The ProPo project, a DIY proportional servo

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Tobe
Posts: 376
Joined: 16 Feb 2018, 06:19
Location: Varberg or Stockholm, Sweden

The ProPo project, a DIY proportional servo

Post by Tobe »

Sometimes I got too much time and I end up in "projects" and here is one I would like to share with you all...as you know I have built a few complete homebuilt TX an RX combining a few other projects here like Phil's NRF24 FHSS Tx & Rx but realized that if I was not going GG I had to use commercial Digital Proportional servos. The size is comparable with my latest GG Modular actuator.
20210306_091725.jpg
Here is the result from my tinkering lately:



What you see is a simple basic digital proportional servo that could easy be done with what most of us have in our workshop.
The basic concept is to avoid any spur gear to connect the feed back pot to the motion of the servo arm/motor and I have come up with this solution, the motion will not be fully linear but barely noticeable within the range of operation. Actually the servo will show slightly higher precision around center, speed set to 0.18s/60deg .
20210306_091741.jpg
The motor I use the same G12-N20 motor/gear set as in my GG actuator with just a different gear ratio and as a feed back pot I use a 5k 180deg stick pot.
20210306_094530.jpg
For the time being I'm using tradition servo amp. based on NE544/HT7001 but eventually there might be a custom made similar to the Recoder used for the GG
...and yes, eventually I will share the files and building instructions.
Attachments
Assem2.JPG
Assem1.JPG
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Wayne_H
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Location: Wellington, NZ
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Re: The ProPo project, a DIY proportional servo

Post by Wayne_H »

Yet another extremely impressive project Tobe 👏. Here's hoping you have lots more "too much time" opportunities ;) :lol:

Would I be correct to assume(?) that the mounting plate could be modified into a 2 servo version, either tandem or side by side? 🤔
Cheers,

Wayne
Once a Retrobate, always a Retrobate............ ;)
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PaulJ
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Joined: 16 Feb 2018, 19:01
Location: Ipswich, UK

Re: The ProPo project, a DIY proportional servo

Post by PaulJ »

Brilliant Tobe! :P I look forward to having a go at some when you make the files available. :)
Tobe
Posts: 376
Joined: 16 Feb 2018, 06:19
Location: Varberg or Stockholm, Sweden

Re: The ProPo project, a DIY proportional servo

Post by Tobe »

Would I be correct to assume(?) that the mounting plate could be modified into a 2 servo version, either tandem or side by side? 🤔
If I got it to develop in the direction I'm hoping for there are all possibilities for combinations including a " 2-3 channel brick"
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Shaun
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Location: West Yorkshire

Re: The ProPo project, a DIY proportional servo

Post by Shaun »

Excellent , what a great idea pal. 👍

Shaun
GarydNB
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Joined: 15 Feb 2018, 23:12

Re: The ProPo project, a DIY proportional servo

Post by GarydNB »

I've probably missed something important here but is the triangular output plate necessary? Could it be omitted altogether and just use the arm which moves the plate to operate the pushrod directly?
Gary
Tobe
Posts: 376
Joined: 16 Feb 2018, 06:19
Location: Varberg or Stockholm, Sweden

Re: The ProPo project, a DIY proportional servo

Post by Tobe »

There are many way to do it and this is my way so feel free ...
The triangular plate is connected directly to the feedback pot and the arm with the dowel pin is the driving unit connected to the driving motor. The dowel pin will slide in the slot of the triangular plate and the the relation of the 2 operation radius is such to minimize the error caused as angle change. As the triangular plate rotates by the driving arm it will also give the proper feedback of its position via the pot to the electronics. This is normally achieved in regular servos by connecting with spur gears the pot with the driving shaft.
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ProPo.JPG
maxresdefault.jpg
Tobe
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Re: The ProPo project, a DIY proportional servo

Post by Tobe »

This is for you Wayne.
ProPo Twin SbS.JPG
ProPo Twin Tandem.JPG
I have realized that there are too many critical tolerances and all printers are different so I will not be able to adapt it properly to all different machines and due of its construction only ABS parts will work...but if you really want to give it a try PM and lets see what we can do.
The motor/gearbox and the pot are press fitted in the base, the rudder arm is the press fitted to the shaft of the pot and the hole in the base for the rudder arm is sized so it works as "bearing/support" for the shaft of the rudder plate and basically it's the same principle for the driving plate to.
Most components are press fittings on the tights side and I mean in the range + 0.005/0.01 mm -0.005/0.01 mm, second as I use a motor set up with a gear ratio of 298:1 the bond between the motor shaft and the driving arm needs to be rock solid to not strip, so there I use thin CA that actually melts slightly the ABS and penetrate so when it cures and the ABS gets solidified again after a few hours it makes a very solid bond. As every servo neither this one should be moved/rotated by hand!
I'm going to supply at cost however a semi-kit like I do for the DIY, 3D-printed parts and hardware but no electronics
In the .zip folder you will find .stp files of the assembly of all 3 models, all tolerances are set after my printers and ABS but if you are used to deal with .stp files you know also how to modify after your requirements. There are out there a few .stp viewer that free if you like to take a peek and this one is just what I use https://stpviewer.com/
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ProPo.zip
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ProPo Twin Tandem.PDF
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ProPo Twin SbS.PDF
(54.48 KiB) Downloaded 13 times
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Phil_G
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Re: The ProPo project, a DIY proportional servo

Post by Phil_G »

Tobe wrote: 06 Mar 2021, 08:49...For the time being I'm using tradition servo amp. based on NE544/HT7001 but eventually there might be a custom made similar to the Recoder used for the GG
Homebrew servo amps are easy peasy :D
Many years ago when hobby-robotics was just getting started I made a very powerful servo from a car windscreen-wiper motor.
Electrically it was very similar to the current GG hardware, just a processor chip and a discrete bridge using big 2N3055 and 2N2955 power transistors. The processor measured the incoming pulse from the receiver in a 16-bit counter so it held a value of around 1000 to 2000 (μS). The chip read the feedback pot into a 10-bit analogue input, giving an ADC value of zero to 1023. Then a value of 1000 was added to the ADCreading, giving 1000 to 2023. Next this result is compared with the pulse width in the counter, if its greater then the bridge is switched in the direction to reduce the ADC reading, if its less then the bridge is switched in the other direction to increase the ADC voltage. If you relax the comparison to say 'at least 10 greater' and 'at least 10 less' then you have a dead band of 20μS. It was quite slow so not much overshoot and needed only a small deadband. I dont know what happened to the windscreen-wiper servo, it was two house-moves ago and I dont even remember which chip it was (mid 90s, maybe an 8748?) though it may still be buried here somewhere, it did work very well and easily steered an R/C lawn-mower :D
Cheers
Phil
Tobe
Posts: 376
Joined: 16 Feb 2018, 06:19
Location: Varberg or Stockholm, Sweden

Re: The ProPo project, a DIY proportional servo

Post by Tobe »

I love it...what's is "easy peasy" for one person is a live away for an other and the opposite! The only thing I find "easy peasy" in a servo amp is how to get the "blue smoke" released from been locked up in the different components.

So "easy peasy" is the common ground for multidisciplinary collaboration! That's one of the things here on the forum I appreciate and value the most
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