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balsaman
10-07-2003, 10:16 PM
Have a look at the surplus DC motors available at The Surplus Center:

http://www.surpluscenter.com/sort.asp?UID=2003100720063464&catname=&byKeyword=yes&search=dc%20motor

I like the 1/8 hp 24 volt DC ones for $7.95. Take off the brake, add an encoder and you are good to go! 4:1 belt drive sounds perfect (or 2:1 with a fine pitch screw?).

There are other nice ones there too.

Eric

ezland00
10-07-2003, 11:51 PM
Nice find. I don't know much about motors. How does it work?

Mr.Ed
10-08-2003, 07:28 AM
But why take off the brake? It brakes when power is shut off. Wouldn't that be nice in an emergency situation? You hit the Emergency switch and it stops instantly.

I would consider buying one if i could be pursuaded :D

Would it have good vertical bearing capability? (that is, if you run it straigh attached to an end-mill.

Give us your thoughts on this DC engine.

Ed.

NeoMoses
10-08-2003, 11:08 AM
Very nice find, indeed! I'm looking @ some of those 1/4 HP, low RPM motors for a BPort, and possibly some of the 1/8 HP for a router. Now, I just need to find some more money.:p

Mr.Chips
10-08-2003, 11:54 AM
From a NewBie
You mentioned adding a "Encoder". Could you tell me or give me a link that explains this.
Are these "Stepper" motors?
Thanks

deft
10-08-2003, 12:08 PM
what would one of these 1/8 hp motors be equivalent to in a stepper motor?

kong
10-08-2003, 01:08 PM
Stepper motors move in steps, usually about 2 degrees, so one "pulse" from your PC would move the motor one step. Servo motors have no such stepping, they are either on or off. The encoder is a device that is connected to the servo motor and feeds-back the amount the motor has turned to the motor driver (interface device between your pc and the motor). The motor driver can then interpret the pulses from your pc, and turn the motor on, until the encoder has sent back the correct number of pulses back to the controller to indicate it has moved the required amount. It is like the wheel on your mouse, a small plastic disc with lines on it, read by an optical sensor. Each line can indicate one degree (depending on the resolution of the encoder) and sends that info back to the controller. Hence, servo motor controllers are more complex and expensive than stepper controllers.
That's probably as plain as mud!:p

deft
10-08-2003, 02:24 PM
great explaination, of how servo motors work but would the 1/8 hp servos be equivalent to a 100 oz/in stepper, 200 oz/in stepper (or something else)?

ehiebert
10-08-2003, 02:51 PM
Here's an simplified explanation for the newbies to help understand servo motors.


The holding torque of the servos whould me much greater than the steppers. Just look at the power dsifference....

100 oz. in. Stepper
------------------------
5.2V and 1.2 A/ph = about 6 W

1/8 HP Servo
----------------
1 HP = 746W so these are 93.25 W



Even and extremely inneficient servo motor will probably have more holding torque than a 100 oz. stepper.

Servo motion electronics are much different than the stepper. It is a controlled motion system. The encoders are used to tell the controller where the motor currently is. The controller compares this position to where the motor is supposed to be. The difference between the two readings is the position error signal (feedback signal). The greater the error signal is, the more current the controlle applies to the motor to bring it into position.

Conversely, a stepper driver just applies the full power to the motor with each required step. The stepper solution is not encoded so the controlling program has no idea where the motor is. It just assumes that the motor has not missed a pulse. It is up to the designer of a stepper system to ensure that holding torque limits have not been exceeded while running the toolpath. An example of how this can happen is if your router hits an very hard knot in a wooden workpiece, and the user used a feedrate very close to the motor torque limits.

For a heavy duty precision mill I would want servo motors... especially for the precision part. However, be aware that the motor drivers/controller is going to mucho more expensive than a simple stepper controller.

balsaman
10-08-2003, 06:04 PM
I am currently using 1/8 hp DC motors (115 volts, 1700 rpm). Running on 75 volts I am getting 150 imp rapid moves and plenty of "push" at cutting speeds. I am using direct drive.

Eric

High Seas
10-08-2003, 06:30 PM
Like maybe - I should race out and get the last of these!
After your great explaniations and experience maybe I'll wanna upgrade before they're all sold out.
As an aside - if this kind of great info was available (well it was I know - but I din't know what I 'didn't know) maybe I'd have gone a different route - alas - I now have a PPPI.. (pre planned product improvement)!
:cheers: Jim
BTW - how much more is 'mucho" 2x, 3x?

kong
10-08-2003, 06:37 PM
A 3 axis stepper controller from xylotex will set you back about $125, but for servo's, you will need something like three Gecko 320's @ $114 each + encoders.
Sorry, linkies:
http://www.xylotex.com
http://www.geckodrive.com

jimbo
10-08-2003, 06:51 PM
The motor mentioned says intermittent duty. Not sure if this would be a problem. Also picture shows splined shaft but description does not mention it, so you may want to find out for sure.

