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Robin Hewitt
30-05-2009, 01:10 PM
I see they have a NEMA34 3.5Nm Hybrid stepper on special offer at 34.95 inluding tax

I could use that if I sawed the shaft off the back.

Unfortunately there is no torque/speed curve, what a surprise, so you can't tell if it's a wonderful thing or a total lemon.

They don't have a contact email so you can't ask for more info, OTOH, at that price I suppose I could suck one and see.

Can't decide.

Should I be bothered? I mean they're not exactly trying. Maybe I should wait until it arrives in "Clearance bargains", then 'phone and negotiate for 3 :joker:

Robin

John S
30-05-2009, 01:33 PM
Because as Gary says it all depends on what driver and what power supply you use.

If someone does publish a torque speed curve then how do you know it's for that motor? You buy it and how can the average Joe test it ?

.

Robin Hewitt
30-05-2009, 03:26 PM
You're right, I have to wait until Gary has the equivalent Changzhou motor back in stock. Any data is better than no data :beer:

Gary
30-05-2009, 04:05 PM
Buy it, the price is good, and the current is the same as the ones we do, so they should perform about the same.

It will be 3A in series and 6A in parallel.


You're right, I have to wait until Gary has the equivalent Changzhou motor back in stock. Any data is better than no data :beer:

Robin Hewitt
30-05-2009, 08:03 PM
Buy it

Yes Sir, I bought 3 Sir, got free shipping Sir :eek:

Cost me 91.17 after I knock the VAT off what I owe darling Alistaire.

I'll let you know if it was a bargain when I find out how fast they can turn my little handles before clacking out :whistle:

irving2008
31-05-2009, 12:32 AM
Yes Sir, I bought 3 Sir, got free shipping Sir :eek:

Cost me 91.17 after I knock the VAT off what I owe darling Alistaire.

I'll let you know if it was a bargain when I find out how fast they can turn my little handles before clacking out :whistle:What are you going to use them on, Robin? I'm wondering if i should get a set too on the anticipation of CNC'ing my mill.... even tho that might be a year away.... but the price looks good and I'm sure they wont get cheaper (as a rule)

Robin Hewitt
31-05-2009, 09:42 AM
What are you going to use them on, Robin? I'm wondering if i should get a set too on the anticipation of CNC'ing my mill.... even tho that might be a year away.... but the price looks good and I'm sure they wont get cheaper (as a rule)

I'm going to try them on my mill, see if I can get the G00 speed up a bit. I've got 40v drivers in there at the moment, top speed is 10mm/s so I run it at 6mm/s to be safe. If it looks hopeful I'll uprate the drivers. With the extra oomph I could, theoretically, halve the pulley reduction and make it zippy. I'd like 20mm/s but more would be nice.

John S
31-05-2009, 01:27 PM
On the X3 kits we used to do we used the type 23's triple stack 312 oz/ in ? driving 5mm screws direct.
Running on the big drives at 72 volts we were getting between 2000mm/min and 2500mm/min in rapids so in mm/sec that's 33mm/s to 42mm/s
However that's far too fast for a machine this size and we used to modify the XML so they maxed out at 1500mm/min in X and Y and 1200 mm/min in Z

On the test machine we nearly got 4000mm / min in X before loosing steps, this was just done to see where the limits were and not dick slapping.

Often times you can get more speed out of smaller motors than larger because of the initial acceleration.

I have a big rotary table powered by a 42 stepper and it crawls round in comparison to my 6" table. On the last Bridgeport BOSS1 I have done I took the original type 42's off, rated at 1100 oz/in and replaced them with 34's rated at 920 oz/in and the speed nearly doubled because of the efficiency of the newer squarer motors and better magnets than the old outdated round ones.

.

Robin Hewitt
31-05-2009, 02:12 PM
I currently use a 16t:40t pulley combination with a 1.2Nm motor.

The 5:2 reduction gave me a convenient 200 half steps/mm.

The gutsier motor should allow me a 5:4 reduction thus halving the motor speed and keeping me in the motor torque band, hopefully.

The screws have just under 10um backlash so a 10um half step may be the way to go, approx 0.0004".

I could go for a whacky step resolution, all the software does is take the required X, Y, Z in millimeters, multiply by steps per mm, round it to an integer and off it goes. Any value for steps/mm is okay, I just change the SPM variable, recompile it and everything sorts itself out. The only thing I would lose is convenient cogging on the handle dials.

I cut the cheeks for the Z axis yesterday and it came out oversize, everything bent under the tool side pressure when I removed the last 0.5mm on the finishing pass. I got +35um in the X and +55um in the Y, give or take 10um. Probably would have got a lot better if I'd repeated the pass. This is so much better than before I changed screws, it used to be that within 200um was a good day :beer:

Gary
02-06-2009, 10:48 AM
The Datasheet is wrong, they say that the current is 3A in series and 4.2A in parallel.
This cant be right, also the holding torque is different in series to parallel.
I think they are getting confused between unipolar and bipolar.

Also a 10mm shaft is a bit small, but that is not a real problems.

I suspect the motors are surplus.






I'm going to try them on my mill, see if I can get the G00 speed up a bit. I've got 40v drivers in there at the moment, top speed is 10mm/s so I run it at 6mm/s to be safe. If it looks hopeful I'll uprate the drivers. With the extra oomph I could, theoretically, halve the pulley reduction and make it zippy. I'd like 20mm/s but more would be nice.

Robin Hewitt
02-06-2009, 01:20 PM
The Datasheet is wrong

Now you look at the datasheet when I have 3 of them sitting on my desk :joker:

I did notice the discrepancies, but I have low expectations of rhyme or reason when looking at stepper specs. May be okay, may be lucky they were cheap :rolleyes:

I'll let you know

Robin

Gary
02-06-2009, 01:38 PM
I dont think you will have any problems, it is just because AU know little about stepper motors, and have not put the correct info on the datasheet.
Run it in series first at 3A and then try in parallel at 6A, and monitor the temp.


Now you look at the datasheet when I have 3 of them sitting on my desk :joker:

I did notice the discrepancies, but I have low expectations of rhyme or reason when looking at stepper specs. May be okay, may be lucky they were cheap :rolleyes:

I'll let you know

Robin