my new cheap servos

[Dan S]

I found these servos on the net, and they are dirt cheap, so I just had to get them.

the website where i got them

http://www.cnczone.com/gallery/data/...85myservos.jpg

I posted a message on the gecko forum asking if they where any good and Marriss replied with the following.

“
Use a 36VDC power supply.
No-load RPM at 36VDC = 3,130
(Ke = 11.5, KRPM = 36V / Ke)
80% of no-load RPM = 2,500 RPM
Leadscrew RPM @ 120 IPM, 5TPI = 600RPM
Reduction Ratio = 2,500 RPM / 600 RPM = 4.1666:1, Use 4:1
Kt = 1.351 Ke = 15.5 in-oz / amp
Maximum continuous current = 3 Amps
Maximum continuous torque = 3A * Kt = 46.5 in-oz
Torque on leadscrew = 46.5 in-oz * 4:1 reduction = 186 in-oz
Leadscrew thrust = pi/8 * TPI * in-oz = 365 lbs
Maximum speed at full load = 2500RPM /(ratio * TPI) = 125 IPM
Maximum speed, no-load = 3,130RPM / (ratio * TPI) = 156 IPM
Power delivered to load = RPM * in-oz / 1351 = 86 Watts

Mariss
“

If these servos are even half that good I will be happy.

-Dan

[ezland00]

I don't think they have encoders. Do they?

[HomeCNC]

I just got my one servo that I ordered to check it out. It looks like they can be modified to hold an encoder. I'm going to reverse the end caps because I like the cap where the wires connect as the front. I will turn off the knurl as well.

[Dan S]

If your using belt drive isn't it better to hook the encoder to the screw, and not the servo?

Jeff

whats knurl??

-Dan

[barbwirebi]

Jeff & Dan

I'm still in the conception phase of my router design and don't really know what I exactly need yet. But I could not pass on this deal!
I bought five.
Guees this resolves my Stepper versus Servo Issue

So how much can I expect to pay for encoders?(.001 resolution)

I want my router to handle 4' x 8' sheets of 3/4" MDF
If I slave two motors together do you guys think I will have enough torque to move a (aluminum)gantry along @ 60 IPM
cutting .500 depth of cut in MDF?

If thesse motors cant do it, perhaps I should build a small mill first.


Thanks in advance
This is a great forum!!
Barbwire Bill

[arvidb]

Originally posted by Dan S
If your using belt drive isn't it better to hook the encoder to the screw, and not the servo?

-Dan

You might get problems with chasing if you hook the encoder to the screw, unless you have a backlash-free coupling between motor and screw.
I.e. the servo driver sees a position error and commands the motor to compensate, the motor compensates and then the position error changes sign, and the motor has to compensate in the opposite direction. This is normal with servos but if you have backlash between motor and encoder the motor will beat back and forth; you will get nasty vibrations and it might overheat the motor.

Arvid

[HomeCNC]

I use USdigital encoders on my servo motors. I get the E2 with a 250 CPR wheel. They work great with the G320 drive from Gecko. The cost of an E2 is $36.00 each. That would make these servo motors cost under $50.00 each. Not counting the machining time needed.

[barbwirebi]

(Post #5 )

Jeff

I want my router to handle 4' x 8' sheets of 3/4" MDF
If I slave two of thesse motors together do you think I will have enough torque to move a (aluminum)gantry along @ 60 IPM
cutting .500 depth of cut in MDF?

Should I build a small mill first?


Thanks
Barbwire Bill

[HomeCNC]

I have an aluminum gantry router using one of my 430 oz/in servo motors belt driven at 2:1 ratio. I am using .2 pitch ball screws and can move my gantry at 200 IPM rapids. Cutting at 60 IPM .5 deep should be fine if you keep the spindle RPM high and you are not trying to do this with a large router bit like 3/4"

I need to do some testing of these 'Cheap servo' motors against my new ones from Poly-sci. My new motors are a bit longer and are 1/2 pound heavier.

[barbwirebi]

Thanks Jeff

I was planning on using the example that "Mariss" gave
.2 pitch with 4:1 reduction
I would be happy with 125 IPM rapid
I also would like to use the "Timing Belt " concept for x,axis drive
But I dont know how much thrust it would use to run with no load.

Thanks
Barbwire Bill

[Snipes44]

Hey Jeff, just curious if you ever got a round to doing some test on the 'cheap servos' ? Was thinking about picking up a couple. Hard to pass up at that price.

-Wes

[mjse]

Hi Dan
What is web address of "gecko forum " .
Thanks