# How much torque do I need to turn my servo?

I'm designing a bomb bay door for my RC place. Fuselage has circular base, I want to recover the door to its original position after deployment, so I decided to use servos for the job. But I think payload might move the bomb bay door when I don't need to. So my question is how much torque do I need to move my servo? So that I can calculate my payload weight accordingly. I tried other configurations for the dropping, but no other configurations worked for my payload.

• Your question is asking how much torque you need, so the first thing you should probably do is learn what torque is. You can't estimate how much torque you need when you don't even know what torque really means. Apr 10 at 15:33
• I learnt about torque as you said, but still i haven't figured out the answer, may be you can answer. my updated question is how much torque will be needed to move an unpowered servo arm of 5kg-cm?? Apr 11 at 10:40
• Oh, so your question is not a powered servo driving something, but backdriving an unpowered servo? That is different and is not the torque rating of the servo. However, it can't be determined without without detailed design information about the servo's gear train and motor. In any case, it is not good to rely on an unpowered servo holding position. If you want the servo to not constantly need to exert a torque to keep the cargo bay doors closed you will need to change the design so that the cargo bay doors cannot be backdriven. Apr 12 at 17:16
• For example, worm gears or a hinge with a slotted sliding pin where the force exerted by the cargo on the doors is 90 parallel to the servo lever arm. That would probably require some 3D printing or machined parts. Or making a mechanism where the first part of the servo travel opens the doors but the second half of the travel unclips the load. That way the cargo bay doors are not load bearing at all (as is done in a full sized bomber). Apr 12 at 17:18
• Thank you, I'll look into design. Quick question, is there a device i can use to hold the bay doors without relying on servos?? I thought of using a device called as servoless payload release from E-flite, but it's not reliable when closing bomb bay doors. I even thought of using a couple of puzzle like design for bay doors, but they too proved to be non reliable while closing, is there any way you can suggest?? Apr 13 at 15:27