DIY Brushless Motor Spindle

Hello everyone,

First, let me point out where I got the original idea from.

Diy brushless spindle

I would highly recommend a read through if you are contemplating doing this as well.

I have decided that I want to build my own spindle for my desktop cnc. I am trying to keep it as economic as possible while still being fairly quiet and able to light milling on aluminum, wood, and plastics.


Here is the basic design for your scrutiny. All constructive criticism welcome :)

Basic Features:
ER16 10x100 mm straight shank collet chuck
ER16 10MM X 100MM STRAIGHT SHANK COLLET CHUCK #L27

2 Angular contact bearings
7000B Bearing Angular Contact 10x26x8 Ball Bearings

Brushless Motor

Turnigy 63-54-A 250Kv Brushless Outrunner
same as: XYH63-54

The chuck is mounted directly inside the motor housing, replacing the original shaft.


My current questions are, does anyone know of a US vendor that I could that brushless motor from? I have only seen 1 british and 1 french. Or even know of other brushless motors that features a 10 mm shaft ?

If I go down to an 8mm shaft, my motor options dramatically increase but that makes finding decent 8mm angular bearings hard to find. Also, ER16 chucks with an 8mm shaft have a higher run out.

For the bearings, do you think shielded bearings are worth it? I feature them in my drawing but the linked ones are not. I figured if I used shielded, then I would not have to worry about incorporating a labyrinth seal. I plan on having the bearing - housing fit be a light press fit. I have read that bearings come with a loose fit for the inner shaft.

There was also a thread going on here.
http://www.cnczone.com/forums/genera...tors_used.html
Al.

yes, there are USA made brushless servos. beside 10mm shaft, what other specs you looking for?

I don't see any means of preloading your A/C bearings.

bob

Quote:

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Originally Posted by rowbare

I don't see any means of preloading your A/C bearings.

bob

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If the spacer is machined correctly, shouldn't that apply a preload?

Quote:

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Originally Posted by mike_Kilroy

yes, there are USA made brushless servos. beside 10mm shaft, what other specs you looking for?

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I'm not entirely sure, I as I have just begun researching them and am currently basing my choice off what other have used. The one I chose is:

Input Voltage : max. 37V (10S Li-po)
Kv : 250 rpm/V
No. of turn :14 Delta
Max. efficiency current : 50A
Current capacity : 65A/60s
Internal Resistance : 59 mohm
No Load current @ 7V: 2.16A
Number of poles/magnets : 14

Quote:

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Originally Posted by Al_The_Man

There was also a thread going on here.
http://www.cnczone.com/forums/genera...tors_used.html
Al.

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Thank you, I'll give it a look.

Quote:

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Originally Posted by cncEnthusiast04

If the spacer is machined correctly, shouldn't that apply a preload?

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Not as drawn. Your inner races are floating on the spindle shaft. The bushing you have keeps the outer races apart but that does nothing for the inner races. You need another bushing to separate the inner races and you need a nut to hold it tightly in place. The preload will come from the difference in length between your outer bushing and your inner bushing. Which of the two is longest will depend on if you are mounting the bearings back to back or front to front.

bob

Quote:

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Originally Posted by cncEnthusiast04

......I have just begun researching them and am currently basing my choice off what other have used. The one I chose is:

Input Voltage : max. 37V (10S Li-po)
Kv : 250 rpm/V
No. of turn :14 Delta
Max. efficiency current : 50A
Current capacity : 65A/60s
Internal Resistance : 59 mohm
No Load current @ 7V: 2.16A
Number of poles/magnets : 14

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ok, so turning this into normal motor data, you are looking for:

Kv=4V/Krpm
Kt=0.067nm/amp (pretty whimpy motor!)

so .067nm/a*50a= 3.3nm continuous torque rating
and if 37v is some max voltage, this puppy will go a max 37v/(4v/krpm)=9,250rpm.....

Not very efficient design..... such low voltage and high current means lots of losses..... I just had a very similar motor designed (10 pole - needs 600hz for 6000rpm - over most drive amplifiers max, let alone 14 pole and 9000rpm) and built for a space station camera application and its efficiency is horrendous. the motor inductance is soooooooo low (27uH), no drive can run it without external inductors, which then cause the voltage required to go up very significantly, so with all the losses, you will probably end up needing 100v bus and loose 1/2 the power in heat in the inductors..... are you open to more reasonable design? if so, what are you really after (torque, speed, physical size, hp ratings)?

so it is rated 50a*1.73*37v=3.2kw or 4hp

1) So you want about 4hp motor good for 8-9000rpm max speed? is this the spec you are after?
2) If so, what is physical size limits? can it be 10" dia x 30" long?
3) is it to be frameless (rotor/stator set)?
4) does it need feedback or will you provide that?

If you add this kind of detail there will probably be a lot more than just me who can give you a list of possible USA manufactures.

Quote:

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Originally Posted by rowbare

Not as drawn. Your inner races are floating on the spindle shaft. The bushing you have keeps the outer races apart but that does nothing for the inner races. You need another bushing to separate the inner races and you need a nut to hold it tightly in place. The preload will come from the difference in length between your outer bushing and your inner bushing. Which of the two is longest will depend on if you are mounting the bearings back to back or front to front.

bob

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douh! of course it needs an inner spacer. However, wouldn't the flanges in the housing and on the face plate, once bolted together hold everything together tightly? If not, how would you recomend adding a nut to hold it together?

Quote:

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Originally Posted by mike_Kilroy

1) So you want about 4hp motor good for 8-9000rpm max speed? is this the spec you are after?
2) If so, what is physical size limits? can it be 10" dia x 30" long?
3) is it to be frameless (rotor/stator set)?
4) does it need feedback or will you provide that?

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I'm open to any design, so suggest away!

The machine that I would be fitting this spindle too is rather small at just over 15inx15inx20in and currently uses a dremel tool so size was the major reason for heading this route as this particular design is only about 1.75 x 5in. I was also looking for an alternative that is considerably quiter than a dremel as I use it in my apartment at the moment.

I'm not expecting/trying to mimic full size cnc's but I would like to be able to do 3D profiling and engraving with aluminum. I plan on providing my own feedback and the motor can be either frameless or not. Feedrates will be pretty slow as well.

As far as for actual numbers. The bearings I have selected along with the arrangment will be rated to around 14000 rpm so around 10,000 rpm should suffice. I would like to keep the overall size to under 4x10.

so a complete motor upto 4" dia x 10" long, good to 10,000rpm?

how long would it run? is a DC BRUSH motor an option?
I should also have asked for price point: you can get a frameless motor say 2"dia x 1" long that would prob output 2x that torque to 10krpm - from some places for around $ 1000.00 - out of the range? If so, what is the price range? Keep in mind you also will need a servo drive to run it and that too can cost perhaps $ 300-1000....

Ah price point. Well to put things into retrospect the current cost is:
$75 for motor
$12 for 2 bearings
$50 for collets and chuck
$60 for motor controller and power supply

So i'm looking to keep it around $200 for everything all together which is way below the option you suggested. Unfortunatlly my machine is not worth spending that kind of money on for just the spindle.

the guy did a good job in the first link first post looks wise. I wonder what kinda runout you can achieve with this. This is the most critical part. ALso, how much heat and noise do those things generate anyway? I assume a lot in both cases?