Need ID on Hathaway Servo

[eightball]

I'm in need of some help, I found a few Hathaway servos for sale for pretty cheap but the seller doesnt have any specs on them, just the part number = 9925093 rev=A , they're 24V dc, and the optical encoder's part #= 101948-01 rev=B Date code = 8752 . Since Hathaway doesnt exist any more, its just about impossible for me to find the specs on them. If anyone can help me find the oz-in ratings, the nema size, and any other info on these servos, id greatly appreciate it. Also what would be recommended to drive these? I saw some syke (?) product that was no longer in production for driving dc brushless (i dont even know if these are brushless) and last i heard gecko didnt make anything for them.

[Al_The_Man]

If you do a search here, there is info for extracting the approx size of the servo's.
The fact that you know they are 24vdc then this makes at a bit simpler to obtain the details.
If you can tell if how many leads actually go to the motor itself, excluding a ground it will be 2 for DC Brushed and 3 for DCBL or AC.
Al.

[eightball]

I cant find anything in the forum about hathaways except one guy who had the same model but had no idea what its specs were either

[Al_The_Man]

The links I mentioned are not specifically for any one make, it is a method of extrapolating the motor characteristics empirically.
I can see if I can dig it out and repost it.
Al.

[eightball]

i'd apreciate you doing that for me. But i don't know how much can be extrapolated from the very limited info i have. sure wire count might be able to say if its brushless or not, but theres no way to really tell the torque which i am most concerned about at the moment. I have an enco clone of the RF30 and i was thinking i'd need about 300 oz-in per axis. If i were using a mini-mill i dont think torque would be so much of an issue because i would think just about any motor would work. Do you agree with my torque requirements? (going to be primarily milling alum and a little bit of steel.)

edit: Heres some specs i dug up from the other thread for these servos:

Diameter: About 2"
Length: About 6.5" overall
Shaft: About 1.5" long
cost for 3x new ones = $275 (not sure if manufacturer price or not)

[Al_The_Man]

Here is the notes I posted earlier, they may help you.
You can skip the math and do the practical tests and it should get you in the ball park.

This is some notes I made when I was looking for similar information and found them in various sources:
equations are:
1. V=Ia R + Ke omega (Ia=armature current, R=armature resistence,
Ke=electr. constant, omega=speed)
2. Tg=Kt Ia (Tg=costant, Kt=torque constant)
3. Tg=J d(omega)/dt (J=inertia, d(omega)/dt=accel.)
The DC motor transfer function is:
Gm(s)=(1/Ke)/(1+s(Rj/KtKe)), which can be written Gm(s)=(1/Ke)/(1+sTm)
where Tm=mechanical time constant.
To measure the parameters you are asking for, I suggests the following:
A. Measure the armature resistance as below, then apply voltage to the motor without load and measure the current and speed. From equation 1. you can easily derive Ke.
B. Apply nominal current to the motor (with the shaft locked) by means
of a variable voltage source. Measure the torque on the shaft. From this you can derive the torque constant Kt=Torque/Amp.
A spring scale and string attached to a pulley of known dia or a shaft attached at right angles to the shaft can be used, obviously the scale should be of enough size to prevent rotation.
C. You will find that Kt is approx. equal to Ke
D. For the inertia you can obtain it by calculation from the size and
material of the rotor.

Note1: inductance can be ignored- the electrical time constant is
very short compared to the mech time constant so that it can usually be
ignored.
You can measure the mech time constant by running the motor up to
speed at no load, disconnecting the supply and letting it coast down- plot speed vs time and fit to exponential N=No(e^-t/Tm) time to drop to 36.8% of original speed is the time constant.

Note2: If it is a permanent magnet motor, you can determine the internal emf by spinning it at rated speed and measuring the open circuit voltage. The voltage at any other speed will be directly proportional to speed. To measure the winding resistance, lock the rotor so it doesn't turn and measure the current with a small voltage applied (so as not to exceed rated current) Don't bother using a multimeter's ohm range- not worth the effort.
For inductance, you should use a scope- apply a voltage, rotor locked and look at the current trace vs time.
This will be of the form i=K[1-e^Rt/L] where i is the current at time t.
In most cases the inductance can be ignored as its effects are generally swamped by the mechanical inertia in transient cases and is of little importance for steady state.

Al.