If vertical shaft can be of several lengths, we still need to know the maximum length.
What power is available?

 

Ground detection. Example: running current 1A. stalled current 2 A with sense resistor in - supply lead of .35 ohms. Running V drop about .35V, not enough to turn on a NPN transistor, but at stall, V goes to about .7V & transistor turns on. We would use a comparator for tighter control. Starting current signal would be bypassed.
I just found an interesting spring, .618 " ID, 5.5 turns of .09 " wire , almost big enough to fit over shaft & too stiff to turn by hand. Adding an arm & weight measured only 8 in.lb. @ 90 deg., maybe 1 ft.lb. @ 135 deg. That will be a lot of spring to be useful.

 

Why a servo and not a stepper. The cost of the servo motor and driver is more expensive than a stepper and drive. Also at low speeds, stepper motors have great torque and quite often don't require a gearbox. Servo motors have very poor torque at low speeds and require a gearbox to overcome the torque issue. I have used Arduino's to drive large stepper motors and they can work within the voltages you have shown.

 

Why a servo and not a stepper. The cost of the servo motor and driver is more expensive than a stepper and drive. Also at low speeds, stepper motors have great torque and quite often don't require a gearbox. Servo motors have very poor torque at low speeds and require a gearbox to overcome the torque issue. I have used Arduino's to drive large stepper motors and they can work within the voltages you have shown.

That is just not true, a DC motor is quite capable of high torque at zero rpm, in fact the peak torque occurs at the point of zero rpm.
Stepper motors are power wasters when and if the motor is not turned off when in position, the motor rated torque current is constant, whereas with a servo, the current can be as low as zero at this point, even in the process of holding position.
In the CNC world, which I have worked in for the past 50yrs, I have not seen any major manufacturer use steppers.
When drives are set up in the torque mode of operation, servo's are superior to steppers IMO. and can achieve a much finer degree of positioning, i.e. do not exhibit the cogging effect of steppers.
Max.

 

Generally the only really fundamental difference between any servomotor and stepper motor is that stepper rotates with the "teethy-motion". It accelerates/decelerates/accelerates/decelerates. Some applications are touchy about that. Whilst servos are going with all time permanent speed. However any stepper is smaller, stronger, and probably, especially if Nema-17, then cheaper.

 

Generally the only really fundamental difference between any servomotor and stepper motor is that stepper rotates with the "teethy-motion".

There are a few more 'Fundamental' differences than that!
The torque ability is practically identical between the two, for the same rated torque , the big advantage with servo's is they are closed loop, wheras steppers are generally open loop.
Servo's only consume energy when required, also making them much more efficient.
Just for a few.
Max.

 

RE: MaxHeadRoom - difficult to agree about force, if the say tape cassette recorder motor having identical dimensions to NEMA-17 first is able to turn some few grams to centimeter sized capstan, while second may make the kilograms of push to my cnc stand. Logically, if to compare the equivalent POWER, then You are absolutely right, the egg-sized NEMA with dog size collector motor. However I suspect the answer for riddle are samarium and neodimium, where they are inside is small and strong, and where is only cobalt or alnico that are heavy and weak, probably. So, I will not wonder if You will show some indeed competitous servo what are so new I never kept in hands.

 

There is a place for steppers, where in some applications it would be rather overkill to use servo's and they offer a more suitable option, but in the general machine positioning arena such as CNC etc, the servo is considered the more superior of the two.
Although the DIY builders of CNC often use steppers because it is more economical for the small/home machine.
You pays your money, you takes your choice.
Max.

 

I worked for KUKA under contract. There were many useful things I learned from that experience.

DC servo motors are superior to steppers. You can get fast efficient acceleration/deceleration performance with servos.
Steppers don't have to be stepped. You can analog step a stepper motor.
If you want maximum holding power at zero power input, use a worm gear.

 

On an allied subject, I remember when BLDC motors first came on the scene and was told my one manuf rep, of all people, that a BLDC motor should be used with a G.B. as they 'Cog' badly at low RPM.
Which, if used in an open loop situation, is true.
But when used with a PID, loop torque mode controller that operates at 12Mhz+ feedback, they can be equally as smooth as a DC brushed motor, I found this out, using systems using the Galil Motion cards for one-off applications etc.
Max,

 

With programming might slow the motion to reduce over shoot oscillation?