All about servos

From BEASTX Wiki
Jump to navigation Jump to search

Which servos can be used with MICROBEAST / MICROBEAST PLUS ?

A rule of thumb to find well suited servos for you flybarless helicopter: As strong as necessary, as fast as possible, with less dead band as available.

Servo torque in kg/cm should be at least 3-4 times the heli weight (in kilogram). Speed should be at least 0.1s/45°. The faster the better. In addition the servo should be very precise, have little gear backlash and a low dead band. And of course it should be a digital servo that supports high frame rates (200Hz or more). Also using special heli servos which are designed for maximum vibration resistance is a good choice.

Note that all the speed is useless if the torque is not enough. In doubt when two servos of a series are only slightly different in speed and torque, normally the more powerful is in advantage.

Anyhow, if in doubt ask the manufacturer of the servo if it can be used in combination with flybarless/gyro systems. Not all servos can handle the additional stress of getting different control signals every few milliseconds. Also it must be said that not all servos can be used at maximum frequency even if so it is told on the servo's data sheet. Depending on air temperature, voltage level and heli size it is possible that servos can not be driven at their limit as the servo motor or electronics may heat up too much.'

My servos are getting warm/hot, is this normal?

Similar to a tail gyro a flybarless system is constantly working and correcting. So the servos are moving much more frequently than if they are controlled manually. Additionally to that the servos are usually driven with higher frequency to enable the system giving commands to the servos as often and quick as possible. And because of the abolition of mixing levers and the support of the auxiliary rotor plane the servos have to resist higher forces in flight.

This results to a higher power consumption and a stronger heat generation which is usually not critical. However under adverse conditions this can reach a critical range (e.g. at very high air temperatures or even if the servos are installed near other heat sources such as electric motors). In this case try reducing the driving frequency and/or the input voltage.

Servos react somehow "notchy" at high frame rate. Is MICROBEAST damaging my servos?

If the servos are approved by the manufacturer to this driving frequency, this is a normal effect. The servos get new positioning signals four times faster than if they are connected to a conventional remote control receiver. Especially servos with brushless motors run very hard and direct which causes slightly jerky movements in modes with high servo frame rate. This is totally harmless to the servos and you will not notice in flight operation.

From MICROBEAST firmware Version 2.0.0 onwards a special filtering algorithm was installed which slightly mitigates these rough servo movements.

Why do the swashplate servos run very slow when testing on the bench?

This is absolutely normal. With the transmitter you only give a command to rotate the helicopter in a specific direction at a given speed. The sticks no longer control the servos directly. So you can't say exactly what MICROBEAST will do with the servos when you move one of the sticks.

Adjusting servo deflection in the transmitter does not work.

I use DualRate in my radio to decrease rotation rates / cyclic pitch but MICROBEAST / MICROBEAST PLUS still drives my servos to full deflection when testing on the workbench!?

This is absolutely normal and doesn't say anything about the rotation rates you will see in flight. Similar to the tail gyro in HeadingLock mode the system measures rotation rates and tries to maintain the rotation rate that is commanded by stick input. It automatically finds the necessary amount pitch to maintain the rate. Now if you move the stick while the heli is standing on the ground you tell the system to rotate the heli with a given speed. The system measures the speed and sees that nothing happens. So it will apply more and more servo input in order to move the heli but as the heli won't move the servos will be driven to the maximum allowed deflection.

Measuring and limiting the cylic pitch is counterproductive and not necessary. Always allow the system to have as much pitch as possible. Decreasing the rotation rate simply is done by decreasing the stick output signal. This can be done on transmitter side using the DualRate function or on MICROBEAST side changing the Control style at Parameter menu point B.