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Thanks for the links; I love this stuff. I can see the laser rangefinder [1] being expensive. But what makes the xsens gyro/accelerometer [2] so expensive compa

by Tempest1981 11y ago

Thanks for the links; I love this stuff. I can see the laser rangefinder [1] being expensive. But what makes the xsens gyro/accelerometer [2] so expensive compared to a smartphone sensor, and why does a robot need that?

sean-duffy 11y ago
Yeah that thing seems way overpriced, or at least far too high-spec for most applications. Quadcopter flight control boards containing gyros and accelerometers can be had for less than $20, and those do just fine.
Animats 11y ago
Accurate heading info requires good gyros and is moderately expensive. It's a lot cheaper than it used to be. When we did our DARPA Grand Challenge vehicle ten years ago, we had about 3 degrees of heading noise, which kept the system which integrated LIDAR data into a terrain map from reliably mapping. The system had a MEMS gyro with too high a drift rate, and a magnetometer compass for long-term correction. But there were enough magnetic fields from the onboard equipment to mess up the magnetic compass. The software could detect trouble, and would stop, tilt the laser head to scan the terrain ahead and get a clean image, then advance. So the vehicle kept stopping to rescan. We looked into better heading gyros, but they cost about $20K at the time.
michaelt 11y ago
If you think that's expensive, have a look at an OXTS RT3000 [1] where you can spend closer to $20,000 - that's the sort of thing you buy for your prototype self-driving car. Or at least, it was when people were competing in the DARPA Grand Challenge eleven years ago. Applications for IMUs include dead reckoning (working out your position based on rotation and acceleration measurements), orientation sensing (figuring out which way is down is much easier than dead reckoning, because you can just sense gravity), and compensating sensor readings for robot motion. Some cheap sensors aren't very precise; you won't notice if your phone thinks it's rotating two degrees a minute around the vertical axis, but a robot will if it moves for five minutes then it's ten degrees off course. I haven't looked at the market for a long time - I suspect the cheaper IMUs are better nowerdays. Eight years ago they didn't offer very good precision and the open source software could be very fiddly to get working, if you could get it working at all. [1] http://www.oxts.com/products/rt3000-family/ http://www.oxts.com/products/rt3000-family/
- Animats 11y ago
  At the 2004 DARPA Grand Challenge, the IMU/GPS unit that CMU's team used required 4U of rack space and air conditioning. There's been a lot of progress since then. The ADXRS642 MEMS gyro[1], which costs $50 in quantity, has a drift rate of 20°/hour. Ten years ago, you were lucky to get 20°/minute from a MEMS gyro. If you're doing sensor integration while moving, you need a stable orientation reference. Alternatively, you can use SLAM to process video and align to the world, which works well today. The OXTS RT3000 has impressive specs - 1cm accuracy in world coordinates. That's better than you need for most robotics applications that aren't running blind. The Trimble AP10 [2] has the same functionality at much lower cost, but is not as accurate. A lot of progress in robotics comes from component improvement like this. There was a time when just getting a wireless data link to your robot was a big deal. [1] http://www.analog.com/en/products/mems/mems-gyroscopes/adxrs642.html#product-overview http://www.analog.com/en/products/mems/mems-gyroscopes/adxrs... [2] http://www.trimble.com/gnss-inertial/AP10.aspx?dtID http://www.trimble.com/gnss-inertial/AP10.aspx?dtID

sean-duffy 11y ago

Yeah that thing seems way overpriced, or at least far too high-spec for most applications. Quadcopter flight control boards containing gyros and accelerometers can be had for less than $20, and those do just fine.

Animats 11y ago

Accurate heading info requires good gyros and is moderately expensive. It's a lot cheaper than it used to be. When we did our DARPA Grand Challenge vehicle ten years ago, we had about 3 degrees of heading noise, which kept the system which integrated LIDAR data into a terrain map from reliably mapping. The system had a MEMS gyro with too high a drift rate, and a magnetometer compass for long-term correction. But there were enough magnetic fields from the onboard equipment to mess up the magnetic compass. The software could detect trouble, and would stop, tilt the laser head to scan the terrain ahead and get a clean image, then advance. So the vehicle kept stopping to rescan. We looked into better heading gyros, but they cost about $20K at the time.

michaelt 11y ago

If you think that's expensive, have a look at an OXTS RT3000 [1] where you can spend closer to $20,000 - that's the sort of thing you buy for your prototype self-driving car. Or at least, it was when people were competing in the DARPA Grand Challenge eleven years ago. Applications for IMUs include dead reckoning (working out your position based on rotation and acceleration measurements), orientation sensing (figuring out which way is down is much easier than dead reckoning, because you can just sense gravity), and compensating sensor readings for robot motion. Some cheap sensors aren't very precise; you won't notice if your phone thinks it's rotating two degrees a minute around the vertical axis, but a robot will if it moves for five minutes then it's ten degrees off course. I haven't looked at the market for a long time - I suspect the cheaper IMUs are better nowerdays. Eight years ago they didn't offer very good precision and the open source software could be very fiddly to get working, if you could get it working at all. [1] http://www.oxts.com/products/rt3000-family/ http://www.oxts.com/products/rt3000-family/

Animats 11y ago
At the 2004 DARPA Grand Challenge, the IMU/GPS unit that CMU's team used required 4U of rack space and air conditioning. There's been a lot of progress since then. The ADXRS642 MEMS gyro[1], which costs $50 in quantity, has a drift rate of 20°/hour. Ten years ago, you were lucky to get 20°/minute from a MEMS gyro. If you're doing sensor integration while moving, you need a stable orientation reference. Alternatively, you can use SLAM to process video and align to the world, which works well today. The OXTS RT3000 has impressive specs - 1cm accuracy in world coordinates. That's better than you need for most robotics applications that aren't running blind. The Trimble AP10 [2] has the same functionality at much lower cost, but is not as accurate. A lot of progress in robotics comes from component improvement like this. There was a time when just getting a wireless data link to your robot was a big deal. [1] http://www.analog.com/en/products/mems/mems-gyroscopes/adxrs642.html#product-overview http://www.analog.com/en/products/mems/mems-gyroscopes/adxrs... [2] http://www.trimble.com/gnss-inertial/AP10.aspx?dtID http://www.trimble.com/gnss-inertial/AP10.aspx?dtID