Mecanum Wheels Programming

[daltore]

Magnitude has to be between 0 and 1. The most general way to do it is to have the Y and X axes of one joystick just act as point-and-shoot and use Pythagorean theorem (Magnitude = sqrt(X^2 + Y^2)). However, this results in a scale of 0 to 1.141, which means that with the limiting blocks they have inside Holonomic.vi, when driving while using multiple joystick axes with high values, come of the motor values will get capped, so you won't quite end up with the right vectors (because the over-1 magnitude will cause the motors to try to go faster than they can).

One way to get around this is to multiply the magnitude by .7, which will bring the max value back down to 1. However, this means that you can't go as fast forward or sideways, and you're only getting full speed diagonally. The way I prefer is to measure all of the motor values, and if any of them are out of range, scale all of the motors down to the most out-of-range motor (if the fastest motor is getting a value of 1.141, divide all of the motors by 1.141). This allows you to have full power in all directions, while maintaining correct vectors.

[jhersh]

Originally Posted by daltore

One way to get around this is to multiply the magnitude by .7, which will bring the max value back down to 1. However, this means that you can't go as fast forward or sideways, and you're only getting full speed diagonally. The way I prefer is to measure all of the motor values, and if any of them are out of range, scale all of the motors down to the most out-of-range motor (if the fastest motor is getting a value of 1.141, divide all of the motors by 1.141). This allows you to have full power in all directions, while maintaining correct vectors.

Just FYI, very similar changes were made to the WPILib code a while back and will be in the next update.

[fimmel]

Originally Posted by jhersh

Just FYI, very similar changes were made to the WPILib code a while back and will be in the next update.

Is there a date as to when this is going to be released?

...Forest

[BryanF]

Just to let you know with mechanum wheels it is very important that you have all WHEELS turning the same speed because as we all know motor speed is not very accurate some time i recommend putting encoders on your wheels using one joystick and a button to switch between tank drive and strafing back to the encoders 100% sure you will need to use PID but the benefits will show when you get it working

[jhersh]

Originally Posted by fimmel

Is there a date as to when this is going to be released?

Looks like it will be next week.

[bladetech932]

the best way to scale the input into the holonomic drive vi is to set a case for overflow
if > 100 then = 100
that way
.70=.70
.80=.80
.90=.90
1.00=1.00
1.41=1.00

[daltore]

Originally Posted by jhersh

Just FYI, very similar changes were made to the WPILib code a while back and will be in the next update.

So, this has happened twice so far this season First, it's the scaling I added in, and then this week, it was the single Jaguar CAN refnum VI I hacked together (and got working, thank you very much) that we just got the update for. I seem to be coding one step ahead of release...

[Greg McKaskle]

Great minds ...

And that is also why WPILib ships with source code in each of the languages. So you don't necessarily have to wait for us.

Greg McKaskle