pic: Steering mechanism

[jskene]

loading photo ...

[sanddrag]

The steering is very interesting, but what I'm even more curious about is how did you adapt to the strange gear on the jideco motor?

[Rick TYler]

Pretty cool. Most teams use tank steering. How did you decide to use "automobile" steering instead?

[CRAZYMADI]

The gear is biult to give more revolution per mintue to our four-wheel steerign drive. Keeping in mind that there will be six robots on the field at the same time, Robots must move on sharp angles and possibly on faster pase. Our steering system fulfil the requirements and is pretty light. So far with the gear boxes, four wheel steering system and arm, we are still under 115 lbs.

[Lil' Lavery]

Nice. Typically you only see tank or "skid" stearing, or a form of omni-drive. Occasionally a robot who can "crab drive" or strafe too(especially in stack attack). But very rarely akerman(sp?) steering.

[sanddrag]

Team's that I remember having it are Crescenta Valley 589 in 2003 and Archer (#?) in 2004.

[Greg Perkins]

this kinda looks like what 121 did in 2001.

except they made their robot turn in the middle via a vandoor motor. basically 4 wd with tthe robot looking like this...>o<... with the <'s being the wheels and chassis, and the o is the pivot...

it was pretty amazing

i like this approach to driving, most drivers allready own a car (or drive one) so any time a car steering system comes up its second nature.

[jskene]

Yes, this type of steering mechanism is referred to as Ackerman steering. Each wheel turns around its own turning axle, in our case both the front and rear wheels turn, so we get a very small steering radius.

Due to the sharp turning angle we have (45 degrees), the fact that we turn all 4 wheels, and the extreme grip of our tires on carpet (coefficient of friction is about 1.2!), we cannot tolerate any slip angle (difference between the angle the wheel is actually turned to and the angle it should be turned to to remain tangent to the turning circle), so we had to make the inside and outside wheels turn different amounts, so they remain tangent to the circumference of the turning circle they are supposed to follow.

It makes for some interesting mechanical design, as well as some neat programming.

Here is a photo of the steering shafts (note that we also have 4 wheel drive in addition to 4 wheel steering):

The steering arms of the left wheels are connected together, so their steering angle is identical. The same is done on the right wheels. The left and right sides are driven by independent steering motors, each with its own steering angle sensor. When the driver pushes the joystick to the left, say 20°, the left wheels become the inside wheels, and the left steering motor turns the wheels to the desired 20° steering angle, as measured by a potentiometer connected to the steering axle.

So, referring to the diagram below, we can calculate θo as follows:

tanθi = W/Xi
So Xi = W/Tanθi
Tanθo = W/(Xi+T)
θo = ArcTan(W/(Xi+T)
= ArcTan(W/(W/Tanθi +T)

We are also using an electronic differential, by setting the relative speed of the inside and outside motors to be proportional to their respective turn radii.

We also plan to add speed-sensitive steering, so at high speed the ratio between joystick angle and turn angle is reduced. Hopefully that will minimize the chance of flipping over with our 100" arm extended.

[Mirza95vx]

pretty sweet. Very diffrent and original

[jskene]

Originally Posted by sanddrag

The steering is very interesting, but what I'm even more curious about is how did you adapt to the strange gear on the jideco motor?

We CNC machined an adapter out of delrin. Email me if you want the G-code. We also did one for the Denso window motor, as the one FIRST provides is a bit bulky.

[Jeff K.]

Whoa, that is insanely cool...But will it last all of the competitions?

[jrocket567]

one word to describe it: wow ... thats incredible.. that must be one heck of a program to determine everything that fast.. hope yall will be at VCU, can't wait to see it!

[jskene]

Originally Posted by jrocket567

one word to describe it: wow ... thats incredible.. that must be one heck of a program to determine everything that fast.. hope yall will be at VCU, can't wait to see it!

Yes, we will be at VCU, also in Atlanta.

[Fixen]

This is just downright awesome. Akkerman steering is something I didn't expect in this competition.

If you guys don't win the regionals, you'd at least awe the people.

[psquared]

very nice design, that whole programming team must be really amazing