Tank Drive Car
 

Does anybody know where you can get a tank drive car, or how to make one. I don't mean a go cart, I mean an actual car. Our team members have been using tank drive so much, they've come to the point where they have no other way of steering, myself included. So does anybody know these things?

Re: Tank Drive Car
 

I'm pretty sure you can't get such a thing. Car steer because they are made for going in a straight line without a lot of stop and go. Robots have skid steer since a zero turn radius is useful and they stop and turn quite frequently. If you're looking for a good industrial example of a skid-steer, check out a bobcat.

Re: Tank Drive Car
 

There is this for a laugh.

But in reality skid steer would be quite dangerous at high speeds and damaging to roads, plus everything is designed to handle a large turning radius that results from a car.

Re: Tank Drive Car
 

You might be able to buy one from a Tire Store. ;) They would probably give you the car if you would promise to buy your first N sets of tires from them.

Re: Tank Drive Car
 

Every once in while somebody posts an M113 for sale on e-bay. They are quite reasonably priced, agile, configurable (APC, medical evac, command and control, engineer, utility, etc.). And the US government will be disposing of THOUSANDS of them over the next six years. These tracked vehicles are 1960's era skid steer and some (all?) use the differential lever type steering you're looking for... "tank drive".

All modern agile tracked vehicles (military high mobility platforms) use a steering wheel, accelerator, and brake pedals. The newest ones might even start using a joystick. I don't see them going back the two stick design, it's not in any trade studies I've seen anyway.

Have any teams looked at user interface studies on "tank drive"? Our results from an early season test this year showed that independent up-down and left-right (axis 1 and 3) on a PlayStation style Logitech game pad was twice as fast for combined gross and precision movements. Our study involved at least 5 untrained users (users unfamiliar with the platform, not unfamiliar with various control methods) and the results were consistently half the time, even for those asking for "tank steer". Why is "tank steer" so popular?

Re: Tank Drive Car
 

Seriously, there's several major reasons why nearly all motor vehicles user Ackerman based steering instead of tank drive, including but not limited to cost, tire life, safety, ease of use, mechanical complexity, maintainability, etc.

Re: Tank Drive Car
 

Make these guys an offer. :eek:

Re: Tank Drive Car
 

Shoulda wired up an RC car controller to your robot, like we did....

http://www.chiefdelphi.com/forums/sh...23&postcount=6

(my old bulldozer has tank drive, complete with metal tracks, but steering requires using the brakes as well as pulling the steering clutches)

Re: Tank Drive Car
 

I didn't intend to have the car "street legal", just able drive with tank drive. A few of our senior and junior members (who have licenses) really want to try it out, and for some strange reason, our mentors said yes. So, they're anxiously awaiting for me to send them this thread. I do like that tank one......

Re: Tank Drive Car
 

Think about how far the outside rim of a steering wheel moves when you drive a "normal" car. Then think about the levers you'd use to get this same action from a tank drive setup. Would the leverage ratio be the same? how would it work?

Re: Tank Drive Car
 

Easy. Build this years kit bot Jenny-rig a seat on it then put to control system in there lap.

But if you want to acctually want to drive something full size, a tank is your best bet (ps some tanks are street legal in France).

Re: Tank Drive Car
 

I know a Jenny-ring is 8675309 but what is a Jenny-rig ?

Re: Tank Drive Car
 

This may very well be a big part of the future of racing, the ability the combine a traditional car system with hub motors to cause differential motion AND generate yaw would be very good in the corners indeed. Apparently a few Formula Student teams in Germany are working on exactly that.

Re: Tank Drive Car
 

Waaayyyy back when I was the drive coach on my old team, we did a study that showed that drivers all did better with "arcade drive" than with "tank drive" (then weren't known as that back then). On that team, we forbode "tank drive" after that.

I've been wanting to go to independent fore/aft left/right for years. We finally did it this year, but NOT with two sticks. We use one stick for the fore/aft and a spring-loaded knob for the rotational movement of the robot. This setup was extremely intuitive the drive, and it even eliminates the "turning in the opposite direction while the robot is facing you" problem with a stick. I'm thinking we'll stick with this configuration for a while.

Re: Tank Drive Car
 

She would be Jerry Rig's sister.

