2WD diagonal System

[Tom McCurdy]

I was wondering if any team has attempted to create a 2WD diagonal system. Our team is currenlty attempting this at the moment. If you have any information on the subject please let me know how it worked out.

[Greg Ross]

Originally Posted by Tom McCurdy

I was wondering if any team has attempted to create a 2WD diagonal system.

2WD diagonal system? Doesn't ring a bell for me. Can you describe what you're envisioning?

[greencactus3]

do you mean as a "square robot" with its wheels on 2 diagonal corners and 2 on the other 2 corners? will this robot drive straight like that or will it drive with one caster "point" as forwards?
if you are going for a diamond sahped robot thats cool. but its still a center 2wd so itll be very manueverable as in very turny. but harder to go straight than a 'normal' 2wd and if you mean as in

PW=powered wheel
CW = caster

....(forwards)
PW----------CW
|....................|
|....................|
|....................|
|....................|
|....................|
CW----------PW


then this robot will turn in the left direction much better than in the right direction. this i think will be hard to drive too. as the pivot point in a one side braked-and-other-side-powered-turn different in each direction. i see no reason to do this.

................CW
............../......\
............/..........\
........../..............\
.......PW..............PW
..........\.............../
............\............/
..............\........./
................CW
would be a fine design i think.
it would be a wider stance than most robots. but will sacrifice a bit of foot print as to make it work well you'd want to make it a all same sided square and the rule's dimension is not like that.

[Tom McCurdy]

Let me see if this helps

Top Left
Top Right
Bottom Left
Bottom Right
TL TR
________________________












----------------------------
BL BR

we have the gearbox run BL and TR instead of the top 2 or bottom two in an atempt to allow the bot to rotate quicker. The bot is not square but retangular.

[Don Reid]

How does it turn?

[Mr. Ivey]

Just thinking about it, having the frame in a diamond shape would work well, but square, i believe it would have a tendancy to rotate an un-needed amount. But that's just my idea...
ivey

[Tom McCurdy]

I am not sure how the setup would be for a diagonal ... could u draw something out?

[Greg Ross]

Originally Posted by Tom McCurdy

I am not sure how the setup would be for a diagonal ... could u draw something out?

He tried above, but the formatting got messed up. I think I got the idea. See if this helps:

Originally Posted by Tom McCurdy

Let me see if this helps

Top Left
Top Right
Bottom Left
Bottom Right

          TL                                 TR
          ________________________
          











          ----------------------------
         BL                                   BR

we have the gearbox run BL and TR instead of the top 2 or bottom two in an atempt to allow the bot to rotate quicker. The bot is not square but retangular.

[tkwetzel]

Originally Posted by gwross

He tried above, but the formatting got messed up. I think I got the idea. See if this helps:

That was the same person who posted the question. I think he was asking about a diamond shape versus a rectangular shape.

I think this (posted by greencactus3) might help:

................CW
............../......\
............/..........\
........../..............\
.......PW..............PW
..........\.............../
............\............/
..............\........./
................CW

If you are looking for something else, please specify what else you want to know. I actually thought about doing something like that, with omni-wheels in the two CW positions perpendicular to the two drive wheels. I also thought about making a square/rectangular robot with one wheel on each side parallel to the side, so it would work like the above design, but still be larger. Than only problem with that would be the weight that is out on each corner, because it wouldn't be supported by all four wheels. I hope this post made sense.

[greencactus3]

no, that wont rotate faster. actually slower as it will have more scrub. if you want fast turning, have the 2 powered wheels parallel to eachother with the axis of both being on the same line.


W........................W
H........................H
E........................E
E........................E
L........................L

the easiest way to prove this is make a model. doesnt matter how small. lego/knex would work just fine.
just make a rectangular frame, and mount the wheels in a 'normal' 2wd configuration and spin it. it spins quite well with the turning axis (yaw axis) in the direct center of the 2 wheels.
now try it with the diagonal setup.
see? lots more scrub because the yaw axis is at the center of the 2 wheels and that means the line connecting the yaw axis and the center of the wheel is not perpendicular to the wall of the wheel. which means it scrubs. if you want to know more about why scrub is not optimal, look up ackerman. you will probably find info about car steering and how the inside is tighter than the outer. wel anyways. i would say this diagonal is not a good plan. hard to drive, and there is nothing that is better about it than a normal 2wd. if you want fast turning, make a 2wd machine with the yaw axis right on the center of gravity. to make it go straight easier, have the center of the yaw axis behind the cg as so it will "push" but this means going backwards will "pull" which equals very sensitive to non equal right and left power outputs. so the most consistent, easy to drive 2wd in an application that will go equal amounts fore and aft id say is center 2wd. which there are threads against and for, again the search thing will work well to look these up.

[Mike Ciance]

the best way to go is having all the wheels drive. if you just chain the front and back axiis together the robot will perform much better

personally, i think 6wd is always the way to go with tank drive.

[Greg Ross]

Originally Posted by tkwetzel

That was the same person who posted the question. I think he was asking about a diamond shape versus a rectangular shape.

Oops. Sorry.