Servo Circuits

I volunteered to turn a friend of mine's Warhammer 40K Imperial Rhino personel carrier into a remote controlled item. Little did I understand the undertaking that I had agreed on! My requirements for this project were that the transmitter and receiver had to be a single chip design, done all in software. I succeeded. The receiver chip uses a Panasonic 4602 38KHz receiver and that's it for external components. It has the serial input (GP3) , two RC hobby servo outputs (GP0/GP1) and three digital outputs (GP2,4,5). Here is the code for the receiver chip.

This Robot is still being constucted so if you have any ideas please send them to me. I would apreciate if those people who keep sending me e-mails for me to send you my project schematics, look at the "Schematics page" located to your left on the menu. I dont have anymore schematics for the time being.Also is there anybody who knows how to controll a servo?

The interface uses a PIC16F876 microcontroller and not much else. It performs channel mixing, current limiting, and noise rejection. Push the stick forward, both motors move forward, move the stick to the left and the robot moves left. It makes the robot very driveable. You can use a wheel transmitter meant for cars to control it, in other words, one channel is throttle(both forward and reverse), the other steering.

The JavaBot1 is a small line following robot designed to follow a black line drawn on a dry erase board. It is designed to follow very tight curves. The software still has lot's of room for improvement but works well as is. The JavaBot1 uses 2 Cirrus CS-70 servos that have been modified for full rotation and have had their controller boards removed to convert them from servos to gear motors. Servos are a common motive power for small robots due to their low cost, ready availability, standardized sizes and the fact that it only requires 1 bit on your processor to control the motor.

Linear regulators are easy to implement and have better noise and drift characteristics than switching approaches. Their largest disadvantage is inefficiency: excess energy dissipated as heat. Several well-known techniques are available to minimize the input-to-output voltage across a linear regulator. I had been looking for an inexpensive, easy-to-implement, and efficient preregulator to reduce the dropout voltage of a linear regulator. Closed-loop, self-oscillating preregulators built around a switching transistor, a comparator, and a filter are difficult to predict in terms of frequency.

This circuit takes standard 0-10V control voltage (for example from analogue light controlling desk) and outputs a standard 1-2 ms RC servo motors control pulse.

The PICmicro ® microcontroller makes an ideal choice for an embedded DC Servomotor application. The PICmicro family has many devices and options for the embedded designer to choose from. Furthermore, pin compatible devices are offered in the PIC16CXXX and PIC18CXXX device families, which makes it possible to use either device in the same hardware design. This gives the designer an easy migration path, depending on the features and performance required in the application. In particular, this servomotor has been implemented on both the PIC18C452 and PIC16F877 devices, and we’ll look at the MCU resources required to support the servomotor application.

The simple circuit design in Figure 1 lets you measure all components of a current flowing in a dc servo motor. The rectified output of the circuit uses ground as a reference, so you can measure the output by using a single-ended A/D converter. The current-sense resistor, R1, has a value of 0.1Ω. The Zetex (www.zetex.com) ZXCT1010 IC converts the differential signal across R1 to a single-ended signal. Two of these ICs form a signal rectifier. The single-ended signal makes measurement by an A/D converter cost-effective, small, and frugal in power consumption.

I was in need to modify four expensive JR-DS8231 Ultra Digital servos to rotate 360° instead of the standard 130° or something. The mods were required so they could be used with a tethered blimp. The infra-red and night vision camera equipment is mounted underneath the blimp on a special frabicated aluminum cage and is radio controlled (R/C). I choose a digital 10-channel radio transmitter merely for the needed channels and reliability of JR products.

Using a modified version of the last program, we can control as many servomotors as we have I/O lines on port B. In the next listing, we will control two servos in the same manner as we controlled a single servo in the previous program. The circuit is shown in figure 4 (below). The program uses two pulsewidth variables, pw1 and pw2; and two sets of routines, left1 and left2, right1 and right2; one for each motor. As you can see in the schematic, the first servo is wired as per the previous circuit. The second servo is now using B3 as it's pulse out, and B4 and B5 for the SPDT switch.

