Sunday, 22 August 2010

Step by Step

After taking some calming medication to bring down my excitement, it is time for a test setup. Who would own an Arduino and stepper motors and leave them in the cupboard? Impossible !

Basically, the chain of command is PC >> USB >> Arduino >> G251 >> Stepper. Nothing fancy, no complex programming, just a simple constant step rate. A simple program creates one half-pulse per millisecond (wait for getmillis() to change, then toggle output, stir and repeat).

I added a current-limiting 1kOhm resistor to the G251 to keep the maximum current down to 1A. At this time I don't intend to drive the stepper at high power and I didn't want to take the time to connect the G251 to cooling fins, which you'd need at 3.5A.

The main challenge actually was to find the right cables. I realised that all my electronics cables are of the 'tiny' sort. In the end, an old power cord had to be sacrificed as a trip to Jaycar would have taken too long.

The image below lets you see the beauty of the very first setup. Prizes can be won if you can tell if the stepper motor is actually moving at the time the picture was taken. Yes, the Arduino program is loaded and running. It's a technical challenge, not a trick question.

Arduino, G251, and Stepper in action...

With hardware at hand a large number of new sub-projects await...
  • Write a proper interrupt-driven driver routine for the Arduino.
    • Learn the guts of the Arduino "operating system"
    • Learn the finer details of the Atmel microcontroller.
  • Investigate G-Code programming on and Arduino. Some people have done some of it, but I may want to start from scratch - just because I can.
  • Create a construction plan for the cnc router. There is one in my head, but that ain't enough.
  • Put it all together (I almost forgot)

Saturday, 21 August 2010

Electric Christmas

Stepper motors, drivers, breakout board and power supply arrived in the mail. I can't wait !

Delivery from ausxmods was quick. I had made the eBay purchase on Tuesday night and the package arrived Friday morning via registered mail through Australia Post, strangely, without a request for signature despite this Australia Post claim. Ummmh.

The items were well packaged, and everything promised was in the box. Notably, there is no documentation.

Nicely packaged, but small for the money :-) ...

3 Stepper motors and drivers in sight. PSU at top and breakout board at right. A first glimpse at what will keep me occupied...

Unloading the goods...
PSU, stepper motors, drivers, breakout board.

48V, 8.3A Power Supply. Made in Sep 2009.

The stepper motors are from MS-Motor. Their web site does not list that particular type number, nor any torque graphs. I guess the time of theoretical discourse is over and we'll just have to see how things work out.

A few months back I had contacted MS Motors directly for a quote. While the stepper motors were cheap (USD27 for a 24H290-28-4A), they had pretty steep shipping rates (USD98 for 3 motors) and I wasn't sure about warranty, insurance, shipping time frame. So, buy from your local importer...

And since you asked, wiring goes Black (A+), Green (A-), Red (B+), Blue (B-).

Stepper motors manufactured by MS-Motor.

I won't need the breakout board since I intend to go through my Arduino, but it might come in handy as a fall-back. It's well-designed, and surprisingly carries the copyright of Homann Designs, a company in Victoria, Australia.

The breakout board is (c) 2009 Homann Designs.

Finally, the GeckoDrive Gecko G251. Tiny, but well-designed. I'll be exciteeededeeeeed to see its top-speed. Documentation can be found here (pdf).

The Gecko G251 Driver by GeckoDrive.

Stop blogging now! Time to find that Arduino and get started.

Wednesday, 18 August 2010

Steppers, Drivers, PSUs

As the regular reader might remember, I already own shafts and bearings, and an Arduino microcontroller, but am still in need of stepper motors, drivers, and power supplies.

Based on a delicate combination of advanced mathematics and wild guesswork, I decided to target a 48V power supply, and NEMA 23 stepper motors with around 1.6Nm to 3Nm torque and matching ideal voltage near 48V.

So, after an afternoon browsing on eBay and various web shop fronts, I had put together a list of potential stepper motors. The decision parameters are...
  • Torque between 1.6Nm and (preferrably nearer to) 3Nm
  • Ideal voltage to be near 48V (calculated as 191 x PSU Voltage / current / induction in mH)
  • High corner speed (calculated as 32 x sqrt(mH))
  • Low price (the table shows single motor prices including shipping in AUD)
  • and perceived vendor support and reputation.
And the candidates are...

