Nine Eagles Solo Pro / Bravo SX brushless conversion - RC Groups
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Sep 05, 2011, 12:42 PM
Registered User

Nine Eagles Solo Pro / Bravo SX brushless conversion

Hi micro-heli-modders out there,

I want to go brushless with my NE helis and found lots of info spread over the web ... but it is still hard to get all your experiences together.
I think it could be really helpful, to have a single thread, to bring it all together!

Lots of questions arise, thinking about the conversion project:
Which motors are suitable (KV-rating, weight, mounting, ...)?
Which ESCs to use?
How to convert PWM to PPM?

So, I would greatly appreciate, if you, who succeeded such a conversion, would share your experiences. I think, a list of components (links, where to get, would be great), some comments on the performance and maybe some pictures would be really benefitial.

Maybe kind of a template like this:

Modding project:

Main Drive
  • Main brushless motor:
  • Main ESC:
  • Main PWM to PPW converter:

Tail Drive
  • Tail brushless motor:
  • Tail ESC
  • Tail PWM to PPM converter:

  • Battery capacity used:
  • Flight time:
  • Comments on flight performance:

Links to buildlogs (if there are some):

I would sugest, to discuss the projects in there original threads, to have a clear knowledge base here ...

Thanks in advance,
Stephan from Germany
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Sep 07, 2011, 07:08 AM
Brosol's Avatar
I'm also interested in Bravo SX brushless motor conversion too.

I wish custom parts such as PWM to PPW converter and motor mount was available to purchase for those who lack the tools & skills to program/make their own. ESC, BL motors can be purchased from sellers like HobbyKing.

By YXmotor


Last edited by Brosol; Sep 07, 2011 at 07:20 AM.
Sep 16, 2011, 12:48 PM
Registered User
Hi all,

nobody out there to share some information?
Maybe on a specific question: Did anybody analyse the PWM output of the Nine Eagles 4in1? I tried a WK-WST-10A-LT since I thought it might work without converter. But it does not really run. So, what is the NE PWM-frequency? Is it positive or negative PWM?
Any suggestions for the best place on the board to connect the PWM-outputs?

Sep 16, 2011, 04:38 PM
Vienna calling...
Donaldsneffe's Avatar
As already written elsewhere:
I did not get it running with the Xtreme converter, several ESCs (XP-3A, DP-3A, XP-7A, and some more) and the Turnigy 1015.
Maybe I'll try a "TheSteves" new version later on, now use old versions on my mCP x anyway and do not need the new one anymore (has extremely decreased rpm control).

Sep 17, 2011, 07:46 PM
Registered User
You have to use a converter of some type. The ESC expects a signal typically from a receiver, a 5 volt positive pulse (TTL) that repeats every 20 msecs or so with an on time of between 1 and 2 msecs depending on the speed you require. The motor output is going to be a pulse width modulated signal with a 0 to 98% duty cycle and a base frequency of typically 1kHz (1 msec) or greater and switches by allowing current to flow through the motor so the signal does not have to be the typical voltage rails (0 to +Ve). This is why a resistor (2.2Kohm typical) is place across the motor output terminals and is used to convert the current flowing across it into a voltage for the input of the converter (ohms law volts=current*resistance).

Can you(or anyone you know) program a PIC microprocessor? Code exists for the NE boards. The PicKit USB programmer is about 25 or you can build your own programmer from schematic on the net.
Sep 18, 2011, 03:10 PM
Vienna calling...
Donaldsneffe's Avatar
Originally Posted by h106frp

Can you(or anyone you know) program a PIC microprocessor? Code exists for the NE boards. The PicKit USB programmer is about 25 or you can build your own programmer from schematic on the net.
Me not, for sure

Maybe some of the guys in the German forums, but I do not dare to ask them (they are on Walkera and now mCP x - Nine Eagles helis are "toys" for them ).

Sep 29, 2011, 01:08 PM
Registered User
Hi all,

I found some reports, where people used ATtiny controllers for making converters. There is a programmer available for €20. Does anybody know, which controller is more powerful to do dual conversion on a single chip (which would save power, weight and wiring effort)?

Sep 29, 2011, 05:32 PM
Registered User
Originally Posted by thecubist
Hi all,

I found some reports, where people used ATtiny controllers for making converters. There is a programmer available for 20. Does anybody know, which controller is more powerful to do dual conversion on a single chip (which would save power, weight and wiring effort)?

Only used PICs myself so i'll comment on those....