Re: Tank Drive Car
 

To your knowledge, does this interface already have a unique name, and if not have you given it one that we could use here on the forums?

Re: Tank Drive Car
 

No, we haven't given it a name. We've been talking about using this interface since the 2008 game, but this is the first year we've actually done it.

Feel free to think of a good name. I'm not very good at coming up with names.

Re: Tank Drive Car
 

Chris,

Do you have any idea why using the knob works better than a joystick when the robot it facing the driver?

I have suggested a rotating control to our team several times, but none of the students seem interested. I just figured it was the gaming mentality coming out.

-Hugh

Re: Tank Drive Car
 

I know you addressed this question to Chris, but while you are waiting for him to answer...

It is because with the twisting action of the knob, the driver intuitively thinks of rotation as a clockwise/counterclockwise thing (which is independent of the orientation of the robot) rather than as a go_left/go_right thing.

Re: Tank Drive Car
 

Excellent point! I didn't think of that... Thanks Ether.

I will try that point with the students...

Any ideas for a good supplier of a centered spring return pot?

-Hugh

Re: Tank Drive Car
 

Thank you Chris for confirming my quick study!!

We call that type of interface, "RC Car steer", because they are independent sticks (used with your thumbs).

Chris's design is more like a modern RC car where you have a throttle and a wheel on the side of a gun like stick... sounds like he has it laid out flat though? mini steering wheel then?

Either way, they are independent up-down and left-right axes where you cannot inadvertently bump one when doing the other. I'd call all of them "RC car" steer.

We also used speed encoders and stiff proportional gain to enforce the selected turning angle... At that point it felt like a highend RC car (linear turn angle response), except that it really slowed down in the turns. We put neutral axis steer within a deadband of zero speed. The problem was that the stiff gain was a serrious battery killer and we ended up going open loop during tele-op.

One of my objectives in software for team 302, is to push the actual driver interface to the drive team to program, or at least become an itegral part of its development. If we have multiple drivers, they can have different "crew stations." One driver can have tank steer and another RC steer, and different buttons for "turbo" and "crawl", or this year's "spin throw". Different joysticks with different dead zones... the trick is to create a module which generates the same high level commands.

This architecture is shown a little bit in our VIRSYS example code... where among other things, we will be driving a virtual robot before it's built and able to practice anytime/anywhere. http://www.chiefdelphi.com/forums/sh...ghlight=VIRSYS

Re: Tank Drive Car
 

Ether said it exactly.

If a student has a hard time thinking of clockwise/counterclockwise, I say the following to them: "place your index finger on the front of the knob (part of the knob farthest from you), and your thumb on the back of the knob (part closest to you). Now, the front of the knob (your index finger) represents the part of the robot farthest from you - regardless of which direction the robot is facing. The back of the knob (your thumb) represents the part of the robot closest to you - regardless of robot orientation." That works better for some students. It's really depends on the person as to how they sort things out in their mind, but the knob keeps things much more consitent regardless of robot orientation.

We looked like crazy for an off-the-shelf spring-loaded knob. We couldn't find one. If anyone knows of one, please let me know.

We had to make our own spring-loaded knob out of a potentiometer. We did the spring loading by drilling a hole into the knob then running some surgical tubing from the hole to a screw in our control board about 10 inches away. It was a bit crude, but it worked. We wanted to create a better solution eventually, but you know how it goes when you have a million other things to do to get the robot shipped and the current solution works.

Re: Tank Drive Car
 

these ones

http://www3.towerhobbies.com/cgi-bin/wti0093p?&C=JAC


each have two spring center off loaded pots. one for steering, one for throttle.

Re: Tank Drive Car
 

Surprised you didn't just use the twist axis of a "side winder" (take the stick off and put a knob on there), that has a nice return. Or a "3D mouse" or "space ball" has a nice twist axis and would work too. It's easy if they are recognized as "gamepads" and not mice... not really sure about that though.

Re: Tank Drive Car
 

Here is one:

http://www.precisionsales.com/potent...ringreturn.htm

-Hugh

Re: Tank Drive Car
 

That won't work because it is is spring return to one end, not to center.

Re: Tank Drive Car
 

Anybody had a look at the Playstation Ultra Racer?

Re: Tank Drive Car
 

What is the meaning of this, then ?

Re: Tank Drive Car
 

Oops, i guess it will work.