VEX Gyroscope and Accelerometer Information

[Brandon Martus]

VEX Analog Yaw Rate Gyroscope V1.0

The VEX Gyro measures turn rate, so it can be used to calculate how much a robot has turned. This allows for very precise turning (example - you can program the robot to turn exactly 90 degrees to the left). Using the VEX Gyro a programmer can also adjust for any drivetrain drift; this turning correction can be used to ensure a robot drives straight. The Gyro could also be used to create a self-balancing robot and to measure robot tilt (such as detecting if the robot is on the ramp or tipped over).

• ±300 degrees per second full scale
• 0-5V analog output
• Uses the LISY300AL chip
• LED indicated power and proper connection
• Mounts directly to VEX
• Price: $49. Availability: November 2008

LISY300AL Chip Information:
The LISY300AL is a low-power single-axis yaw rate sensor. It includes a sensing element and an IC interface able to provide the measured angular rate to the external world through an analog output voltage. The sensing element, capable of detecting the yaw rate, is manufactured using a dedicated micromachining process developed by ST to produce inertial sensors and actuators on silicon wafers. The IC interface is manufactured using a CMOS process that allows a high level of integration to design a dedicated circuit which is trimmed to better match the sensing element characteristics. The LISY300AL has a full scale of ±300 °/s and is capable of measuring rates with a -3 dB bandwidth up to 88 Hz.


VEX Analog Accelerometer V1.0

The VEX Accelerometer measures accelerations on three axis simultaneously. By measuring the acceleration of the robot, one can calculate the velocity of the robot, and more importantly the distance this robot has travelled. Accelerometers are also great for detecting collisions and determining if the robot is stopped or moving.

• Three Axis Accelerometer
• Selectable sensitivity via jumpers: ±1.5g, ±2g, ±4g, and ±6g
• 0-5V analog output (one for each axis)
• Uses the MMA7260QT chip
• LED indicated power and proper connection
• Mounts directly to VEX
• Price: $39. Availability: November 2008

MMA7260QT Chip Information:
The MMA7260QT low cost capacitive micromachined accelerometer features signal conditioning, a 1-pole low pass filter, temperature compensation and g Select which allows for the selection among 4 sensitivities. Zero-g offset full scale span and filter cut-off are factory set and require no external devices. Includes a Sleep Mode that makes it ideal for handheld battery powered electronics.


.

[Quazar]

Originally Posted by Brandon Martus

• Three Axis Accelerometer
• Selectable sensitivity via jumpers: ±1.5g, ±2g, ±4g, and ±6g
• 0-5V analog output (one for each axis)
• Uses the MMA7260QT chip

Brandon,

Thanks very much for the advance info on these products!

I've got a question about the accelerometer, though. The MMA7260QT is not a 5V part, so presumably it'll be powered at 3.3V. This means the outputs will be in the 0-3.3V range unless you guys are adding voltage amplifiers to all three outputs.

This is important since it will effect the effective resolution of the device when used with the 10b 0-5V ADC in the Vex microcontroller. Can you verify the output voltage range of the three signals?

Thanks!
- Dean

[MarkO]

Thank You too!!!!

These are very cool ad-ons.

We really appreciate you at IFI/VexLabs!!

[Bob Mimlitch]

Originally Posted by Quazar

I've got a question about the accelerometer, though. The MMA7260QT is not a 5V part, so presumably it'll be powered at 3.3V. This means the outputs will be in the 0-3.3V range unless you guys are adding voltage amplifiers to all three outputs.

This is important since it will effect the effective resolution of the device when used with the 10b 0-5V ADC in the Vex microcontroller. Can you verify the output voltage range of the three signals?

You are correct about the chip on it's own, however, we added a few parts to the board for VEX. There is a 5V to 3.3V regulator to power the chip from any Analog port's 5V output. Then we added three rail-to-rail op-amps on the output to bring the voltage back to 0.05V - 4.95V.

You just run a PWM extension cable (included) from any Analog port to the board and your ready to go.

[Quazar]

Originally Posted by Bob Mimlitch

You are correct about the chip on it's own, however, we added a few parts to the board for VEX. There is a 5V to 3.3V regulator to power the chip from any Analog port's 5V output. Then we added three rail-to-rail op-amps on the output to bring the voltage back to 0.05V - 4.95V.

You just run a PWM extension cable (included) from any Analog port to the board and your ready to go.

Awesome! That is what I was hoping.
Thanks for the (instant) clarification.
- Dean

[MarkO]

Originally Posted by Quazar

Brandon,

Thanks very much for the advance info on these products!

I've got a question about the accelerometer, though. The MMA7260QT is not a 5V part, so presumably it'll be powered at 3.3V. This means the outputs will be in the 0-3.3V range unless you guys are adding voltage amplifiers to all three outputs.

This is important since it will effect the effective resolution of the device when used with the 10b 0-5V ADC in the Vex microcontroller. Can you verify the output voltage range of the three signals?

Thanks!
- Dean

The LISY300AL is also 2.7 to 3.6 Volt.

[Quazar]

Originally Posted by MarkO

The LISY300AL is also 2.7 to 3.6 Volt.

You are right - on my quick perusal of the spec sheet I saw "Supply Voltage -0.3 to 6 V" but that is the absolute maximum, not the operation range.

I'm guessing Bob's answer applies equally well to both sensors.

Cheers,
- Dean

[Bob Mimlitch]

Yes, both the Gyro and Accelerometer are tuned for VEX with 5V supply and op-amp outputs to 0.05V - 4.95V.

[Edmund Harfmann]

For the accelerometer, will it use one big connector (for 3 sequental port) or will it use 3 connectors so that you could plug it into ports 1, 3 and 8?

Thank you in advance,
Ed

[MarkO]

Originally Posted by Edmund Harfmann

For the accelerometer, will it use one big connector (for 3 sequental port) or will it use 3 connectors so that you could plug it into ports 1, 3 and 8?

Thank you in advance,
Ed

You are asking if the Analog Inputs WILL be Contiguous, or are they separated..


FYI, the Analog Inputs on the Vex's PIC 18F8520 MUST be Contiguous, and start at Port #1, so if the Accelerometer's Connector Block was Contiguous, it might be a positive thing, just to keep people from doing silly things and getting strange results.