10 Days To Zero-G: Boom Deployer Design Review

Sorry for yet another late-night blog post, but I intend to put up some more eyecandy today.

Boom Deployer Work
The main technical thing we got done today was releasing the boom deployer structure for fabrication. Here’s are some pictures of the boom deployer (sans gripper) as currently envisioned:

Back View of the Boom Deployer (sans Gripper)
Boom Deployer Front View (sans Gripper)
Boom Deployer (sans Gripper) with a Dissembodied Arm
Boom Deployer Stowed for Transit

These pictures should give some clarity to what I mentioned in previous blog posts. Basically we have a “can” in the back that the boom is coiled into and uncoiled from. There is a friction roller setup that provides the torque to feed the boom in and out, hold it steady when not being commanded, and prevent it from being backdriven or pulled out. There is a gearmotor and pulley system. There is a set of guides near the front that force the boom to assume it’s proper shape, and which provide significant bending stiffness in both directions. The electronics for driving the boom are mounted in the back near the “can”.

I also previously talked about the Human Machine Interface design. While we are still working on some of the mechanics, the pictures above give the basic idea. On the top of the boom deployer is a arm-strap or two, and a “joystick” for control. We actually found some velcro arm straps from a medical company that makes walker components. Apparently the model we ordered was usually used for horizontal walkers, so the salesperson was really surprised when a 25 year old was calling in to order one. “Don’t worry, it’s for an aerospace project” actually worked this time around.

We didn’t show it on here, but we’ll probably have some sort of harness to help support the weight of this device as well as to counter the moment caused by a cantilevered load with the boom fully extended–this boom can pick up a chair at a distance where the previous boom could barely support its own weight.

In the end, the design has a very anime look to it. Kind of MegaMan-esque.

For this first round, we’re going for sheet-metal aluminum for a lot of the structure, but we may at some point switch that out for polycarbonate, since that would likely still be strong enough, but would allow you to see the innards like before. The sheet metal fabricator originally suggested a week for these, but is going to try and get them turned a lot faster than that. They did some miracle work for Masten a few times in the past, so I’m optimistic. Mike finishes his propulsion final at USU tomorrow, so he’ll be joining us in Colorado tomorrow night. That means that if they can turn those parts around quickly, we may be piecing the boom deployer together this weekend (which is good considering how close the deadline is getting).

EA Pad/Gripper Work
Yesterday’s testing taught me a lot about our system, and about how to work with electrostatics for this application. We almost had enough gripping force with the four pads to lift the ball vertically in a 1g field. With all 8 pads, we should be able to do a vertical lift, and maybe also a horizontal one.

Here’s some other eyecandy from yesterday’s testing:

Jonathan Goff (me!) with Ron Pelrine Setting up the Simulator Ball and the High Voltage Probe
Rev 2a Gripper Electroadhesion Test Rig
Ron Pelrine (in the back), AJ Hoyt (left) and Jonathan Goff (me, on the right) Setting Up for a Pull Test

The good news is that the joint lockers appeared to be holding firm the whole time. We could go up to the next size of joint lockers (about 1″ diameter vs. 0.8″), but had already ordered a batch of 5, and would’ve had to ordered new rotational sensors as well if we went to the next size of joint locker.

We found out that the stainless steel ball we picked was magnetic, so I also ordered a copper float from McMaster (that didn’t show up today–boo for FedEx!). The good news is that this provided an easy way to provide the “ground path” for a single-pad test:

Turning Lemons into Lemonade...

AJ is currently working on getting some of the modeling done on the Rev 2b Gripper, which we’re hoping to have ready to release to Wayne soon. This will incorporate four bogeys instead of two, and will have twice as many pads. We’re thinking of switching to a plastic like Torlon for the rev 2b bogeys (the crescent shaped parts), because an insulator will make our lives better when it comes to dealing with high voltage in the pads.

One of the other elements we’re going to have to work on is that the gripper and high-voltage electronics all have to be easily detachable from the boom, because in order to fit in the Pelican case we can use for a carry-on, the boom is stored fully retracted. For the flight test, this means that we’ll need to be able to reattach it firmly while in-flight, with a minimal number of tools. This isn’t a show-stopper just a design consideration.

I’m really enjoying working with this team. The SRI guys have been extraordinarily helpful, and have a deep background on this technology (not surprising seeing as how Ron was one of the inventors). AJ’s many years experience with slot-car racing has paid off very well with all of the intricate pieces we’ve had to configure, and all of the hands-on work we’ve had to do for getting the test setup put in place. And without Kirk working project management, Forrest working electronics, and Mike working on the boom deployer, we wouldn’t have a prayer right now.

3 Responses
  1. So, just so I understand this, you’re going to provide an arm mounted boom deploy system and a metal soccerball to someone to take onto a zero-g flight…. why do I get the distinct impression that someone is going to yell out “go long!”

  2. Paul

    I fully expect to see, by about the third arc, someone using the boom to haul themselves from one side of the plane to the other. Like a very slow spiderman. Giggling like children.