2015: Year of the Mecanum

[hexane]

From our team's experience, the only time that mecanums have ever had troubles were on the bridges in 2012. Even then, the problem was the lower coefficient of friction rather than getting up on them, and we were still able to balance 2 robots better than most teams.

[chrisfl]

Originally Posted by hexane

From our team's experience, the only time that mecanums have ever had troubles were on the bridges in 2012. Even then, the problem was the lower coefficient of friction rather than getting up on them, and we were still able to balance 2 robots better than most teams.

It was the same for us. We used mechanum in 2012 and our only problem was staying in one place on the bridge. We had no problem going up and down it while at an angle.

[Bruceb]

never used macanums before but really considering it this year. what is the prefered gearbox for these?

[JosephC]

Originally Posted by Bruceb

never used macanums before but really considering it this year. what is the prefered gearbox for these?

If you have not prototyped mechanum or done it before, I would not recommend bringing it out this season. It doesn't seem difficult at first, but you will end up spending far too much time on your drive train instead of allocating proper time to your mechanisms.

[Brandon Zalinsky]

The biggest hitch in developing a mecanum drivetrain is code. It requires lots of code testing. The hardware is much easier. The wheels are placed in standard configuration and require very minor differences in hardware required from a 4wd skid. The biggest hitch in the hardware is that you need four separate transmissions.

1058 has used 9:1 transmissions for a few years on our mecanum drives.

[Peyton Yeung]

461 used toughbox minis last year with a 12.75:1 ratio on 6" wheels. The biggest issue we had was due to a lack of suspension, one of the wheels did not contact the floor like the others.

[AutodeskGeek]

Originally Posted by Brandon Zalinsky

The biggest hitch in developing a mecanum drivetrain is code. It requires lots of code testing.

For those teams that have used mecanum in the past, this is a non-issue. There's also plenty of help with algorithms online that teams trying it for the first time can use. Probably not too much testing unless you are implementing original drive styles with your mecanum wheels.

[Ben Wolsieffer]

Originally Posted by AutodeskGeek

For those teams that have used mecanum in the past, this is a non-issue. There's also plenty of help with algorithms online that teams trying it for the first time can use. Probably not too much testing unless you are implementing original drive styles with your mecanum wheels.

Yeah, the programming is not that difficult. WPILib for C++ and Java has a function for field oriented (or robot oriented) mecanum drive that works well. I don't know about Labview.

[The Doctor]

Originally Posted by lopsided98

WPILib for C++ and Java has a function for field oriented (or robot oriented) mecanum drive that works well. I don't know about Labview.

You do realize that the libraries will probably be very different since the introduction of the RoboRio.

[Ether]

Originally Posted by The Doctor

You do realize that the libraries will probably be very different since the introduction of the RoboRio.

Not that different. 2015 WPILib Java:

    /**
     * Drive method for Mecanum wheeled robots.
     *
     * A method for driving with Mecanum wheeled robots. There are 4 wheels
     * on the robot, arranged so that the front and back wheels are toed in 45 degrees.
     * When looking at the wheels from the top, the roller axles should form an X across the robot.
     *
     * This is designed to be directly driven by joystick axes.
     *
     * @param x The speed that the robot should drive in the X direction. [-1.0..1.0]
     * @param y The speed that the robot should drive in the Y direction.
     * This input is inverted to match the forward == -1.0 that joysticks produce. [-1.0..1.0]
     * @param rotation The rate of rotation for the robot that is completely independent of
     * the translation. [-1.0..1.0]
     * @param gyroAngle The current angle reading from the gyro.  Use this to implement field-oriented controls.
     */
    public void mecanumDrive_Cartesian(double x, double y, double rotation, double gyroAngle) {

[Aedan Hawke]

Originally Posted by Bruceb

never used macanums before but really considering it this year. what is the prefered gearbox for these?

We've used mechanums for the last couple of years with success. Last year we made our own gearboxes and built them into our chassis. They worked exceptionally well but, obviously, were a huge drain on time. Other years we used Andymark ToughBoxes and those worked well for us. I'd recommend them unless you'd like the challenge of the custom gearboxes.

[Mecanum Wheel]

Originally Posted by Aedan Hawke

We've used mechanums for the last couple of years with success. Last year we made our own gearboxes and built them into our chassis. They worked exceptionally well but, obviously, were a huge drain on time. Other years we used Andymark ToughBoxes and those worked well for us. I'd recommend them unless you'd like the challenge of the custom gearboxes.

Hi Aedan. Just for future reference, it's spelled mecanum. It's an easy mistake to make.

Is anyone using 6 inch mecanum wheels with CIMple boxes? We will be and are going for ~11 ft./s.

[dawonn]

I think we may also going the CIMple Box route with the 6" standard Andymark mecanum wheels, with HTD belts geared for 12.5 fps.

In the past I have used a gyro just as stated above to keep the robot driving straight. It worked so well that we had a motor come disconnected and didn't notice for a few hours.

[GeeTwo]

Originally Posted by Mecanum Wheel

Hi Aedan. Just for future reference, it's spelled mecanum. It's an easy mistake to make.

Is anyone using 6 inch mecanum wheels with CIMple boxes? We will be and are going for ~11 ft./s.

That sounds way too fast! A CIMple box has a gear ratio of 4.67:1 (14:3) which is an "80%" speed of 5310 rpm * 2 * pi radians/rev / 60 sec/min * 3 / 14 * 3 in / 12 in/ft * 0.8 = 29.8 fps! Get some 2-stage gearboxes!

If you want to calculate a gear ratio, a CIM-driven robot with an 80% efficient drive train, 1:1 gearbox and a 1" diameter wheel would go 18.5 fps (if it were on some sort of weird rail that let this happen, or it were an offset gearbox). Multiply by your diameter in inches and divide by the gearbox ratio to get your 80% speed. To calculate a gearbox ratio, multiply by your diameter in inches and divide by the desired speed. In your case, that would be 18.5 * 6 / 11 = 10.1:1. As you seem to be shopping at AndyMark (and so do we), the 10.7:1 TB Mini looks like a good option.

[Mecanum Wheel]

Originally Posted by GeeTwo

That sounds way too fast! A CIMple box has a gear ratio of 4.67:1 (14:3) which is an "80%" speed of 5310 rpm * 2 * pi radians/rev / 60 sec/min * 3 / 14 * 3 in / 12 in/ft * 0.8 = 29.8 fps! Get some 2-stage gearboxes!

We will be using sprocket reductions.