OK - coffee made - where were we?

Hopefully when you've wired them single coil you should see quite an improvement in torque (should be around double). Now ideally (given the spec of your drivers) we'd like to up your voltage from 24V to 30V which I think is the max your driver allows so that we can maintain as much of the the torque as we can while we up the speed. However there's no quick fix to your PS to do that. You could get/build a new PS but frankly you're not going to get much extra for your money. You'd need 48V to double your speed at whatever the current stall speed of your motors is with your new torque (~8in/min?).

So first off I'd get rid of your 3:1 reduction. You'll increase your speed by 3 obviously (~24in/min). But I think I remember you saying you were about to get some new ballscrews? well if you do - consider a larger lead than your current 0.1 inch. In my first post I asked if you really needed the theoretical resolution of your current system. Decide what resolution you can work with and spec your screws accordingly.

So for example - if you go to 1:1 reduction your res will be 0.00016 * 3 or 0.00048. Double your lead and you'll be around 0.00096 - still within a thou. (@ ~48in/min) Anyway you get the idea.

EDIT: I'm just going to throw this in to possibly spoil a nice party - sorry  - You're motors are currently doing up to ~3 revs/sec. With these changes we'll hopefully see that increase. I'm now thinking we'll see how good these Chinese drivers are at mid band resonance compensation. 

Cheers

Ian

Ian

WWWWHHHHJEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE. Not quite the sound of my motor. I'm sorry, I was quick off the mark, having read your post just now - particularly the bit about the meter reading.

No harm done, it would seem. I wired in parrallel and got the motor up to 30 ins per min. I ran through 1/8 to 1/2 steps, but I have ended of 1/8 phase again. I settled on a modest 15 " per min for reliability. This is still nearly four times faster. Even at 20" per min it was good, with only the occiasional stoppage.

I will take heed of your warnings however, and disconnect two of the coils, C and D, and see if it makes any difference. It certainly did so far.

Meter reading for parrallel - 0.7 amps. I must admit I thought this was far too low.

Jim - That's a shame - I bet you could have fried an egg on your drive output transistors. Talk about destructive testing  . You've been lucky - but if you do this again you're running the risk of considerably shortening the life of your drivers.

Right -

I rewired all three steppers - to two single coils, refitted them all.

Great - I can now get 16 in per minute on all axis. This is fabulous - 4 times what I was getting on bipolar series wiring.

This for me is fine. My mill table is only 12" by an effective 10" so I can move any where in 45 secs. In lathe mode the length of the leadscrew is 18" so I can move from end to end in about a minute.

Thanks for the other suggestions, but altering the gearing, which are timing belts is a bit difficult, because I have glued the gear onto the motor shaft, although this would increase the speed. The Z axis I would leave because I want the torque when drilling and it can be up and down in seconds.

The voltage increase is also a bit difficult, because I use a pair of traction batteries to provide a very steady 24 volts.

That leaves the leadscrew, which I will replace eventually, to cut backlash, and I will certainly consider increasing the pitch of that.

If there are any more suggestions thanks - and thanks for the help etc already - a fourfold increase for no expenditure is excellent.

Jim.



 

Jim,

Fourfold increase, excellent and without frying your drives!

Details of my Novamill/Routout drive setup as promised.
Set to 1/8 microsteps
Sanyo Denki 2A size 23 motors 0.83Nm bipolar (four wire) 0.8 ohms/phase, 3.8 mH/phase
Ballscrew 5mm pitch
2.5:1 reduction
CNC4PC C11 BOB
Max speed 2.0 m/min motor speed 1000rpm.
Max Acceleration 383 mm/sec/sec
Mach set at 45kHz an 800 steps/rev

To give you some idea of the friction reduction using ballscrews, with the stepper disconnected, I can push my table by hand and rotate the ballscrew. That would be impossible with a 10 tpi leadscrew and nut. So your idea of fitting a new leadscrew would certainly make a big difference. A Gecko 203V would give you the amps to drive the
stepper windings in parallel, no need to alter your novel power supply. You might be able to reduce the diameter of the leadscrew pulley and use a shorter belt.

Ian

I may get shot down in flames but this is my experience with the need for speed.

First off i bought an all in one system that sells on ebay it goes on about not needing a dodgy printer driver.  But although it has some advantages it just wasn't up to the task. i did a lot of research about cnc "which i should have done first" i found Mach.

I disconnected the drives from the system and tried it on a BOB from cnc4pc every thing about it was so much better in terms of smoothness but i still couldn't get the top speed. More research and i came to an article on the Geko site it mentioned the ratio of voltage supply in relation to motor voltage.

I measured the power supply on my ebay cnc box the voltage was 25 volts similar to you Jim. So Mach was much smoother but i still couldn't get the top speed as the motors stalled.

I sold the lot and bought drivers from Motion Controlled Products "Keling" with 80 volt power supplies and MDS980 drivers.

This setup is fantastic. So my overall statement is more voltage = more speed, more amps = more power you need both.

As this is on a mill I CAN run the motors at 3500mm/min with no stalling BUT i only run it at 2000mm/min max feed rate this gives me a big comfort zone in not missing steps.

I have had to tweak the acceleration as with a larger mass it takes a while to get up to and slow down from speed.

So IMHO Jim you will not get the desired effect from your current setup but i have no idea if 25volts would be OK for a router as the tables have less mass so maybe that voltage is OK then.

HTH
Phil_H

EDIT i have just remembered i did the original test 25V ps and Mach CNC4PC bob, the motor was unconnected on the shaft IE i was only spinning the motor, i couldn't go above 1500mm/min without stalling "Sorry Bad Memory"

So my statement is that For high top speed you need maximum voltage.

That's weird when i first posted i didn't see all the earlier replies so that's why i am somewhat late.

Phil_H

Thanks for the replies - I'll bear in mind the Gecko 203V card if any of my present ones fry. I can put the motor(s) back to parrallel then FLYYYYYYYY.

Hi Jim - I've been doing a bit more thinking on this.

It all comes down to the fact that steppers are generally over driven in terms of Voltage in order to extend their torque range over the increased speed. However they should not be overdriven in terms of current.

All drives must therefore have some mechanism for limiting the current through the motor regardless of the Voltage. I know how this is achieved in chopper drives but not so clear on how in non-chopper drives.
 
Anyway - The bottom line is that IF your drive is a chopper, then you should be able to set the current it at its output to the current it "delivers" to the motor. If it isn't a chopper, then at the moment I don't know. However IF you can limit your drive to its max current of 2.5Amps or 3Amps (you've stated both so I'm not sure which it is), then you WILL be able to wire your motors in parallel with no ill effects on your drive.

The advantage of this is that if your drive is 2.5A max then the motors will still only get 2.5A but the current will be less than the rated parallel current of your motor - therefore you'll get less motor heating than with single coil wiring - not that I suspect you get much heating anyway.

IF indeed your drives are max 3A then you win even more - that is still less than your motors rated parallel current but obviously more than the max 2.5A of your motors single coil current.

Obviously the ideal would be to run your motors at their rated parallel current but given your driver isn't up to this then this is probably the best you can do with what you have.

Ian

Yes Ian - I,ve thought of that too.

I can set the output current on the drives. If this is current limiting to the drives, then I would think that I can put them in parrallel, and get the benefit from using both coils.

On the quick experiment I did on parrallel, it would seem that there is more power than in single coil config, and I get a little more speed, which gives me a bit more choice.

I will get on to the supplier on Monday and find out. If I can use them in parrallel without problems I think I will