arm that pivots from the dome's center.
  3. Side to side movement of the head. Rotation of the entire arm or track accomplishes that movement.

Some disadvantages of the arm are the leverage that the head and mechanisms would have on the center elbow, requiring a reasonably strong servo in that position. Another problem might be tolerances and ensuring that the head attachment plate remains neatly under the sphere's top.

A disadvantage of the car and track are that it would require a larger framework, and that framework needs to fit properly within the sphere without binding. However one data point in favor of this approach is the photo of the removed access panel. In that photo, there is a structure along the inside edge of the sphere that doesn't align neatly with the panels, implying it may be part of the hamster's internal structure. 3 or 4 poles like that would provide the necessary framework for the track & car system.

Magnetic Considerations

The club doesn't have a lot of experience with magnets yet, however there are things to note:

  • Everyone has played with magnetic games or toys where a car follows a magnet manipulated by the player. For numerous reasons the car always follows in a jerky and erratic fashion. The modified Sphero toy exhibits this behavior. Balancing the magnetic attraction, friction and movements to prevent that might be fairly challenging. Since the head needs at least two magnets to maintain orientation, a several-magnet system may help reduce this effect.
    • Partially this is because dynamic friction is always lower than static friction. So once you finally get enough force to get it to break free, then it moves quickly. Low static friction is probably key.
    • Too much friction, eg too strong of magnets or too rough of a sphere, will likely aggravate this behavior.
    • Rapid motions may cause the inner carrier to jerk away from the head, requiring the head to catch up. You'll notice that BB-8 in the video has very smooth and controlled movements.
  • Remember that Magnetic Force is even worse than other forces that follow the inverse square law. Magnetic attraction can decrease with the inverse cube of the distance between the magnets.
    • So if you go from 3mm to 6mm distance, you don't lose 1/2 or 3/4 of the "power" of the magnet, you have pretty much only 1/8th of the attraction of the closer distance!
    • One overcomes that with stronger magnets, which make the system trickier to balance.
    • If you can't keep the distances reasonably similar due to variations in the dome wall, it will either gain or reduce force by a large amount. The aforementioned 3mm to 6mm distance may be enough variation to either cause your head to fall off, or to pinch so hard it can't move.
  • Really big magnets are dangerous. Something with 1 or 2 lbs of attraction at 1" can have 35 lbs of force when right next to each other. They can pinch or smash fingers.
    • If you have a 5kg head with magnets designed for a 2cm "gap", then those magnets will be strong enough that a very large human could hang from the ceiling on them if they were directly connected.

Alternate Mechanical Construction

A perfectly valid alternate mechanical design for the droid is to have two separate robots, a hamster robot inside the body sphere, and an independent balancing robot on the top of the ball, stabilized with gyros or other techniques. For builds with spheres that are not very regular internally this may be preferable.

In the two robot system, the hamster would control the main movement of the droid body, preferably using a holonomic drive for any-direction control. That motion would then "tip" the head in the direction of the movement. The head would have an additional holonomic drive to keep itself on top of the body. The head would use it's gyro and accelerometer to determine the direction of movement and keep itself oriented correctly and keep itself on top of the body. The operator could then deflect the head from that nominal position to effect expression of the puppet.

Alternate Hamsters

To simplify the design, builders can consider non-holonomic hamsters.

The simplest would be an R/C type car that would move the ball as it drove. The disadvantage would be that it would require 3 point turns like a car, so it wouldn't be as flexible as the droid shown on stage.

Another variant is a 2 wheel tank-drive system for the hamster. This would allow some flexible amount of rotation and turning. Downsides are that it would need additional supports to keep from tipping within the sphere body. Additionally if the operator wanted to drive forward and then ninety degrees, they would have to turn the hamster before proceeding. Though not as limiting as a simple R/C car, it doesn't seem like the 2 wheel system would have the full range of motions demonstrated on stage.

Simplified Armatures

Of course one way to simplify the BB-8 build is to reduce the number of degrees of motion in the armature that supports the head (presuming you're doing the armature head design). That will necessarily reduce the expressiveness of the droid, but it might be an option for a first build, or as a waypoint to a more advanced build. The simplest of these is the modified Sphero toy where the head remains in a somewhat fixed position.

Balancing Bots

At least one BB-8 is being built as a balancing bot. Kind of like a circus bear, the bot controls the movement of the ball by driving around the top of a lightweight ball. This prevents the "peering" behavior that we saw on stage though as the head has to always be on top when the ball is still.

References

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