Team 871 - Homebrew Segway

[GregTheGreat]

I was just wondering what type of wheels the KnightKrawler uses? I have been looking at many different types of wheels on skyway and other sites, but really haven't found anything that can support the weight and is thin enough.

Thanks

[MrB]

Originally posted by Adrian Wong
Hello. Excuse me for intruding, but something has been bothering me since I started reading this thread.

Isn't the Segway and these other gyroscopically stabilized platforms an example of the common "inverted pendulum" control theory experiment?

You are 100% correct! That is exactly what it is ....

[D.Fahringer]

The wheels are one of the best things because they are so good and so cheap! I got them from Northern Equipment, a hardware chain and they were only 7 bucks each...with two 1/2" I.D. bearings included.

The wheels are 12" in diameter, and get fantastic traction.
Skyway makes this type of wheel and tire in many sizes, they sponsor FIRST, and will give you a deal if you need a different (larger) size.

How much weight?

[GregTheGreat]

Originally posted by D.Fahringer
The wheels are one of the best things because they are so good and so cheap! I got them from Northern Equipment, a hardware chain and they were only 7 bucks each...with two 1/2" I.D. bearings included.

The wheels are 12" in diameter, and get fantastic traction.
Skyway makes this type of wheel and tire in many sizes, they sponsor FIRST, and will give you a deal if you need a different (larger) size.

How much weight?

Well I was looking at skyways tires, and I couldn't find something in a 14". I think that 14" would be about the right size. I was also considering wheel barrow wheels, because they are very inexpensive. I was actually considering having our mentor contact them to see if they could get us some 14" wheels. I think that they might be the best choice. Thanks much Fahringer.

[Matt Krass]

How much would 14" wheels cost? We were looking in to 9" skyways cause we had them, but 14" would benefit us much more, so if the price isn't too insane maybe we could swing them.

Thanks Guys!

[MrB]

I liked the size of teh wheels on the knightkrawler, but was also thinking of going to 14 or even 16" wheels.

I may get one set of each just to experiment with.


...oh yeah, and I agree, Northern us a great company to deal with...

[Matt Krass]

How are the prices on those? Are we talking 20 bucks area? 'Cause I know I can swing that even if I pay for it myself

[D.Fahringer]

I vote for 16" wheels from Skyway! When you only have two window motors for power it is best to stay small and light. (12" wheels)

If I were to make another, I would go for that big motor now.

[Matt Krass]

Anybody know of inexpensive 14" wheels? Also, how big is "too big"? I'm thinking around 3 feet the wheels might be stretching it

[Matt Leese]

Originally posted by D.Fahringer
The lower the CG the easier it is to remain upright it seems to me. The fact that I can stand on the KnightKrawler without turning it on displays some inherent stability. The students and I have a little trick we do on it where we set the speed and a mild turn and then let go of the controls....(the "No Hander Meander").

Take a base where you stand above the axles of the wheels
and one where you stand below and try to balance....no contest!
If the wheels are free to turn the first one will get you in trouble right away!

I am keeping in mind that a yard stick is easier to balance on my hand than a 6 inch ruler and the yard stick's CG is further from my hand but I feel that is just a reaction time matter.

Anyone else have thoughts about this? It is interesting!

It's going to be easier to balance something with a higher CG (within reason). They physics behind it are fairly simple. If you have an inverted pendulum (which this is the same thing as), you can consider all of the weight of the pendulum to be at the CG. Now, in order to balance the pendulum, you have to keep the CG in roughly the same place. Because of this, you move the bottom of the pendulum back and forth. Now, if you have a higher CG, you can move the bottom of the pendulum a greater distance while keeping the CG in the same place. This means that you can have less precision in your movements. It gives time for the control loop to settle down to a more stable state. So that's why a yard stick is easier to balance than a ruler.

Matt

[D.Fahringer]

It's going to be easier to balance something with a higher CG

So it would be easier to balance a machine with the rider standing over the wheel axles than under the axles? Hmmm...

A pendulum platform stabilizes at least some of the weight it is supporting, of course the overall CG is very much above the axles. It does this naturally and should require less power from the motors to keep a rider upright. In an inverted pendulum base all weight is in an inverted pendulum status and all of it requires stabilization.

The following example shows two yard sticks one supported at its end the other also supported at its end (superglued) but it is nested in a balsa pendulum.

Any difference between the two?

[Adam Y.]

It's going to be easier to balance something with a higher CG

The opposite is true I thought. I always thought that tightrope walkers carried that big stick is that it lowers there cg and makes it really hard to fall.

[Matt Krass]

My brother explained to me like this:

With the platform above the wheels, the motors are always playing catchup when trying to balance. With the platform below the wheels it allows the motors do what they need and have the platform follow instead of the other way around. I hope that helps, it definitely cleared it up for me.

[MrB]

hmmm...

well, it wouldn't be hard to adjust the deck height to change CG on the design we are going to build, so we'll probably try both.

But the Segway looks as if the deck is above the wheels, so that is our goal :-)

[sanddrag]

Originally posted by MrB
But the Segway looks as if the deck is above the wheels, so that is our goal :-)

Uuuuummmmmm? On the Segway, the entire deck is below the axis of the wheels' rotation and the surface on which the operator stands is just a tad below the axis of the wheels' rotation. www.segway.com