My team cannot decide on a drive train. We are either going with the four-wheel drive that FIRST provided or with a rear wheel drive and front wheel steering.
These are our arguments:
4WD:
Simpler design
Turning in one spot
Using 2 transmissions
Steering:
No chains to break
Easier control (programmed with steering wheel or 1 joystick)
So what should we do?, are there any other pros and cons to this?
My team members need some convincing! :ahh:
It depends what you feel is need for the startegy you are going for…
if your strategy needs lots of pushing with other robots and protecting goals then 4wd is good…
but stearing has its good points too…
With 6 robots on the field and a lot of tight corners to get stuck in, I would go for the spin-in-place 4WD, but that is just my opinion.
I would not go with a steering robot. I’ve seen many robots go that route for the good theoretical reasons, but in reality I have never seen it work too well on a FIRST robot. It is less maneuverable and actually harder to control. As far as chains go, for 4 wheels drive you could buy two more gearboxes then have a separate one for each wheel I suppose.
Car like steering = Hard to maneuver!
I would go with 4 wheel drive.
A steering robot is like driving a car in a crowded parking lot… Except you do not have to stop to shift into reverse!
Instead of 4wd you could have a 4 wheel drive to 2 wheel drive conversion by simply lowering casters that pick up the 2 front or 2 back wheels.
We have done this the past 2 years and we have used both Pneumatics and a Globe motor.
its a small field with 6 robots buzzin around on it… the steering better have a heck of a turning radius… also for the steering, im assuming you are thinking about how a car turns, more or less… hope you have a heck of an idea on how to do that easily and efficiently at ALL speeds… its not as easy as it looks… with 4wd, if you tension the chains correctly, and align the wheels and sprockets right, the chain will never break… the problem with 4wd is the differential in turning… the outside wheel needs to go faster than the inside wheel… find someone with a 4wd truck and ask them to go drive it in tight circles in a dry parking lot in 4wd…its not pretty… a robot will not have the drastic effects that the truck did, but you better make sure that it is well built and aligned properly… unless you have a proven method for the front wheel steering, I would go with the proven 4wd.
j
yup one more for 4wd here. The only year the steering made sense was for Stack Attack because it just made sense for going around the wall and up the ramp into the pile of boxes. You’re just going to be weaving between too many robots and tetras in this game to make it worth while. On the other hand, it will be a blast to drive.
Yet another vote for 4wd…You won’t have room for even a tight turning radius and defense will be important this year, so you’ll need the 4WD’s power.
Ditto on the 4WD, its been said. Car steering on a crowded field is simply just too difficult to control. 4 wheels does have its cons, but if you do go car steering, im sure you will quickly discover that it is very difficult to maneuver. In my past years I’ve seen teams with that kind of drive struggling.
…(this post not meant to slander the steering drive name)…
i’d have to stick with our drivetrain and go with 4 wheel drive. We use it every year now and it just works the best. It also has the most control especially when driving at your top speed
Plus… i dont get your argument against 4WD about the breaking chains?
4WD, i could see you getting stuck with front wheel steering. Also, try driving a remote control car in a scaled down field fron about 20 to 50 feet away, hard isn’t it.
the only problem with 4 wheel drive is your more likely to get stuck against a wall or something straight…
Steering is hard to program / control i would say. You need to find a good method of controlling with the joysticks for that. …
If you have the weight you could play with a 4wd and 2 wheel steering system. People have used this in the past with some success. Change the non-steered wheels to omni-wheels and you can now strafe (aka Wildstang 2004 w/o the pnematics to go up and down). If you want simplicity 4wd tank is the way to go.
http://www.wildstang.org/gallery/view_photo.php?set_albumName=2004_Invitational&id=P2201799
I didn’t know you can get stuck, wouldn’t your robot just spin out of it?
Or howabout 6WD…Even more maneuverable than 4WD, i think i spelld that wrong. Oh well. Because the turning radius would be around which ever side has the more weight because the middle wheel is slightly lowered. This may add some more weight though, but you could just have two gearboxes, one for each side, and then have the gearbox placed in the middle of the robot and attach the middle wheel to that and use two sprockets, one for the front and the other for the back. That’s a basic 6WD drivetrain. If you’re using the gearboxes from the KOP, you are going to have to machine wheel hubs because the wheels they provide do not fit onto the shaft. Also you may have to purchase new sprockets to fit onto the shaft coming out of the gearbox because I don’t believe that the two sprockets including the wheel can all fit on the gearbox. I dunno, that’s just what I gotta say. Good luck on your robot.
How can you get stuck against the wall? The only way you could if you intentionally tried to get wedged under something like the arena wall, but that would totally take out the arena wall too…That would be insane.
But o well, I might be wrong.
If you really want a 2wd, you could use two small omni wheels or casters on the front (or rear) of your robot and drive like a normal tank drive. We did this in the past and it did work well, you just don’t have as much pushing power as a 4wd would. However, it should be lighter than a 4wd too, and still be fairly maneuverable. 
I would not use a car type steering on a robot because of the limited area in which the robot must operate. It could be done, but I think that it is more trouble than it is worth.
yeah our team is planning on using 2WD instead of 4WD. If we don’t use casters nor car steering, what is a good substitute?
I assume you are having four wheels, with two driven. I would suggest making the driven ones really high traction and the non-driven ones fairly low traction.
were using 2 driven wheels, and dropping the casters and replacing them with teflon skids…something really slick…
j