Servo gearing question

[Bigrhamr]

My table uses the Animatics "Smart motor" servos and they appear to be geared very high as it is currently set up.

According to the motor manufacturer the upper safe usable RPM limit is
8,000. I have 28:1 gearboxes. So if I used a more conservative max RPM of 7000 I would have 250 RPM out of the boxes. The final drive is a 1.8" pulley and belt drive.
My calcs (which may be off) say that 1.8" x 3.14 = 5.652" of travel per revolution x the 250 RPM gives a rapid speed of over 1400 IPM. I have it set for about half of that which is fast enough for me.

I don't have the best understanding of servos but is my thinking correct that this is costing me a lot of torque and acceleration which is important plus some resolution which may or may not have any noticable effect with 2000 line count encoders?

If I changed to a 1" pulley that should give a max rapid of about 785 IPM and greatly increased power and acceleration. Is there any reason I would not want to do that as long as I still have all the speed I want?

Thanks for any input and if my numbers are off please let me know.

[jcc3inc]

Sir,

If you can tell us which motor you are using, we can comment better on your situation.

Regards,
Jack C.

[Bigrhamr]

The motors are Animatics model SM2315D-S2

The company does not have specs for it online that I can find, I'm assuming because it's not a current model. I have requested specs with the torque curve and optimum RPM range but so far all I have received is: "The max speed with no load is 10000 rpm. The usable range is 20-8000 rpm depending on load."

Thanks.

[jcc3inc]

Sir,

Looking up your supplier, they have a similar motor, SM23165D, for which one can buy their 28:1 gearbox (see their specs). The above motor has 10,000+ max RPM, it is one of their smaller motors in the 23 frame size. Continuous Torque = 40 Oz-In. *Probably* this is close to what you have!

With the 28:1 gearbox, Max torque out using 40 Oz-In motor will be 112 In#, continuous torque is 70 In#. With your 1.8 inch D. drive the continuous force will be 112/.9 = 124# force. At 250 IPM, motor speed will be 1237 RPM. Unless you are driving a heavy machine, this seems to be plenty of force.

If you go to 1" D., max force will be 112/.5 = 224#. Here motor speed at 250 IPM will be 2228 RPM. This is probably a better ratio. A more ideal situation would be to have more reduction in the gearbox so that you could use the larger dia. pulley.

Regards,
Jack C.