drive training

this is probably nothing new but it is worth a shot. as im sure most of you know telescopes are not the only machines that used stepper feedback motors. any cnc 2 axis mill or plasma cutter, ect uses feed back motors which have to be trained. on some equipment there are provisions which maintain this with an automated process. others require manual periodic training to compensate for wear. the only x,y table i worked with required that this be done with a dial indicator. since i happen to have one i thought i would give it a shot on the scope (etx 125ec,at #497). it seems to have worked flawlessly. with the scope resting on the work bench near the vise ,i started the train motor sequence. at the point where the instructions said to center reference object i attached the magnetic base of the dial indicator to the vise and adjusted it so the shaft was half way through its travel and set it to zero. with the tip of the indicator on the side of the tube near the dust cover. then i pressed enter. the scope slewed, i pressed the button to return to reference and watched the dial when it reached zero i stopped. i repeated this process for the remaining three steps. and thats about it. questions or comments are welcome. shiva

Interesting....

First question. Couldn't you have done the same thing using a high power eyepiece on a star to make your reference point? Just wondering why you went to all this trouble. I'm not well up on ETX's but will it remember this training when it's switched off and on again?

One slightly off topic thing, but with reference to a point you make in your initial post. My understanding is stepper motors are non-feedback devices. i.e. the motor moves but unless encoders are attached to the shaft there is no way of telling if it actually moved (or if it slipped). I think the motors in the ETX are servo motors (again open to correction).

Triumpfan, thats a very interesting experiment you did. It's only in trying our stuff like this that new techniques develop.

Some mounts (equatorial) have whats know as Periodic Error Correction PEC in built. This is effectively a way the motor control remembers inaccuracies. The information is provided by an inital training session where the actual errors encountered are corrected by the user and the scope remembers these.

Good work!!

in response to your first question i believe a higher level of accuracy can be achieved with the process i used, in that it does not rely on the operators eye for center reference. in earlier drive training sessions i was always left feeling like "i wonder if that was good enough" now there is no question. second yes the drive training is stored through the switch cycles. drives on the etx should be trained after service,at intervals, and if the hbx is switched to another scope.as far as the stepper motor vs. servo motor you are correct a stepper motor works with pulse counts so feedback is not required. and yes the the motors in the etx are feedback servo, with encoders that are near the final drive in the gear sequence. the encoders are used as the sole locating feedback so i was surprised to find the encoders in my scope stuffed with grease. cleaned them out straight away. then on to drive training which brings us to the beginning. about pec have not been able to find the info im looking for about that. like most of the meade products i have and use, im left feeling like i only have a vague notion of how they actually work. what i think i know about pec is this. pec for the etx is only available in polar, when active the user makes small adjustments to alignment (recenter object)and those adjustments are stored for the duration of the obs session. unless parked the data will be lost between switch cycles. any help on that issue would be much appreciated . thanks shiva

almost forgot drive training must be done on fixed objects because when in training mode there is no sidereal. so the stars would move across the eyepiece and throw off the training.

*Moving this to the Beginners forum*