In our first program , we will simply sweep the servomotor from CCW to CW and then sweep back. The program will be kept simple as to demonstrate the priniciples of controlling a servo with a the PIC Basic language. The schematic can be seen in figure 2 (below). The variable pw controls the pulsewidth, and is started at 100 (extreme left, -45 degrees). The program sends the pulse out to the servo, and then is increased by a value of 1 until it reaches 200 (extreme right, 45 degrees), at which point it will reverese the rotation.

Typical remote-control systems and robotics applications use standard R/C servos, which often require a reversal of the direction of rotation. Since varying the input signal's pulse width between 1 and 2 msec controls the servo's output position, a circuit that adjusts the pulse width to cause direction reversal can often come in handy. Many such circuits exist that use relatively sophisticated servo-control ICs, but the implementation in Fig 1 uses a standard CMOS IC to produce a reliable design at low cost.

To use Servo Commander just click your mouse on a position by each control knob. Holding and dragging the control knobs will work also. Once you release the mouse button, the motor will move into position. You can also click on the (tick marks) around each control knob, or the knob itself. Each motors position data will remain visible under the motors control knob until you change the position of the control knob. You can move up to 8 motors into the position you want and then record the position data. The value under each control knob is the actual value that will be serially transmitted to the PIC16F84 or the Basic Stamp.

The circuit presented on this page attemps to be an interface to convert pulses such as provided by a Basic Stamp or R/C receiver to a dual PWM(Pulse Width Modulation) signal required by an H-bridge. The simplest circuit would use a small microcontroller like a PIC. This circuit takes a more traditional approach. Many experimenters will have all the parts already. Total parts cost should be equal to a simple espresso drink, although I have stopped drinking coffee I still remember how much it costs :-)

This circuit (figure 1) will impose a maximum slew rate on a signal; positive and negative rates can be independently controlled. The circuit is useful in servo applications where the error signal needs to be limited to be within the power rails to ensure predictable operation.

The simple circuit design in Figure 1 lets you measure all components of a current flowing in a dc servo motor. The rectified output of the circuit uses ground as a reference, so you can measure the output by using a single-ended A/D converter. The current-sense resistor, R1, has a value of 0.1Ω. The Zetex (www.zetex.com) ZXCT1010 IC converts the differential signal across R1 to a single-ended signal. Two of these ICs form a signal rectifier.

The circuit in Fig 1 uses a servo potentiometer, as opposed to a rotary switch or encoder, to provide the necessary drive pulses for a stepping motor. This motor positions a pointer by the rotation of a manual control. The circuit must be precise, allow a rapid response, and be simple to use. (This circuit was part of a complex apparatus used for a series of physiological tests.) Another requirement is that the control had to be a small, handheld, battery-operated device.

Optical tachometers have many advantages in precision servo applications. Compared with dc-generator types, optical tachs are relatively inexpensive and, because they lack wear-prone commutator brushes, they're long-lived. Frequency-to-voltage conversion circuits provide a convenient means to integrate the output of optical tachs into analog, unidirectional motion-control loops. However, for bidirectional servos, where you need a bipolar angular-velocity readout, you need a more unconventional solution, such as the circuit in Figure 1.

Hard-disk drives for laptop and other portable applications need to withstand significant g-force shocks when operating. A typical 1.8-in. drive writes servo information over less than 15% of the disk's active area, which means that the read/write head spends more than 85% of the time outside the servo loop's control. A g-force shock during this time could cause the read/write arm and head to move away from the current write track and to permanently write corrupting data on an adjacent track or elsewhere.

Using a modified version of the last program, we can control as many servomotors as we have I/O lines on port B. In the next listing, we will control two servos in the same manner as we controlled a single servo in the previous program. The circuit is shown in figure 4 (below). The program uses two pulsewidth variables, pw1 and pw2; and two sets of routines, left1 and left2, right1 and right2; one for each motor. As you can see in the schematic, the first servo is wired as per the previous circuit.