Comments on: Steve Canfield and his marvellous mechanical joint

By: Once Upon A Time In Heaven: Commercial Space Takes Off « Once Upon A Time in Heaven

Fri, 09 Jul 2010 16:53:06 +0000

[...] details a solution drawing an interesting innovation from his work on tethers–the Canfield joint: He called it a “Trio-Tristar Carpal Wrist Joint.” I thought that sounded like a real mouthful [...]

By: Ed Minchau

Ed Minchau — Fri, 02 Jul 2010 08:18:15 +0000

I really like this design. Look what happens when you connect several of them in series and drive them all at the same rate: ExtendaTruss. This could also make serpentine robots easier to use and more capable. Can you imagine what the nanotech version of this would enable? Yoikes.

By: Kirk Sorensen

Kirk Sorensen — Tue, 22 Jun 2010 17:11:45 +0000

If he’s interested in robotics, he ought to think about Canfield as an advisor for grad school. Canfield does lots of robotics work, not so much aerospace. I’ve been the one coming up with aerospace applications for his ideas.

https://www2.tntech.edu/me/Faculty_Bios/scanfieldbio.html

By: Charles Grimm

Charles Grimm — Tue, 22 Jun 2010 16:56:22 +0000

Thanks, Kirk, I’ll give him a poke. I’d like to get him to work on space applications. His master’s thesis was on robotic joint movement with curved arms, if I can oversimplify. Interesting applications, fewer motors for the same movements, which is why I forwarded the Canfield joint to him.
Since I haven’t met Stephen Canfield, the best ME I’ve ever met is my dad. He got a dollar each for his pile of patents, including some for a process called Xerography. (James J Grimm, uspto.gov)
I’d like my son to follow in his grandfather’s footsteps, but a recent grad recently married may not have space applications on the front burner .

By: Kirk Sorensen

Kirk Sorensen — Tue, 22 Jun 2010 13:34:45 +0000

I’m a mechanical engineer myself, and Canfield’s the best mechanical engineer I’ve ever met. You might suggest that your son take a longer look at the design. Rotating the tether in the plane he describes isn’t feasible for a variety of reasons.

We went through many napkins and a bunch of Diet Cokes to get to this point. But he’s invited to improve on it if he can.

By: Charles Grimm

Charles Grimm — Tue, 22 Jun 2010 13:20:16 +0000

I forwarded this to my son, the mechanical engineer, who had this response:

It looks cool, but it’s kind of an overcomplicated solution, in my opinion. If you replaced each of those legs with a prismatic joint, in the form of a linear actuator, then, not only do you have fewer things to worry about, you’ve answered question #2: How do we drive this thing?

Anyway, the question itself seems flawed. Why not take your tethered craft and rotate it in a plane perpendicular to the sun’s radius? That is, parallel to a plane tangent to the sun’s surface. Then, one side of your craft is always facing the sun, and one side is always away.

However, if for some reason that wouldn’t work, and you only need to drive the panel through a few specific orentations, it would be a good candidate for a Spherical Four-Bar, like the ones I did in grad school. The benefit being that it would only take a single motor to drive through the cycle, instead of 3.

Sounds like something that needs a few napkins and a beer to work through.

By: Patrick

Patrick — Mon, 21 Jun 2010 18:57:02 +0000

That’s the coolest mechanical doodad I’ve ever seen. And “Canfield Joint” sounds like something out a Heinlein novel. Excellent!

Is the

By: Trent Waddington

Trent Waddington — Mon, 21 Jun 2010 01:13:44 +0000

There’s (very brief) mention of “Electrodynamic Tether Propulsion. Artist’s Concept of ISS Reboost.” in the NASA Chief Technologist’s town hall meeting.

http://www.nasa.gov/pdf/457884main_OCT_town_hall_rev4.pdf
http://www.youtube.com/watch?v=btc70vURm4o

By: Kirk Sorensen

Kirk Sorensen — Sun, 20 Jun 2010 21:18:49 +0000

Hey John, thanks. I’ll be talking about the gimballing thruster in an upcoming post.

By: John Bossard

John Bossard — Sun, 20 Jun 2010 20:48:43 +0000

It should also be noted that Kirk was instrumental in putting together a program in which a small thruster could be attached to the Canfield joint, thus making a gimballing spacecraft thruster. The thruster’s feed-lines could be run up through the legs of the joints. Since all joints are hinged, this configuration results in no pressurization-rigidization loads on the joint, unlike what can happen when using flex-lines. This thruster on a Canfield joint was demonstrated with a small GO2/GH2 thruster in 2005. It was recently publicized in NASA Tech Briefs, Vol. 34, No. 5, pp. 55.
I don’t know about the Canfield joint in general, but the gimballing spacecraft thruster is indeed quite available for general use. Contact Sammy Nabors, MSFC Commercialization Assistance Lead at sammy.a.nabors@nasa.gov Refer to MFS-32520-1.
Lastly, I will totally vouch for Kirk’s comments about Dr. Steve Canfield. Steve was almost embarrassed about the joint being called “the Canfield joint”. But I think its a great name, totally appropriate, and way cooler sounding than the “Trio-Tristar Carpal Wrist Joint”. Thank you, Kirk, for your support and dissemination of this technology. Without you, it would not have reached the TRL that it currently resides at.