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Old May 30, 2009, 05:12 PM
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Using the HK-T4A RF-module in an Inopo AFM2 pistol grip transmitter

Hi,

I have been following this thread with great interest from the start planning to convert my Longsun/Inopo AFM2 transmitter to 2.4ghz using the RF-module from the HK-T4A 4-channel transmitter (FS-HF020A V11).

The AFM2 transmitter is as I understand it a clone of the Futuba A3PM 3-channel pistol grip transmitter with 10 model memories and uses a module box (not compatible with Futuba) for AM or FM with the following pins outs to the module (see attachments):

PPM signal Out
GND
12v
5v
GND
Signal In

I have tested the voltage of the PPM signals on both transmitters:

HK-T4A
PPM = 2.13v

AFM2
PPM = 0.45v

Something tells me I have to modify more than I had hoped

I am no electonics wizard and do not want to destroy anything in the process and would like some feedback from you before I commit to the modifications.

What I would like to know more about:
- Do I have to increase the PPM signal from the 0.45v range to 2.13v range?
- How do I increase the voltage of the PPM signal?
- How can I find out if I need to invert the PPM signal?
- Can I use the existing PPM out pin to lenghten the connection between the RF-module and the 2.4ghz antenna?
- Anything else you believe is useful

Thank you for all your great efforts in improving/hacking the Flysky 2.4ghz sets
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Old May 30, 2009, 11:18 PM
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Joined Feb 2009
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hi i recently got this tx, my first and i was looking to set it up but i'm not very sure what each control means, could someone help me out by giving me a default setting so that i can adjust from there? i'm flying a gaui 200 with 120swash plate. ccpm. thanks. or if anyone can guide me in msn. thanks again.
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Old May 31, 2009, 05:43 AM
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Espaņa, AL, Sevilla
Joined Apr 2007
515 Posts
Quote:
Originally Posted by kjetilei
...
I have tested the voltage of the PPM signals on both transmitters:

HK-T4A
PPM = 2.13v

AFM2
PPM = 0.45v

Something tells me I have to modify more than I had hoped

I am no electonics wizard and do not want to destroy anything in the process and would like some feedback from you before I commit to the modifications.

What I would like to know more about:
- Do I have to increase the PPM signal from the 0.45v range to 2.13v range?
- How do I increase the voltage of the PPM signal?
- How can I find out if I need to invert the PPM signal?
- Can I use the existing PPM out pin to lenghten the connection between the RF-module and the 2.4ghz antenna?
- Anything else you believe is useful

Thank you for all your great efforts in improving/hacking the Flysky 2.4ghz sets
Possibly, the low voltage level you're measuring is because of signal polarity.

HK PPM signal (described here), has negative going pulses form high voltage (5 V at trainer port, 2.4V at module input). As there are 7 low pulses of 0,4 mS each 20 mS, de duty cycle of the signal (on time/total time) = 1-(7*0,4/20)= 0,86. If your DC voltmeter is measuring average DC, then it should read 0,86*2,4V=2,06V, approx the same as the 2,13V you posted.

On the other hand, if your AFM2 signal consists of 5? (4 channel?) positive pulses of 0,4mS, then duty cycle is 0,1, so your measured 0,45 V would mean 4,5V peak voltage, approx 5 V, wich seems quite possible. You could confirm this measuring peak voltage with a diode and capacitor, as I said at post#835. Also, you could check signal pulses using a sound card oscilloscope (see here). In that website, there's a lot of info about signal level and signal polarity adaption. Note that this kind of scope may give an approximate idea of signal shape, but i't's not good for level measuring or even signal polarity, as it's AC coupled and I wouldn't trust if it's inverting or not the input.

Once you've determined signal peak level and polarity, it would be possible to answer most of your questions. I think somebody posted about using HK module with positive going pulses, but I'm not sure about it. If it detects signal edges, maybe it would work OK with both polarities, but on the other hand, maybe it's not designed to work with less than 6 channels (7 pulses). I've read at another thread that HK 4 channel also otputs 6 ch PPM signal.

