Electronic Lead Screw Project

Tony.

Jeffree talks about changing the voltage which gave a lot more power. What are you running at. And what power does your psu put out?

Edited By Zan on 06/12/2019 16:44:31

Hi Zan,

I will have to ask my son who I am seeing on Sunday, as I really don't want to give you guys false info.

Tony

Usually the stepper driver will have an upper voltage which could be upto 40 volts and it provides the current to the stepper motor (set with jumpers).

I'm using a 24v supply in my setup and it drives the lead screw OK but I've not tried threading yet.

I'm just wondering but does anyone know if you can attach another encoder to a normal stepper and where would it plug in, as I have a few encodes and several types of stepper,us t trying to save a few penniesj

Are you trying to make it a servo type to get a closed loop system? Clough42 shows this, but looking at the eBay stepper listings, the servo steppers seem to come with a blue rather than black driver. I don’t know where any servo adjustment for the closed loop takes place but I think it’s in the driver which monitors the pulse out to moratorium then compares it to the sensor and adjusts the output.

so I think it’s a different system altogether ant I think that’s a no no, but perhaps somebody has full info

Thanks Zan I remember now that Clough42 plugged the encoder into the driver so it looks like I will be getting a servo motor and driver. I might try it with just a stepper to check what torque motor I need as I have some. I'm still at the thinking/waiting stage until I get some parts arrive, i also thinking of adding a magnetic clutch in the lead screw drive chain so i can still use the handle on the end without worrying about induced voltages generated by the motor, as i said still at the thing stage

Lionel

The closed loop steppers are a direct replacement or substitute for conventional steppers. There's no reason that I can think of why a closed loop stepper/driver couldn't be used in this project.

The closed loop only exists between the motor and its driver - there's no need for any additional wiring back to the ELS itself.

Martin.

Great blowlamp exactly what I thought then. Only prob is that the closed servo system is a lot more expensive, eBay seems to have them at abt £90 as opposed to abt £30 fir open loop

Came across this example of an all in one package for a Nema 34 with driver and power supply, do you think this is a good deal and would be OK for an ML7?

Dennis

https://www.ebay.co.uk/itm/8-5Nm-NEMA34-Stepper-Motor-Driver-Power-Supply-Closed-Loop-8-5N-m-Hybrid-Drive/223770601237?_trkparms=aid%3D555018%26algo%3DPL.SIM%26ao%3D1%26asc%3D61046%26meid%3D273350ecaba14a628828b44ff26609cb%26pid%3D100005%26rk%3D1%26rkt%3D12%26sd%3D283094369235%26itm%3D223770601237%26pmt%3D1%26noa%3D0%26pg%3D2047675&_trksid=p2047675.c100005.m1851

LINK

Edited By Dennis R on 06/12/2019 23:07:34

That’s massive! Would power an els on a 12” lathe!

I bought my kit (just a stepper motor and driver) from Stepperonline, they were quite cheap and deliver from different countries and they have some offer codes at the moment (I have no affiliation with them)

LINK

.

This is of no consequence, Dennis ... but you might like to know

Everything from the question mark onwards, in that long ebay address is superfluous

it’s tracking information, to tell ebay how you reached the page.

MichaelG.

.

Try: https://www.ebay.co.uk/itm/8-5Nm-NEMA34-Stepper-Motor-Driver-Power-Supply-Closed-Loop-8-5N-m-Hybrid-Drive/223770601237

Edited By Michael Gilligan on 07/12/2019 08:34:30

I have a question about the type of stepper motor to use for this application, why is the servo option considered to be better?

My understanding is that a servo with feedback is Ideal where positional accuracy is required, say a cnc axis control.

This application requires synchronisation between the spindle and the leadscrew if steps are missed due to external factors then the synchronisation is lost and adding steps on will not recover that synchronisation between the spindle and leadscrew.

I would think spending extra on a more powerful stepper motor would make more sense leading to no missed steps in the first place.

Or have I missed something?

Iv been mulling this over as well. I don’t know how many steps would actually be lost, but here’s my calcs

1 turn of the 8 tpi leadscrew takes 200 steps x 8 micro steps = 1600 per rev

Lost motion per lost step ...... cutting an 8 tpi thread, so 1 turn of  Leadscrew gives saddle move of

0.125” / 1600= 0.000078” Not very much!

So 10 lost steps = 0.00078”. Still very little.

as most threads I cut are at 24tpi+ this is reduced by 1/3 to 0.000026” and 0.00026”

can a humble myford work to these limite? Are my tools ground accurately enough? What effect on the thread does my chaser present? How accurate is my leadscrew?

conclusion, servo ain’t worth the extra cost

Edited By Zan on 07/12/2019 10:30:08

Edited By Zan on 07/12/2019 10:32:12

In addition any lost motion will present itself as a tiny tiny extra cut on the trailing flank It is also reminiscent of the clough42. Calculations for floating point calculations within the code

You are correct that if the motor is large enough and properly set-up then closed loop should not be required. The advantage of closed loop is that it corrects for any lost steps. This keeps the positions correct to the end but would not correct any surface finish issues caused by the missed steps. A correctly sized and set-up open loop motor that does not miss steps is better than a closed loop one that does but corrects. These units are not strictly servo systems, they are steppers with monitoring and automatic correction.

Edited By Robert Atkinson 2 on 07/12/2019 11:08:04

From what I understand ( I could quite easily be wrong) as Robert says if the stepper is large and accurate enough a closed loop is not required however bearing in mind that most? of us are not prepared to buy industrial quality motors and are probably not of that standard. As the spindle encoder is calculating position ever milli second or so (if I remember right from the video) the servo motor is checking position at each calculation and adjusting if required whereas a stepper motor could (like a servo) miss a step or two - through additional torque required through cutting forces on a tougher spot in the material - the servo will correct the small amount on the fly while the stepper will compound the error to the end of operation.

Lionel

Having converted my Denford Starturn 8 CNC lathe from NEMA 34 to a 24 sized closed loop stepper system, there is no way that I would go back to a conventional stepper setup.

I find many improvements, such as faster top speed, the system is far smoother with virtually no mid-band vibration and has better acceleration & deceleration, which is vital if your lathe varies its speed when a heavy cut is applied or removed. Also, if steps are missed such that the closed loop can not recover the situation, then a fault condition will cause the driver to halt and send a fault signal back to the ELS (if it has such a facility to acknowledge) or the CNC controller.

I couldn't personally live with the idea of lost steps being acceptable, even if only a few, because that would certainly not work when we're talking about repeatable work, particularly on diameter with a CNC lathe.

It's good to know your machine is maintaining correct position and will do so all day. It gives peace of mind compared to my previous experience whereby there was an uncertainty about parts reliably coming out to size.

Martin.

Thanks for that insight Martin, not worth potentially spoiling the ship for a h'p'orth of tar.

Re the motor controller, is it always necessary to set it up from a PC or are they normally supplied pre-configured? I'm thinking particularly of the hybrid stepper kits from Stepperonline?

Roy

For almost all applications (99% I would think) they are ready to go. My understanding is that the driver constantly monitors & updates its output 'on the fly' to best suit the current operating conditions - I believe that is why they are based around a very powerful processing chip.

Martin.