Thursday, August 24, 2006

To spin or not to spin? - That is the question.

I'm excitedly expecting my education set (last I heard it was on a boat but my imagination has not really accepted how far away that boat is in time/space/reality).

To that end I am exploring rovers that can both be independant and great little BT remotes. I want to have speed for the remote but also have it drive itself at similarly high speeds. To that end I am abandoning the tank style dual drive motor turning system for a rack and pinion (or may be just rotation) based steering.

Tank style driving is nice because you can have your sensors all point forward and simly sit and spin to get an idea of whats going on. Even thought NXT makes this style of driving alot smoother, the car style of driving I think can go faster - especially if higher speed motors are used.

Car driving allows a forward view or a head bobbing view that follows the direction of the turning wheels.

I am, however, exploring a concept where a minor turning of the wheels causes a large movement in the UltraSonic sensor head so that while in motion it can wiggle the wheels to sweep and decide to go left, right or random and how severe a turn to make.

Does anyone know how an Ultra Sonic sensor reacts to a perpendicular plane near its source of radiation? In short can you put blinders on it so that it ignores "low" obsticals - or would it simply continually detect the shelf. Also I am curious how it reacts to driving with the US near a wall or floor?

So what are everyones comments and preferences when it comes to Car, Tank or other steering styles...


At August 24, 2006 2:22 PM , Blogger Brian Davis said...

Why do you think "the car style of driving" is faster? In both cases, you have two motors availible for producing driving torque... actually, there are gearing systems for a "tank style" that can utilize all three motors, using a differential, so for maximum power availible you *don't* want a steering drive. More importantly, in either case I suspct you can go much faster than is practical. At 1 m/s (easily attained - the NXT or the RCX can go much faster) if an approaching wall is "seen" 40 cm out (and usually you don't get detection until closer), you have under half a second to stop the vehicle... a vehicle with a significant momentum... ouch.

As for putting in "low blinders", this shouldn't be a problem. A glancing angle of incidence for the US sensor does an excelent job of not returning a signal. Great for not observing the floor... conversely, not great at all if you are approaching a wall at a shallow angle (and here, "shallow" could mean anything less than 30-40 degrees).

For any number of reasons, I usually go with a skid-steer (tank-style) platform, unless direction changes are needed *without* slowing down... for instance, line-following (with no sharp turns) is sometimes a good venue for steering vehicles.

Brian Davis


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