Gyro degrees/second

[futz]

Check this one:

**broken link removed**

I know, it's not the analog interface, but the price seems to be right for testing/learning.

Oh! That's tempting. Good price.

 

[Papabravo]

I'm not sure that Coriolis force and the spinning gyro are related. I'll have to get back to you on that one. The links you provided, including the movie, were not much help in understanding the undelying physics of the MEMS and Piezo devices. That's hardly surprising since I've not previously considered similar systems.

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* The following contains a popular misconception
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It was my impression that the Coriolis force is responsible for the direction of flow in a flush toilet(wrong) and is a nearly negligible effect when compared to the spinning rotor of a standard gyro when the direction of its angular momentum vector changes(correct). In the case of the toilet the velocity of the water is down and the omega of the Earth is horizontal (East West), so v cross omega is perpendicular and points North-South in the northern hemisphere(wrong).

The source of my confusion was the difference between v cross omega and omega cross v, and weather there was a minus sign or not. It's tough to remember this stuff if you don't do it everyday.

 

[futz]

I'm not sure that Coriolis force and the spinning gyro are related. I'll have to get back to you on that one. The links you provided, including the movie, were not much help in understanding the undelying physics of the MEMS and Piezo devices. That's hardly surprising since I've not previously considered similar systems.

It was my impression that the Coriolis force is responsible for the direction of flow in a flush toilet and is a nearly negligible effect when compared to the spinning rotor of a standard gyro when the direction of its angular momentum vector changes. In the case of the toilet the velocity of the water is down and the omega of the Earth is horizontal (East West), so v cross omega is perpendicular and points North-South in the northern hemisphere.

Maybe not for spinning gyros, but every paper on MEMS gyros mentions it. Seems like spinning gyros use precession instead (speaking of precession, I love to watch airplanes do Lomcevaks)

This paper is excellent! Really goes into detail. Get it in PDF, or go to the link below:
https://www.analog.com/library/analogDialogue/archives/37-03/gyro.html

Selecting gyroscopes requires an understanding of angular rate measurement techniques.

Optical gyros permit the reflection of a laser ray many times within an enclosure. If the enclosure rotates, the duration between the moment of laser emittance and eventual reception differs. With ring laser gyros (RLF), the laser reflection is achieved with mirrors inside the enclosure. With fiber optic gyros (FOG), the laser reflection is achieved with a coil of optical fiber.

Spinning mass gyros use a steadily-moving mass with a free-moving axis (gimbal). These gyroscopes are very fragile and require regular maintenance. When a spinning mass gyro is tilted, the gyroscopic effect causes precession – motion orthogonal to the direction tilt sense – along the axis of the rotating mass, indicating that the angle has moved. Because mechanical constraints cause numerous error factors, the axis of a spinning mass gyro is usually fixed with springs. Spring tension is proportional to the precession speed.

Vibrating gyros use micro-electro-mechanical system (MEMS) technology and a vibrating, quartz tuning-fork to measure Coriolis force. When rotated, a vibrating element (vibrating resonator) is subjected to the Coriolis Effect, causing secondary vibration orthogonal to the original vibrating direction. By sensing the secondary vibration, the gyro can detect the rate of turn.

 

[Papabravo]

Thanks, that ".pdf" was a great help in understanding the discussion. The degrees per second mentioned in the original post is related to the full scale output voltage and the sensitivity. What it means for a particular gyro is that it can measure angular rates (velocity) from some small number close to zero up to some maximum value.

 

[Sceadwian]

Futz, a micro controllers resolution to measure a pulse train is only dependent on it's clock, with a PIC or AVR you're going to end up with a LOT more usable bits of resolution than from the ADC on the same microcontroller. The problem is it's a balancing bot, which needs a fast update rate as well. I'd look into modern 'digital servo based' heli gyros. The digital servo output means it can do a very fast update rate to a digital servo, 'heading hold' gyros are expensive but modern gyros can hold a heli rock steady in even heavy buffeted winds. Gotta be good enough for a balancing bot.

 

[futz]

Well, I made my decision. Decided on a ADXRS150 150deg/sec unit. Got a few other toys while I was ordering from Sparkfun. You'll see them on my site eventually.

And I'm finally replacing my el-cheapo Canadian Tire multimeter (it needs to be in the work van anyway) with a nice new one.