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May 26, 2021, 09:41 PM
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Reducing/adjusting a constant DC Reversible Signal

I have a motor that is wired directly to the receiver. It runs at a fixed speed in either direction when the joystick is moved.

Joystick in neutral position: Motor is off
Joystick is in the up position: Motor runs in one direction
Joystick is in the down position: Motor runs in the opposite direction
(not proportional)

The fixed speed is to high, I need something that will allow me to reduce the speed (voltage) in both directions. I can't change the gearing on the motor. Don't want resistors that will cause heat. Any ideas?

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May 27, 2021, 12:58 AM
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Skylar's Avatar
It will help if you say what the application is. But it sounds like the motor is controlled by an on-off switch. Is it supposed to run in both directions? (application again).

A brushed motor ESC would provide speed control depending on the gimbal (joystick) position, provided the receiver outputs the correct signals.

It sounds like a boat application. Maybe you will get better advice in the boat forum.
May 27, 2021, 03:43 PM
Boaters are nice people.
Hi Lew,

No motor is connected directly to the receiver, maybe the box that houses the receiver, but there will be a switch, mechanically or electronically, that delivers the current to the motor.

If you are proficient in reverse engineering the switch board, you could change the components that determen the speed the motor runs at.
If it's a boat, reduce the pitch, or size (or both) to reduce the speed it'll run at.

Regards, Jan.
Sep 14, 2021, 11:27 PM
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Thread OP
Well, in this case the motor is connected directly to the receiver. This is a "toy crane" where all the electronic parts are on one circuit board. In this instance the wires run from the receiver to the traverse motor. Moving the traverse stick right or left turns the crane by reversing the polarity. Problem is crane traverses too fast. Using a power resistor will not help because of battery consumption.
Sep 14, 2021, 11:28 PM
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Last edited by LewZeeRC; Sep 14, 2021 at 11:30 PM. Reason: Duplicate
Sep 15, 2021, 10:51 AM
New to this whole thing...
A DC-DC buck converter with an adjustable output voltage would let you dial in the output voltage that you want without wasting a lot of power.

Something like this:

You'd have to pick one with a suitable voltage range and current-handling ability for your usage.
Sep 15, 2021, 06:25 PM
Registered User
Just be careful with these low cost toys - I had the task of fixing a battery operated toy crane and rather than use H-bridge polarity reversal or 2pole, 2 position switches it used a center tapped battery tray. It used 4x AA cells tapped at 2 cells and the motor was switched either OFF (center) or fwd (left) or backwards (right).
I'm assuming the crane was always too fast and it's not developed a fault. If it is battery operated, check out to see if you could replace one cell with a dummy shorted link to reduce voltage. Ideally you want a lower rpm motor with the same mounting pitch and same shaft diameter and just swap it.
If the battery tray is not tapped then the Buck convertor attached directly after the power source may work but it's about equivalent to dropping a cell (or more).

Sep 30, 2021, 04:00 AM
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Thread OP
Thanks for responding. As other movements (caterpillar, hook lift, boom movement) are OK I don't want to reduce the battery voltage. Plus, the unit may not work with less voltage. Just need the traverse to go slower. I tried a buck converter but it does not work when the voltage is reversed. Gears might be an option, so I'll need to take it apart again to look.
Sep 30, 2021, 06:04 AM
Registered User
Sounds like the buck converter may have been a bit too far down stream of the voltage source. You want it before the place where the motor gets reversed - back nearer the battery source.

The other thing you could try is putting silicon diodes in series with just the traverse motor - 2 strings arranged in inverse parallel. Each diode will drop about 0.8V under load so you may only need 1 or 2 in each string rather than the 3 I've shown, depending on the total voltage and how much you want to reduce it by. Any general purpose power diode such as 1N4001, 1N4002 etc should be fine. As shown the diodes will drop about 2.4V under load regardless of the polarity presented to the motor. The diodes can go in either the +ve side of the motor or the -ve side - it won't matter. They may get a bit warm during use. Good luck.

Sep 30, 2021, 06:16 AM
Wake up, feel pulse, be happy!
Piece's Avatar
I don't know if I see the problem with adding a resistor here. How much power could a toy crane really be using to begin with?

If it has a gearbox, you could fill that gearbox with thicker grease. Otherwise.... resistor.
Sep 30, 2021, 07:10 AM
Registered User
If the load is constant a resistor is appropriate but if it varies then the fixed drop of the diodes will provide more constant torque.
The ideal is to increase the gearing ratio to get lower speed and higher torque but this is usually not easy to do.

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