Servo Motor

What are Servo Motors?

Servo refers to an error sensing feedback control which is used to correct the performance of a system. Servo or RC Servo Motors are DC motors equipped with a servo mechanism for precise control of angular position. The RC servo motors usually have a rotation limit from 90° to 180°. Some servos also have rotation limit of 360° or more. But servos do not rotate continually. Their rotation is restricted in between the fixed angles.

Where are Servos used?

The Servos are used for precision positioning. They are used in robotic arms and legs, sensor scanners and in RC toys like RC helicopter, airplanes and cars.

Servo Motor manufacturers:

There are four major manufacturers of servo motors: Futaba, Hitec, Airtronics and JR radios. Futaba and Hitec servos have nowadays dominated the market. Their servos are same except some interfacing differences like the wire colors, connector type, spline etc.

Servo Motor wiring:

The Servo Motors come with three wires or leads. Two of these wires are to provide ground and positive supply to the servo DC motor. The third wire is for the control signal. These wires of a servo motor are color coded. The red wire is the DC supply lead and must be connected to a DC voltage supply in the range of 4.8 V to 6V. The black wire is to provide ground. The color for the third wire (to provide control signal) varies for different manufacturers. It can be yellow (in case of Hitec), white (in case of Futaba), brown etc

Servo Control

The servo motor can be moved to a desired angular position by sending PWM (pulse width modulated) signals on the control wire. The servo understands the language of pulse position modulation. A pulse of width varying from 1 millisecond to 2 milliseconds in a repeated time frame is sent to the servo for around 50 times in a second. The width of the pulse determines the angular position.

 

For example, a pulse of 1 millisecond moves the servo towards 0°, while a 2 milliseconds wide pulse would take it to 180°. The pulse width for in between angular positions can be interpolated accordingly. Thus a pulse of width 1.5 milliseconds will shift the servo to 90°.

 

It must be noted that these values are only the approximations. The actual behavior of the servos differs based on their manufacturer.

 

A sequence of such pulses (50 in one second) is required to be passed to the servo to sustain a particular angular position. When the servo receives a pulse, it can retain the corresponding angular position for next 20 milliseconds. So a pulse in every 20 millisecond time frame must be fed to the servo.

Power supply for Servo

The servo requires a DC supply of 4.8 V to 6 V. For a specific servo, its voltage rating is given as one of its specification by the manufacturer. The DC supply can be given through a battery or a regulator. The battery voltage must be closer to the operating voltage of the servo. This will reduce the wastage of power as thermal radiation. A switched regulator can be used as the supply for better power efficiency.

Servo Motor Control through Keypad Using 8051 Microcontroller (AT89C51)

DX Fun Web Cluster

DX Fun Web Cluster is in essence a "chatroom" or node into which amateur radio DXers can post information about DX either worked or heard. Physically, it is a central computer that collects, stores and disseminates information that ham radio operators send to it. There are thousands of nodes around the world, connected together via the internet or radio. Connection to a cluster is by either telnet or packet radio. The networked nature of DX clusters is perhaps its most powerful feature as it gives amateurs almost instant access to information about rare and unusual DX conditions such as meteor scatter or VHF ducting.

Cluster users will use computer software (for example, many logging programs have this capability) that is capable of communicating with the cluster. On initial login, users will be asked to provide station information. This allows other ham radio operators to compare DX openings to their physical position. DX is one of the most fascinating aspects of the hobby.

Hamradio Homebrew 2 Meter Square Dipole Plan

Here is a plan for homebrewing a 2 Meter Square Dipole plan. The advantage of this antenna is that it is unidirectional, and it takes less space than the regular 2 meter dipole. The calculation included on the diagram below is for building the antenna using copper tubing, you should use MMANA-GAL or other antenna simulation software to come up with new dimension for other materials (aluminium, wire, etc).

Click on the diagram to enlarge it. Hopefully this will help you in brewing new antennas! Original plan taken from KOFF website

Antenna In Less Space – The Inverted Vee

Another space saving installation method is to mount the antenna in an inverted vee configuration. This type of installation has worked well for me over the years and I highly recommend it for those of which enjoy HF Radio and are in a limited space situation.

 

Unfortunately, there is no such thing as the perfect antenna. There are just too many variables for that to be possible. So the theoretically perfect antenna just doesn’t exist.  Ham Radio is all about trying out new things, and homemade antennas are no exception.

Experimenting with Ham Radio Antennas and using your creation to talk with other Amateurs all over the world is definitely one of the most accessible and enjoyable aspects of the Amateur Radio hobby.

Short Ham Antennas For HF

For many ham radio operators, it is not feasible to put up a a full length dipole on HF.

But, a linearly loaded dipole just might fit in your available space!

A linearly loaded dipole, as illustrated below...

• ... is about 30-35% shorter than a "classic half-wave dipole" at the same frequency of resonance!
• ... has a radiation resistance around 35 Ohms. (You will need an impedance matching tuner at the other end of the coax!)
• ... just as effective as a "full length" half-wave dipole! :-)

Note that it "looks" like a folded dipole, but the top part is open! You should add a ceramic end-insulator in the opening, to add mechanical strength. (The insulator is omitted in the drawing to make the opening obvious;-).

Shorter Dimensions!

Here are "ballpark" dimensions for a linearly loaded dipole for each ham radio band. These dimensions are intentionally slightly long! You will have to obtain the final dimensions experimentally, on site, by "pruning" to resonance.

Forgot the technique to prune a dipole to resonance? Refresh your memory on the page about the ham radio dipole!

Linearly-Loaded Dipole Approximate Dimensions
10 meters (28.5 MHz) 12 meters (24.9 MHz) 15 meters (21.1 MHz) 17 meters (18.1 MHz) 20 meters (14.1 MHz) 30 meters (10.1 MHz) 40 meters (7.1 MHz) 80 meters (3.6 MHz) 160 meters (1.85 MHz)	3.5 m. (11.5 ft.) 4.0 m. (13.2 ft.) 4.73 m. (15.5 ft.) 5.51 m. (18.1 ft.) 7.08 m. (23.2 ft.) 9.89 m. (32.44 ft.) 14.06 m. (46.14 ft.) 27.74 m. (91.0 ft.) 53.97 m. (177.08 ft.)

Construction Of Linear Loaded
Short Ham Antennas

I use commonly available 390 Ohm "ladder line" with #14 stranded, copper-clad conductors. It is sturdy and lasts for years.

For the central "attachment" I use two LadderLoc center insulators, head-to-head (available at Radio Works).

I recommend 3/16 in. Mil Spec Dacron® rope to tie the ends to tall supports such as trees.

Bonus Configurations!

Linear-loaded short ham antennas do not have to be limited to horizontal installations!

You can save even more space by installing them as "slopers", inverted "V"s and inverted "U"s.

http://www.hamradiosecrets.com/short-ham-antennas.html