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#4289471 - 08/22/16 05:51 PM DIY force-actuated joystick  
Joined: Aug 2016
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irgendeiner Offline
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irgendeiner  Offline
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Germany
Hello!
After lurking for some time, I decided to show the Joystick that I am working on.
As my last attempt of building a Joystick with a cam-mechanism didn't work out as planned, I tried to create a force-sensitive Joystick using strain gauges.

Some pictures (please excuse the quality, I have only my phone to take pictures):
The prototype (the design of the grip was a bit rushed and is too small):

This is the rod with attached strain gauges (only one pair connected to a cable yet):

A look on the electronics:


Each pair of strain-gauges is connected to a Wheatstone bridge (top left). The bridge-signal is amplified with an instrument amplifier (lower middle) and then read using differential analog-digital converters (upper and lower right) which are connected to the Arduino via an SPI-bus.

The force needed for maximum deflection is 6 N, but I have to check my calculations as that seems quite low (the real F-16 stick has up to 75 N to 140 N depending on the axis, although it is reported as being quite a handful to actuate).
It works surprisingly well, but as I have the electrical circuit built on a breadboard (the final version will have a pcb) the trimmers for adjusting the bridge are a bit loose and have to be adjusted every time before I use the stick. Another Problem is a small creep in one axis over time which I think could either be an electrical fault or a fault of one strain gauge. I can even fly helicopters as bad as I do with my other Joystick (a Logitech Extreme Pro 3d, so not much of a reference), as there is nearly no noticeable axis-bleed, which I had read about as being a problem with force-sensing sticks.

The next step is designing an adapter for the grip of an TM Cougar, which I hopefully receive next week.
I plan to upload the schematics once the design of the PCB is finished, but that could take a while.

Cheers,
Bernd

PS: If there is interest I can write a bit about the details of how it works.

Inline advert (2nd and 3rd post)

#4289494 - 08/22/16 06:47 PM Re: DIY force-actuated joystick [Re: irgendeiner]  
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CyBerkut Offline
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CyBerkut  Offline
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Florida
Welcome! Yes, by all means, feel free to share more information. thumbsup

#4289514 - 08/22/16 07:29 PM Re: DIY force-actuated joystick [Re: irgendeiner]  
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AndyB Offline
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AndyB  Offline
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Ayrshire, Scotland
Hi Bernd,

I for one would be interested in more info and the schematic.

As a Comanche pit builder that would make it just that bit more realistic as it's a force sensitive stick in the real one (before they dumped the project).

Cheers,

Andy


Andy's simpit: http://www.simpit.me.uk
#4289518 - 08/22/16 07:39 PM Re: DIY force-actuated joystick [Re: irgendeiner]  
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robv Offline
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robv  Offline
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Netherlands
Hey that is a great thing! I made my own mechanical joystick but didn't think about force-actuation.

Perhaps this helps you? http://www.daco.co.uk/modular-controllers/force-joysticks

#4289525 - 08/22/16 07:52 PM Re: DIY force-actuated joystick [Re: irgendeiner]  
Joined: Jan 2014
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mega_mozg_13 Offline
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mega_mozg_13  Offline
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BELARUS, Minsk
Quote:

and then read using differential analog-digital converters (upper and lower right) which are connected to the Arduino via an SPI-bus

Hi, what ADC used?

#4289692 - 08/23/16 07:01 AM Re: DIY force-actuated joystick [Re: irgendeiner]  
Joined: Aug 2016
Posts: 5
irgendeiner Offline
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irgendeiner  Offline
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Germany
Hi,
Thanks for the interest! I will try to write everything up in the coming weeks, but as I have exams at the moment it might take a while.
Originally Posted By: robv

Thanks for the link, it seems the use the same technique as I do. My inspiration was the x65f, of which I found one picture of the applied strain gauges ( at the ED forums). This made me realize that it would be easier than thought (I had the Image of the milled load cell in mind before and as I have no access to a milling machine something like that was out of the question).

The ADC I use is a Microchip MCP3301 (data sheet), but any differential ADC will do. But as I use the amplifier (TI INA2126, data sheet) in the configuration shown on page 16 of the data sheet (only +5 V and Ground supplied, no -5 V Rail) I loose a bit less than 1 bit range of the ADC, that means that I have only 12 bit available while the MCP3301 supplies 13.
In my final configuration I also will replace those two ADC by only one with a Multiplexer, but as this was my first time interfacing with SPI on my own I wanted a simple solution.

Originally Posted By: AndyB
As a Comanche pit builder that would make it just that bit more realistic as it's a force sensitive stick in the real one (before they dumped the project).

Interesting that there was a helicopter that had a force-sensing stick, especially since the F-35 gets a normal side stick (with force feedback) because the hover-requirements instead the stick that the F-16 and F-22 use.

I will try to get the schematics into a representable state and upload them soon.

Greetings,
Bernd

Last edited by irgendeiner; 08/23/16 07:02 AM.
#4291919 - 08/30/16 06:45 PM Re: DIY force-actuated joystick [Re: irgendeiner]  
Joined: Aug 2016
Posts: 5
irgendeiner Offline
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irgendeiner  Offline
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Joined: Aug 2016
Posts: 5
Germany
Hello,
In the last week, I have received my Cougar and have adapted the Stick to fit it (I printed an Adapter to mount the Grip to the rod and written a routine to read the buttons).

While I like the feel of the Metal of the Grip, I have run into a new problem: As the Grip is both higher and far heavier, it acts like a Pendulum. If you don't hold the grip and give it a small nudge, it oscillates around the zero-point. Now that is not a big problem, but it is something which I want to eliminate later on by making the design more rigid.
I also soldered the Wheatstone bridges to a prototyping board which eliminated most of the headaches with the calibration (only the plugs of the cables to the strain gauges are a bit loose).
(Now that this is done, I try to have the schematics for you soon smile2)

Greetings,
Bernd

#4292039 - 08/31/16 03:59 AM Re: DIY force-actuated joystick [Re: irgendeiner]  
Joined: Jan 2014
Posts: 274
mega_mozg_13 Offline
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mega_mozg_13  Offline
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Joined: Jan 2014
Posts: 274
BELARUS, Minsk
irgendeyner
if you're interested, I can offer a little cooperation.
I have a working project joystick "MMJoy2", MCP320X family already there working(to add MCP330X there not a lot problem).
You do not need to "invent the wheel" with joystick/usb environment, and focus all efforts on the development of sensor.

Last edited by mega_mozg_13; 08/31/16 04:00 AM.
#4295330 - 09/11/16 08:21 PM Re: DIY force-actuated joystick [Re: irgendeiner]  
Joined: Aug 2016
Posts: 5
irgendeiner Offline
Junior Member
irgendeiner  Offline
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Joined: Aug 2016
Posts: 5
Germany
Hello,
mega_mozg_13, I am interested, but at the moment it already works as intended. I will surely come back to you when I integrate other things.
Andy, I have finally come around to make a preliminary schematic of the project:

On the left you can see the Wheatstone bridges which are calibrated using a trimpot each, in the middle the dual channel Amplifier and on the right the two ADCs (they will be replaced by a single ADC in the final design). Not pictured is a microcontroller (in my case it will be an Arduino micro pro).

Greetings, Bernd


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