Finally, regarding your question about using signal out pin to lengthen the connection between the RF-module and the 2.4ghz antenna, I'm afraid it's not possible, as this connection is designed for much lower frequencies (35-72 MHz), and would have very high losses at 2,4GHz. This is why commercial 2.4 GHz modules don't use this connection. You should keep the original antenna and its connection cable to avoid RF losses. At 2.4 GHz an impropper antenna connection migt be even worse that not having an antenna at all!
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Old May 31, 2009, 07:39 AM
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Joined Jun 2008
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Compatible 3-channel receiver

I just checked the 3-channel pistol grip transmitter from Flysky (FS-GT3) and it uses the same transmitter module as the 9-channel transmitter (FS-TH9X).

The 3-channel pistol grip transmitter is delivered with a 3-channel receiver (FS-GR3A). This receiver could most likely be used together with parkflyers to save a little bit of weight. Has anyone seen this receiver available for purchase on the net?

FS-GT3 manual: http://www.flysky-cn.com/pic/down/FS-GT3MANUAL.pdf
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Old May 31, 2009, 07:46 AM
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Dear MoFL,

Thank you very much for all the great help you provide!

I think I will try to hook up the RF-module to the AFM2 transmitter Tonight.

As I understand it there should be no fear of destroying the transmitter or RF-module due to possible inverted signal or lower input signal than expected.

Please advice if I am completely wrong

Quote:
Originally Posted by MoFl
Possibly, the low voltage level you're measuring is because of signal polarity.

HK PPM signal (described here), has negative going pulses form high voltage (5 V at trainer port, 2.4V at module input). As there are 7 low pulses of 0,4 mS each 20 mS, de duty cycle of the signal (on time/total time) = 1-(7*0,4/20)= 0,86. If your DC voltmeter is measuring average DC, then it should read 0,86*2,4V=2,06V, approx the same as the 2,13V you posted.

On the other hand, if your AFM2 signal consists of 5? (4 channel?) positive pulses of 0,4mS, then duty cycle is 0,1, so your measured 0,45 V would mean 4,5V peak voltage, approx 5 V, wich seems quite possible. You could confirm this measuring peak voltage with a diode and capacitor, as I said at post#835. Also, you could check signal pulses using a sound card oscilloscope (see here). In that website, there's a lot of info about signal level and signal polarity adaption. Note that this kind of scope may give an approximate idea of signal shape, but i't's not good for level measuring or even signal polarity, as it's AC coupled and I wouldn't trust if it's inverting or not the input.

Once you've determined signal peak level and polarity, it would be possible to answer most of your questions. I think somebody posted about using HK module with positive going pulses, but I'm not sure about it. If it detects signal edges, maybe it would work OK with both polarities, but on the other hand, maybe it's not designed to work with less than 6 channels (7 pulses). I've read at another thread that HK 4 channel also otputs 6 ch PPM signal.

Finally, regarding your question about using signal out pin to lengthen the connection between the RF-module and the 2.4ghz antenna, I'm afraid it's not possible, as this connection is designed for much lower frequencies (35-72 MHz), and would have very high losses at 2,4GHz. This is why commercial 2.4 GHz modules don't use this connection. You should keep the original antenna and its connection cable to avoid RF losses. At 2.4 GHz an impropper antenna connection migt be even worse that not having an antenna at all!
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Old May 31, 2009, 08:59 AM
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kjetlei, to be sure, I'd measure the peak voltage, just to make sure it's 5V.

And, in this case, add a divider at the module's input. Just 2 10K resistors would do
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Old May 31, 2009, 10:53 AM
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Dear MoFl,

Thank you once again.

I really appreciate the help and knowledge you share with us!

Quote:
Originally Posted by MoFl
kjetlei, to be sure, I'd measure the peak voltage, just to make sure it's 5V.

