Servo motor identification help

[kong]

I have just purchased these, for the princley sum of £10 + p&p. They should be arriving tomorrow, so I was wondering how I can safely test them? The guy says the resistance of the coils is good, but that means nothing to me. Also, I was wondering if anyone knew anything about these motors/manufacturers as i have no info on the motors apart from:
Evershed and Vignoles Ltd
London W4
Split Field Servo Motor
Type FB6A/A1/B
Serial No 1335473

Field windings are 1.74 k ohm
rotor is 11.5 ohm
Wt of each motor 4Kg
I have no servo drives, so testing with them is out, and unfortunately the company no longer exists! All help appreciated!

[HuFlungDung]

Hi Kong,

At least since the windings show a decent resistance reading, you'll know they aren't "open" (broken wire) and since they do not measure 0 ohms resistance, they should likely not be shorted out either, but there is no guarantee.

Can the seller tell you what application they came from? Maybe this will give you an idea of their power capacity.

I'm more familiar with permanent magnet servo motors, where no field winding is used. You might need a fancier drive amp to run that type, because of the live field windings. Maybe Google a bit and see what kind of info you can come up with on that general category of motor, or survey the online drive amps catalogues and see if they advertise what kind of motors they will run.

[Mariss Freimanis]

1) Connect the field coil and the armature to a power supply you intend to use with this motor.

2) Use a tach to measure the motor no-load RPM.

3) Calculate the Kv by dividing the supply voltage by the measured RPM and multiply the answer by 1,000. That will be the motor's Kv (volts per 1000 RPM)

4) Multiply Kv by 1.351 to get the motor's Kt. Kt is in-oz per Amp.

5) Calculate the max continuous torque by dividing the motor's rated voltage by its armature resistance. Multiply this by 0.2 and multiply the result by Kt from (4). That will be the maximum continuous torque you can use.

hope that helps.

Mariss

[ToyMaker]

Please correct me if I have this wrong;
When you connect the field coil and the armature coil to the same supply, when the voltage polarity reverses the magnetic fields in both windings also reverse and the motor runs in the same direction.
If the above is true then you have to connect the windings separately so that the direction of rotation can be changed.

robotic regards,

Tom
= = = = =
In a perfect union the man and woman are like a strung bow. Who is to say whether the string bends the bow, or the bow tightens the string?
- Cyril Connolly, critic and editor (1903-1974)

[kong]

Thanks for the help guys, but I'm still in the dark! I have searched google for quite a while and found nothing that I completely understand, and the seller does not know what app. they were previously used in. Unfortunately they haven't turned up yet, so I have no extra info.
As for testing them, hopefully the coils will be marked so I know which is which, but as for power supply, I have no idea what to go with. Oh, and I don't have access to a tachometer! It makes me wonder if the guy was selling them coz he was in the same boat as I am in now!

[kong]

Partial success! I found the firm that deals with these motors, and a guy there sent me some data sheets. The thing is, they are way over my head! If someone has five minutes spare, would you mind looking over them please. Links to four pages:
page 1
page 2
page 3
page 4

[ToyMaker]

kong:
The translation goes like this IMO (everyone else should look at this, too)

FB6A =
3.4 kg wt, 173mm length, 85.7mm flange, 10x24.6mm shaft, 1.2x3x17mm key

/AI =
80 mA field excitation (max), 220 Volt armature (max)

/B =
brush grade

It looks like you supply a constant 220Vdc (rectified mains supply) to the armature, and then vary the field current (maximum 80 mA) to control speed.

I think I would be concerned that these will produce enough torque to be useful for motion. It looks like the maximum torque produced is 33 oz-in, which in cnc machines is tiny . But let's see: 220V x 0.080 A = 17.6W. At 746W/horsepower this is 0.02. Yeah, they are very low power.

robotic regards,

Tom

[kong]

Oh well, it was only a tenner! I think I may attatch some fins to them and call them fans! Thanks for the help.

[balsaman]

Kong,

Don't give up hope! You can supply the field with the 80 ma and vary the armature with a gecko drive and it will work fine. As for torque, if it is indeed only 33 oz/in then yes they are not too powerful. But! They look too big to be only 33 oz in. The 80 ma is the field current, the armature current may be much more. We have 400 HP DC motors at work that have a 7 amp field current. The armature current is 750 amps max.

You need to know what the max armature current is to figure out the HP.

Eric

[ToyMaker]

Eric:
You are correct, I completely forgot about the armature V-I when I did the horsepower calculation.
Unfortunately, the torque value (33 oz-in) came from the data sheet (chart - average motor characteristics, curve T/N(FB) ).
As to armature current: the table on the Electrical Data page says the armature current is 1.5 amps. So, 220V x 1.5A = 330Watts. Which is almost 1/2 horsepower (!!) at 746W/hp. I don't know how the field and armature powers inter-relate.
It sure seems like an awful lot of power in to produce only 33 oz-in torque out.

robotic regards,

Tom
= = = = =
i've been so wrong about so much so often that i probably ought to just shut the ---- up.
but that's no fun

[balsaman]

yeah I saw the 33 oz/in...funny. I wonder if it's a typo? I know that you need to reduce the field current to overspeed the motor. In industry the drives increase the armature current to the max armature current, then they weaken the field to overspeed the motor. Want to see the motor scream? Turn off the field. Stand back as the motor comes apart!

[kong]

Hooray, the motors turned up today, and they are huge! Well, by stepper standards anyways. So I'm itching to test them, but don't want to blow myself up. On the back I have six connectors. A1 A2, C1 C2, F1 F2. From page 3 of the manual, I see that A1 is armature + and A2 is -. As the voltage is 220dc max, i assume I could use a 12v or 24v supply, as that is all I have available at the moment. Now C1 and C2 are the two field coils positive, and F1 and F2 are negatives. It says to use only F1 or F2, I guess switching these will reverse direction? Also, it says max current 80ma, so I guess again that the voltage will be 220v max, so I should use the same voltage as the armature. The stupid question is how do I limit it to 80ma, or do I need to limit it at all, as I'm guessing it may only draw 80ma max from whatever supply I use. As you can tell, I know nothing about electronics, and even less about servos! Ok, looked up the current limiting and I obviously need a resistor to do it.
I can supply a photo of the connectors if needed. Thanks!