Go Down

Topic: Motion Capture with Due (Read 1 time)previous topic - next topic

ChaseRLewis73003

Dec 26, 2012, 09:38 pm
I'm thinking it should be possible but i have only basic arduino experience (few wireless sensor projects but that's it). Arduino is just going to organize the data each frame and send it over wifi to a PC that will do all the heavy lifting. 14 bytes per vector component with the sensors I plan on using which we will round to 16 bytes since I might pad the values in memory should be 16 x 6 = 96 bytes per sensor x 18 sensors x 60 fps x 8 bits per byte = ~830k bits per second (103.7k bytes per second). Seems well within the range of a xbee. Is that reasonable with a Due and Xbee combo?

Thing is at my work we use Magnetometers and Accelerometers to calculate orientation but motion capture suits in the industry seem to do accelerometer and gyroscopes which confuses me since you need a calibrated reference to work with a gyroscope (I think) because it just reads changes in rotation not absolute rotation (unless I'm not understanding something by reading the white pages on different ones). Anyone who worked with a accelerometer and gyroscope able to explain to me how you get absolute orientation using that combo? I have some parts in the mail so I could probably answer the question myself in a week or so but always like hearing from people that know a bit more than me.

HazardsMind

#1
Dec 26, 2012, 09:48 pm
What do you mean by absolute orientation, the accelerometer and gyro output a range of numbers. This range is based on the position the accel / gyro is in, if it is tilted 45 deg, then you will get a number like 564. It does not output exact degrees unless you have a high end model, or do it yourself with a map function.

Degrees = map(value_gotten, lowest, highest, -90,90);

If your using the accel to get your values, then you may also want to contrain the lowest and highest values.

constrain(value_gotten, your_set_lowest, your_set_highest);
This would go before the map, not after.
My GitHub:
https://github.com/AndrewMascolo?tab=repositories

ChaseRLewis73003

#2
Dec 26, 2012, 10:23 pm
I understand it gives a number that is mapped between two values. That's how most electronic sensor's work even if they have to be ADC'd first.

Absolute orientation is using the angle values to calculate an actual vector direction in your reference space. So how does 'up' change from 1 point to another (or forward or whatever direction). It is important to have that information so rotation information can be calculated on the PC. A lot of the whitepapers I read like the gyro's only outputs angular velocity not angular position. If the IMU's output the actual orientation then that makes everything really easy for that. I have ordered a few parts to play around with to make sure I can get 1 sensor working correctly at the specs I want before I do several. I was just inquiring on what to expect in that regard.

Go Up