Re: [EE]: Synchronising 4 Linear Actuators with 4 x Op Amps and 6 MOSFETS

I've had some experience with linear actuators of that style - but not
this specific brand.
The internal POTs are mediocre at best. Expect skips and dropouts
across the range of travel.
Ask yourself what happens to your circuit if one of the pots has a dead spot.
Also, the pots DO NOT go from zero -> max. Expect them to cover 50-80%
of the range. And every actuator covers a different portion of that
range.
e.g. 100mm extension is not the same value on all actuators, not even close.

There's also an assumption here that the slave actuators can move at
least as fast as the master so the controls can modulate to keep up.
What if the master is faster than the slaves?
(which is likely because the control electronics to the slaves is
going to have more losses than the direct power to the master)

Are you actively trying to avoid a microcontroller here?
To me this feels like about $40 in modules from Amazon and an
afternoon to puke out some crappy arduino code.

BTS 7960 modules are available in the $5-10 range (4 for $22
https://www.amazon.com/dp/B09W8VV6RH)
They claim over 40A capability (those actuators draw about 3A ea) Add
an arduino board and possibly a voltage regulator for the logic side
power.

Just my 2 cents.

-Denny

On Sat, Apr 19, 2025 at 7:11 PM Justin Richards
<[email protected]> wrote:
>
> resending without attachment too big.
>
> I struggled to find any example circuits that dont use a micro controller
> so here is my attempt at an analog design.
>
> Hoping the List could quick glance and critique before I bread board.   The
> design seems simple and experience suggests it is never that easy so I am
> obviously missing bits.
>
> Problem:
>
> To assist popup section of Echo Chobe camper trailer.
>
> For this task I dont think the 4 Linear Actuators actually need to be in
> sync. When the humans do it, it is definitely not synced - unwieldy
> perhaps.  As such could simply connect to the toggling polarity output of
> the DPDT  to the 4 actuators and the job would be done but ...
>
> Parts:-
>
> 4 x Linear Actuators TS-LD-HS with internal 0-5000 ohm pot. 150mm stroke.
>  These actuators have built in end stop switches.
>
> 1 x LM324N Op Amp (parts bin).
>
> 6 x IRF540N MOSFET (parts bin)
>
> 1 x DPDT wired to toggle polarity reversal of 13.8v house battery .(LiFeP04
> 120Ah my video showing how it failed if interested
> https://www.youtube.com/watch?v=hDA7KEEZ5p4 )
>
> Theory:
>
> Closed loop control where all the slaves chase the master by attempting to
> maintain the same resistance of their internal pots.
>
> A DPDT switch to provide the polarity reversal and eliminate the need for
> each slave to be driven with a H-Bridge.
>
> Design:
>
> All internal pots are connected across the polarity toggling supply and the
> wipers are all connected to the non inverting inputs of their respective
> opamp,
>
> The Master Linear Actuator (the slowest) has its opamp configured as a
> buffer,  Its output is fed to all the inverting input of the other
> opamps as a ref.  This is the ref the others chase. The supply leads of the
> Master are connected directly to the  polarity toggling supply.
>
> The Slave  Linear Actuator main power in are connected to the polarity
> toggling supply with two MOSFETS in series. The two Drains are connected.
> (This allows the power to be controlled regardless of the polarity of the
> supply and relies on the internal body diode.  This seems to be ok practice
> but not sure.) The gates are connected to the output of their respective
> opamps.
>
> Schematic was attached but too big so a copy is here
> https://hackaday.io/project/202902-synchronising-4-x-linear-actuators
>
> Cheers Justin
> --
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