Servo trouble

If you can spin the servo without power it will not hold anything reliably. If the servo has a gear mechanism like illustrated above, it will hold. If not you can add one.

The servo drives the top gear and the load is connected to a shaft driven by the lower gear.

You should not need a brake as Douglas was referring to.

However, if a brake is required, solenoid control of a rubber pad against the lower gear will prohibit movement.

-Steve

Note there are many different systems that fall under the name of SERVO. The one you linked in may be geared but not like the one shown above. A typical Remote control plane/Car/Boat servo is based on simple rotary gears, not a worm drive as shown

Steve is correct with his visual and description, this arrangement will hold very well. The one you linked will not. I would think any manufacturer would be bragging about the fact theirs would be WORM drive so look out for that

Due to the limited turn range of the radio control variety, you would not get much mileage out of adding the above to one of those. But any motor that keeps turning  and having this added should work well

There are many worm gear actuators that produce torque in excess of 500 kg-cm.

There are several modules that will convert standard DC motors into RC servo motors. such as this (RC Power Servo) or (http://www.robot-r-us.com/motor-controller/pololu-simple-high-power-motor-controller-18v25.html)

There are lots of DC gearmotors with worm gears that can be converted to servo motors.

There are many servo systems that outperform RC servos.

There are many motor controllers that may suit your requirements.

We need to know range of motion, size, weight, speed and cost requirements as well as torque to make any kind of suitable suggestion.

I don't want a controller: just a servo

size-  40*40(4.7 max0)

range of motion- stationery i.e. 0

weight- 78gs{ 100 g max(the lesser the better)}

speed-useless( because range of motion- stationery i.e. 0)

cost- 70${80$ max(the lesser the better)}

torque-40kg{no lesser(38kg min with adjustments)}

Hope this is helpful

What about winch servos?

-Radio Control Planes, Helicopters, Cars, Boats, FPV and Quadcopters - Hobbyking

I don't quite get why a servo is needed if no motion is needed.

A fixed bracket could do the job described.

If you want to apply a variable torque - a servo is probably not the best way.

Any linear actuator could supply holding "torque" - many can do this without power.

Greetings Royston, There's something your not telling us. Is the servo only being used to stop movement or is it being used to control the movement.  For example move the load to a position ans hold it there.

Without knowing what it's being used for it difficult for us to help you design this thing you are building. For some reason you are forced to use servos when other devices may be more efficient.

You have some very good ideas here. Maybe we don't understand your requirements.  A little clarification of what it is your trying to make would be extremely helpful.

-Steve

Hi Royston,

Sometimes it is hard to know where to begin, because the question could be interpreted in many ways. It may take up days of your time to reach the correct answer.

This was an interesting site just for occasionally referring to (I check it from time to time). If I'm asking a question on forums I'll often pause and then maybe delete and re-type the whole thing:

https://www.biostars.org/p/75548/

However probably nowadays it should also state that where possible a picture/diagram can also say a thousand words.

Here is the full explanation.

   1)Why are you using servo?

Ans:It is because in my project I would like to build a transportation jet. The load I want to carry is 15-20kg. A very powerful motor drain all the amps of the battery within no time. So I thought a servo to lift weight. Then I realized it would also drain amps. I was not going to move the servo. It would be stationery. So why should I power it if it can lift the weight without power and signal. SO that is why I  asked the question. Hope this clearifies the problem.

Thanks Royston, but I am still a bit lost. To me a transportation jet is a vehicle with a gas turbine engine.

It looks like you want a robotic wheeled vehicle to transport a 20 kg load, but I am just guessing.

It looks like you want a servo motor to lift the load onto the vehicle. If this is true, you can simply turn off power to the servo (or DC motor) after the load is on the vehicle.