Re: tank drive in this years game
 

I believe we will be doing a 6wd tank drive with a slightly lowered center wheel. we will also try to encourage it to ride on the back 4 most of the time.

Re: tank drive in this years game
 

We have decided to do a 4WD -wide with the wheels shifted back. This will increase maneuverability and because of the trailer, we're not as concerned about tipping forwards.

Re: tank drive in this years game
 

Could you please provide a link to this paper?

Re: tank drive in this years game
 

Here you go:

http://www.chiefdelphi.com/media/papers/1917

Re: tank drive in this years game
 

Personally, i like 8 wheel 1 motor = 2 wheels l:cool:
tones of traction but a bit on the heavy side:eek:

Re: tank drive in this years game
 

Our mechanical team's basic idea was to use a 4WD system and then make getting it to actually work a programming issue. Although we've also got a "steering booster" system using a gyroscope to help us make sharp turns.

Re: tank drive in this years game
 

We are also thinking of 4 wheel tank drive on a wide chassis? We have also considered a long wheel base with the wheels moved toward the rear of the bot. Just a few questions, has anyone tried running the wheels directly from the toughbox gearbox? Does it work? Are their any modifications needed to make the wheels run directly from the toughbox? We are thinking that the weight from four toughboxes near the wheels will increase friction by increasing normal force near each wheel.

Re: tank drive in this years game
 

what makes a wide base better than a long one?

Re: tank drive in this years game
 

Generally having a shorter wheelbase makes it easier to turn. It's the same concept as having a 6wd with the center wheel dropped, you are basically creating to 4wd systems with shorter wheelbases.

Re: tank drive in this years game
 

4 wheeled tank drive is what i think my team will do *696* MAYBE because we finish designing our bot tomorrow or the next day *this is with complete design with sensors and exact dimensions etc.

Re: tank drive in this years game
 

"Better" is a relative one. The ease with which a base with tank steering and 4 wheels touching the ground turns is related to the ratio of wheel track (width between wheels) and wheel base (front-to-back distance between wheels).

A robot with a long wheel base and narrow wheel track (in FIRST, the 28" wide 38" long configuration) prefers to drive straight, whereas as robot with a short wheel base and long wheel track will turn easier, but have a harder time driving completely straight.

The reason for this is because a 4wd tank steering system requires all of the wheels to skid sideways slightly when turning. If you imagine the robot trying to turn around its centroid, the wheels ideally want to be rolling along the circle circumscribed by their radius to the center of rotation (aka the wheels would prefer to be rolling tangent to the circle described by that radius) But because the wheels are all oriented in the same direction (which is not tangent to the circle), it's easy to see that they will all be sliding sideways slightly in addition to rolling forwards or backwards.

Now go back to the long and narrow versus short and wide base. The wheels on the long and narrow base are pointed at a steeper angle away from the ideal tangency than those on the short and wide. The extreme case for the long and narrow is when your frame gets so long and narrow that it becomes a line, with one wheel at each end oriented to roll along the line. Trying to turn around the midpoint of this line will cause the wheels to only skid sideways and not to roll forwards or backwards. Thus we see that the higher the ratio of wheel base to wheel track, the more skidding is necessary and the harder it is to turn. In addition, because the wheels are laterally closer to the centroid, the torque they can apply to the center is less. In the extreme case, the wheels cannot apply any turning moment to the midpoint of the line, because the applied force is going straight through the point of rotation and thus the lever arm is zero. Conversely, if powered, these wheels will drive ONLY in a straight line, because they cannot turn.

In the extreme case of the short and wide base, it again becomes two wheels on the endpoints of a line, but this time the wheels are oriented to roll perpendicular to the line. In this case, the wheels ARE rolling along the line of tangency, and therefore are not slipping sideways at all. This is the theoretic best case for turning, but the wheels are much more susceptible to being rotated, since they do not resist the rotation at all.

In the context of Lunacy, a while wheel base provides a better turning ability. When you have a trailer attached, it becomes easier to drive a wide base in a straight line because the trailer is trying to straighten out the robot, and it also becomes easier to turn because your wheels can provide the maximum torque about the point of rotation.

Re: tank drive in this years game
 

i dont think any kind of special drive trane is going to be that much of a help because the wheels slip around no matter which way they are oriented. persoanally i love tank drive but i am thinking about arcade (which i hate). the reason being is that both sides of the robot will turn exactly the same rate. on a normal playing surface the human error between the two sides was negligable but on this surface any amount of wasted traction is a lot. but i dont know yet, we need to test out on the regolith on wide set base. its been agreed that a wide set base is definitely the way to go. this will allow more space in out colletion system, and the large space between the wheels will lessen the differential between the wheels. but of course, we have to try it first.

Re: tank drive in this years game
 

Theoretically, crab drive will give you an advantage.

Skid Steer is just that - skidding your wheels. Which, as we all know, takes a substantial hit in the friction depart. Theoretically.

The crab drive's advantage is threefold:

One, you do not skid the wheels when turning.
Two, you do not need to impart angular momentum to your robot to turn. In fact, if you drive in the direction you want to go, the trailer will help turn your bot for you.
Three, you can turn your wheels sideways. According to the theoreticals, the sideways friction is much higher than the linear. So, again theoretically, a tank drive robot trying to push a crab robot will not be able to if the crab turns his wheels sideways.

In the past, we were always limited by torque. Now we're limited by friction. However, the weight of crab may be an issue for many teams less familiar with it (like ours). You're going to need a good deal of manipulation on your robot - pickup, accumulation, release... those probably won't be lightweight.

Re: tank drive in this years game
 

I am becoming increasingly convinced that people are underestimating the tried 'n' true skid steer bot this year. All indications I've seen from those who have tried it with the rover wheels are that turning and moving aren't really problems.

Will a crab drive give better performance? Sure - it always has and always will. But the drive system style is dwarfed by strategy, driving ability, and scoring function when it comes to who gets to stand in the winner's circle. Some teams have the resources to make a crab drive to go along with an excellent robot in other areas. Others don't. I am not convinced that you will see any more crab drives hoisting blue banners than in other years.

Re: tank drive in this years game
 

I think that 4W drive may be the best solution. We looked at crab drive systems. However it seems that once you take into account the trailer, you will have less control given that a sudden change in direction would cause the trailer to jackknife and spin the robot around.

Have any teams done testing with a crab drive and a trailer?