# DC Motor Speed Control from Boost Converter Input

#### k1ng 1337

Joined Sep 11, 2020
911
Hi I am looking for a solution that allows me to control the speed of a DC motor using the output from a boost converter as seen in the attached image.

My input it 5v and I want to be able to adjust the speed of the motor by bringing it from a stall (less than 2v) to 13v, I would like to incorporate an H bridge for the occasional reverse but a DPDT switch would be fine.

A simple inverting buck boost works for my design but my goal is efficiency, I suspect that using a synchronous boost converter paired with a PWM to set the average voltage to the motor would be most efficient but I am having trouble understanding the no load condition during the OFF state of the PWM signal without a feedback network and if it is even necessary.. I can't seem to find any algebra that relates effects and losses in a converter that is being switched from a load to no load condition.

Thanks

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#### MrAl

Joined Jun 17, 2014
11,271
Do you intend to regulate the speed of the motor or just adjust it manually?

The difference is when you adjust manually any load on the motor may slow it down.
When you actually regulate the speed the speed stays fairly constant even when the motor is loaded or unloaded.

For a rough example, with a manual adjustment if the motor is adjusted to go 1000rpm with no load and then a significant load is applied it could slow down to 700rpm or even 500rpm.
With an actual speed regulation circuit if at no load it goes at 1000rpm then with significant load it may slow down to 950rpm with a cheap regulator circuit or maybe only down to 999rpm with a good feedback system regulator.

#### k1ng 1337

Joined Sep 11, 2020
911
Do you intend to regulate the speed of the motor or just adjust it manually?

The difference is when you adjust manually any load on the motor may slow it down.
When you actually regulate the speed the speed stays fairly constant even when the motor is loaded or unloaded.

For a rough example, with a manual adjustment if the motor is adjusted to go 1000rpm with no load and then a significant load is applied it could slow down to 700rpm or even 500rpm.
With an actual speed regulation circuit if at no load it goes at 1000rpm then with significant load it may slow down to 950rpm with a cheap regulator circuit or maybe only down to 999rpm with a good feedback system regulator.
I had not considered a dynamic load on the motor, I'm still pretty new to motors much less power electronics.

I am building a remote control car that using two DC motors with propellers, if you ever driven a bobcat or skidsteer this offers a very simple control mechanism - both motors 100% = forward and any combination less than 100 is a turn. Until now I had only imagined a constant current while moving on a horizontal surface, so to answer your question I am looking for an electronic throttle like a gas pedal

I have an Arduino and a wireless module that will eventually drive this, everything else I would like to design myself and I don't want to use the Arduino anymore than is logically necessary.