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Old Jun 03, 2011, 04:16 PM
OlliW is offline
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OlliW
Joined Sep 2009
2,922 Posts
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GA250 Coax Gyromixer: The Ultimative Boardless Brushless Conversion?

Hey coax enthusiasts,

to start with, I know, the title is a bit provocative... there is certainly nothing such as "ultimative" in this hobby...

Anyhow, I am kind of active in this forum since some time but have never ever actually started a thread, so I thought I could open one and share my latest project with you. The project I am going to describe is in some way the most simple approach to a BLBL conversion but at the same time also the most "stupiest"... I am sure you will have your own opinion on this.

Current state of affairs (Oct. 23 2011)
This project evolved since the first posting quite a bit, in particular Tommy@LA from RCline Forum successfully build a GA250 gyromixer Big Lama BLBL, and his problems with the gyromixer helped me a lot to improve it and solve the issues (many thanks to him). As with Version 0.21 I think the project is kind of mature and I hence consider it now as stable. I have updated all the sections below accordingly.

I have also added a full list of the hardware and software which is needed for completing the hardware modding of the GA250 and running it.

I understand that for many of you the hardware modifications and burning the bootloader(s) may be scaring off. So, if that's the case but you would otherwise have liked to give this project a try I do offer this: If you send me all required hardware together with a return ticket, I will do the modding and burning and send it back to you (all for free).

(the statement "all required hardware together with a return ticket" should mean that I get everything needed so that I do not have any financial cost including the shipping and the "only" thing I have to do is to do the work, I don't have the financial resources to stockpile things )

Terms of usage
The software/firmware is not free. You may use it gratis and freely for private purposes. However, you may not use the work in full or in parts in any manner that is intended for or directed toward commercial advantage or private monetary compensation without explicit agreement by the author.

About this project
As you know, in a BLBL conversion all electronics except of maybe the reciever is removed, and replaced by devices which provide the five functions reciever, gyro, mixer, BESCs, and BEC. From these five functions the two most critical ones are the gyro and mixer. The choice of the BESCs is mainly dependent on the power requirements/desirements, but otherwise rarely a problem since essentially all BESCs of today will work fine. The BEC is usually integrated in the BESCs, and no concern either. And the choice of a reciever has often been made way before venturing into BLBL. In contrast, the choice of the gyro and mixer is critical. This is seldomly because of perfomance issues, but because of communication issues: the mixer has to deal with an asynchrounous inflow of PPM signals from the reciever and gyro, and it's not garantueed that any mixer will work with any reciever and gyro combination. In fact, reviewing the various brushless conversion approaches presented in the past, one may summarize them as the never ending story of how to deal with the gyro and mixer functionalities in the BL game...

I will here describe how to modify the hard- and software of the ASSAN GA250 gyro (a MEMS gyro for 10$ at HK) such as to work as both gyro AND mixer - I call this a coax gyromixer. As a result, it becomes the only other electronic piece required for a full BLBL conversion besides the reciever and BESCs. As you will see, the hardware is the simple part in the game since not much has actually to be done here, just some simple solder work. However, though the GA250 provides a convenient hardware platform, its software has to be redone to get it to work as a gyromixer. Since the GA250 does not come with any means to adjust parameters, such as gain or prop, one has also to implement a means to "program" it. This could be done via the usual transmitter-stick-up-down-procedures, which I however don't like much, in particular if many parameters are provided. I hence decided to realize the parameter setting via a programming box which can be connected to the GA250 gyromixer, and I found the Robbe Programming Box V2 to be an excellent hardware platform for that matter. In the meantime I have also developed a Windows GUI which allows setting the parameters of the GA250 gyromixer from a PC. I called it AvrConfig. Hence, these two alternatives exist now; the PC option is certainly cheaper while the programming box option may be more convennient (but is not easily found in the US).

So, this project, the GA250 coax gyromixer project, consists of four things, the hardware modifications to the GA250 gyro, the firmware for the GA250, the AvrConfig PC program, and the firmware for the Robbe Programming Box.

During development of such a project it can hardly be avoided that the micro controller(s) need to be reflashed often, it is hence quite convenient to use a bootloader. I am using the bootloader by Haagen published in a German forum, http://www.mikrocontroller.net/topic/95839#new. It is powerfull yet compact. Thanks to Haagen for this excellent piece of work!

I will start with chating a bit about the background of this project. I will then describe the hardware of the GA250 gyro and Robbe Programming Box, will then present the remodelling of the GA250 gyro, and spend some words on the firmware for it. If you are not afraid of German, or reading a google English translation, you may follow the project also here: http://www.olliw.eu/2011/ga250-fpkoax-gyro-mischer/
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Last edited by OlliW; Dec 14, 2011 at 08:51 AM.