4WD Turning Difficulties

[Kris Verdeyen]

Originally Posted by Joe Johnson

...the engineering challenges are fun, not well understood and provide significant advantages...

...now if only I weren't worried about loosing the audience...

Exactly right on both points. I'm really pumped about the new robot building challenges, but as for the game as a whole, my gut says it will be boring to watch. Of course, for examples of my gut being wrong about such things, one needs only look at the games from 2004 and 2008, so who knows.

[SWIM]

Originally Posted by Kris Verdeyen

Exactly right on both points. I'm really pumped about the new robot building challenges, but as for the game as a whole, my gut says it will be boring to watch. Of course, for examples of my gut being wrong about such things, one needs only look at the games from 2004 and 2008, so who knows.

It's a safe bet the game will be boring for the spectators, considering how slowly the robots will be moving, and how much distance they have to cover.

[RoboGeek99]

Were debating between 2 kinds of drive systems...tank style and car steering (back wheels are powered)...which do u think would be better on this lack of traction situation? (keeping the trailer in mind)

[ZakuAce]

Originally Posted by RoboGeek99

Were debating between 2 kinds of drive systems...tank style and car steering (back wheels are powered)...which do u think would be better on this lack of traction situation? (keeping the trailer in mind)

I really like the car style because it doesn't require you to whip around the trailer every time you turn. I also like that you can keep your wheels pointed (at least as close as possible) to the direction you want to move in. The only disadvantage I can see is the robot can't turn on a dime.

Also if you do the car style, make the turning wheels powered. It will be easier, maybe the only way, to turn in the direction you want, since the surface is so slick your unpowered turning wheels may have little effect.

[neugebauer]

What about having a 2wd? Are the two wheels without motors easier to turn than wheels with motors? Or is it just as ineffective as the 4wd?

[=Martin=Taylor=]

Well we hitched the trailer up to our 4WD "long" bot (wheels on long sides)...

It sucked a** trying to steer...

Our driver came up with a novel solution of jack-knifing the bot back and forth which worked pretty well.

We'll have to try out some other configs to see how they do.

[writchie]

Originally Posted by neugebauer

What about having a 2wd? Are the two wheels without motors easier to turn than wheels with motors? Or is it just as ineffective as the 4wd?

One wheel and two wheel drives are definite possibilities. Whatever you plan to do, understanding the physics behind turning and towing are going to be critical. The trailer is both a field element that you cannot damage and an integral part of the robot. With some designs there me quite an interesting set of forces at work on the hitch.

[dlavery]

For all those that are making early design decisions based on driving experiments involving driving Robots on the "Regolith" flooring without a Trailer attached, I would urge exercising a LOT of caution. The driving/handling characteristics of a Robot with a Trailer are COMPLETELY different than a Robot without a Trailer. Learning how the Trailer affects the performance and agility of the entire vehicle system is critically important. And once you understand those effects, learning how to use them to your advantage is equally important. And don't make a decision too early - a driver with about an hour of practice will learn how to use the Trailer to spin the Robot through turns and pivots with a lot more agility than may have originally been anticipated.

As one benchmark, after a bit of practice I was able to take a standard kit-bot system with trailer attached and run it from one end of the Crater (starting with the Trailer touching the Alliance Station Wall) to the far end, execute a 180-degree turn and make contact with the far wall, and run back to the starting wall in about 12 seconds. This was repeatable several times.

-dave



.

[Greg Peshek]

Originally Posted by ZakuAce

Think you can put this year's wheels on your robot and give us a demo?

That was my first thought, but the setup of the robot doesn't allow the wheels to fit on the differential shaft, and since the differential wheels and steering wheels are different sizes - it would be uneven and just bad.

If only we could..

[rilesmitch]

Think of being on ice. The smaller the tire foot print, the higher the psi, and thus.... better the traction. Let's say the wheel provided has a footprint of 1 square inch, your robot comes in at 120 lbs and you have 8 wheels with the weight evenly distributed. Then you have 15 psi. Go to 6 wheels and your at 20 psi. Go to 4 wheels and you are at 30 psi, 2 wheels.... I think you get the idea.

Ideally, one wheel would be best. Let me know how to make that work.

I'm still in search of a very large bucket!

[Travis Hoffman]

Originally Posted by Dick Linn

Could you use a 2 WD hooked to a sulky and rigidly couple the trailer to that?

[off topic] My dad had a Gravely! Cool machine. [/off topic]

Originally Posted by dlavery

As one benchmark, after a bit of practice I was able to take a standard kit-bot system with trailer attached and run it from one end of the Crater (starting with the Trailer touching the Alliance Station Wall) to the far end, execute a 180-degree turn and make contact with the far wall, and run back to the starting wall in about 12 seconds. This was repeatable several times.

-dave

.

Was that standard "wide" kitbot or standard "long" kitbot?

[Dick Linn]

Travis, I'm not kidding about the Gravely form factor. That aside, they are interesting machines.

[FriedLiver]

So.. Our team was debating over what drive system to use. Last year was out first, and we chose to go with a 4-wheel tank system. This year, we are not so sure about using the same system because of what is being said here; the friction will just be too little. That brought us to active steering in the front or rear, not including all of the other crazy suggestions. We were wondering, would rear-wheel turning on a 4-wheel drive pose any significant handling issues in comparison to front-wheel steering. Our current design ideas leans in favor of a rear-wheel system, but we don't know exactly how that will impact our performance. Any input would be greatly appreciated.

- Team 2496

[GUI]

I think a rear steering system will have drastically less turning ability than a front steering system. With a front steering system, all the non-steering wheels are behind the steering wheels, so they will follow them. In a rear steer system, I think that the non steering wheels being in front and behind the steering wheels will reduce the turning ability, and lead to awkward handling characteristics. Take this with a grain of salt though, I am having a little difficulty imaging a rear steering robot with a trailer turning, so I'm probably missing something.

[FriedLiver]

Yeah.. We figured that maybe because we have the trailer attatched it may not be too much of a problem. Technically it would be steering from the middle with a pair of stationary wheels still behind the steering wheels. I am not quite familiar with the characteristics of a rear-steer (Ackermann), so I'm afriad there will be some crucial factors I am leaving out.