CompanyMotor/LinkTorqueCurrentPriceRInductanceUidealCorner speed
greynurse2001 eBay24H290-35-4B2.7Nm3.5A$71.91Ohm2.8mH54V936rpm
greynurse2001 eBay24H290-28-4B3Nm2.8A$64.91.4Ohm5.6mH76V585rpm
greynurse2001 eBay23H276-28-4B1.9Nm2.8A$56.51.2Ohm4.7mH69V697rpm
Zapp Automation LtdSY60STH88-3008BF3Nm4.2A$75.170.65Ohm3.2mH57V682rpm
Zapp Automation LtdSY57STH76-3008B1.9Nm4A$54.690.5Ohm1.6mH40V1433rpm
Keling282 OZ-IN2Nm4.2A$60.850.46Ohm2.2mH47V992rpm
cnccomponent eBayno code2Nm3A$52.231.2Ohm4mH64V764rpm
cnccomponent eBayno code3Nm2.8A$72.691.5Ohm6.8mH83V482rpm
easycnc eBay57J18802.2Nm4A$85.530.7Ohm1.8mH43V1273rpm
easycnc eBayno code2.7Nm4A$98.530.7Ohm1.8mH43V1273rpm
savebase eBay57BYGH76-401A1.9Nm2.8A$68.21.13Ohm3.6mH61V910rpm
yuntat eBay57J18802.2Nm4A$79.740.7Ohm1.8mH43V1273rpm

Similary, I put together a list of potential drivers, considering: "effective" voltage, as opposed to the often advertised maximum voltage (smoking can kill); vendor reputation, and price. The contenders are:

SrcEffective VMax VCurrent ACost+Ship in AUDURL/IDComment
verycnc - ebay?605224.95CNC 3 Axis, 60V/5.0AIncludes breakout board; microstep to 1/256
verycnc - ebay?605277.76CNC 3 Axis 60V/5.0A IIHas better breakout board than above; microstep 1/256
www.GeckoDrive.com48V503.5263.03G251Offers midband resonance, step morphing, recirculation mode, U.S. made.
Zapp Automation Ltd?404.2377.32PM542Excludes shipping; microstep; goes with 40V PSU in kit. Max Voltage is 50V. At web site GBP44; on ebay gbp56.87; used shipping and item charge from ebay GBP15
Zapp Automation Ltd48V755.2262.5PM752Excludes shipping; "Typical 48V" ! Output current 3.7rms; current 2.8A 3.5A 4.2A ...
Keling Inc68V908.2433.44KL-9082Excludes shipping;
Keling Inc68V807.8399.84KL-8078Excludes shipping; typ 68V
Keling Inc48V605.2292.15KL-6852Excludes shipping; typ 48V; 3.7A rms
Keling Inc48V806302.23KL-8060Excludes shipping; typ 48V; current 2A 2.57A 3.14A 3.71A 4.28A...
Keling Inc36V505.2328.16KL-5056, KL-6056
Keling Inc48V605201.43KL-6050Excludes shipping; half and 1/8 step modes; Typ 48V; current steps are 1.5 2.0 2.5 3.0 3.5...
Keling Inc36V504.2235.03KL-5042Excludes shipping. Typical 36V; 50V is abs max
Wantai Ebay?808.2339.5SD-2H086MBInc. Breakout board; CNC Control Kit for 3 Axis Stepper Driver,80VDC/8.2A ; shipping is estimated. looks like KL-9082
cnccomponent ebay?605218.34CNC 3 Axis 60V/5.0ACNC 3 Axis Stepper motor Driver ROUTER,MILL , 60V/5.0A
cnccomponent ebay?605.6301.28KL-6056Brand New Three Axis Stepper Motor Drivers, 60V/5.6A
cnccomponent ebay?806301.22KL-8060C25Three Axis Stepper motor Drivers, 80V/6.0A, inc breakout board
cnccomponent ebay48V605210.45KL-6050Three Axis Stepper motor Drivers, 60V/5.0A, inc breakout board
Homanndesigns.com48V503.5222.99G251Assume pickup, hence no shipping Shipping
yuntat?505.6275.07KL-6056 equivalent ?
yuntat48V807.8350.112m982 equiv KL-8078 ?Current regulation steps are wide (1.8 2.5 3.5 4.3, ...)

Without going into great detail about the subsequent analysis, which was supported by copious quantities of strong espresso, the deal maker was a currently offered kit from (greynurse2001 on eBay). It consists of Gecko G251 drivers and 2.7Nm stepper motors.

The stepper motors offer good torque and a higher corner speed than the similar 3Nm steppers. Plus, I had been watching the store for a number of months now and they have a 100% positive rating on eBay.

The kit comes with a 1 year warranty. It ships from Sydney within a few days and everything comes in a single package all at once. I could probably have shaved $60 off the $529 inc shipping, but I would have had to use several vendors and may have had to wait longer.

So, decision made, money well spent:
  • 3 x Stepper motors 24H290-35-4B; 2.7Nm, 3.5A, 2.8mH, Uideal 53V, corner speed 936rpm, dual shaft.
  • 3 x Gecko G251 drivers
  • 1 x Power Supply 48V 8.3A

Please Mr. Postman...


It's been a while since my last post, but I am well prepared with a list of totally believable excuses..
  • Busy at work, meeting unreal deadlines
  • Went to Europe for 7 weeks
  • Wife and girlfriend didn't get along -- again!
  • Garage too cold in winter
I promise my next and very productive post will be published shortly...