RCKillough

While reading news in lugnet.technic I found a link to a very interesting page, Leo's LEGO Designs, there I found this page describing a pretty uncommon propulsion system named after it's inventor, Killough. I recalled that I had seen it before and that I thought it moved pretty spectacularly. So I decided to build one myself. I remembered that the one I previously saw was controlled with the Mindstorms RCX, but I went for remote control using the same radio control equipment I always use.

After studying several other LEGO Killoughs I left the computer and went to my building table and four hours later I was done. It took about three hours to assemble it and one hour to make it stronger so it would not fall apart and tweaking the RC stuff.

I really think that you should build one of these babies of your own! They are much fun to play with!

How?

Since this is a pretty remarkable"vehicle" I thought that I should try to explain how it moves.

It uses six wheels that are rounded and spins them in wrong direction, tilting them around instead of rolling them. The "normal" spinning axis is free to rotate. The reason there are three pairs of wheels is that when one wheel tilts it will loose contact with the floor unless it lowers it's chassis (gravity will) or something else holds the chassis in level, here's where the additional wheel comes in play. The wheels are mounted with a 90-degree displace to each other, thus, when one wheel tilts so that it looses contact with the floor, the other wheel gets contact instead. So there will always be a wheel that has contact with the floor.

Here is how that works, looking at the Killough from the side and only drawing the wheels. The wheels tilts in the direction of the arrows.

First

then tilting 45 degrees

finally tilting another 45 degrees

To drive in a straight line forward, two of the motors are turned on in different directions. Looking at the picture, it's the "red" and "green" motor that's turned on, creating the force displayed by the orange arrows. They add up to the black arrow and the platform moves in a straight line "forward". If the axles in the wheels were fixed this would create a lot of stress on them from the friction against the floor, now they can rotate freely and there for there is no skidding and the platform moves with ease.

If the green and red motor changes directions the platform will travel "backwards" or down in the picture.

If the red motor is turned off and the blue motor is turned on instead, the platform will change it's direction of travel as displayed by the picture.

If, in the previous case, the red motor never was shut off while turning on the blue motor the platform would perform a pretty big turn since the blue motor causes the platform to rotate..

If all three motors turns in the same direction the platform would rotate around it's center and not move in any direction.

If only two motors drive in the same direction the platform rotates around the center of the third pair of wheels. In the picture the red and green motor drives the platform around the center of the blue pair of wheels.

I forgot about only driving one motor when I played with the platform, but it causes the platform to rotate around the other two motors shared center.

Of course one can swap between these behaviors at any time and this is what makes the platform so versatile and maneuverable. And also so difficult to drive nice, I had some good exercise when I collected my brothers sons toys in a nice pile :)

Here is an overview pic to start with. Notice that I even took the time to cut the background out. The main factor that made me invest in a new camera is the trouble I had with video camera pictures and cutting out the background. Now I love this :)

It's always a challenge to fit non LEGO elements in the projects and rubber bands works OK mostly.

Tipping the Killough on it's side displays the underside, as always :) Notice that I added extra support in the center in form of black 1x6 beams.

Zooooming... I had to use some 1x2 plates with one centered stud to make the battery box fit. I still had to use a little more force then normal to stick it there so it don't fit great but it fit's good :)

I also used some external support beams. Notice the use of half beams to connect the technic beams with each other. They provide for a stronger fit then normal 1 x Y plates.

The platform is built up using three of these setups. There for this was a quick build when I had figured out how to make one I just built another two copies. cklickety-brick :)

And flipping... Notice the sparse gearing for less friction.

And as always, here's that ON | OFF switch fetishism of mine...

Displaying more radio equipment, here is the receiver.

Servo. It took some time to get that polarity switch up there. I cheated and used a rubber band to keep the parts together. I never tried with out it so I might have been fine w/o cheating but why take a chance?

Side view. It don't have very much of ground clearance but it's pretty though in rough terrain like carpets, door steps and thick cables.

Top view. Have you perchance noticed that I arrange my pictures in alphabetical order?

So, what's to see here? Perhaps the blue antenna mounted in a setup of 2x4 technic plates and a short pin? Nah...