In the past we have went with regular wheels and Arcade drive. But just last week (or 2 weeks ago) we got ourselves a set of macanum wheels.
I was wondering if someone can explain the logic behind these wheels and Where to start to actually programming this so we can use 1 joystick and go in all directions using the wheels.
1514
Whcirobotics
(Accidentally named the thread “ddrive” sorry for that its just “drive”
There are several whitepapers you can look at.
Getting the wheels on in the correct orientation is where people seem to have the most trouble.
The code is pretty simple, just be sure you connect the correct PWM to the corresponding wheel.
This code also assumes you’ve purchased a joystick that twists.
The code that you have attached in the thumbnails > why does it only have 3 axis? I was told macanum drive or Holononic Drive has 4 axis? And that code is enough? I thought it was more complicated…
But more important than the code provided… can you explain me how they function. The logic behind it. I want to program it from my understanding and see if it works. If you could explain me the logic please. 
1514
whcirobotics
How do we get the macanum - cartesian under the holonmic Drive?
A 4-mecanum-wheel robot has 3 degrees of freedom: fwd/rev, strafe, and rotate. To obtain these 3 degrees of freedom, you have to issue coordinated commands to each of the 4 wheels
And that code is enough? I thought it was more complicated…
That code is enough. It is not complicated.
But more important than the code provided… can you explain me how they function. The logic behind it. I want to program it from my understanding and see if it works. If you could explain me the logic please.
This explains the kinematics (the “logic”). It shows a mathematical derivation of why you must drive each of the 4 wheels at a certain speed in order to obtain a desired vehicle motion.
This tells how to write your own mecanum code for 3-axis joystick or for two 2-axis joysticks. It includes constants for adjusting the sensitivity of each of the three degrees of freedom.
**
O wow … i thought it would be more complicated. I will try this code with mac wheels and see if it works.
Thanks for clearing up that it only needs 3 axis. I had looked at someones code and seen that they had 4 axis… there code wasnt working. now i know why…
I will try this and get back with the results
You guys may think why i am starting many new threads everyday with different questions, the reason is because last year our robot did not have a functioning kicker code and in the competetion out of the 8 or so games, we only played in 3… because it wasnt communicating wirelessly.
I have been able to fix these problems in the past few days and i am thankful for chiefdelphi helped me greatly.
1514
Whcirobotics
Note that Mark’s code is really used for a joystick that twists (the kit joysticks don’t).
If you have a joystick that doesn’t twist, you usually program 2 buttons to rotate the robot in different directions (you may have experienced this concept in video games, where the rear controller buttons rotate the vehicle/whatever you’re in).
If you want to do this, you basically test both buttons and send different values to that Rotation terminal based on which button is pressed, if any. Doing that might get complicated, so if you can’t figure it out, feel free to post back or check out this recent thread that is very similar. They talk about controlling a motor with two buttons.
You can also use a second joystick. The first joystick will control what I call “move” (forward/ backward relative to the robot’s center) and “translate” (left/right relative to the robot’s center). Assign the Y axis to move and the X axis to rotate the robot. The second joystick can have its X axis assigned to rotate the robot about its center.
Hope this helps!
I think there’s a typo. You have “rotate” assigned twice. One of them should be strafe, right ?
If you have drivers who are already proficient with a tank drive interface, and you want to take advantage of that, you can use two 2-axis joysticks in standard “tank drive” mode to control the mecanum vehicle.
The left and right joystick Y-axes act just like tank drive to control fwd/rev and turning.
The X-axis on one of the joysticks controls strafing. To avoid inadvertent strafing, you can activate the X-axis command only when a trigger held down.
**
@ Buildmaster5000 and @ Ether
I have attached a picture of what you guys suggested. Is it correct?
And plus, how do i get “Macanum - Cartesian” under the Holonmic Drive. Like what Mark has in his picture.
@ RoboMaster
so the Joystick, Attack 3 we got in the kit is not sufficient? What joystick is to be used then? And if any what extra bit coding is involved?
1514
Whcirobotics
Macanum Snippet Chinmay.doc (82 KB)
Macanum Snippet Chinmay.doc (82 KB)
Have you installed the LabVIEW update released 2/15/2010?
O there is an update :S i will do that right away
That depends on what driver interface you are trying to implement. Can you explain what you think this will do, from the driver’s point of view?
**
The Attack 3 joystick is not sufficient for extremely simple, basic wire-up programming and control of holonomic drive. If you want to use it, you’ll have to do a little more programming to work with what you’ve got. But that’s where you have options based on how advanced you want to be or what you think is easiest to drive or program.
