Wednesday, July 20, 2011

Great Walking Things, Part 2

Did I mention I like walkers?

I think I did. I promised I would revisit the subject and give you my ideas on how a Victorian era walker is somewhat more plausible. First, however, John Bear Ross pointed out that I'd neglected his Martian walkers for Rebel Minis. My appologies for the oversight, John. They are indeed fine models.

Here's a small one armed with heat ray and autocannon.

Here's a big honker, much more imposing in my opinion. (Love the hair.)

Now, as I mentioned before, I have what strikes me as a fairly simple solution to the tripod walker imbroglio. I like my idea, but to be honest, I like almost all my ideas, so you'll have to be the judges. The basic notion is that all three legs do not need to be equal. A single central leg mounted dead center in the bottom, which simply swings forward and back and goes in and out -- essentially a great big steam-powered piston with a rotating "foot" on the end -- provides all of the motive force and most of the support for the vehicle. The other two legs are mounted to either side and provide balance, not motive power.

Here are some side-view diagrams to show how it works. Obviously this is an early prototype, as it features an exposed driving compartment and is piloted by the inventor's portly assistant.

These may be a bit hard to read. The first diagram (Position 1) shows the walker beginning a standard stride. The Driver Leg (the central motive piston) is all the way forward and fully extended. The two balance legs are planted.

The second diagram (Position 2) shows the walker in mid-stride. The walker has been moved forward by the rotating driver leg, which is now also partially retracted (to keep the chassis of the walker at a constant height). The right balance leg is also still in its original position while the left balance leg has lifted and moved forward.

In the third diagram (Position 3) the walker has moved further forward on the pivoting driver leg, which is again fully extended, now to the rear. The left balance leg remains planted but the right leg now moves forward.

In the fourth diagram (Position 4) the walker briefly balances on the two balance legs as the driver leg piston retracts and then swings forward. When it passes the centerline, the center of gravity moves forward and begins to tip the walker as the piston extends, which will put it back in Position 1 to start a new stride.

So that's how a tripod walker can function without a gigantic gyroscope. The motion of the balance legs and the central piston is controlled by a cam arrangement to keep them in sync, with the driver controlling speed and adjusting the extension of the balance legs to compensate for uneven ground.

Piece of cake.


  1. An intriguing idea. I'm not entirely sure it would work, though. Especially the last "step", with the central leg off the ground while the two balancing legs are at various angles, looks very precarious. No way to be sure without sitting down with pen and paper, but I suspect the movement of the balancing legs must do some pretty interesting things angular-momentum-wise.

    Incidentally, as an undergraduate (and boy, doesn't it feel *that* was back in 1889) I had the opportunity to attend a lecture by one of the NASA people involved with the Mars Pathfinder rover. He talked at length about how they trialed a wide array of possible arrangements, including various multi-pods, and it all pointed to the articulated six-wheel suspension being superior. Of course, all those NASA tests took place in a Universe where the aether doesn't exist...

  2. The Germans Army early in World War I viewed a test of a walker to get around the trenches. The walker collapsed on its first trial.

    Needless to say, there is not a lot of data on this test.

  3. Aris,
    That is the one point in stride which becomes precarious. The easiest way to solve it is to have an auxiliary "prop" leg which stays back there all the time (or almost all the time) to keep the machine from falling over backwards. The main driving leg swinging forward and extending woild then move the center of gravity forward and let it tip onto the driver. The problem with thiss is largely aesthetic -- it's not a terribly graceful solution and it's not exactly a tripod anymore.

    A second possibility is Andrew's idea (from the previous blog posting on walkers) for a steam-powered balance piston, which would shift the center of gravity forward while the driver leg was recovering from behind and then steadily shift it back as the driver leg made iots scycle.

  4. Jon,
    They still cannot get a robot walker to run very well, but are getting pretty good at having them walk and climb. That said, without a gyroscope and a pretty good on-board computer, a walker with fewer than about six legs is a very iffy proposition.

    The trick, it seems to me, is to come close enough to plausibility that people do not get distracted wondering how it manages not to fall over, and that is best handled by 'fessing up to the problem and then providing a novel solution, which may or may not really work, but is different enough people are willing to give it a pass -- "willing suspension of disbelief" it's called. As I think I mentioned previously, I had no problem buying into Scott Westerfeld's bio-engineered "beasties" in LEVIATHAN, but his big two-legged steam-powered walkers actually running through the woods and sliding sideways to a halt pulled me up short and broke my reader's trance repeatedly.