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Without going into too much detail, what would you replace some 3.4Nm (continuous rating) 138V DC servos with?
Budget won't allow for new AC servo replacments, and I'm not sure how much of a sacrifice steppers would be.
I'm wondering what the frugal members of this forum would suggest.
Hard to say without knowing what machine they're going on, the mass of the axes they are driving, the pitch and diameter of the ball-screws and what speed and acceleration you got with the DC servo?
Well the complete machine weighs about 1500kg and has been stripped for parts, so until I physically get it, that's all I know. I'm just wanting to know possible options for now without getting into too much detail.
I have a couple of 1200 kg bedmills that have triple stack nema 34 motors running on 85v power supplies. The tables are 42" x 9" bridgeport, and will happily run at 3m/min on rapids,
That sounds reasonable. Any idea what Current rating the steppers are?
This machine is a couple hundred kilos heavier than a bridgeport, and the table will most likely be a bit heavier. I think the servos are all connected via belts, so gearing shouldn't be too hard to alter. I'm still trying to aim for some reasonable speed though, as the X travel is just short of 2 feet, and I'd quite like closed loop.
I've been pricing up a few options, but I need to decide on what controller to use before making any decisions.
Plus there's the issue of geting the thing home and into the workshop!
They're running at half step on a 2.5:1 reduction on 5mm pitch ballscrews. Current is 3amp.
If you can afford servo's from DDM they would be excellent, since you'll get high rapid feedrates and much higher resolution:
http://www.dmm-tech.com/Files/DHT_Servo_Motor.pdf
Their 60EM-DHT-36, 400W servos would be plenty, or even the 300W servos. Send them an email and they will calculate which is best suited to your machine if you know the mass each axis is moving. I've not bought from them yet, so can't comment on the quality first hand, but from reviews I've seen on CNCzone they seem to be excellent...but it will cost more than a Nema 34 stepper motor system.
Or there's some on eBay, but you said you can't afford servo's so...
If using Nema 34 stepper motors I would get mains voltage drivers since this will greatly increase the torque at high speed. For example:
Zapp Automation Ltd - Stepper motors & Stepper Motor Drivers - Servo motors and Servo Motor Drivers - Ballscrews & linear motion products. : 2M2280N (High Voltage Stepper Driver) [2M2280N] - £176.40
Although they've gone up in price since I last looked, so maybe:
CNC Cut Nema 34/42 stepper motor driver DQ2722M,7A 110-220VAC www.wantmotor.com | eBay
or
2MA2278 CNC Stepper Driver For Nema34,Nema42,Nema51 Stepper Motors 7.8A 110/220V | eBay
If I actually had something useful to do with my micro lathe I'd get one of those drivers for the spindle.
So the machine had 1Kw servo motors on and a 300W servo motor will give you plenty enough power? Without getting more info on the machine it would be wrong to say that....
Even i am assuming that the motors are 1Kw, so i am unable to suggest the right motors without making an assumption.
If the motors are rated at 3000 RPM, they are 1Kw motors, that would give you about 3Kw of peak power. that is over three times what you suggested.
Going to steppers would be a big step backwards, even running them at 230V. While its a big step back, it will still work, but dont even think it will be close to what it was with the servo motors on.
Oh and the price of the 2M2280N has not gone up in price in 3 years. VAT is shown in the price at the moment, so an easy mistake to make.
Fair enough, that's why I suggested contacting the supplier as my estimate may well be optimistic and yes I didn't spot the VAT which was pretty bad of me...Quote:
Originally Posted by Gary
From the figures I've found, a similar mill using an older posidata drive used 3/4hp motors combined with a 1.1hp drive.
The motors that are currently on the mill, come in around 1kw from what figures I've found (they're SEM) but the owner wants them as spares for the bridgeport interacts he's got.
I know steppers will mean a hit on performance, but it's how big a hit I'm trying to quantify.
The DMM 750W servos should come in under £500 each before shipping (depending on how customs class them), comparable in price to the HBS86 closed loop steppers. Performance wise I doubt there will be that much practical difference. Steppers will produce less torque at speed, but this mill won't be cutting at speed, so low speed torque is more important.
I really want something closed loop, and all the options start around £500.
Options I've priced are Dynomotion K-flop + Kanalog, combined with Nema 34 steppers and US digitial encoders, and high voltage drivers which is around £1700 all in.
HBS86 closed loop are around 500 each plus power supply.
Thanks for the suggestions guys.
Here's the link to my Closed loop findings has promised M_C.!! Leadshine Closed loop stepper - YouTubeQuote:
Originally Posted by m_c
Cheers Jazz.
I got an email back about the cost of the DMM servos and shipping, and by the time you factor in all the extra bits (cables, software etc) it's about 1900USD, before getting hammered by tax/vat/fees at this end.
Plus the 750W servos are limited to 1080rpm, so there's not that much of an advantage over steppers in terms of where power/speed is needed.
Yep and this is exactly why the closed loop steppers are going to knock the spots off low speed low end servos like this. They work just has good and far easier to set-up, non of this PID tuning etc. It's available if you want to play but they will work just fine straight from the box and infact the drives auto config handles it has default and really it is just an advanced feature if you want to tweak.Quote:
Originally Posted by m_c
After much looking, thinking, calculating, etc., I'm currently thinking Dynomotion K-Flop for controller regardless.
Then use the biggest stepper motors from Zapp combined with high voltage drives (£285 for motor+controller) combined with encoders from US Digital (aprox. £120 per axis for E3 or E6 single ended, or £140 for E6 differential). Then close the loop in the K-flop, as that means I can kill the power to the drives, and still have the k-flop/mach know the axis position by having the encoders on a seperate power supply.
Plus at current prices, it works out around £100 an axis cheaper than the Leadshine closed loop option, and gives slightly more power, aswell as having encoder outputs easily accesible.
I do already have one of ArcEuros biggest steppers, a Gecko G203V and all the required power supply bits sitting doing nothing, but I'm not sure if it's worth the hassle of setting up the Gecko and powersupply, as if i upgrade in future, it will all have to be ripped out, whereas a high voltage drive will almost be a swap out replacement for a servo drive.
Have the price of hbs86 come down quite a bit since last year or am I missing something?? These seem more and more appealing!Quote:
Originally Posted by m_c
http://www.zappautomation.co.uk/en/h...0-ec-1000.html
That's the 4Nm ones you've linked to, but yes they have dropped in price.
I'm still going for servos though, however all time lately has been going on a couple different projects, and all money is needed to pay for a holiday. I'll hopefully get back onto this in another month or so.