I think Ether and buildmaster5000 were actually talking about two different drive techniques. But they’re both good basic ideas. Let’s see if I can describe them:
“Strafing-based holo drive” (what I was describing with buttons and buildmaster5000 with a joystick): one joystick controls strafing (wire up X and Y from joystick to X and Y on holo drive VI), while buttons or another joystick axis control direction/rotation (wire something else up to the Rotation terminal). This means that to turn around a corner you drive straight with the first joystick, but at the same time you need to rotate with your buttons/other joystick so that your direction changes too.
“Tank-based holo drive” (what Ether was describing): robot is driven normally like a tank: two joysticks control the left and right wheels of the robot. But, when the driver presses a button, the robot switches to strafing only, where one joystick controls strafing. This might be a little trickier and would require a combination of the holo drive VI and the tank drive VI (switching between the two based on if the button was pressed). However, this is nice and easy to drive because you normally just drive with the tank drive technique, which is intuitive. The strafing is like an added bonus.
(Note: you could use arcade drive instead of tank drive, which would require only one joystick. The point is that you’re switching between that and holo drive to enable strafing).
Sorry if that was super abstract and hard to describe. But there are many ways to actually drive and control the robot with holonomic drive, just like how you can control a basic drive with arcade or tank drive, take your pick. So yes, the holo drive programming itself is easy since we have a nice holo drive VI, but there’s still a bit more you have to do to apply it.
I might post visuals of the programming I described if you want. Right now I have to do something else, though. Hope that helps!
I think the code will enable the Joystick 1 ( also called move joystick) to control the Up and down and Strafing part of the driving. And the Joystick 2 ( also called the Translate Joystick) to control the left to right part of driving.
For a first test to make sure everything works the way you expect, I’d suggest using just one of the Attach 3 joysticks and using the simple code as-is.
Assuming you get the LabVIEW update installed.
That just means rotate will be controlled by the throttle on the Attack 3, so make sure that’s centered when you start.
Once you’re sure the mechanics all work properly and the PWM wiring goes to all the correct motors, then start improving the controls.
Correct. You use the Y axis of each joystick for tank drive.
But, when the driver presses a button, the robot switches to strafing only
That’s not what I was describing. When you hold a button down, it enables the X axis of, say, the right joystick. The X-axis controls strafing. But the Y axes are not disabled. The Y axes of the 2 joysticks continue to operate as tank drive in this mode, controlling the fwd/rev and rotate degrees of freedom. So the driver, if skilled enough, can control all three degrees of freedom simultaneously.
The button is not required. You could leave the X-axis (strafe command) enabled all the time. Field experience has shown, however, that it is useful to disable the X-axis unless it is needed. This way, the driver doesn’t unintentionally command strafe when he doesn’t want it.
This might be a little trickier and would require a combination of the holo drive VI and the tank drive VI (switching between the two based on if the button was pressed).
All it requires is the cartesian mecanum vi. No switching is required. Calculate (Y1+Y2)/2 and feed it to the cartesian mecanum vi “Y” input (fwd/rev). Calculate (Y1-Y2)/2 and feed it to the “rotation” input. Feed X to the X input (strafe). This will provide tank drive with the left and right joystick Y axes; and when X is not zero you will get strafing too.
However, this is nice and easy to drive because you normally just drive with the tank drive technique, which is intuitive. The strafing is like an added bonus.
Exactly.
(Note: you could use arcade drive instead of tank drive, which would require only one joystick. The point is that you’re switching between that and holo drive to enable strafing).
You could use 2 joysticks for arcade+strafe with the cartesian mecanum vi: Y1 for fwd/rev, X1 for rotate, and X2 for strafe.
**
Wise advice.
Something I’ve found to be helpful too: Put the robot up on blocks and observe the wheels:
When you command straight forward, all four wheels should spin forward.
When you command straight backward, all four wheels should spin backward.
When you command pure CW rotation, the front and rear port side wheels should spin forward and the front and rear starboard wheels should spin backward.
When you command pure CCW rotation, the front and rear port side wheels should spin backward and the front and rear starboard wheels should spin forward.
When you command pure strafe left, the front port and rear starboard wheels should spin backward, and the front starboard and rear port wheels should spin forward.
When you command pure strafe right, the front port and rear starboard wheels should spin forward, and the front starboard and rear port wheels should spin backward.
Pay careful attention to how you have the mecanum wheels mounted too: * *Right way * * Wrong way
**
Good points, Ether, thanks.
Yes, I suppose I should have said it was my version of your describe drive, but I was just being general and as simple as (I thought) possible. But you explained your control ideas very well in your (second to) last post, thank you. I new you could probably drive a robot tank style with the holo drive VI, but it would require complex converting of two joystick axis into the X and Y holo drive terminals. Thanks for your explanation of how to do it easily!
I have finished coding it and i have attached a picture. Is it accurate? i just want to make sure so i dont disappoint the construction crew that worked so hard to make me a test frame with attached macanum wheels.
macanum code.doc (86 KB)
macanum code.doc (86 KB)
