Comment by William Premerlani on May 8, 2009 at 12:40pm

@Tom

First, I agree with you, Tom, about the vibration issue with the LISY300. I stipulate that the LISY300 is vulnerable to vibration at 4 kHz. As you say, enough vibration at that frequency will rattle the LISY300 hard enough so that there is nothing you can do. So, I do not recommend that anyone use my new board in high-vibration applications, at least not without testing it first. You are right, the new Analog Devices gyros with a 15 kHz resonant frequency should be less vulnerable to the vibration that a helicopter generates. If I ever get around to designing a board for helicopters, I will probably use the Analog Devices gyros.

That said, I think there are things that you can do to mitigate the vibration issue for the LISY300. I mount my board in my planes with velcro. In addition to making it easier to install and remove, it does provide quite a bit of isolation from shock and vibration. Though velcro might not be strong enough for helicopter applications, it could work for fixed-wing aircraft with internal combustion engines. It works perfectly well in fixed-wing electrics.

Also, at first I definitely did see a shock issue with the LISY300s on my prototype board. Whenever I flicked the board, the DCM algorithm jumped. However, that problem completely went away when I raised the sampling rate. So it is not entirely clear to me that any problem anyone has ever had with the LISY300 is a vibration issue. They may simply have not used a high enough sampling rate. I think that with vibration, it is a question of degree. I think that if there is moderate vibration problem, you can improve the situation with a higher sampling rate to prevent aliasing of the response to vibration. If there is a large problem, there is nothing that you can do.

@Brian

Regarding the Invensens gyros, it is my understanding that Paul Bizard had some problems with those. Paul bought the 5 DoF IMU from SparkFun with the IDG-300 X-Y gyros. I convinced him he needed a third gyro for our DCM algorithm, so he bought a LISY300 later on. He built a copy of my UAV DevBoard. He never got it working to his complete satisfaction. There appeared to be a huge amount of drift from the IDG-300. He was able to do a direct comparison between the LISY300 and the IDG-300, the LISY300 was drift-free by comparison.

I have not ever tried the IDG-300, so I do not know. As I am sure you know, as you move up to higher range gyros, the issue of drift becomes aggravated.

I assume that you have tested the Invensens for drift, in which case I am sure that everyone would be interested in what you found.

Finally, I like your idea for providing some shock and vibration isolation in the mounting of your board.

Best regards,
Bill Premerlani

Comment by Brian Wolfe on May 8, 2009 at 12:58pm

Hey Bill,
Paul's findings would be consistent with a friend of mine who had a terrible time taming the drift of the IDG300. We're working under the assumption that the new series will have fixed or at least minimized the issue and that is why the IDG300 is being replaced by the IDG500/600.
I have access to a rate table for testing and I'll be sure to keep everybody posted on what I find. I hope to be running hardware by the 15th.

thanks,
Brian

Comment by William Premerlani on May 8, 2009 at 1:10pm

Hi Brian,
I am very impressed with your board, I must say it is very sophisticated and complete. Good luck with it.
Bill

Comment by Jerry Rodberg on May 9, 2009 at 11:05am

I'm hoping to hear good things about the IDG500. Combine that with an ISZ 500 (or any other gyro out there, really) and you won't need vertical boards any more.

Comment by OlivierD. on May 9, 2009 at 2:14pm

@Bill: How about using an IDG-650 and and ISZ-650
Link: http://www.invensense.com/products/idg_650.html
Link: http://www.invensense.com/products/isz_650.html
The IDG 650 is $40.00, no price info on the ISZ650 yet.
They can do 2000 deg/sec. Or is that overkill?

Comment by William Premerlani on May 9, 2009 at 5:36pm

@Olivier:

The IDG-650 and ISZ-650 look good on paper, but the only way to know for sure is to test them. I think it is certainly worth trying them out.

I think that 2000 deg/sec is overkill. That is 5 revolutions per second.

There is a price to be paid in going to a range that is too high, you lose resolution unless the A/D has a lot of bits, and you are more susceptible to noise and drift. You should use a range that is just high enough to cover the requirements of your mission.

Comment by OlivierD. on May 9, 2009 at 8:23pm

@Bill: Makes sense. Even an high-end aerobatic plane rolls around 500 deg/sec anyways, I don't see why we should need more!

Comment by Rob Eckel on May 15, 2009 at 2:39pm

@Bill

I'm eagerly awaiting your next devboard release! Have you gotten to do any more testing this week? Are you still satisfied with the choice of new sensors? How is the early June ETA looking at this point, for the board to be available for purchase from sparkfun?

Comment by William Premerlani on May 15, 2009 at 2:59pm

@Rob,

I have done some more testing this week, I am still satisfied with the choice of sensors, though I caution that anyone who wants to use the new board in high-vibration applications (such as helis), should test them first.

One of the improvements we made to the board is to run the sensors and the A/D reference all off the same regulated 3.3 volt supply. That completely eliminates drift due to power supply variations. So the firmware no longer has to make a correction for supply voltage drift.

I have revised all of my firmware so that it will run on either my old board (the green one), or my new board (the red one), and tested it out. As soon as the new boards come out, I will release the new firmware. Each file will come with two projects in it, a "green" one and a "red" one.

SparkFun has told me that the new board may be out before the end of May, but we will see. I will certainly make an announcement as soon as I know.

SparkFun is now taking back orders for the board. I notice that the price is still listed as $299, but I am pretty sure that will come down as soon as they are ready to sell the new boards. My guess is the price will change when they put up the picture of the new board, but I do not know what the new price will be.

Comment by OlivierD. on May 29, 2009 at 9:26am

Wow! $150 price drop! That was well worth the wait!

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