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Unread 04-23-2012, 08:11 AM
Mike Hawk Mike Hawk is offline
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Mecanum wheels interaction with ground Motion Study

Hello

I am a last year student in elektromechanics and for my thesis i have to draw a robot in solidworks and simulate the movement using Labview

The robot has 4 special wheels on it called Mecanum Wheels. These wheels let you drive in any direction you want (sideways, left, right) .
Check youtube if you want to see them in action.

We currently use these mecanum wheels on the actual robot http://www.fingertechrobotics.com/pr...mecanum-set-cg

The problem I face is establishing the sideways driving. If you want to drive sideways, for example left: you have to turn the 2 wheels on the left side towards each other and the 2 wheels ons the right side away from each other.

When is start the motion study with this setup the robot doesnt move in the desired direction instead it just goes back and forth slightly going to the opposite direction (right)

In this link i included the robot design with the motion studies. check motion study 3 for the setup i explained
http://dl.dropbox.com/u/53407846/Sol...ts%20forum.rar

I hope you guys can help me out a bit
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Unread 04-23-2012, 10:40 AM
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Re: Mecanum wheels interaction with ground Motion Study

If i remember correctly, you have to tell it that each caster provides a certain force in a certain direction when you rotate it a certain direction. Simulating Mecanum is tough stuff, and I have only done it once as part of a team of 4 (2 students and 2 highly experienced mentors) and it took us a while.

Edit: not all "certain direction"s are the same direction
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Unread 04-24-2012, 05:46 AM
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Re: Mecanum wheels interaction with ground Motion Study

I tried adding forces to the design but it would be much easier if the wheels interact properly with the floor.

if i add forces i can only move in one direction (the one of the forces) and then the wheels dont really matter because i'm actually pushing the robot in that direction instead of letting the wheels do the work

Doesnt it has anything to do with the friction between the ground and the wheels? i made my mecanum wheels as perfect as i could (no bumping when going forward) so i dont think it has to do with my design

M
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Unread 04-24-2012, 08:51 AM
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Re: Mecanum wheels interaction with ground Motion Study


Is your assignment to do a dynamic or kinematic simulation?

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Unread 04-24-2012, 09:11 AM
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Re: Mecanum wheels interaction with ground Motion Study

kinematic

The objective is to drive the motors through a labview program.
So in my motion study i already put motors on the 4 axes.

according to how i let the wheels turn in labview they have to move the right direction, so the only thing i have to work with is gravity, friction and the wheels turning i guess. No external forces.

M
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Unread 04-24-2012, 09:15 AM
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Re: Mecanum wheels interaction with ground Motion Study


What exactly is your assignment? For example, what vehicle motions are you required to simulate etc etc?

How are you calculating what each of the 4 wheel speeds should be?

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Unread 04-24-2012, 04:35 PM
Mike Hawk Mike Hawk is offline
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Re: Mecanum wheels interaction with ground Motion Study

Hello sorry for the late response.

I have to make it able to drive sideways (left, right), straight ahead en back, diagonal, clockwise turning and counter clockwise.

Actually all possible directions, the only problem is the sideways driving and diagonal driving since all the other motions are easily achieved with normal wheels, but we are using mecanum wheels ...

the 4 wheels turn at the same speed with every motion except with the diagonal movement then 2 diagonal wheels turn slower than the other two.
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Unread 04-24-2012, 05:16 PM
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Re: Mecanum wheels interaction with ground Motion Study

Quote:
Originally Posted by Mike Hawk View Post
I have to make it able to drive ... clockwise turning and counter clockwise ... Actually all possible directions
How are you calculating the wheel speeds under the above conditions?


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Unread 04-25-2012, 02:31 AM
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Re: Mecanum wheels interaction with ground Motion Study

I can give whatever speed to the wheels, i didnt calculate anything. i want to give them a speed of 1-2km/h.

With the labview program i can set 3 parameters: distance, speed and acceleration.

so when i put for example distance = 360; speed =10; and acceleration = 10
it should move with a speed of 10 degrees/sec and the wheel should make 1 turn (360degrees)
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Unread 04-25-2012, 07:14 AM
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Re: Mecanum wheels interaction with ground Motion Study

Quote:
Originally Posted by Mike Hawk View Post
I can give whatever speed to the wheels, i didnt calculate anything. i want to give them a speed of 1-2km/h.
Let me re-phrase the question. You said the assignment required you to simulate the vehicle "clockwise turning1" and driving "in all directions".

How are you determining (calculating) what the speed of each wheel needs to be in order to accomplish those vehicle motions?




1 like this, at 0:37 to 0:41
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Unread 04-25-2012, 08:21 AM
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Re: Mecanum wheels interaction with ground Motion Study

actually I didnt got that far to be honest. The speed of the wheel will be calculated with the labview program.

we are working with 2 students on it and the other student is making the labview program. I have to make sure the wheels interact properly with the ground floor or else the labview program will have no use.

I checked some of these documents from this post: http://www.chiefdelphi.com/media/papers/2390

but i dont know how to tell solidworks that the rollers on the mecanum wheels need to provide a force in a certain direction
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Unread 05-04-2012, 03:55 AM
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Re: Mecanum wheels interaction with ground Motion Study

I have been trying to reply to this message for a few days but it wont let me.. hope it works now.

We work with the FRC library from labview which calculates the speed of each wheel in a specific motion.

But first i need to make sure that those mecanum wheels interact properly
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