How about some reviews on some smaller servos?

[jeffie8696]

July,,,,,,,,,

[Merf]

Not much happening in this thread. Typical example of a huge number of promised reviews not done...is RCModelreviews dying/dead?

[Jakob01]

I am working on a project - it's not a CNC project, but rather a little electro-mechanical device. I hate to be secretive but I am working on a design for someone else and I can't say exactly what it is, but I can say that it has a platter that will rotate. The platter will be about 4" diameter and will be mounted "upright" so that the axis of the platter will be horizontal and parallel to the ground. The platter weighs 400 grams and will rotate at low speed.

It would be ideal of the rate of rotation could be varied from about 4rpm to 8rpm and it would be great if I could control not only speed but also position. But the most important factors are noise (it must be close to silent) and power draw - it must run on batteries so it needs to be quite efficient.

I can use a stepper or a small precision DC motor with a gearbox. I've seen some microstepping demonstrations and they are very quiet, especially at low RPM's... but they were also with unloaded motors. I wonder if I can keep it smooth at low RPM with a load attached?

I also have read steppers are 50-70% "efficient" whereas coreless DC gearmotors can get up to 90% efficiency. However, small coreless motors run at 10,000RPM or thereabouts, and require a gearset to reduce the speed, and most of those gearsets are about 50% efficient.

So it is my understanding that a stepper may actually be more efficient? Am I correct there? When I am not moving the platter, I don't need to hold it in place - so the energy used would only be during rotation. But I am worried about noise or jerkiness with such a low speed. I can also gear it down a little and run the stepper faster if anyone has any ideas on optimum RPM's for energy efficiency and noise?

[SailServo]

SailServo has been set up to research and sell "Captive Drum" sail servos. By "Captive Drum" I mean sail drum servos which retain the sheet when no load is applied. This eliminates the need for loops of cord around your boat, pulleys, springs etc.

My research has shown that manufacturers torque figures are mis-leading. Hitec 785 says 13kg.cm, the best I could achieve was 9.0. I have developed a Test protocol which can be seen on Utube.

I have been looking at selling digital drum servos from HobbyKing. After extensive testing I have had to make an commercial decision No. The failure rate is too high.

When choosing a sail drum servo you need to establish the sheet load, sheet travel and sheeting time. My on-line calculator will do the calculations for you; It even calculates wind forces at different heights.

I would be interested in your comments, suggestions etc. Shortly I will be offering continuously rotating servos.

My own boat is 1/10 scale of the Jolie Brise and its main + top requires a sheet load of 6kg.cm including a factor of safety of 2.

tony@sailservo.co.uk and tony@joliebrisemodels.co.uk

[jeffie8696]

October