What gyro to use?


#1

I’m looking for a gyro that has PWM capabilities so that I can mount the RIO somewhere other than the center of rotation for the robot. Or is this not even an issue? Alternatively, I could use some help finding an extension cable for the normal AnalogDevices FRC Gyro (ADXRS450) that attaches to the SPI port.


Best mecanum gyro?
#2

I’m not sure what you mean by pwm capabilities, but mounting in the center of the robot is really not that important.


#3

What I meant was the ability to wire it using a pwm cable to the roborio rather than using an I2C or SPI


#4

PWM ports are outputs and not inputs. Many gyros like navx or pigeon use cables. The navx plugs into the Rio mxp port, the pigeon can plug in to any talon srx motor controller. We always made our own spi cables so I can’t help you there.


#5

Ok. Thanks for the help.


#6

If you’re not opposed to using the SPI port or the MXP port, either of the ADI IMUs would work as they are tri-axis. It’s also not super important for the gyro to be at the center of rotation either, the ADI IMUs (or any gyro or IMU for that matter) will function the same regardless. These boards also both feature mounting holes to secure the board to the RIO (or the robot, as the case may be).

There are some still available on FIRST Choice:
https://www.firstchoicebyandymark.com/fc-adis16448brd
https://www.firstchoicebyandymark.com/fc-adis16470


#7

Many people use the NavX or the PigeonIMU.

By the way, your usage PWM does not make sense. PWM stands for pulse width modulation and is a method of emulating a lower voltage by oscillating between high and low signals. Maybe what you meant was that it could connect to one of the analog or digital input ports?


#8

Thanks for the advice. And yes, I did mean connecting to the analog or digital ports on the rio, when I said PWM I meant that I wanted to use a pwm cable to connect the gyro to the rio.


#9

A lot of people in FRC refer to any 3 pin ribbon cable as a PWM cable. I’ve tried to break my team of that usage, but old habits die hard.

To the OP: I’m a big fan of the NavX. I had a hard time with other sensors, but the NavX seemed to “just work”. I know other people who have been successful with other sensors, but my personal experience is that NavX is easy to use.

The sensor does not have to be at the center of rotation. It is much, much, easier to use if it is mounted horizontally (i.e. parallel to the floor). The easiest way to mount them is to just plug them directly into the Roborio and use the mxp port in the constructor, but it works perfectly well to have the NavX board detached. and connected via a USB cable to the RoboRio, and then use the usb port in the constructor. Of course, this year you might be using both usb ports for cameras………ah, tradeoffs.


#10

Some people have already mentioned the plugging a pigeon into a talon SRX. However, if you don’t have any SRX’s on the robot you can always wire it into your CAN Bus. Although, that does mean you have to run additional power to the pigeon.


#11

Note it is also used to encode information into the duration (width) of the pulse. Common uses in FRC include controlling motor controllers (1.5ms = stop, 1.0ms = full rev, 2.0ms = full fwd) and some sensors (ex: some MaxSonar Ultrasonic rangefinders encode distance @147us/inch)


#12

FYI, Pololu offers an assortment of pre-crimped wires, connectors, and housings that can be used to build custom cables: https://www.pololu.com/category/71/wires-with-pre-crimped-terminals