The TO's Tech Talk.

From Tony Collins, AusBG TO.

Hi all, from your friendly TO.

In this the fourth of the articles, I will show some circuit diagrams for simple control devices used in our ships.

Speed controllers.

To control the throttle and the direction of the ship, some sort of speed controller is used. This name is confusing but commonly used and the devices are better termed forward/reverse throttle controls. There three main types are electronic, wiper and switch type.

The electronic type is available from hobby shops but they have a few disadvantages. The are very expensive, and very sensitive to water. Very very sensitive to water! They also generate a lot of heat and may melt your waterproof conatiner. You will have to very careful and thorough with your water proofing. The advantages are they are light and have proportional control, meaning that how far you move the stick on your transmitter is proportional to how fast it goes. If you are thinking of going this way, make sure you get one that has reverse. The common variety is made for cars and does not have a reverse as they are made for R/C cars and planes.

You will find that the price for those with reverse is higher than the ones you see on the shelf in the shop.

The wiper type is where a wiper arm, with a electrical contact, is attached to your servo. As your servo moves the arm "wipes" across a series of contacts, which go through a resistor or two, so controlling the speed of your motors. A simular design has the arm moving across the resistor itself. There are several types available, but the most common is some made to control R/C cars. There are some that will do reverse as well. These are suitable for use in our ships, but care must be taken to keep clean the contacts, as these are usually just thin copper-plated plastic board and will corrode. (I know, as I had one and this happened to me!). But they will last if such care is taken. Depending on the type (and there are several) they will give a varied degree of control of the speed of your ship.

The third main type is the most used, as it is simple, cheap and reliable. This uses a plain switch or two that controls whether the ships moves froward or backwards. These are operated by the servo.

Here is some good examples of this,

The negative wire is to the left and positive to the right. Simple in operation, the servo moves one way and the motor spins in one direction. The servo moves the opposite way, and the motor moves the other direction. No speed control, but it works and is simple. Most people use this method, using microswitches glued to the servo.

 

 

Another type of this switch type is the following one. I haven't seen this fitted in a ship yet, but gives you something to think about.

 

 

Other types.

Other types of control could be used but the ones described above are the main ones used. One that also could be used is a R/C switch. These are electronic circuits that take the place of the servo and are plugged directly in the receiver and when the stick is pushed one way, a relay operates, push the stick the other way, and another relay operates. The circuits for these are available, as are kits and completed modules.

Speed limit control

Now, with the electronic speed control, you can adjust the maximum speed of your model by an adjustment on the controller, but for the others (with the wiper type you might need it) you will need a speed-limiting resistor. This is a high wattage ceramic resistor, which limits the amount of current supplied to your motors. This usually has three contacts, two at the ends, and one that is adjustable along the length of the resistor. These come in various sizes and ratings. It is recommended that the resistors have a rating of at least 20 watts. This means it can stand a fair amount of current at the voltages that we normally use.

Left is one mounted in the DKM SeaSlug.

The arrow points to the adjustable contact, the band around the resistor.

The resistance rating to use depends on a lot of factors, motor size and type and the voltage used to drive them. Most people use a 3ohm for a small 6volt motor or system, 5 ohm for a medium sized 6-volt system. For 12volts, 10 ohm is normally used, but a big 6v system using big motors the 10ohm maybe needed.

Notice that it is mounted away from the side of the hull, these will get hot!

Markings on the resistors usually looks like this :- 3W 15W This means that it is a 3 ohm, 15 watt.

But as with most things in our hobby, there is no hard and fast way to do it. It is whatever works for you and your ship.

Till next time,

Keep on Battling,

Tony Collins, AusBG TO