What type of drive train is the most maneuverable?

[Tom Bottiglieri]

A well designed 6 or 4 wheel drive system has always had the best ratio of pros to cons in my opinion.

http://www.chiefdelphi.com/media/papers/1443

That paper should show you how to get it set up correctly.

[thegathering]

While mecanum provides a nice balance of maneuverability with traction, the wheels themselves are fairly complicated, fragile, and can be expensive to machine/purchase. A two drive wheel two caster design is cheap in comparison and still provides great maneuverability. We chose the two caster design for our bot this past year.

[EHaskins]

another drive is the holonomic drive. It uses 3/4 wheels mounted 120/90 degrees apart. It is very maneuverable, but can be easy to push.

Vex Holonomic(the 8th post in this thread has the code needed to drive the robot) http://www.chiefdelphi.com/forums/sh...ad.php?t=46560
3 wheel vs. 4 wheel http://www.chiefdelphi.com/forums/sh...ight=holonomic
advantages of holonomic http://www.chiefdelphi.com/forums/sh...ight=holonomic
The math involved in driving a holonomic http://www.chiefdelphi.com/forums/sh...984#post354984

[Bill_Hancoc]

What have you done in past years. We usually do a 4 wheel skid steer drive type and have not had many problems with maneuverability. We usually do some grippy wheels in the back and some less grippy wheels in the front to reduce scrub when turning.

Kiwi and Mencanum seem very complicated to me if you are a lower budget team and unless you have access to a machine shop (and have people who know how to use it) i wouldnt recommend them to a team on a tight budget.

[AdamHeard]

team 294 has used a very simple solution the past two years.

Kit transmissions to 6 skyway wheels, the center wheels were treaded with waffle tread and lowered. We didn't have the best traction or turning ability, but we turned well and could push decently. Also, we were able to finish the base assembly in a day.

[Pavan Dave]

Team 118 used a crab drive, drive train. A crab drive lets all four wheels move together. So if you want to go left, your robot is still facing forward, but your wheels all turnto the left. It is THE most manuverable because it lets you get anywhere in a short amount of time because instead of wasting time turning your robot around, all you do is move the wheels and that made this previous years game easy because we could score while moving from one side of the field to another.

This what our wheel box looked like for our practice bot,


and this is what all four of them looked like.

[mluckham]

Originally Posted by Pavan

Team 118 used a crab drive, drive train. ...

What are the joystick controls you use? I can see that the robot can slew around very easily, but what if you really do want to face the robot to a different heading?

[Pat McCarthy]

Originally Posted by mluckham

What are the joystick controls you use? I can see that the robot can slew around very easily, but what if you really do want to face the robot to a different heading?

When HOT did crab in 2005, we used a regular black Flightstick (forward, backward, left strafe, right strafe) and a Playstation steering wheel to change the robot's orientation.
We just opened up the case of the steering wheel and soldered some wires onto the potentiometer to put into a gameport connector.

[PandaMan]

Although swerve drive can maneuver around objects, it is not the most physical of drive trains. From what I've seen, the most effective drive seems to be the 6WD.

[FourPenguins]

MORT's best drive train was a 4-wheel.
It used 5" (I think, I'm sure Brandon can correct me) Colson wheels with a very short, wide wheelbase (long robot, short wheelbase) to cut down on scrub. The tipping problems of a short wheelbase were solved with 4 ball casters, one on each corner. It handled beautifully, could get up some decent speed, and was a pretty vicious defender. (I'm pretty sure that robot provoked the no-wedge rule.) Keep in mind however, that this was a flatland drive train for triple-play.
General suggestions based on that bot:
*Colsons rock
*Find the happy balance in the ratio or use a 2speed tranny. (I don't remember what our ratio was.)
*Short, wide wheelbase reduces scrub.
*Ball casters are beautiful on flat land.
*Keep the game in mind. A flat game needs no clearance, a ramp does.

[MattLi]

Just an off topic post. If you want manuverable go with a wide robot. Doesn't matter how many wheels you have, it will still be better than a long robot.

[Madison]

Originally Posted by MattLi

Just an off topic post. If you want manuverable go with a wide robot. Doesn't matter how many wheels you have, it will still be better than a long robot.

All other things being equal, a typical six wheel drive along the long axis will have a shorter effective wheelbase than a four wheel drive arranged on the short axis.

[Joel J]

Is there a way to calculate the force (or torque, whatever) required to have a robot turn?

[dlavery]

Originally Posted by M. Krass

All other things being equal, a typical six wheel drive along the long axis will have a shorter effective wheelbase than a four wheel drive arranged on the short axis.

Uhhhmmmmm, not so fast there. As a general statement, this is not true.

It all depends on how you are going to define a "typical six wheel drive" and what assumptions and caveats you are putting on that definition. I will maintain that in a "typical" six-wheel drive, all six wheels are co-planar. In that case, the wheelbase of the six-wheel drive is established by the Conservative Support Polygon, which is defined by the four outer wheels. As specified in the original statement, the wheels are arranged along the long axis of the robot. The four outer wheels determine the resulting wheelbase, which by definition is longer than a four-wheel drive arranged along the short axis of the robot.

This fundamental truism is only modified if the definition of a "typical" six-wheel drive is altered to promote non-standard configurations. For example, the common practice of moving the middle pair of wheels into a non-planar configuration. On a hard planar surface, this causes the robot to ride on the middle set of wheels and one of the "end" set of wheels. Only four wheels support the robot, not six. Thus, the wheelbase becomes approximately half of the long dimension of the robot. But this is actually no longer a true six-wheel mobility system. It is a set of two four-wheel systems that share a common pair of wheels (the center ones). In this case, you lose many of the advantages of a six-wheel drive (ie. distribution of weight across more points of contact with the floor, greater stability across the longer wheelbase, etc.).

-dave

[Lil' Lavery]

In terms of pure maneuverability, mecanum is the best, as it can travel in any planar direction, change direction almost instantly, and can conquer inclines easier than a holonomic drive. Holonomic and ball drives can also travel in any planar direction and change direction almost instantly. Swerve drives can also travel in any planar direction, but they recquire time (often very small though) to change the orientation of their wheels. "Crab drives" (a variant of swerve drives where all the wheels are linked together) are the simplest swerve drive, but recquire more power (as the have to overcome more scrub) to move in curves. Afterwards comes the plethora of different scrub (tank/skid) steer systems.
4WD, 6WD, 2WD (and 2WD+caster), and many others all fall into this category. While some may recommend the caster system, I would advise against it. From my personal preferance, while quite maneuvable, the lack of control on the casters can cause more problems that it solves. It significantly reduces your control over your bot, and therefor reduces the amount of accuracy you can drive with. Momentum can often cause the rear end (assuming your casters are in your rear) of your bot to swing further than you want it to. It also makes you a relatively easy target to push (and incredibly easy to rotate out of position).
The "best buy" for maneuverability (in my opinion) would be a 4WD with 2 omni-wheels.