Graupner Bellamatic controller with ATtiny85

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MaxZ
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Location: Boskoop, Netherlands

Graupner Bellamatic controller with ATtiny85

Post by MaxZ »

Hi all,
Bruno (F2B) and I are discussing designing and building a controller for a Graupner Bellamatic servo using an ATtiny85 and two of these: https://www.kiwi-electronics.nl/download/KW-1580.pdf (the 5V 150mW version)

From the datasheet I calculated a current of 30 mA, which is the maximum the ports of the ATtiny are specified for. Is there anything else I should consider? Is an inductive load a problem for the chip? Should I pair two ports in parallel to drive a single relais using direct port access or is there no need for that?

Cheers,
Max.
Tobe
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Location: Varberg or Stockholm, Sweden

Re: Graupner Bellamatic controller with ATtiny85

Post by Tobe »

It has been done but i preferred to use a H-bridge like the DRV8838, basically the same type of recoder I use in the different GG set up i build as it gives a lighter set up with the possibility to pulse if as thre critical point is when the actuator is stalled at the end position and can easily pull close to 200 mA or more when installed in an airplane with full linkage. Have found out that it's not unusual that Bellamatic as most old actuators for reed set ups need to have the motor remagnetized to properly work and have some strength. My single action actuator design is built to be able to work more or less like a Bellamatic and have played with it quite a lot.
Cheers,

Tobe
MaxZ
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Re: Graupner Bellamatic controller with ATtiny85

Post by MaxZ »

Tobe wrote: 09 Aug 2020, 15:06when the actuator is stalled at the end position and can easily pull close to 200 mA or more when installed in an airplane with full linkage.
I do not have a Bellamatic myself, we are investigating for a mutual friend who wants to operate it in a new/vintage model (Graupner Kapitän). But I understood the Bella has a slip clutch which allows the motor to continue running when the arm hits the end stop, so how can it stall due to flight loads? Besides that, the intention is to use relais similar to the original controller, and they are specified for 3A, so even 200 mA will not be a problem. Or were you referring to your H-bridge type?

Cheers,
Max.
Tobe
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Re: Graupner Bellamatic controller with ATtiny85

Post by Tobe »

I was referring to my set up. I sure remember theirs clutch system, worked nicely but as everything with time deteriorates. I have a few Bellamatic all well kept and taken care of and they show different signes of their age.
Demagnetized, corroded/broken centering spring and clutch set up on the stiff side but all quite easy to fix so just some TLC and you surely going to have a nice set up.
Personally I'm not a fan of relays and always aimed for relayless but that is personal
Hope this info could be of help.Suggestion is to replace the "reeds" with 2 outputs of the ATtiny85
Attachments
Bellamatic A RCM.pdf
(385.17 KiB) Downloaded 169 times
Bellamatic B RCM.pdf
(555.79 KiB) Downloaded 173 times
Cheers,

Tobe
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Phil_G
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Re: Graupner Bellamatic controller with ATtiny85

Post by Phil_G »

MaxZ wrote: 09 Aug 2020, 14:18 Hi all,
Bruno (F2B) and I are discussing designing and building a controller for a Graupner Bellamatic servo using an ATtiny85 and two of these: https://www.kiwi-electronics.nl/download/KW-1580.pdf (the 5V 150mW version)
I've done the same thing, driving period reeds servos from a conventional channel signal. I used a transistor driver to get enough current for the relays and to isolate the inductive bemf. Works perfectly.
I used relays in preference to bridges so that they could be wired to any standard reed servo straight from its supplied diagram. viewtopic.php?f=62&t=327&p=1440#p1454

Files attached, I checked them this morning hence they have todays filedate, they're from 2011 ish


IMG_20200814_144920_635.JPG


Mitigating bemf is personal preference - many use a DC buzzer straight off an I/O but if you'd scoped it you wouldnt. The Atmel ovp clamping diodes are only 2mA so you need something Max.

Its all inline code so the PIC will translate easily to Arduino, basically its 4 lines, use pulsin, if > neutral operate relay 1, if < neutral operate relay 2 else release both relays:
Attachments
reed_servo_relay_driver.zip
(1.33 KiB) Downloaded 154 times
MaxZ
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Location: Boskoop, Netherlands

Re: Graupner Bellamatic controller with ATtiny85

Post by MaxZ »

Yes Phil, I read your stuff on that subject, as a matter of fact it set me off to search for a local source of those little relays. I take it you share my concern about inductive loads straight from the ATtiny, so a transistor driver will be required to take care of the bemf. Or would a Schottky do it, as the coil current is only 30mA, so the port on the Atmel should be able to drain that?

Cheers,
Max.
MaxZ
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Joined: 31 Jan 2019, 11:48
Location: Boskoop, Netherlands

Re: Graupner Bellamatic controller with ATtiny85

Post by MaxZ »

Thanks Phil. I had already made a stripboard layout with exactly the scheme you included, I still have to write the arduino sketch. But Bruno is well on his way to produce an alternative using a H-bridge driver chip to drive the Bella, so i'll see what he comes up with first.

Cheers,
Max.
Martin
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Re: Graupner Bellamatic controller with ATtiny85

Post by Martin »

The thread and sketch for my ATtiny85 decoder/H-bridge driver for pulsed systems is here: viewtopic.php?f=25&t=579. It would likely work with relays too, but I've never tried that.

The ATtiny85 takes up to three input channels - one for rudder which biases left/right, one for elevator which alters the pulse rate, and a third one which controls the proportion of time the outputs are being driven, versus 'coasting'. You don't have to use all three channels, of course, but even if you want 100% power all the time, it's still useful to connect that third channel to a switch on the transmitter, so that the flapping action can be switched on before launching, and off once the plane has landed.

There are also options for connecting a potentiometer locally to the decoder, so that you can set the pulse rate using a pot on board the plane, if you're not using a suitable transmitter with spare channel(s). See the thread for more details if you're interested.
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F2B
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Re: Graupner Bellamatic controller with ATtiny85

Post by F2B »

Hi Martin,

Credit where credit's due...
I have used your receiver.ccp and receiver.h files for establishing numeric values for two received (propo) channels.
From there, manipulating those in order to control H-bridges, in turn driving two rudder machines like the Bellamatic, was relatively easy.
Even for the non-programmer hardware hack I am.... :mrgreen:

Here's what the decoder alone does on an emulated SC signal (it's my Nano protoboard).
Red LED for port, green for starboard.... :mrgreen:
https://vimeo.com/446748177
F2B or not to be....
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