6 Degree of Freedom, anybody?(Accelerometer/Gyroscope board)

Philldapill

I just got on the Mouser.com homepage to look up something totally unrelated, when I saw this. I've kept up a little bit with the new produts various companies are coming out with, but I had forgetten about ST Microelectronics' gyro's. They had announced them many moons ago, but the products wouldn't be for sale until this summer. I gotta say - Wow. A dual axis gyro for $6.72(mouser pricing). They make these in various sensitivities, and also 3 different axis orientations(only 2 axis per chip). ST Also makes some really nice accelerometer chips, too.

I'd like to get some of these for·my (someday) quadrocopter project. These chips are a pretty hard-to-solder surface mount part, so I think I'm going to get a few boards professionally made, rather than do my home-brew single sided boards. I'm just curious if anyone else would be interested in one of these.

What I had in mind, was a board consisting of a tri-axis accelerometer, a couple of gyroscopes, and an ADC. The ADC I have in mind is a TLV2543(12-bit, 11channel, 66ksps). The accelerometer and gyro have analog outputs, so the ADC would read these. With this setup, the accel/gyro would eat up 6 ADC inputs, but the board would have 5 extra inputs for various external·uses. The whole interface would use 5 I/O pins. There is an object in the OBEX for the Propeller for the ADC(written by the fantastic Timmoore).

SRLM

I'd vote for the MCP3208 ADC, but I'm a little biased (since I wrote some code for those...). If you can maintain the low pricing then I'd buy one or two. Four chips, for say $25. A board for $10 (average?), and assembly for $20? Still a good deal, even once you add in a margin.

However, I would request that the chip ADC outputs are broken out, or, if there isn't enough room, then pads are provided so that we can solder on wires. Also, a DIP format would be very nice.

Javalin

Sparkfun do a number of IMU type boards. Re-inventing the wheel?

James

Philldapill

Re-inventing a cheaper wheel, maybe. I think I can do a few of these boards for about $50 a pop. A quick search with sparkfun revealed one board - $125. Ouch.

Post Edited (Philldapill) : 9/3/2009 2:01:32 PM GMT

SRLM

I think you competition is at DIY drones. A 6 DOF IMU there is about $105, plus some assembly.
store.diydrones.com/ProductDetails.asp?ProductCode=BR-0006-10

mctrivia

Add a digital compss. And. Gps

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Timmoore

FYI, I took Jason's 5Dof code and extended it for 3x gyro, 3x accelerometer and a compass, and modified it to run in 1 Cog. I have just been modifying it again to use cessnapilot's fixed point math library to speed it up, its now running at 47 updates/sec on a single cog for all axis (as against 12/sec for floating point maths)
Its currently being tested with 2x IDG300, 1 ADXL330 and 1 CMPS03 with a tlv2543 but the object doesn't contain the A2D it runs outside the object. So I run 1 cog for the A2D and 1 cog for the IMU. The A2D object needs to output its values in a hub array that you also config into the imu object. This allows the A2D to be used for other analog inputs as well. The imu object also takes the gyro gains and other hardware config during initialization so it should work with most gyro/acc/compass.
I will post the code as soon as I have finished testing the new version. I also have the new sparkfun diydones imu and will be testing on that with a hmc5843 compass.
If you are building a imu I suggest you look at the hmc5843 compass and include that. A compass is needed for the 6th axis to stablize the gyro.

PS It you want to cut the cost of the sparkfun diydrone at the cost of a bit more work. You can use sparkfun for the main board and pololu gyro (its the same gyro) for the add on boards. The extra is the 3.3V and Gnd are switched in the pololu board so assembling it is harder but it addon boards are cheaper.

PPS. If you are thinking about the tlv2543 take a look at the tlv2556, its the same with a few extra options but also can be run faster. The current object is slowed down to the tlv2543 speed, with the tlv2556 it should be able to be run faster but the current code should run as is.

Post Edited (Timmoore) : 9/3/2009 3:57:42 PM GMT

wjsteele

Hi Timmoore,

Any updates on your code?

Bill

erco

WOW, $7 for a dual axis gyro? Sign me up! Holy smokes! I have no idea what I need them for, but I simply MUST have them and master them!

Kneel before Zod! We will crush the son of our Jailer!

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·"If you build it, they will come."

Timmoore

@wjsteele, I haven't been able to work on it for a while, but I have had a chance recently to get back to it though I have been working on a driver for the ITG-3200 that they are looking at for the quadcopter. I have the driver working but need to integrate it into the rest of the imu code. I need to look at whether you get better results from analog gyros with a separate A2D or an integrated device like the itg3200. In theory with the itg3200, axdl345 and hmc5843 you have a fully i2c solution.
@erco, take a look at the itg3200 - triaxis gyro for $15

erco

Timmoore: Thanks, will take a look. Are these gyros suitable to build a balancing robot (Segway-style), or are accelerometers still preferable?

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·"If you build it, they will come."

Timmoore

I dont know if they are enough without accelerometers, I have always used them in combination with accelerometers. My understanding is they have different characteristics - accelerometers respond slower than gyros but have better long term stability i.e. drift isn't a problem.