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radio controlled model boats, R/C, scale, BaD, Dumas, Crockett, Monterey, Warship, ship, model, 1/96, wood, balsa, plank, strip, craftsmanship

All about Speed Controllers
by Roger Harper
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Every R/C boat has a speed control, whether you know it or not...   Really!!!

In the world of radio control, one of the more important items is the speed control device.   Speed controls come in many different types and are designed for different types of boats.  Speed boats and scale tug boats have a different speed control requirements. Finding the right control for the right application can be difficult for the novice.  There is a wide assortment of confusing terms ( Maximum Current Load / Maximum Current Rating / Etc. ), to describe what the various speed controls will handle safely.  And it's real easy to buy the wrong one, or more importantly, the wrong size.   

Even when  model boat kit manufacturer recommends a certain speed control system for their kit, the modeler can still get into trouble.    Most of the speed controls used for boats today are the same ones used in the  R/C car industry.  The modeler has to be wary, because these manufactures are always changing and improving their products.  So what is available today, may not be available next year. Remember that the speed controls are mostly made for cars and not for boats.  The technology in electronic speed controls (ESC) is rapidly improving, but they do not tolerate moisture of any kind.  They are designed for cars, trucks and buggies.  There is an exception, where a few ESC's are made for boats.  It's not that you can't use them in boats, just that the manufacturer's build them for the car modelers. 

The speed control simply controls the amount of energy that flows from the battery to the motor. In other words, it controls the speed of the boat. Speed controls come in many flavors: Mechanical, Wire Wound Resistor Types, Electronic Variable Speed Types (Servo Operated), Electronic  Variable Types (Radio Operated).   I will cover the types of speed controls and how to select the right one for your boat.  This article will hopefully take the grief out of selecting your next speed control.

Selecting The Right Control

When it comes time to select a speed control for your boat, there are several factors to consider.  If you take the time to consider each of these factors, it will help you select the right speed control for your application.

1. We use DC motors in our boats. You need to know how much "Current or Amps" your motor(s) draw?  What is the voltage of your motor rated in number of cells?  (1 cell equals 1.2 volts)

2.  Is the motor direct drive or are you going to use a gear drive system?  Gear drives reduce current loads, lower propeller rpm's to give more realistic speeds and extend run times. 

3. What is the diameter of the prop or screw you plan to use?  The larger the prop, and the more pitch the prop blades have will increase the thrust produced.  This will cause a larger load on the motor, battery and the speed control.

4. How big is your model?   Larger and heavier models need a bigger speed control to handle the bigger current/amp load.  Nuff said.

5. What type of boat is it?  A Deep Vee has a different requirement than a scale Destroyer or Tug boat.   The task  for you is to match the right speed control to the job the boat and you demand of it.  For example, speed boats do not require reverse, but scale ships need a speed control to handle running at very slow speeds.

Does Size Really Matter?

Most women say it's not the size, but how you use it.  Oh, that's another subject....  In the world of speed controls, size does matter.  Bigger is better.    If the correct size of speed control is not used, it could over heat and cause a FIRE!  This is more likely to happen with mechanical speed controls which are very inefficient and can sometimes be dangerous.

This is caused by causing the speed control to overload.  Using a modified motor on a speed control used for stock motors is a good example.  "Speed Freaks" will often fall into this situation.  Most Ready To Float (RTF) speed boats often come with mechanical speed controls.  The modeler often adds a "hot" motor to the boat but doesn't change the speed control.  This can result in disaster.

On the other hand, those who use tugs, scale warships or tow boats need a bigger speed control.  This is because the slower speeds puts a great load on the speed control.  At full speed, the speed control is simply allowing the full battery power to flow to the motor.  But at slow speeds, it must reduce the amount of energy going to the motors.  The process of reducing the amount of energy flowing to the motor produces HEAT in the speed control.   This heat, if not controlled can cause the speed control to fail.  Most ESC's sold today have heavy duty transistors.   The manufacturers even add aluminum heat sinks to the transistors to help them dissipate heat and cool the speed control better.

Since Tug or Towboats work at lower speeds, they often also push or pull loads.  This can also add to the load that the speed control must handle.  More work the motor has to do will cause it to draw more amps.  The larger the transistors in the ESC, the more amps the ESC can handle.  But as the quality of the transistors increases, so does the cost!  Be prepared to shell out about $50.00 for a good quality ESC with reverse.

Smooth Proportional Control

Not all speed controls are designed to operate in the same manner.  Be aware of the simple "on-off" or "step" speed controls.  These controls do not give you the smooth proportional control.  This means that the motor increases in speed as you increase the throttle on your transmitter.  This gives you an indefinite range of speed settings, as opposed to the three normally in a step type of speed control.  This is most desirable for scale boats and ships. 

Keep Your Speed Control Happy

As stated earlier, the speed control produces heat.  This heat can build up and damage the speed control.  The location of the installation of your speed control can effect the heat build up.  If you install it in a confined space, a small fan may be needed to circulate air over the heat sink.   Also consider the weather at the time to run your boat.  Hot summer days, the sun can play havoc with the speed control.  Pay attention to the heat build up inside the hull on hot days.  Again, a fan may be needed, or just a few ventilation holes may work.
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