Robot With Mecanum Wheel Controlled
We started with a new project, a Mecanum Wheel omni directional robot . One of the most fun and interesting projects that we can do with a processor.
We recall that an omnidirectional robot is one that can move in any direction with any or no body rotation . The combination of both components, translation in any proportion and rotation, means that they can follow any movement, such as turning with respect to any point.
Mecanum Wheel robots are really interesting . It is almost hypnotic to see them in operation moving smoothly in any direction. Although it is a more expensive project than the equivalent with Omni Wheel wheels.
As usual in our series of projects, in this post we will see a general presentation and the budget of the project. In the following we will see the assembly, the electrical diagram, and the programming.
What Are Mecanum Wheels?
The Mecanum Wheel is an idea that may be simple, but it doesn’t stop it from seeming great to me. They consist of a conventional wheel that has a series of rollers around its circumference .
The rollers have a configuration of 45º with respect to the plane of the wheel . Also, these rollers have a curved shape so that, seen from the side, the wheel maintains a circular profile.
The operation (and genius) of the Mecanum Wheel is that, when rolling, the rollers cause the force to be transmitted to the ground at 45º with respect to the main axes of the wheel . By itself, a Mecanum Wheel would tend to scroll diagonally.
However, as the rollers can rotate freely, they can absorb external forces. When multiple Mecanum Wheels work together they can offset forces to generate any movement. This is precisely where “the magic” happens, as we will see in the next section.
Since then, various commercial products have used Mecanum Wheels. You can look for examples of conveyor platforms, lifts, wheelbarrows, or even wheelchairs.
Of course, there is a wide variety of Mecanum Wheel, with different types, sizes, load capacity, number of rollers and, of course, price.
In particular, internal solid roller designs are more suitable for high loads, while centrally attached split roller designs perform better on uneven or uneven terrain.
Finally, in case anyone wonders “How come all cars don’t have these wheels yet?” comment that, although appropriate to support heavy weights, in general, Mecanum Wheels have problems in high-speed applications.
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Robot With Mecanum Wheel
Mecanum Wheel robots are truly omni directional. That is, they can move in any direction, with any rotation, or no rotation at all.
To do this, it is only necessary to have four wheels in parallel arrangement , as we would do with a conventional wheel.
This is an advantage over Omni Wheel robots, which require an axial wheel arrangement .
The wheels have to have a suitable configuration (they are not all the same). In fact, a greater number of wheels can be used, provided they are chosen correctly. Thus, you will see certain industrial platforms that have multiple wheels.
Here you have a video of the robot that we are going to assemble, doing the basic movements. (The milk crates are because in this first stage without batteries, it weighed little and slid on the parquet)
As we have said, the movements of the robot depend on the speed of rotation of all the wheels . Thus, to move the robot forward or backward we simply turn the wheels as in the case of conventional wheels.
If we analyze the movement we will see that the force exerted at 45º by each of the wheels cancels the lateral components, and the resulting movement is forward or backward.
To make turns around the axis of the robot, it is again identical to using normal wheels. That is, we advance the wheels on one side and in the opposite direction those on the other.
Here we have the explanation in terms of force composition where we see that, in this case, no cancellation of forces occurs.
Finally, and the most interesting, to make the robot move laterally we turn the wheels on one side inwards, and those on the opposite side outwards.
If we observe the explanation in terms of composition of forces, we observe a cancellation similar to that of the case of longitudinal displacement, where there is cancellation of longitudinal forces and addition of lateral forces.
These are the basic movements of the robot. But, as we have said, by combining them we can achieve a totally omnidirectional behavior and make the robot move in any direction, or rotate with respect to any point.
Things ahead, a robot with a Mecanum Wheel is one of the most interesting and fun robots, but it is not a cheap robot .
My first attempt was to make a small robot, with cheap wheels and DC motors + Encoder. To see the control dynamics, it should work.it didn’t.
My advice is to run away from this type of wheels . It’s a waste of money, they have too few rollers to allow smooth movement. Movement (even forwards and backwards) is “jumpy”, and side movements are in a kind of erratic “zig-zag”.
Of course I wasn’t even remotely satisfied, and I really wanted a robot with a Mecanum Wheel. So I moved on to the next version, which is one of my biggest and most powerful robots.
On this robot we mount 4-inch Mecanum Wheels . The cost about $90 for all four. Yes, you can buy them in Kit, because you need two “left” wheels and two “right” wheels (all four are not the same).
We also have the engines. Some Nema 17 type stepper motors. Mine are not quite standard, 3D printer type, and you can get them for about $10. If you want them with more for, it could cost up to $20 each.
In order to connect the wheels to the stepper motors you will need some couplings (or Hubs). Add about $8 for each one. On the other hand, we have the “L” brackets that bolt the motors to the deck. Another $7 each, approximately.
Finally, we have the electronics. Stepper motor drivers, Arduino, breakout board, etc. So, without counting the batteries, we are talking about a robot of the order of $200 . It is not a cheap robot.
But, in exchange, we have a multipurpose omni directional platform that can move more than 10Kg. As always, then everything you want to add or put on top . A robotic arm, a Raspberry Pi with a camera, a Lidar,or a tray to bring you a plate of squid. there you go!
As I said, a robot with a Mecanum Wheel is one of the most interesting projects that can be done with . They are still not seen too many, so they are spectacular and surprising.
Unlike an Omni Wheel robot, which forces an axial layout, a Mecanum Wheel robot looks like a conventional 2WD or 4WD wheeled vehicle. In fact, you can turn any RC chassis or vehicle into an omni directional robot.
In fact, the “normal” movements (forward and backward and rotation) are identical. But, add the omni directional possibility. And getting full control (for example, rotating about a point, or following a curved path) is interesting and tricky.
As disadvantages, it is a somewhat expensive robot . And the movement, even with good wheels, is not as smooth as conventional wheels (the rollers generate tapping, vibration, and a “rattling” noise).
Of course, we are just building a multi-purpose platform. The final functionality will depend on the sensors, communication systems and actuators that you want. Do you want to put sensors on it and make it park? What follows a wall? Put a robotic arm and a camera on it and make a “demonstrator” type robot? The possibilities are endless!
This is precisely why I like this project so much. The platform is great and can do anything. With a few small changes, it can be turned into as many projects as you can imagine.
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