Author Topic: Removing brakes from Servos  (Read 15459 times)

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Offline bj

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Re: Removing brakes from Servos
« Reply #15 on: February 04, 2012, 11:57:14 am »
   Just a slightly documented opinion of magnets losing strength----I think some of it might depend on what type
of magnet is involved.
   Just to do it, I removed the armature from a small cheap DC motor.  I had tested it with a model aircraft prop on
it, and measured the RPM.  Anyway, put it back together (as exactly as I could) and tried again.  Got an approx.
25% loss in rpm.   Power draw was less, and I guess that makes sense.  This one had ceramic mags in it.
   Tried the same thing with one that had  alnico mags and got so little difference, if any, I couldn't measure it.
   Only one test, so it proves nothing, but is food for thought?
"Even a blind squirrel will find an acorn once in a while"
bj

Offline m12ax7

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Re: Removing brakes from Servos
« Reply #16 on: February 04, 2012, 07:38:51 pm »
bj,  I have never heard claims that ceramic magnets from standard DC motors would loose their strength.  I serviced a number of Leesson and Baldor DC motors, ranging in size 1/3 to 2 hp.  These were all commutator/brush type motors.  Often needing the bearing replaced and the commutators turned down, sometimes needing their brush holders replaced.  These motors were removed from serviced, repaired and returned to service without any (performance) problems observed.

I believe that the loss of magnetic strength is limited to SERVO motors, which use rare earth magnets.

Offline bvan1941

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Re: Removing brakes from Servos
« Reply #17 on: February 04, 2012, 09:14:45 pm »
Birdhouse,
I've reread what you've posted for disassembly of this Fanuc have tried to follow them and have some questions.
I've removed the screws form the front of the case and have split the case apart just about 1/8"all the round. I seem to be stopped from spreading the case any farther by something that feels real solid. You mentioned there was a "spring washer" that had to be compressed during this process.

First question:   Is this what's stopping me from splitting it apart?  If it is, is this the "spring washer" visible from the back end? If it is, must it be collapsed inward or back towards the plate that held the "tachometer"?
   
Second Question:   The bearing/rear case probably will not slide easily off the shaft because it being a "press fit" on the armature shaft correct?

Probably being too cautious but then I don't want to ruin the motor either. Should I keep forcing the case apart at this point ?
Bill

Offline birdhouse

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Re: Removing brakes from Servos
« Reply #18 on: February 05, 2012, 06:11:00 am »
bill-
like i said, it was a few years ago.  i do remember having about four wood chisels, three pry bars, a hammer and cedar shims around to get it open.  i think the spring washer is a non-issue.  it just takes some brute force to get that bearing out of its press fit seat.  it's hard because normally you could "de-seat" a bearing with a hammer and punch, but in this case you don't have access to the side of the bearing to get a hammer in there, so prying hard is the only way. 

the thing is built with very rugged parts, so as long as you don't nick/short a coil, you should be just fine. 

i remember putting it back together.  i used the four big bolts and tightened them evenly.  the rear bearing would pop a little here and there as i tightened the bolts.  once the bolts were fully tight i had to use a piece of just the right size pipe to tap the rear bearing to where  it wanted to be.  my memory says using the bolts over pushed the bearing, and the pipe brought it back some so it sat in the right spot. 

adam

Offline bvan1941

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Re: Removing brakes from Servos
« Reply #19 on: February 05, 2012, 09:42:05 am »
Birdhouse,
Thanks for the patience and good advice as I follow steps in getting this motor on a tower. I will try documenting as well as I can so that future Servo users can attack this process more confidently. I will say that looking on line (any other place than these forums) for any help is / has been fruitless so far.  For us Noob's it's nice to have people with that real experience to ask specific questions during a project.
Bill

Offline bvan1941

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Re: Removing brakes from Servos
« Reply #20 on: February 05, 2012, 04:22:59 pm »
Birdhouse and all,
I've succeeded in separating the case/s and removed the brake assembly, leaving the "coil" in it's recessed spot. Out of over enthusiasm I put the back cover back together and temporarily screwed the cases together again, (It went together without any resistance) but the rear plate that holds the bearing in place popped right out the back side of the rear cover. I intend to take it apart again to take some pix's and ensure all wires are not going to get pinched, etc. I now understand Birdhouse's statement about "tapping the bearing back in place." I will have to do that during final assembly too. 
The front case kept the armature in place very nicely during the process and while cases were apart, so no worries about losing any magnetism--- I hope!!
That's all I have for now but will try and show some pix's and relate how I went about splitting the cases further if anyone is interested. In short, It went just as Birdhouse explained.

Going to watch the Superbowl now-- Go Giants !
Bill

Offline ghurd

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Re: Removing brakes from Servos
« Reply #21 on: February 05, 2012, 08:46:08 pm »
AGAIN,  I am not saying do as I did,  just saying what I observed in my little world.

It was power output.  IIRC, it was across the board output.
Young Mr Fungus is a smart little cookie, and honest, and I would not 2nd guess his findings.
Just saying I personally trust him 111%.

A 'keeper' contains BOTH poles of the field.
Magnets on a motor's rotor do not when they are removed from the stator (the laminated stator acts as the keeper).
G-

Offline bvan1941

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Re: Removing brakes from Servos
« Reply #22 on: February 06, 2012, 07:02:12 pm »
97 fishmt, Birdhouse and all,
Well since last session, I've cut the unnecessary tachometer/ brake wires and put the motor back together and it works!! LOL
Like birdhouse described, it was necessary to "tap" the bearing back into position, no real problem. If your not familiar with the last statement, the rear bearing stays attached to the rear aluminum housing plate when the case is split apart enough to access and remove the brake assy. What you have when the motor is apart is that the front case half and armature is held in place along with the stator.  The brake assy is screwed (Tight!!) to the rear housing over the coil!  I had to use vise grips to break the Phillips screws loose then remove the (3) pieces of the actual brake parts. Don't for get to pull all the springs and spacers and put them aside.  After that, I made sure the three 3 phase wires were placed back where I saw them on disassembly and cut the rest off close to the signal control  socket.

