drive styles control and general info

alright so i have been thinking if i were to use a drive style like the one pictured bellow what would be the best way to control it? i would want to be able to use it like a normal bod so you can spin around like normal but also add the capability of going side to side using the perp. wheel i has thinking of putting the standard drive on one joystick and using the other just for the side to side movement.

also i would like to talk about honolomic (spelling?) drive. so i know that it enables you to go forward, back, side to side but can it also allow you to drive on the 45’s by driving two wheels that are parallel to each other and leaving the others off. plus how can you spin around using this drive system? i guess my question is really how do you control it? i know you need a program but that is no trouble i am just stuck on after writing the program how to use the joysticks to enable all of this.

I’ve never programmed one of these so I’m going to take a crack at it, although the ones who actually used this might be able to help you more than I can. ;).

To go in a 45 degree line, that would that your robot is going forward/backward and left/right at the same time. Now when you go forward, you can’t really turn the left and right wheels cause then it’ll change the orientation of the robot, you would have to turn the center wheel.

Using a VEX controller, The way I can think of is that one of the joysticks controls the x and y directional movement, while the other joystick’s x value controls the center wheel. So when you want to change the orientation you take joystick1 and jam it either left or right, but if you want to change actual position left or right, then you jam joystick2 either left or right.

But that’s just how I would go about implementing it. If you actually want code in RobotC, then PM me. :D.

And did you try to search for this? Cause I’m sure that a drive train as juicy as this has not been left out. :D.

The Robowranglers(148) 7-wheel omni-design was fantastic in 2009 Elevation!

I think you have the right idea for joystick control. Just have side by side motion on the joystick controlled by ch1 or ch4 on the joystick.

as for the 45 degree drive i was talking about holonomic drive. how do people usually go about controlling that. especially for spinning around.

also why does it seem like nobody uses the small omni wheels?

I assume that you actually meant, “nobody uses the small omni wheels for holonomic drive robots” right? It’s because a direct-drive 4" wheel is reasonably fast, but direct driving the 2.75" wheels is slow. If you use the small omnis and want to go fast you need to put a gear train in, which complicates construction. Also, the 4" omnis have better grip than the smaller wheels. I 4" omnis.

It would be fantastic if they could add 2 more channels to the vex remote. “Where would you put them?”, you ask. Well, I would make the sticks rotate. 2 axis (x and y) and a rotation. Then you could use the x and y to move forward and back and strafe left and right. turning the stick itself could be rotation of the bot.

Rick is right. Bigger wheel is faster and plus they look daunting. :D.

As for the control, by spinning around you mean…? I’m going to assume that you mean change orientation, in which, you’re robot’s front turns 180 degrees and faces the other side…

In the control, if you take joystick1 and turn it either way, the robot will change orientation and “spin.” Let me know if that was the correct definition.

well what i mean is that if you have a bot with holonomic drive (4 wheels all at 45 degrees right?) and you want it to go forward you would push the stick forward down the stick down and left and right you would push the stick left or right. what if you wanted to spin the bot (like change orientation) what would you do?

also for the original picture i posted it shows 3 motors being used on the 4" omnis is that realistic or just to make for easy modeling? by realistic i mean could a comp bot use only 1 motor per side and 1 on the perp. wheel and still move? does anybody know what the robowranglers used?

Either five or six - one on each of their four rear parallel wheels, and one or two (I think two) on the perpendicular one. They put two on their arm and two on their intake.

See 148C here:

i think two on the perp makes since.

I’m hoping you can explain this some more to me. As I read this, I’m thinking that the center wheel is only having 1/4 the force to move the same weight against what might be greater resistance.

The answer may be as simple as “One motor is all I have left by the time I’ve added everything else on” or “It’s just for slight adjustments so it won’t be running under load for even a full second”. I’m just curious to understand why you made the decision you did.

I think the best “design” of a program would be for the left stick to move the bot in a line. For example, if you push the stick to the upper left corner, the bot would go at a ~45 degree angle. The further you push the stick at that angle, the faster it goes.

You’d have to do some math to get the angles from the sticks, then apply that intelligently to all the motors involved. The stick on the right would use the horizontal (left/right) axis to spin, which would be easy you’d just add or subtract that value from all the motors.

This would be for a 4 wheeled omni bot. I don’t think it matters if your wheels are in the corners at 45 degrees or in the middle of each side parallel, except I bet the corner’d wheels are more resistant to tipping.

I’m pretty sure I saw someone post code to do exactly the driving I mention above.

yeah that sounds like it would be the best way to do it the only thing is i would probably switch the sticks from what you had just out of personal preference.

I am going to bump this thread really quick, cause I gots a question. :smiley:

Um…I’m assuming the 3-D model in this thread is the same as the drive shown here:

Are they using 3 motors total for the drive? And I’m guessing it was rather successful?

All three 148 robots were very successful at Dallas - see the results here. As for their drive base…

Thanks for the info. :smiley:

Hi Sunny,

We missed you yesterday at the workshop.

We had several demo robots using this drive out for folks to test drive.

  • Mr F

Hahaha. I originally planned on coming, but things with parents came up and I couldn’t come :’(.

And Tanner brought back pictures and hinted that I should try this type of drive, so I was just here trying to pick up some info about 148’s drive. I don’t think I’ll be doing this drive though. :smiley: