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[geoff p]

I have a little MJ189 lathe on which the motor is rated at 100 watts.  It has just two speeds.

A "proper" variable-speed motor and controller would cost an arm and a leg so....

I've been kicking around the (probably daft) idea of using a model-type brushless motor and speed controller, with an Arduino to supply the servo pulses.  These brushless motors seem to provide oodles of power - 680 watts for $12.35 from Hobby King etc etc.  Obviously, it would be geared-down, as is the present lathe-motor.

Problem:  what on earth do all the battery "codes" mean?  What is a 3C or a 3S battery?  A discharge-rate of 40C tells me sweet nothing towards matching the ESC, which I just happen to have had for years and never used, whose label says "xp.35A-SW", and "xxxx17V"  The xxxx is unreadable where the label is scratched from being in the junk-box for a long time.  (35Amps x 17Volts = 595 Watts, which is massively more than my present 100W lathe-motor.)

I'm pondering using a couple of motorcycle batteries (12V) in parallel to give the current, they are much cheaper than NmMLipo hows-yer-father's Nicad, and space/weight is not a problem in my house, near a lathe.   I could hook a charger to it permanently.

But ... can one run brushless-type ESCs and motors off a lead-acid battery?
Geoff,
Thailand

[boatmadman]

Nice little project and there is no reason it shouldnt work.


Codes etc: start with the motor, a 4 number code tells you the can diameter and length. EG 3650 is 36mm dia and 50 mm long. From what you say it looks like the max current of the motor is 35a. and max voltage is 17v. What you havent been able to identify is the kv rating, this tells you the max revs the motor will spin at per volt supplied. The desired rpm will of course be controlled via your arduino.


Battery: 3s is the cell count and tells you it is a 11.1v battery, each cell being nominally 3.7v. The 40c discharge rate is the maximum current the battery can supply, where c is the battery capacity. So, a 2000mah battery with 40c can potentially supply 80a.
The 3c is the safe maximum charge rate for the battery, and in the above example would be 6a.


There is no reason why you couldnt use 12v lead acid batteries - or any other type of battery for this application.


Good luck.


Ian

[essex2visuvesi]

rather than mess about with an arduino, why not use one of these?

http://www.ebay.co.uk/itm/Servo-Tester-/151266826563?pt=UK_ToysGames_RadioControlled_JN&hash=item2338349943
simply connect the esc to it and bobs your uncle, turn the knob to increase the speed
I would agree with boatmadman, Lead Acid batteries would probably be more suited to this application.
No reason why you couldn't use a 12v bench power supply either (unless of course you want portability)


I used the ESC from a 500 class RC helicopter as this gives a soft start option which increases the motor speeed at a fixed rate no matter how quickly you wind it up the motor will only accelerate at a fixed speed, thus reducing current draw and reduces wear.


I have done this exact mod to my Unimat classic "toy" lathe and its made a huge improvement in performance.

[geoff p]

Many thanks, guys. 

As I said in OP, motorbike batteries are cheap-enough over here, and hopefully, if they can provide current for an electric-starter, they can manage the odd occasion when I need full-whack from the lathe.

Essex, what motor have you put on your Unimat?  Is the performance good at low-speeds?  Your idea of using a Servo Tester is brilliant, and cheaper than an Arduino.  Could I beg of you, some photos of your Unimat installation?

Ian, I did wonder about using a bench power-supply but balked at the 35A to 60A that these motors seem to like, which is why I'm thinking Lead-acid batteries and keep a charger hooked on to them.

Thanks again,
Geoff

[essex2visuvesi]

I'm using a 17.5T 3650 sensorless brushless motor from a 1/10 RC car, wired to a Hobbyking 60A Helicopter ESC


I'll post up some pics but theres not much to see really, the esc is fitted in a project box with a PC Fan on top to aid cooling, the motor fit perfectly inside the stock casing.
http://www.hobbyking.com/hobbyking/store/__28369__Hobbyking_YEP_60A_2_6S_SBEC_Brushless_Speed_Controller.html

[geoff p]

My brain (???) hurts.  I've ordered a servo-tester from Hobby King and meanwhile I've started playing.

I've bought a 12V 5Ah sealed lead-acid battery, and pulled an Arduino from another project.  Programmed the Arduino from the "servo" examples and got my (unmarked, unknown) outrunner motor running, and responding to a potentiometer.  It don't 'alf gallop at max-speed!

From applying 12V-power to the ESC, it takes 50-seconds of beeps and sing-a-songs before the motor will actually spin (it was about the same with my 27MHz Tx and Rx before I started fiddling with the Arduino.)  Is this normal?

I notice that at low-speed there is hardly any torque - I don't know about it at high-speed, 'cos it burns my fingers!
According to Hobby King, outrunners give better torque whereas inrunners are good for high-speed.  But high speed is the last thing I want on my lathe.

So, next question Essex: how did you couple yours to the rest of the drive system/belts etc?  Do you use any extra stages of reduction between the motor and the lathe's original drive?

Sorry, chaps, I am all questions.

Geoff,
Thailand

[essex2visuvesi]

Mine was a direct swap for the installed mabuchi 540.  Its a 21.5T (Meant for RC rock crawlers) brushless so its only 1800Kv but at 12V that its only about 1000 or so RPM more than the motor it replaced, however the increased torque is noticable and makes the machine far more useable.
this is what I have... it's only a toy really, and I will upgrade at some point when pennies allow
http://www.thecooltool.com/produktgruppe.php?language=e&status=20&sh_id=15&ptitel


If you are looking for torque over speed then a low KV brushless outrunner aimed at helicopters would be a good starting point

[nick_75au]

You probably want to go for a largish low KV outrunner on higher voltage, the original lathe motor probably had a max RPM of 2500, a 100 to  150  Kv motor on 24 volts would be the go or gear down a smaller higher KV motor to an output speed similar to what the original motor was/

[More Coffee]

Cant you get your hands on a AC motor controller , like for a table router?

http://www.ebay.ca/itm/AC-or-DC-ELECTRICAL-MOTOR-VARIABLE-SPEED-CONTROL-TOOL-/121279314983?pt=LH_DefaultDomain_0&hash=item1c3ccf7c27

May have to poke around at some hobby wood working shops, but it would be a lot less invasive than pulling apart the lathe.

It just goes inline with your power chord.. 

And you still get to use the gears.

[More Coffee]

Worse came to woreser ..ifthatseven a word.

Hit the garage sales for a variable speed router that works. just use the guts to power your lathe.

[geoff p]

Thanks, guys, for all your suggestions.  So far, what we have is:

My present motor (110V, 100W, Brushed) is about 4inches (100mm) diameter, with a multi-step drive pulley on its 8mm shaft.  The smallest diameter is about an inch and the largest is about 2-inches. I think it runs at about 4,000 RPM.

Essex2visuvesi's lathe takes a tiddling 500/550-size motor

More Coffee's speed-controller would be great except for two things: 1/ Postage & customs duty will double its price, to more than I'm willing to pay for something that 2/ will provide little torque at low speed (Past experience!)

Nick's suggestions of a Large, Low KV motor are on the right track, I just have to track one down.

Meantime, I've found that multi-vee (poly-vee) belts (originally for a power-planer) transmit much more power than the original O-ring type of belt-drive.  So I'm in the middle of making a whole rake of pullies for a Myford ML7-style of drive, using Poly-vee belts.  Hopefully that, together with a variable-speed motor will get me some decent torque at low-speeds.

Geoff
Thailand

[More Coffee]

I have a Chinese 10x20,also known as a 9x19

Low speed torque isn't a problem , belt changes ,

The problem is the clutch has to be reworked ,it slips way to easily.The dentents for the balls are to shallow and Ive managed to get lubricant in the clutch. It has to be torn down cleaned and modified with deeper detents and heavier springs.
 high speed low torque , is no problem , unless Im trying to part off.
Currently , the motor draws to much current for the donor variable speed router
I do plan on getting two of the controls , one for my lathe and my mill.

Should be an interesting assignment,converting a lathe. Could you post pictures?

[Jon]

Hi Geoff,

Just a point to add, you say your original motor is brushed. I assume it's currently running on AC?
As it's a brushed motor, it will run on DC also. It's called a universal motor.
So another option is just PWM DC directly to the motor to turn your current setup in to variable speed.
All it would take is a largish FET, a few external components and some control from one of your micros.
You could even use a chip like a SG3524 to control it with a knob.
If you'd like any more info, just PM me, or post back.
Rgds
Jon

[geoff p]

Jon,
Though my original motor is DC, and brushed, it's not a universal type: the original switch-box contained diodes to allow for running from 110V AC-mains where I bought it in Taiwan.  (Unfortunately, I bought quite a lot of electrical stuff while I was working there, so now, in Thailand on British-style mains, 240V AC, I have several hefty transformers  to run that stuff.)

For a year or so I was running the motor through a system very similar to your description but it suffered severely from lack of low-speed torque, so I've recently been improving the belt-drive to offer more range, whilst running the motor at full chap.  I did manage to stall it today, on a brutal cut.  My own fault!

However ...  as mentioned before, ages ago I bought an "Outrunner" brushless motor + driver, whose only markings are "35Amp".

Struggling to get a home-made (15cc) engine to start, I Jury-rigged the motor to the engine, using the Hobby-King servo-tester as a speed-control and a sealed lead-acid 12v motorbike battery.  To my surprise, this little motor actually spins the engine, and turns it against compression (and backfires) even at a low speed-setting. 

So perhaps a larger/stronger brushless motor would do for the lathe - especially with the improved belt-drive.

Regards,
Geoff
Thailand