OpenPilot Project

OpenPilot FAQ

Why are your items so low priced?

Q. I've looked around for an AHRS for a project and the OpenPilot AHRS is incredibly priced, everything anywhere else close to your standard is at least twice the price and even then uses lower quality sensors.

A. We are not a commercial project but a community project. This is a hobby and was set up to be a fun community rather than a commercial venture and will remain so. Any money made from hardware goes towards hosting costs and to support the project. We get all the hardware made ourselves to make sure the quality remains high and is lead free, we also want to keep the costs down for the community simply because it is the community behind OpenPilot that makes it so special.

Multi-rotor and Fixed Wing?

Q. You state that the project aims to fly Multi-Rotor helis and also fixed wing aircrafts, is this actually possible I heard it was very difficult?

A. It is very possible and has been done, difficult is a subjective term and depends on the platform design. OpenPilot has been designed to control mutil-rotor craft, fixed wing and helicopters from the start of the project, it is envisioned that there needs to be only some minor software changes for fixed wing flight as of course these aircraft lack the ability to hover.

It appears this myth has been propagated by products that are implementing only very simple PID loops without more complex filtering. Although that architecture can fly a multi-rotor craft to a reasonable level, it does so by running these PID loops at massive speeds in an attempt to average out errors. Because they lack the more complex sensor filtering, they do not handle acceleration conditions well at all and are not suitable for fixed wing flight.

There are currently several projects around that are primarily fixed wing focused and have a similar architecture to OpenPilot with a control board and a AHRS that work well. Additionally, Antoine Drouin has demonstrated a quad rotor bi-plane aircraft that transitions from mutli-rotor style hovering in to fixed wing flight.

Do I need Drivers?

Q. Do I need drivers to connect the board to my PC/Mac/Linux?

A. No. Like a lot of things with OpenPilot we have thought about small details like this, you do not need any drivers at all. Additionally, you do not need any special connectors nor a special board that are a hidden costs, all you need is just a simple mini USB cable to plug in to the board.

Why not a flat AHRS?

Q. Why did you not use gyros that could be mounted flat and have a flat AHRS?

A. A flat AHRS was a design goal originally and we extensively tested all gyros that would allow this. Alas their MEMS frequency was right in the middle of the vibration range of multi-rotor and single rotor helicopters as well as some fixed-wing configurations, this made them totally unusable in real life.

This is a particular nasty trap that other projects, including expensive commercial projects, have fallen in to as although their designs will work well on the bench, they will perform very poorly much later in the project when it comes to actual flight testing. This is how the Jello-Copter [ http://vrhome.net/vassilis/2010/01/imu-potting-in-gel/ ] came about, not really practical and this flat IMU even now still has vibration issues although less so.

Gyro Testing

Q. Did you really test your Gyros with a vibrator? If so which model do I buy if I also wish to test vibration performance?

A. Yes, this is true. MEMS has a resonate frequency, unfortunately for a lot of gyros their MEMS frequency coincides with the frequencies produced by propellers and helicopter blades. We initially used a Dremel with and hex wrench in it for testing but this got a bit dangerous and this is why we switched to the "massager".

We tested several models and found the cheap ones with variable speed control work best. You need to produce frequencies from 2.5Khz to 9Khz which is the vibration level found in most of the aircraft we tested.

Despite the fact you wish to buy it for gyro testing, be warned that most people will not believe you and from experience it is best not to leave it on your workbench when people come over.

Are 9DoM & 9DoF the same?

Q. I understand that with AHRS systems they count the axes they measure in degrees of freedom with 9DoF being the best, what is 9DoM?

A. The OpenPilot AHRS is a 9DoM device which means it has 9 degrees of measurement. The name 9DoF is a nomenclature for 9DoM so they both mean the same thing, although 9DoF is incorrect (until time travel or String/M theory is proven) as there is only 6 physical dimensions that exist, not nine as 9DoF suggests.

Powering the Board

Q. Why do you not have an on board power supply like the MicroKopter?

A. Safety, flexibility and experience.

How do I get involved?

Q. I am not a developer, how do I get involved in the fun and help OpenPilot?

A. With a project like OpenPilot there is always something to be done besides development. The OpenPilot Wiki [ http://wiki.openpilot.org/ ] can always be improved with new information or to make parts easier to understand. As the project moves along we will also need release managers to organise major code releases, this job can be fairly trick and needs dedication as organising developers has been equated to herding cats. Also as this is a community project, spread the word. Let people know about the project and get them involved as well, this way the project improves at a faster rate.

JTAG Questions

Q. I already have my own JTAG, can I use it to help develop the OpenPilot software or do I need the Floss-JTAG?

A. Any JTAG compatible with OpenOCD will work for OpenPilot or AHRS development. The Floss-JTAG [ http://openpilot.org/Floss-JTAG ] came about from the need of Esden [ http://www.esden.net/ ] to develop on the train. He wanted a small, fast JTAG that used a single USB port but would provide JTAG debugging, 5V power to the target board as well a serial interface. If you use your own JTAG be sure it uses the new 10 pin mini JTAG interface, if not a very simple converter design can be found here [ http://openpilot.org/OpenPilot_JTAG_Converter ].