Speed Control with PWM – Can Your Rotary Tool Work Without an Arduino?

April 10, 2025

If you've connected your hard drive motor to an ESC and successfully powered it up, congratulations! Now it’s time to take control—literally. In this 4th post, we’ll explore how to adjust the motor’s speed using PWM (Pulse Width Modulation), both with and without an Arduino. Why settle for a motor that only spins at one speed when you can build a smarter, adjustable rotary tool?

A labeled diagram showing a PWM control circuit using an NE555 timer or Arduino, connected to an ESC and hard drive motor on a wooden workbench, demonstrating adjustable motor speed in a DIY rotary tool project.

PWM is not just a switch. It’s a fine-grained method for controlling speed and torque by sending carefully timed digital signals. If you want to cut, polish, or sand with precision, PWM control is your secret weapon.

1. What is PWM and Why Does It Matter?

PWM (Pulse Width Modulation) is a technique where a digital signal rapidly switches ON and OFF within a fixed time cycle. By changing the “duty cycle” (how long the signal stays ON in each cycle), we control how much power is delivered to the motor.

For example:

100% duty = full speed
50% duty = half speed
0% duty = stop

The ESC interprets these PWM signals and adjusts the motor’s current flow accordingly. This allows Grace’s rotary tool to slow down for delicate polishing or ramp up for heavier cuts.

2. Controlling PWM Using Arduino

One of the easiest ways to generate PWM is with an Arduino. The analogWrite() function can produce PWM signals at 490Hz or 980Hz on most pins.

Basic example code:

int escPin = 9;
void setup() {
  pinMode(escPin, OUTPUT);
}
void loop() {
  analogWrite(escPin, 128); // ~50% duty cycle
}

If you want more precise control, using the Servo.h library allows you to send microsecond-accurate pulses (e.g., 1000µs to 2000µs), which many ESCs expect.

3. Can You Control PWM Without Arduino?

Absolutely. You can generate PWM signals using basic analog circuits, the most popular being the NE555 timer IC. This classic chip is perfect for generating adjustable PWM without any coding involved.

Parts Needed:

NE555 IC
Two resistors (or one resistor + potentiometer)
One or two capacitors
Output jumper wire to ESC signal input

By adjusting the potentiometer, you can smoothly control the duty cycle. Want a manual 3-speed mode? Add a selector switch with preset resistors for low/medium/high speeds.

4. Real-World Setup Example

This is what Grace’s practical setup might look like:

ESC: SimonK 12V drone-style ESC
Motor: 3-phase BLDC hard drive spindle motor
PWM: NE555 circuit or Arduino PWM output
Power: 12V 2A adapter or SMPS

Once connected, changing the PWM duty cycle instantly changes the motor’s speed. Now you have precise control to match the task—whether you’re cutting, polishing, or finishing.

Conclusion: Smart Tools Start with Control

Spinning is one thing—controlling is everything. With PWM, Grace’s DIY rotary tool can now adapt to any task. You’re not just making a spinning tool; you’re building a precision instrument with variable speed control.

Next up: attaching actual sanding discs, safety tips, and putting the tool to work in real-world cutting and grinding tasks. The final part of the series will bring it all together.

ke1