And, in this case, add a divider at the module's input. Just 2 10K resistors would do
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Old May 31, 2009, 12:12 PM
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Quote:
Originally Posted by MoFl
If it detects signal edges, maybe it would work OK with both polarities, but on the other hand, maybe it's not designed to work with less than 6 channels (7 pulses). I've read at another thread that HK 4 channel also otputs 6 ch PPM signal.
I'll be checking about polarity later and report.
I have already checked that the RF PCB works okay down to 2 channels (PPM sequence with only three pulses), and that the synch interval can be as small as 3.2 ms.
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Old May 31, 2009, 12:21 PM
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Thanks, JMP_blackfoot, that removes one of the unknowns because, although Flysky has a 3 ch system using this module, it could output a higher number of pulses, as the 4 ch system does.
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Old May 31, 2009, 01:20 PM
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OK, just did some more tests and as far as I ascertain, here goes:

1) Polarity does not make any difference.
2) Number of channels can be 2 to at least 7 (3 to 8 pulses - I don't have a transmitter with higher number)
3) Synch interval can be fixed (I have tested from 9 ms down to 3.2 ms) or variable (PPM sequence fixed at 20 or 22 ms).
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Old May 31, 2009, 01:30 PM
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I am getting a little more confident (too confident perhaps?) and will try without the signal inverter first, since I do not have the needed components at hand.

If needed I plan on ordering the parts from Thai Shop Etc on eBay. This was the place I could find with the cheapest prices for low volume orders and as a non-commersial buyer.

Then I plan on hardwiring/soldering the parts together and use a hot glue gun to stabilise and secure the components.
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Old May 31, 2009, 01:35 PM
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Thank you for the information!

I hope to convert the AFM2 transmitter Tonight and will submit the result

Quote:
Originally Posted by JMP_blackfoot
OK, just did some more tests and as far as I ascertain, here goes:

1) Polarity does not make any difference.
2) Number of channels can be 2 to at least 7 (3 to 8 pulses - I don't have a transmitter with higher number)
3) Synch interval can be fixed (I have tested from 9 ms down to 3.2 ms) or variable (PPM sequence fixed at 20 or 22 ms).
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Old May 31, 2009, 03:44 PM
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Quote:
Originally Posted by JMP_blackfoot
...
1) Polarity does not make any difference.
2) Number of channels can be 2 to at least 7 (3 to 8 pulses - I don't have a transmitter with higher number)
3) Synch interval can be fixed (I have tested from 9 ms down to 3.2 ms) or variable (PPM sequence fixed at 20 or 22 ms).
These characteristics make hacking much easier!
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Old May 31, 2009, 03:53 PM
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AFM2 successfully converted to 2.4 GHz!

I went ahead and converted the AFM2 to 2.4 GHz a few moments ago.

It was a 5 minute job and went great

The only thing I had to do was open both transmitters, cut the cables to the RF module in the 4-channel Hobbyking transmitter and solder the RF module cables to the pin outs in the AFM2 normally used for the AM or FM module.

I haven't tidied it up yet and must perform a long range check before I declare this as a winner but everything looks great so far!

I hope to be able to post pictures later Tonight
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Old May 31, 2009, 05:44 PM
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AFM2 conversion - pictures

I have now been able to tidy up the conversion and perform a long range test that went great!

As already mentioned I soldered the RF module to the AFM2 module pin outs. I then added heat shrink tube over the soldered module pins for safety measures.

I left one of the two ground pins exposed and heat shrinked the bind wire so that I can quickly perfom a rebind later if needed. I plan to fix this later - either with a new switch or using the switch for the third channel that is currently not in use.

I then secured the RF module to the transmitter PCB with double sided tape and used hot glue to further tighten the 2.4 GHz antenna in the original hole for the AM/FM antenna. This might be a weak spot but I will see if I can come up with a more secure method later.

The only thing remaining then was to close up the AFM2 transmitter and perform a long range test to check the stability of the system.

I took my brushless Kyosho Mini Inferno and drove very slowly while continuosly steering left and right until I could almost not see the Mini Inferno any more and then returned just as slowly performing the same steering test. It was rock solid - unlike how it has performed with the old 27 MHz AM module!

Since I love driving the Mini Inferno I took several more test drives constantly increasing the speed until I went flat out (4900kv motor on 11.1v lipo) in our thight indoor parking

This conversion was really easy to do (why haven't I done it berfore?)! It is also non-intrusive and I can undo everything easily and have two complete transmitter sets if I want to.

Thanks for the great help and information and keep up the good work!
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