Gyro degrees/second

[futz]

I'm shopping for a gyro for my balancing robot, but I have no idea which one to buy. I don't want an RC helicopter style unit though. Too difficult to interface.

Sparkfun has **broken link removed** for very reasonable prices. They come in 75, 150 and 300 degree/sec models. All same price.

Anybody know anything about these things? Which one should I get?

 

[ericgibbs]

hi futz,
Never made a balancing robot, but my gut reaction would be, if the the robot got more than +/-37.5 deg off balance from its COG, would it be able to recover..??

 

[futz]

Never made a balancing robot, but my gut reaction would be, if the the robot got more than +/-37.5 deg off balance from its COG, would it be able to recover..??

With these motors (full rotation servos - no electronics; just motors) and the heavy weight of my bot, not a chance. Other robots I've seen can recover or stand up from prone. Botka, for instance:

**broken link removed**

Big grippy wheels and powerful motors combined with good controls can do amazing things.

Why I'm asking about gyros is because I don't understand what they mean by degrees per second. Does that mean how sensitive the gyro is? In that case, how sensitive do I want it to be?

 

[ericgibbs]

With these motors (full rotation servos - no electronics; just motors) and the heavy weight of my bot, not a chance. Other robots I've seen can recover or stand up from prone. Botka, for instance:

**broken link removed**

Big grippy wheels and powerful motors combined with good controls can do amazing things.

Why I'm asking about gyros is because I don't understand what they mean by degrees per second. Does that mean how sensitive the gyro is? In that case, how sensitive do I want it to be?

hi,
I saw a robovid sometime ago posted by a member, that robot did get upright by shear motor power and heavy duty tyres.!

From my experience with gyro's degrees/sec means the rate of change of signal output with respect to time.

Do you expect your robot to get back upright if it falls over.? or will it always be able to correct its balance before its does fall over.?

Its difficult to visualise your robot not having seen its configuration.

EDIT watched you vid, yes its the same one.

 

[futz]

From my experience with gyro's degrees/sec means the rate of change of signal output with respect to time.

I've been googling hard and am beginning to see what it means. So the higher deg/sec ones are capable of sensing higher rates of rotation. The lower rate ones would be more sensitive? Not sure about that part...

I just don't want to buy one and find out too late that I got the wrong one. I researched accelerometers before buying and got an excellent one. I'm very happy with my purchase. I want my gyro purchase to go just as well.

Do you expect your robot to get back upright if it falls over.?

As I said, not a chance. With different motors/wheels, maybe. Still unlikely. It's too heavy. If I designed a lighter one with less weight up top, yes.

or will it always be able to correct its balance before its does fall over.?

That's what I'm shooting for, for now.

Its difficult to visualise your robot not having seen its configuration.

Bottom of this thread: https://www.electro-tech-online.com/threads/de-accm3d-accelerometer-junebug-a-d-question.38957/

EDIT: Just changed one photo in that thread. Refresh your browser and look again.

 

[ericgibbs]

hi,
Ah I see, its the mechano-bot, made from the recycled metal strips.

I used to have a mechano set as a child, great fun and educational.

Ref the gyro, if I was designing a balancing bot, I would shoot for a high sensitivity, providing the motor response was able to cope and didnt send the mass into oscillation.

Sounds an interesting project, bit like balancing a long pole at the end of your finger.

 

[futz]

I used to have a mechano set as a child, great fun and educational.

Me too. I was a Meccano maniac when I was young. Built tons of cool things with it. Too bad it got chucked many years ago.

Ref the gyro, if I was designing a balancing bot, I would shoot for a high sensitivity, providing the motor response was able to cope and didnt send the mass into oscillation.

Ya. Unfortunately I don't know how much or how little I need. I balance the bot with batteries in it and let it go. It takes (guesstimated) a bit less than a second to fall, so maybe a 75 deg/sec is not enough? I don't know!

Sounds an interesting project, bit like balancing a long pole at the end of your finger.

They're called inverted pendulums.

 

[Papabravo]

The degrees per second refers to the angular velocity of the rotor. The faster it spins the more angular momentum it has and the greater will be the restoring force when the spin axis is displaced. See the following page

http://www.gyroscopes.org/math.asp

 

[futz]

The degrees per second refers to the angular velocity of the rotor. The faster it spins the more angular momentum it has and the greater will be the restoring force when the spin axis is displaced. See the following page

http://www.gyroscopes.org/math.asp

I've been to that site, but it does nothing for me. I just don't have the math chops for it.

The gyro's I'm looking at have no rotor. They're MEMS units. But of course they behave the same way as a spinny gyro.

What I need is a "gyro buyer's guide for dummies" so I can buy my first one and not waste $75 getting the wrong one. I found just such a file for accelerometers (not "for dummies", but a good newb explanation of what features there are and what you want). Once I have one and learn all about it it's easy to select the right one, but then it's too late.

EDIT: Found this quote on Sparkfun's forum:

As for what is most useful, this REALLY depends on the project. A balancing robot would probably love the 75 deg/s part. An airborne INS would either need the 150 deg/s part or the 300 deg/s part (if you're doing tumble applications or have a very maneuverable design). You might be surprised how fast something can turn, especially in the first 5 degrees of a longer turn. Might top out the 75 deg/s part, maybe even the 150 deg/s part.