To keep the weight down you have to go surface mount which means that you will need to make your own boards.

PICs usually come in both thro' hole and surface mount versions of the same chip so you can prototype with socketed chips and vero board before you need to commit to surface mount.
Choose a version with built in clock generation and you do not need the external crystal and caps that will add weight and complexity.

The PICkit programmer kit with a decent chip and all the development software included is about 25. You can code in C or assembler.

I've used PICs and they can do 2 channels. I've done single channel main rotor converter that has worked flawlessly and i've untested code for a tail rotor channel.

You need an interrupt driven program to handle the timing measurements of the input signal without program execution timing issues becoming difficult to control. Get a version with 3 timers, 1 for each input channel and 1 for the base pulse frequency generation - this makes the program fairly straight forward as it lets the micro measure the incoming pulses and generate the output signal while you get on with just servicing the interrupts as they arise for the different tasks - read the timer values or create the output pulses as required.

For my single channel converter a base model PIC at 4Mhz could easily make 5 measurements of the input signal (1kHz PWM) in the time between generating the output signal (20ms period) so an extra channel would not really stretch even a basic processor.

Allow for some sort of trim adjustment of the tail rotor output, this allows you to fix any issues arising from using different motors from standard.

The processor itself does not need to be very powerful (faster clock speeds usually consume more power) if you use the built in hardware timers for the difficult tasks.
Sep 29, 2011, 10:58 PM
Team WarpSquad
Daryoon's Avatar
Anybody else noticed that ClubHeli has the EZBind version of Bravo SX back at $49.99? I remember reading some body was interested and missing out on it the last time around.
Oct 04, 2011, 05:38 PM
Registered User
Thanks to h106frp for all the info. I just ordered a pic-programmer, will probably take a while to arrive in Germany from Malaysia ...
I studied some datasheets so far, and the pics seem to offer more timers. Untill the programmer arrives, I will try to borrow an osci to check the NE-signals ...
Oct 04, 2011, 07:31 PM
Registered User
Attached shoul be text version of .asm file for single channel 1khz PWM conversion - maybe it will give a bit of inspiration

edit:Just a thought, if you download the free development IDE from microchip you can build your whole project in software while you wait for the hardware to arrive. It includes realtime emulation of the PIC units with the ability to generate input signals and monitor the outputs and watch the internal registers as the program runs. You only need to burn the PIC once you are sure that the program executes as expected in emulation. App note 51519a.pdf from microchip has a good walkthrough for setting up your first project.
Last edited by h106frp; Oct 05, 2011 at 03:38 PM.
Oct 05, 2011, 05:27 PM
Registered User
Thanks for your code! It's much longer, than I expected ;-)
My last assembler programming is lots of years ago, so I wonder, if the free IDE also supports some high-level programming language like C?
Motor and ESC are also ordered ... will also take some time, so maybe I will try the emulator, as you suggested. But first, I have to figure out the signal charachteristics of the NE board ...
Oct 05, 2011, 06:42 PM
Registered User
You can use C or a mix of C and assembler, the compiler sorts it all out. The assembler is simple, and the program looks long because you execute just one instruction on a line, so several lines would equate to one high level command in C -( you can get the IDE to display the equivalent assembler for C instructions for debugging purposes).
The advantage of assembler is you can be certain of how long sections of code take to execute - generally one instruction is 1 clock cycle, branches (goto, gosub) take 2. Theres only about 30 instructions to learn in total, most of the time you are checking or setting bits in registers. If you get the PicKit kit it takes you through a few simple demos of LEDs and switches using the supplied board and chip.
A lot of the code at the start of the listing is generated for you by the IDE wizard which produces a template for declarations and interrupt handling.
Oct 21, 2011, 10:30 AM
Registered User

I just received my programmer and figured out, that the PIC12F675 is available at a local dealer in town. So, maybe time for a fast first try at weekend. But: I do not really understand the configuration of the PWM-frequency (you have 1kHz, I need 2kHz) in your code? Could you please give me a hint, where to change the timers configuration?

Thanks from Germany,
Oct 31, 2011, 11:21 AM
Registered User
As the PWM freq is doubled to 2 kHz, the measured period of power applied to the motor for 100% throttle would be half that measured for 1 KHz.

edit: previous posted will not work, we need to multiply the value from the timer by 2 to correct the value for 0 to 100% throttle
add the line in red

RRL W,1 ;multiply the value in W by 2 and keep in W
Last edited by h106frp; Nov 01, 2011 at 04:03 AM.

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