The motors on the following link look an awful lot like the 1500 oz-in ones on ebay going for $450 for a set of three with encoders. No encoders on these though. Anyone used these with their own encoders?

http://www.surpluscenter.com/item.asp?UID=2003100720063464&item=10-1561&catname=

balsaman
10-08-2003, 07:37 PM
Originally posted by kong
A 3 axis stepper controller from xylotex will set you back about $125, but for servo's, you will need something like three Gecko 320's @ $114 each + encoders.
Sorry, linkies:
http://www.xylotex.com
http://www.geckodrive.com

+ 3 encoders at ~$30.00 each

What we need to compliment these motors are a source of encoders for REALLY cheap, say in the $10.00 range.

Eric

balsaman
10-08-2003, 07:43 PM
Originally posted by jimbo
The motor mentioned says intermittent duty. Not sure if this would be a problem. Also picture shows splined shaft but description does not mention it, so you may want to find out for sure.

The motors on the following link look an awful lot like the 1500 oz-in ones on ebay going for $450 for a set of three with encoders. No encoders on these though. Anyone used these with their own encoders?

http://www.surpluscenter.com/item.asp?UID=2003100720063464&item=10-1561&catname=

The problem is they only list the no load current at .35 A. This means nothing. We need the full load current. You can tell something about motor power by looking at the output shaft. These have a 5/8" shaft. Usually motor manufacturers save these heavy shafts for motors in the 1/2 HP range. One would really need to purchase one and hook it up to see what it can do. It probably has plenty of torque.

My motors are 1.1 amps full load, and I am not lacking power. I am thinking they are peaking in the 3 amp area tho, altho I haven't measured.

Eric

jimbo
10-08-2003, 08:43 PM
This link on ebay is the motor I was referring to it is 600 oz in (instead of 1500). At peak torque, current is approx 13.6 amps. It is also only 1500 rpm motor at 50 vdc. This kind of motor only belongs on a large router like a 4x8. I think both motors are ametek brand.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2561761262&category=26261

Ebay is the only place I know of encoders for cheap. I got a couple for $5 dollars each. Havent hooked them up yet so dont know if they work.

balsaman
10-08-2003, 09:44 PM
Seems to me this guy is adding an encoder and making a couple hundred percent.

Eric

HomeCNC
10-09-2003, 12:48 PM
If it's the same guy I have seen. He gets these Amatek motors from some windmill place. He also got a large lot of encoders ( I looked at his history) but the encoders require an external power supply. I also purchased a similar Amatek motor off ebay to see what it was like. My motor was rated at 24 VDC. When I put 24 volt on it I could stop the shaft with my hand.

If you get one of the motors from Balsamans wonderful link then you should try to fit a USDigital encoder 'E2' or similar type. I use them on my servo motors and they work great with the Gecko drives. They are about $36.00 each.

thielert
10-09-2003, 01:56 PM
What is an appropriate encoder count per revolution?
I imagine gear down ratio has a significant affect on this if encoding off the motor and not the screw like Eric does.



Tim

ToyMaker
10-09-2003, 04:32 PM
Balsaman wrote:

What we need to compliment these motors are a source of encoders for REALLY cheap, say in the $10.00 range.

If you know a little electronics and are willing to invest some time you can build an encoder with arbitrary resolution for under $5.
Use an optical slotted switch (an LED/photodiode pair), one digital gate to condition the output, and a disk printed on clear acetate.
The switch and gate are available from digikey.com, mouser.com, allelectronics.com, and many others in a range of prices.
The disk can be drawn in a cad program and printed on any laser or ink-jet printer.

robotic regards,

Tom

balsaman
10-09-2003, 06:25 PM
Originally posted by thielert
What is an appropriate encoder count per revolution?
I imagine gear down ratio has a significant affect on this if encoding off the motor and not the screw like Eric does.

Tim

200-300 counts per revolution is perfect for the gecko 320

Eric

MikeA
10-13-2003, 05:54 PM
Hey guys, I order the motors mentioned, and to the say the least I am under impressed. These look to be pushing WW2 vintage and barely resemble the picture. I find it hard to believe they are new. That being said, I was leary going into it and was wiling to gamble on them. Just a heads up.