Model making servo drive

Today we want to take a closer look at the model servos. In fact, this is a servo drive and not a servo motor because the control is already included. However, the servo drives we know from industry have little to do with them. We have the MG995, MG996R and SG90in our delivery program. The SG90 is the smallest of our servos, this is smaller and lighter than the MG995/6R and is mainly used in model aircraft or model construction vessels. With a weight of only nine grams and a maximum torque up to 1.6kg/cm, this servo is especially suitable where low weight is important, but large loads cannot be moved.

Much larger and more robust with a maximum torque of 9kg/cm is the MG995Yeah. However, in contrast to the MG996Ronly a plastic gearbox, but the setting speed is slightly higher. This is particularly noticeable during life under load. The torque of MG996R was also increased to approximately 11kg/cm. Open MG996R:

In contrast to industrial servo drives, model construction Servos is controlled with pulse width modulation:

The angle to which the servo arm is to be placed is controlled by the width of the pulse. A 50-Hz signal (20 ms period length) is in use which is between 500 microcustomers (left stop, 0 degree) and 2500 microcustomers (right stop, 180 degree) on high level and the rest of the period length on low level. However, many servos have not used their full freedom of movement in this range of values and/or can move between different angles. To increase the range of motion it is possible to "hack" the servo. The mechanical limitation in the gearbox is removed (the small pen on the gearbox on the right):

For positioning control, the servo has a potentiometer connected to the output wave. Through this potentiometer the servo-electronics determines the actual angle of the output wave (to be recognized in the middle of the image).

This is compared to the target angle obtained from the PWM signal. In the event of a deviation between actual and target angles, the electronics control the angle of the output wave via the engine and the gear. One disadvantage of model tree servos is that it is not possible to ask if the servo is overloaded. This means that it is not possible to determine whether the servo is able to start the desired position at all. Some digital servers solve this problem, but this is another article

Until next time:)

 

Produktvorstellungen

3 comments

Willi

Willi

Wie hoch ist eigentlich die Zyklenfestigkeit der Servos bei 75% der max Last?

robby

robby

DAS nicht der Drehmoment wird in Nm oder Ncm oder auch noch daNcm angegeben und nicht in kg/cm. Die angreifende Kraft wird wird mit der Länge des Hebelarms multipliziert und nicht durch diese dividiert. Das heißt, dass bei einem Drehmonent von 120Ncm in einer Entfernung von 10cm von der Drehachse am Hebelarm noch eine Kraft von 12N ausgeübt werden kann. Von einer Kraft ohne die Angabe der Hebelarmlänge zu sprechen ist schlicht Unsinn.

Maclaine

Maclaine

Ich finde es klasse das Ihr bei dem Servo den Drehmoment angebt und nicht wie beim Chinamann üblich die Haltekraft.
Dies ist die Kraft die man aufbringen muss um den Widerstand des Getriebes zu überwinden, sprich bis man den Servohebel drehen kann. Da stehen dann so Traumwerte wie 25 Kg.
Üblicherweise gibt man bei geeigneten Servos auch die Stellkraft bei zulässigen Voltzahlen an. 4,8 V ist ein Wert noch aus der Zeit von NC- Akkus.
Heute werden 6,0 Volt und 7,4 Volt angegeben ( Wert 2er Lipozellen).
Bei sogenannten Hochvoltservos , Kennzeichen HV, sogar bis 8,4 Volt.

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