Reassembly was straight forward. I put the black colored back half of the case, up against the front and put the (4) recessed screws in and tightened them somewhat. then went round the back and (following Birdhouses advice) used a socket and tapped the bearing back in enough to reseat the aluminum back plate that holds the rear bearing to the armature. You'll know when the bearing is seated because it will have a distinct metal upon metal sound when tapping and the aluminum plate will be reseated and back in place simultaneously. I Know that 2 of the 3 phases are working! My friend came in and said he would operate the 18V drill, as I was setting up the meter and putting the alligator clips attached to the meter, in place !!

Some where in this scientific process, he said I nodded and he pulled the trigger and------ I almost wet myself and was making ugly sounds !!!  I finally got my cigarette lit, by clamping the lighter in the vice!!!! SHOOT!!
Have no idea what the RPMs were, but later on with the same set up, it slammed the peg pinning the meter hard on the 30 Volt Scale!!  I think this motor will definitely charge batteries-- with no problem!!
enough for now,
Bill





 

Offline birdhouse

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Re: Removing brakes from Servos
« Reply #23 on: February 06, 2012, 07:42:29 pm »
nice work bill!

do you have rectfiers? 

the next step i took was to hook the three wires up to a rectifier.  then you can measure DC volts coming out.  then i bough a cheapie bicycle speedo.  taped the magnet to the motor shaft.  with some math and head scratching, one can turn MPH into RPM...  so long as you know the wheel diameter the speedo is calibrated to. 

then you can get a 12v cut in rpm. 

next, i started bench testing with an actual battery with an ammeter.  then you can get amps (thus watts) at various rpms.  just be warned, it's AMAZING for a first timer to witness how much torque the motor will push back at you when even generating 200 watts! 

you're on the right track!!

adam


Offline bvan1941

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Re: Removing brakes from Servos
« Reply #24 on: February 06, 2012, 08:22:17 pm »
Adam,
I've got (3) bridge rectifiers somewhere in the mail. I will be doing the testing steps you described next too.
I have to find a machinist to fabricate an adapter to fit the tapered shaft on the motor and the taper from the hub for the "Powermax" blades I bought for the project. I'll have to start a new post For this Fanuc motor as I progress. I'm not even sure anyone would be interested from here on out. We'll see.

Again, I thank you for your help. By the way, keep posting some updates of your own.
Bill

Offline Wolvenar

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Re: Removing brakes from Servos
« Reply #25 on: February 06, 2012, 10:53:16 pm »
Post and they will come.  ;)
I would most certainly be interested in seeing your progress.
Trying to make power from alternative energy any which way I can.
Just to abuse what I make. (and run this site)

Offline klsmurf

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Re: Removing brakes from Servos
« Reply #26 on: February 07, 2012, 07:29:07 am »
Nicely done Bill!   I too, will be watching with interest.

Quote
next, i started bench testing with an actual battery with an ammeter.  then you can get amps (thus watts) at various rpms.  just be warned, it's AMAZING for a first timer to witness how much torque the motor will push back at you when even generating 200 watts!
;D     Very true.
one hand holding a 30# servo and one running a drill. Needless to say I was NOT ready. I decided to clamp the servo to the work bench.

Bill, If you didn't know already, you can set one of those bicycle speedos to a circumference of 167 and the read out to km/h. You then multiply the results by 10 and this is your rpm.

Kevin
"A man's got to know his limitations" ---- Harry Callahan

Offline ksouers

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Re: Removing brakes from Servos
« Reply #27 on: February 07, 2012, 07:33:50 am »
Post and they will come.  ;)
I would most certainly be interested in seeing your progress.

Count me in, too!

As far from the city as I can get but still keep my job.

Offline birdhouse

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Re: Removing brakes from Servos
« Reply #28 on: February 07, 2012, 10:12:17 am »
Quote
Again, I thank you for your help. By the way, keep posting some updates of your own.
Bill

i've thought about reposting my turbine story here in another thread.  seems others are doing similar "old" repostings to get some good content on this site.  i've been absolutely slammed with work, but i think the next posts you'll see of my "stuff" will be the "jerry" 4' mill on a dinky 20' tower, and my passive solar tracker that uses a hydraulic cylinder and pressure from R-134a to track the sun.  i've been SLOWLY...  working on that one. 

Quote
one hand holding a 30# servo and one running a drill. Needless to say I was NOT ready. I decided to clamp the servo to the work bench.

Bill, If you didn't know already, you can set one of those bicycle speedos to a circumference of 167 and the read out to km/h. You then multiply the results by 10 and this is your rpm.

i don't know about bills servo, but mine weighed in at a whopping 65lbs.  i had trouble finding a big enough drill to get more than 240 watts out of it.  the motor fought back with so much torque, that even my BIG boy hammer drill would slip its clutch past 10 amps (@24v). 

good info on the easy conversion with the speedo!!

adam


Offline Wolvenar

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Re: Hydraulic cylinder tracker
« Reply #29 on: February 07, 2012, 11:34:06 am »
I'd love to see that hydraulic cylinder /R134 tracker. That sounds like a great way to do it. I was hoping to add a bit of solar here, but recent unexpected damaged things here may have taken the set away funds. Any which way it would be nice to get a plan in place. 
Trying to make power from alternative energy any which way I can.
Just to abuse what I make. (and run this site)