2x fwd only pwm dc speed controllers : how ti wiite as reversible action from one pot?

Thread Starter

Poor old sod

Joined Jul 25, 2017
193
i need a reversible pwm dc brushed speed controller, driven by 1 pot. centre position = 0v out.
i have a notion it can be done using 2 fwd only devices from a common source and some careful wiring & diodes i haven't thought it thru , cos i'm tired, advice pls.
 

Thread Starter

Poor old sod

Joined Jul 25, 2017
193
think i have it.
using 3wire varristor commoned to both pot inputs, [one reversed] of the speed controllers.. the outputs track in opposite directions as the input varies. the outputs are paired pos with pos, neg with neg, and fed into their own op amps , their inverting inputs swapping between controlers. the op amp outputs feeding the motor. i need 2 op amps vcc 3v-4.5v, abt 200mA each. a common package had better have good cooling. see pic. unity gain appropriate.
 

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LowQCab

Joined Nov 6, 2012
4,026
What is the maximum Voltage and Current at Full-Speed / Full-Load ?

What is the "Locked-Rotor" (stalled) Current of the Motor ?
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Thread Starter

Poor old sod

Joined Jul 25, 2017
193
stall current can't be hi, claimed 40 min runnng on AA sized LI-on, they would be only be base model capacity. wires are thin. oem speed controller no large components, no heat sinks. car abt 350g, 2wd 15kph max. prob stop, crawl, full speed. camera abt 150g, new bat +150g?
 

LowQCab

Joined Nov 6, 2012
4,026
You can't "guess" at the Locked-Rotor-Current,
You must actually measure it,
so that the Op-Amps that You select will not be over-loaded and burn-up.

It would help to know the Inductance of the Motor if You would like
to use a PWM Motor control scheme.
This can save substantial run-time on the selected Batteries.
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MisterBill2

Joined Jan 23, 2018
18,176
What will be the mechanism of reversing the motor rotation??? Is the motor a PM motor so that it is polarity sensitive? Or not??If the motor will reverse with reversed polarity then an H-bridge circuit with an arrangement to drive one side or the other can work. But the scheme will be a bit complex because opposite pairs must be pulsed depending on which side of center the control voltage is on. Well within the range of reasonable digital logic, but not really simple.
 

Thread Starter

Poor old sod

Joined Jul 25, 2017
193
cheap brushed motor. simplicity says use the op amps.with uniy gain, even if i use discrete components. i know measurements are essebtial, and kmart are cheapskates, but a reasonable approximation will do for now. i realize its not built or a long life. it's a throw-away once it dies, sadly, but it's a proof g oncept at this stage. usual story, too many wifi devices in area, can't get clear signal to connect camera. nothing i can do to build better, tho' i could try a repeater i have? router is abt 10m away,
 

MisterBill2

Joined Jan 23, 2018
18,176
Interestingly enough, the output section of quite a few op-amps closely resembles half of an "H" bridge circuit. Unfortunately the one model of higher powered op-amp that I recall was priced about the same as a medium power amplifier, complete and ready to play.
Designs of H-bridge amplifiers suitable for driving motors are available, one source being on the "Schematics For Free website, if they get it working again. And those circuits are all in the public domain, so no patent infringement concerns apply.
 
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