 

[Papabravo]

So we're not talking a mechanical device that generates forces when it is displaced? What's the point of calling it a gyroscope? Sounds like a serious truth in advertising issue. This is like 1984

1. War is Peace
2. Love is Hate
3. Truth is Beauty

 

[futz]

So we're not talking a mechanical device that generates forces when it is displaced? What's the point of calling it a gyroscope?

I think they still are mechanical inside the chip, but nothing rotating.

 

[3v0]

So we're not talking a mechanical device that generates forces when it is displaced? What's the point of calling it a gyroscope? Sounds like a serious truth in advertising issue. This is like 1984

1. War is Peace
2. Love is Hate
3. Truth is Beauty

I seen an all electronic gyro. It was a triangle with a mirror in each corner. They split a laser beam and send half around CW and the other CCW. By measuring how long it took the light to arrive it could tell if it was turning. It was for use in a rocket guidance system. That was in the mid 70's. I have no idea what is inside a modern device.

Wikipedia says "A gyroscope is a device for measuring or maintaining orientation," but then it goes on to talk about angular moment. Maybe we should say the electronic units are gyroscope replacements.

 

[Sceadwian]

Why is a heli gyro too difficult to interface? They're designed to interface directly to a tail rotor control servo. 1.5ms center (no rotation) positive and negative rotation around it's axis will give you a proportionatly higher/lower pulse width based on the rotation change. For ballance rate of change direction isn't too much of an issue, it's update and responce rate for the correction and programming the control loop that are the difficult part.

 

[futz]

Wikipedia says "A gyroscope is a device for measuring or maintaining orientation," but then it goes on to talk about angular moment. Maybe we should say the electronic units are gyroscope replacements.

https://en.wikipedia.org/wiki/Vibrating_structure_gyroscope

The next generation of gyro is the piezoelectric gyro.
Here, there are no spinning bits, only a rapidly vibrating crystal. This crystal wobbles along a particular axis, and as I understand it, turning the crystal will cause disturbances in this wobble which cause a small electric current. This current can be measured and used to adjust your servo position. Piezoelectric systems are very temperature sensitive since temperature affects some internal resistances. This is why they start to drift as the temperature changes. Most piezo gyros now have a temperature compensation circuit to avoid this.

The most modern kind of gyro is the MEMS gyro. MEMS = Micro Electric-Mechanical System. MEMS are molecule sized machines that are fabricated on top of a piece of silicon, along with the electronics to interface to them. I don't know how MEMS gyros work specifically, but they do some sort of differencing on some sort of moving bits

I also read in one place that piezo gyros are at least 10 times as sensitive as mechanical gyros. Lots lighter and smaller and cheaper too.

 

[futz]

Why is a heli gyro too difficult to interface? They're designed to interface directly to a tail rotor control servo. 1.5ms center (no rotation) positive and negative rotation around it's axis will give you a proportionatly higher/lower pulse width based on the rotation change. For ballance rate of change direction isn't too much of an issue, it's update and responce rate for the correction and programming the control loop that are the difficult part.

They're not SO difficult, but analog output is SO easy that it makes measuring pulse widths seem like such a pain. The SPI/analog ones don't cost any more, so that's what I'm going for.

 

[3v0]

Thanks futz. I have been watching your posts regarding motion.

 

[futz]

**broken link removed**. Click on it. Very interesting.

 

[dusko]

Check this one:

**broken link removed**

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

 

[Papabravo]

Which brings us full circle back to the original question about the measurement of an angular velocity in degrees/second and what it actually refers to. We think we understand the measurement for a mechanical gyro, but I am less clear for the other types exactly what angular velocity is being measured. Assuming we can get our arms around that one, then we need to understand how, as a figure of merit, we could apply different non-mechanical gyros to a given application. Like erecting our robots from a supine position. CMOL(Chuckling mildly out loud)

 

[futz]

Which brings us full circle back to the original question about the measurement of an angular velocity in degrees/second and what it actually refers to. We think we understand the measurement for a mechanical gyro, but I am less clear for the other types exactly what angular velocity is being measured. Assuming we can get our arms around that one, then we need to understand how, as a figure of merit, we could apply different non-mechanical gyros to a given application. Like erecting our robots from a supine position. CMOL(Chuckling mildly out loud)

Heh. As far as I can understand, the piezo and MEMS work exactly the same way as a spinning gyro except that they work by vibrating instead of spinning. The same forces (coriolis?) move them internally and the movement gets measured. I see there are types that do rotate thru a partial arc (vibrating back and forth kinda), but none of the ones I'm looking at do that.

In the end you get the same kind of output either way. It tells you how fast the gyro is being rotated in the axis being measured.

Have a look at the photos at the bottom of the flyer for the **broken link removed** (one of my top contenders). See those interlocked fingers? Both halfs vibrate in opposing resonance. Movement in the proper axis causes deflection by coriolis force and the deflection changes capacitance and that can be measured. I'm not clear on the details but it works.

**broken link removed**

Tuning Fork Gyroscopes. Tuning fork gyros contain a pair of masses that are driven to oscillate with equal amplitude but in opposite directions. When rotated, the Coriolis force creates an orthogonal vibration that can be sensed by a variety of mechanisms.