The following is a review of the HDS-577 digital micro servo. My thanks to Arshia of Ashtek Electronics for supplying the servo used for this review.

Overview

Let's start with some pictures to show the relative size of this 'mini' servo in comparison to a Hitec HS-56 :

The technical specifications for this servo (577) are as follows:

As can be seen from the above this servo is larger in size than the popular HS-56, it has similar speed but torque is much higher. One other crucial difference between this servo and the HS-56 is that this servo is a digital servo and therefore has a faster frame rate. This in theory should make it both more accurate and faster to react to commands from the gyro. Obviously being a mini servo this servo is both larger and heavier than the average micro servo but this is not an issue in mounting it to the standard Align tail boom clamps. Care has to be taken to check the helicopter balance after fitting due to the slightly heavier weight..

Flight Testing

After the initial installation and setup of this servo it was time to see what it was capable of doing in-flight. As with all digital servos this servo emits a high pitched noise whilst in operation. My initial thoughts about this servo were that it provided quite a very good hold when coupled with a GY-401, speed and accuracy appeared to be good and its ability to hold the tail when under load was also very good. Backwards flight was handled okay and in contrast to it's 877 brother it does not let go as easily, although it can be can be done.

Following my experience with the 877 I wanted to run this servo for a good number of flights before coming to my conclusions. The servo on my machine is now at around 30 flights and is still going strong. This servo does provide a very good heading hold and for the price I have been impressed with its abilities. Due to the experience with the 877 I also mounted one of the servos on my Logo 10. Obviously this is a much harder job for the servo to handle due to the greater torque acting on the Logo 10 tail. This servo has also had about 10 flights and is still performing well. Although I did recently noticed a slight glitch in the servo at close to full right rudder. I could make the servo do this on the ground but I couldn't replicate it in the air. Both my T-Rex and the Logo 10 have a very solid tail which does inspire confidence when performing 3-D.

Conclusion

Overall I like the way this servo has performed. Considering that it is not an expensive servo in comparison to its rivals and the performance that it delivers I think it represents something of a bargain. It doesn't appear to suffer from the stall current problem of its smaller brother. Add into this that it provides a good solid hold when coupled with a GY-401 and it makes this servo an attractive proposition. Considering this I would recommend this servo as it offers performance at an attractive price.