Servo with or without transmission

[ejkoeze]

Hey there,

I'm scavanging for stuff to build myself a router. I want to be able to mill at least aluminium. I've drawn up a nice concept in AutoCAD and started to get the required materials. The concept is such that at first I will use the skate bearing liniear bearings and have the possibility to upgrade to THK style. The frame will be all aluminium (60x60x4mm) and the machine will me a moving gantry. I plan on using a Kress 900w router as a spindle.

Last friday a visited my local scrap dealer (as I do about once a month) looking for stuff I could use (read THK style rails). I asked If he had any steppers and he showed me a room I hadn't been to before and it was loaded with all kind of actuators. Big motors, cilinders, etc...

Wandering about in it I stumbled upon a pot of gold. There was a large bucked full of bearings, pulleys and 5 large servo motors.

4 Dunkermotor 63x55 with planetary gear box 7:1
2 with brake and encoder 500cpr (one encode busted beyond repair)
2 without brake but with encoder 500cpr
1 Dunkermotor 55x30 with planetary gearbox 7:1 with encoder.

At the moment I'm cleaning the motors and I'm inspecting them. I'm also replacing the power wires as those morons cut the too short. I've run the motors on 34V and they run very smooth. Gearbox is silent and has almost no play in it.

I play to use 2 of the larger motors for my x and y axis and the smaller one for the z. That way I have to two largest axis (1200 and 500mm) with the largest motors. The Z axis (300mm) will be the lightest axis of course.
The two remaining motors can then be used to cnc my lathe in the near future.

What would you guys do.
Is this a good plan or should I give the Z axis the same motor.
Would these servos have enough power to drive a lathe with 500mm between centers. Would you use them with or with gearbox.
Any other advise. I plan to build the servo controller that is being developed at www.cncecke.de under forum Elektrik. This controller is roughly based on http://elm-chan.org/works/smc/report_e.html .

Erik Jan

[2muchstuff]

Congradulations on your finds. I think it is great that you are able to "recycle" someone's trash. I tried to get some info on those motors but my German is quite rusty. That's too bad because because that forum looks interesting. From what I could make out, you should be able to use the motors as you first planned, 2 large and one small. Even better are the attached gearboxes, it will save you a lot of construction time. I would remove the brakes, that would be more hassle than what it's worth.

The motor drive circuit looks promising. Isn't it a serial input, I'm only familiar with parallel inputs, would there be any problems with software compatability to make the drive work. I ask this because I've found a couple of nice stepper drives but they are rs232 input, I'd hate to pass on this deal if I don't have to. I do like the display board idea though, that's cool.

[ejkoeze]

The driver accepts a step/dir signal like any stepper driver and can be controlled as such. The serial port is used for setting P I and D valeus for tweaking your driver / motor combination.

I had a little visit there again today and found another one, even bigger that the other 4 the Dunkermotor GR 80x80 with a max torque of 1250 oz inch !! (885Ncm)
It's got a tacho attached but hey, we've got ebay.

I think I may put this one on my X-axis without a transmission (its fitted with a worm gear 1:20). Then I can have fast rapids and mill along the x-axis and step over to along the y-axis if you know what I mean.

I've attached two pics showing my finds.



EJK

[2muchstuff]

I bet you feel like a kid in a candy store and the sad part of it is that it has been sitting there all along right under your nose. Now if I could find a scrap dealer here in town like yours, I would be set. Is this just a scrap metals place or a scrap in general kind of place. Maybe if shaft sizes are the same, you could remove the tachometer off one and replace it with an encoder from another.
The worm drive one would have to be connected to a 2 or 4 start leadscrew due to it's high ratio (20:1) to get any kind of speed out of it, if there isn't too much backlash.