Power supply
 

Hi guys,

First, sorry my english is not very good so if you don't understand, just ask I'll trh to explain differently!

Okay so I'm building a small CNC machine! I'm doing it the cheap way so I don't want to spend 400$ for the spindle! I've read some forum that you can use RC brushless motor with low kv. So I choose this one :
https://hobbyking.com/en_us/turnigy-aerodrive-sk3-6364-245kv-brushless-outrunner-motor.html

It's a 70A and 37V max motor! At the local electronic shop, they sell 12V 50A power supply and 24V 25A power supply... it's the same power at the end but I want to know if one is going to be better then the other! When I will take a pass with the mill it's gonna take a lots of amp! but I need a good rpm too!

And just to be sure, these are similar to 3phases AC but they can run on AC? need to buy a DC power supply and a ESC?

Thanks guys, hope.you can help me :)

Voltage is also determing the max RPM. That motor says 245kv which means 245 rpm per volt, at 12v that will be arround 2900rpm, at 24v arround 5800rpm.

Yes, you can think of a 3 phase motor but connecting it to a 50Hz 3 phase transformer will only create 50rpm.... You need a brushless ESC and a servo tester to make it work and control the rpm, these systems require a DV voltage.

okay! I understand! I will go with the 24V since a cnc mill need high rpm! The torque will be constant if I change voltage or amps?

As someone who has cnc, router, spindle, ect. I would strongly urge you to buy a spindle.. what your saying sounds great in theory but thats a free spinning rpm. I promise you that under a load the rc setup will not do the job. Even if you got extremely lucky and it worked ut would be sshort lived because the load would generate massive heat and cook the motor/esc. If you are looking for a cheaper option i would drop both ideas and use a bosch router instead. It will do the job nicely for about 125.00.

you are probably right! I might use a old 3hp mitter saw motor! it's 120V AC so cheaper and easier to control for me! I was doing some mecanical calculs and the torque of this super 1hp++ motor is only 12in-# and that will probably not do the job. Even a small bosch will not do it in aluminium! the mitter saw will (I hope...3hp ahaha) thx guys, very appreciate and I will keep you informed! I'll be doing a blog so I'll share the link so you guys can look and maybe it will give you better idea! :p

What you need for a mill is torque, not RPM.

If you have a look at Proxxon type machines (they sell a CNC setup - plug and play with software, etc), you will see they do rely mostly on RPM, but even in their range, the high end machines go down in RPM for a great gain in torque.

This also means you need to choose your tools for the RPM you run. High RPM tools will work but only just, and not in Aluminium (or with great effort and a short lifespan). I know, because I have one of these.

What I would do now, is go for a high power high RPM machine (a die grinder the likes of Makita/Bosch/etc, something professional) and use a V belt setup for the head to spin it down and gain some torque.

Good luck.

The use of a simple brushless motor for a spindle is well known used. Go to several CNC forums and you will know.

http://www.openbuilds.com/threads/br...r-spindle.266/
http://www.cnczone.com/forums/uncate...90495-cnc.html

On the other hand a BL motor, with ESC, servo tester and the total build will cost almost the same as a ready to mount system
http://www.ebay.com/bhp/cnc-spindle-motor

Yeee that's probably what I will do, after some readings of course these have a lot of RPM but this big 2700W motor only got 3in pound of torque, if you run at 80% eff. we can't calculate 100% efficassity because I will have to put a fan on top of it to cool it down! that will slow it and take more amp! and 60A takes a damm big wire too! I'll find a miter saw or someting that have high rpm and that run on AC cause power supply aren't cheap! I'll keep you informed :D