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Can't convert angular velocity to angular position with an Eowave 2D gyrometer.


Roald Baudoux

Roald Baudoux
Jan 27, 2011 at 11:01am

Can't convert angular velocity to angular position with an Eowave 2D gyrometer.

Hello,

I have a 2D gyrometer from Eoweve connected to an Eobody 2 and I want to translate the speed into a angular position delta added to a base position.

The sensor is a bit strange because at rest the value sent is not exactly in the center of the range. Hence velocity ranges aren’t the same size in both directions.

Therefore, I use peak to find the maximum value, then I capture the value at rest. Then, with two split objects I split the range into three parts :
- lower range: rotation in one direction ;
- center range (more than one value because of the jitter): rest ;
- upper range: rotation in opposite direction.

Afterwards, I scale all the resulting values then I use an accum object to convert velocity into angular position.

The problem: values are drifting. If I rotate the sensor in one direction, then back to its previous position, I don’t go back to previous position value.

What’s wrong with my patcher ?

Roald Baudoux

– Pasted Max Patch, click to expand. –
#54631

Roald Baudoux

Roald Baudoux
Jan 27, 2011 at 11:14am

I figured out there was one error in scaling and added a modulo because it’s angular position so here is the updated version.

However my main problem is still not solved.

– Pasted Max Patch, click to expand. –
#196738

stefantiedje

stefantiedje
Jan 27, 2011 at 11:51am

I am not sure if there is anything wrong with your patch.
I would expect, that there is a drift. The method will accumulate any errors out of its principle, there is no absolute measurement of the angle or position…
All technologies I know of would add an absolute sensor, to recalibrate. A wiimote for example can use the infrared sensors to recalibrate…

Stefan

#196739

Roald Baudoux

Roald Baudoux
Jan 27, 2011 at 11:56am

I understand that recalibration is necessary, but in the case of the Wiimote I don’t get how an infrared can recalibrate a gyrometer…

Also, how often should recalibration occur ?

#196740

Zachary Seldess

Zachary Seldess
Jan 27, 2011 at 12:28pm

I’d recommend a 2D or 3D compass sensor instead of a gyrometer, if you want to eliminate the need for recalibration. I’ve used the Honeywell HMC6343 in installations, works very well: http://www.sparkfun.com/products/8951

Connect to an Arduino, Xbee for wireless, etc…

best,
Zachary

#196741

stefantiedje

stefantiedje
Jan 27, 2011 at 5:01pm

Wow, more than three times the price of a wiimote, and thats just the chip…

#196742

Zachary Seldess

Zachary Seldess
Jan 28, 2011 at 5:21am

Does the Wiimote have a magnetic field sensor now (or maybe it always did)? If so, that’s definitely a cheaper option.

Just trying to offering some helpful input. If size is an issue, and if you don’t want to deal with recalibration, then you need something like a compass sensor.

Some of the cheaper iThings these days may have compass sensors too, so that could be an option.

best,
Zachary

#196743

stefantiedje

stefantiedje
Jan 28, 2011 at 1:21pm

No, it does not have a magnetic field sensor, but it can recalibrate itself with the infrared camera…

#196744

Zachary Seldess

Zachary Seldess
Jan 28, 2011 at 2:15pm

Right, so do it that way if you like, and if you don’t want to recalibrate, or the form factor doesn’t work for you, look for a magnetic field sensor solution that fits your budget…

#196745

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