Talk:Servomechanisms (aka "Servos")

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Revision as of 21:23, 24 January 2011 by StefanoCapelli (Talk | contribs)

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The E-2? Robot project has adopted two kinds of servomechanisms as a means to drive its mechanical parts.

Here they are:

HS-645MG this is the smaller one, with 90° shaft rotation (in the simplest configuration) or 180° with a special RC controller or using Hitec's servo stretcher.

HS-785HB this is the bigger one, with shaft angular movement ranging from (-360°*2.5) to (-360°*2.5), two complete turns and a half per direction.

Here we describe how we've tried to assess the continuous torque of one of these devices.

Hitech gives a generic torque specification on the box of their servos and on their internet site: contacted by us, one of Hitec's service managers has denoted that spec as "stall torque", and told us to assume its 80 percent as continuous torque.

In order to test our servo, we hatest Before our test we have follo Before testing, we have done the following:

- opened the case of our servo, fitted thermocouple near the circuitry, then closed it back, with the four screws - mounted a horn on the shaft, to attach a wire. Then the wire's end will be used to apply a force, which, using the horn as the lever's arm, will apply a moment on the shaft - prepared some objects (like water filled bottles, wired together) with adjustable weight: the final weight, divided by the length of the winch's arm (19mm in our case) will equal the tested torque.

Assuming that we can apply a moment using a single force, not a couple of forces equal in modulus (the real torque), we've started our test, using Hitec's designation of continuos torque () as initial guess.

We've tried to provide that force to the horn of one the two servo models, to see what happens when the servo has to lift the mass and keep it still for some time: the measured temperature has risen from 25° to more than 40° in 4 minutes, and we've guessed that actual temperature could be so high as to suggest a lower value of continuous torque.

We've made a second test using ... as the torque, and the same temperature rise has occurred in 10 minutes, which is a reasonable result to take this new value as our continuous torque estimation.