Motors and Speed Control

Choosing a motor...

The most expensive component of any fucking machine is often the motor, and motor selection makes a significant impact on the rest of your build.  Your motor determines your power supply/wiring needs, the eventual size of your machine, etc.  It is a tough decision, and you have plenty of options!  Hopefully this guide helps you out… 

Here are the main points to consider:
AC or DC
DUTY RATING
SPEED
STRENGTH

 

AC or DC Motor?

First off, what is meant by AC and DC?
For the true beginner, we’ll start with a little physics: Batteries and fuel cells produce something called direct current (DC). The positive and negative terminals of a battery are always, respectively, positive and negative. Current always flows in the same direction between those two terminals.  The power that comes from a power plant, on the other hand, is called alternating current (AC). The direction of the current reverses, or alternates, 60 times per second (in the U.S.) The power that is available at a wall socket in the US is 120-volt, 60-cycle AC power.

What does that mean for your build? 
A 115v/120v AC motor can run off a wall outlet while a DC motor needs other electrical components to work off a wall outlet.  Both motors will need a component to help regulate the speed: a 250 RPM motor will thrust 250 times a minute if you turn it on.  You may want to start a little slower. 

So which is better? 
In my opinion, DC motors are much better than AC motors.  They do require more electrical components to work off a standard wall outlet but these pieces can be purchased (or made) for a very reasonable cost.  AC motors on the other hand require expensive electrical components to run at low speeds. 
 
TIP: Go with 90v DC, 115v DC, or 130v DC motors…  These motors will run well when you convert the AC (wall outlet) power to DC using a rectifier or speed control.  Motors with these ratings run well from rectified (converted from AC to DC) line current.

You can certainly use a 12v DC motor (the most common12v DC motor in a fucking machine is an automotive wiper motor).  Keep in mind these motors often lack the speed and torque needed for a high-quality machine.  You will also need to use either a bench-top power supply or computer power supply  with speed control to run the motor (both are heavy and would add weight to the machine).

 

Duty Rating

The “Duty Rating” of a motor tells you how long the motor can run before problems can arise.  There are generally two ratings:
1)  Continuous Duty: These motors should be able to run for hours before there is a risk of overheating.

2)  Intermittent Duty: These motors are built to run about 30-40 minutes, followed by a 30 minute rest. 

TIP: For a high quality motor, look for a “CONT” rating on the motor label. 

 

Speed is one of the most important criteria when choosing a motor.  The speed of a motor is usually given in RPM’s, or rotations per minute.  For our purposes, think of one rotation and being one thrust in and out. 

 

Motor Speed

The most common question I get asked is, "What speed should I look for?" It’s a simple question but it has a complicated answer…  The RPM/motor speed is dependent on stroke length.

I would offer this advice based on my observations: Most enjoy a stroke length of 3" to 5", with 2"-4" of dildo staying inside the user. This results in using a dildo of at least 7"-8". The preferred speed varies with every user: Some enjoy a slow, long stroke (100rpms and 7" of travel), and others prefer a fast, short stroke (600rpms and 2" of travel). For 90% of users, look for a motor that can run around 300rpms, pair it with a quality speed control, and you should be more than happy!

 

Motor Strength

When it comes to a motor, strength is measured in torque and horsepower…  I’ll spare you the physics about how torque and horsepower are measured; you just need to know they offer clues to the strength of the motor. 

Torque
Torque is measured in pounds-per-inch.  For most people, a machine with 30 to 35 in-lbs is more than enough.  If you are in to more extreme play (huge dildos used during anal play), you might need something stronger.
Horsepower
Some people put a high value on horsepower, but the reality is the horsepower really doesn't matter if torque and speed are in the acceptable range. If you need a guide, stick with something in the 1/6 to 1/4 HP range.

TIP: Find a 35 lbs/in, ¼ HP motor.

Where to find the info:

Many motors come labeled by the manufacturer with all the info you need to make a decision. Shown is a sample label found on a Baldor motor.

Speed Control
Speed control basics...

Regardless of your motor, powering your machine isn’t as easy as simply plugging your machine into the wall.  You need some sort of power supply or speed control. 

What is a speed control unit?
Like the name implies, a speed control allows the user to adjust the speed of the motor.  This isn’t an optional item unless your machine runs extremely slow.  Think about this: If you have a 400 RPM motor, your machine will thrust 400 times a minute regardless of your position, stroke length, etc.  You will go from 0 to 400 in the flip of an “on” button.  OUCH! 

Speed control units work in different ways but you’re looking for the same thing: consistent speeds across the spectrum of your motor (both high and low speeds). 

Here are a few options for speed controls, along with pros and cons: 


 

pre-made units

These units offer both ease of use and excellent motor control (even at low speeds). 

These are a little more expensive ($35 + shipping) than other options but are specifically matched to the motor and are easy to wire. I buy them if needed off eBay.

Speed control kits

These are the most cost effective solution (under $30 for the kit) for excellent speed control but they do require some knowledge of electrical components.  I consider myself a pretty “handy” guy but these kits were intimidating at first.  Trust me, they are easier than they look. Give them a try!

Router Controls

These router controls are readily available online and are great for AC motors.  The unit shown is under $20. 

These cannot be used with brushless DC motors and are hit-or-miss with their control at low speeds.

Benchtop Power Supply

These all-in-one units are matched to motor and offer great speed control. These units are often expensive and bulky.  The unit shown powers a 24v DC motor and costs over $100.  

 

Wiring a DC Motor

There are several wiring configurations common to DC gear motors and most will have two or three wires. The most basic has two "power" leads (typically a red wire and a black wire) and maybe a ground wire (usually green in color). Swapping the power leads between positive and negative will reverse the motor.

Converting AC line current from a wall plug to DC current to run the motor is easy. A bridge rectifier does the job. This electronic component has two AC input terminals and two DC output terminals (+ and -). The resulting output is not smooth... it jumps up and down in voltage, which is hard on a motor and may cause noticeable jerkiness at lower speeds. Address this issue by wiring a capacitor across the DC output terminals as shown below.

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