Printable View
After loads of discussion and web reviews of the Gecko G540 driver, admiring it's compact design and connectivity I have decided ...
Over the next few weeks I plan to buy one of these drives with (3) 380oz steppers, is there a source in UK, or do they occasionally come up for sale second user.
I know the chances are slim but if you don't ask .....
I dont think so, and I've never seen 2nd hand advertised....
Thats what I thought, i'll have to order from US then and risk the customs/tax etc.Quote:
Originally Posted by irving2008
You never know, you may get lucky on the tax issue !
Is the Gecko 540 actually different to everyone else's 540 drive?
Could it just be Americans following the herd on cnczone?
The 540 is made by Geckodrives and not sold in this country as it has no CE certification.
I liked the compactness of the unit, plug connections, 4th axis and bob all in one tidy unit. Steppers even come wired with plugs all ready to plug 'n' play.
Priced up locally (UK) some seperate boards to cover (3) axis and seperate bob and similar steppers etc, worked out not much cheaper.
Just had a look on flea bay and someone is selling a g540 http://cgi.ebay.co.uk/Industrial-4-a...201223002r3590
Peter
Just read it again they were selling one!
Well over the budget i'm afraid, but I really appreciate the information.Quote:
Originally Posted by ptjw7uk
Looks like i'm resigned to a local supplier.
well that was a G450 mounted ina abox with all the trimmings... although that sa lot of money to pay for the box given how much the gecko itself is..
Just got my G540 from the US for just under £200 , have to see if ive got to pay tax on that yet. Seams an easy solution with its compact size , yet to see if its easy to setup.
L8r
Hi Buba,Quote:
Originally Posted by Buba b
Problem is finding steppers locally compatible with the Gecko G540, I planned to order the whole kit and kiboodle from US, around $600, add possibility of customs and vat and it's not so attractive
Hope you escape the tax man.
Shouldnt be a problem to find motors to match. Gary has a good selection on his site here.
Mate did a previous search for me, with the Gecko driver the steppers are limited to 3.5A .. interested to see what will suit the gecko
(by the way i'm the newbie messenger)
You can run steppers below their rated phase current, you just derate the torque by the ratio of the currents. So a 4.2Abipolar stepper rated at 1.8Nm will, on a 3.5A drive, give 1.05Nm RMS instead of 1.27Nm RMS
Whoa ... way over my head, although I am led to believe that matching drive/stepper is far better rather than adjusting to suit .... Remember MESSENGERQuote:
Originally Posted by irving2008
Im replacing my Hobby CNC board with the Gecko mainly because the Zaxis on my mini mill needs more torque. Ive got SY60STH86-3008 Nema 23 stepper motors from Zap on my machine and with the 3.5amp in parallel with 3.3k 5% resistors i should have 2.5nm (or 83% of there ) holding torque ( once i figure how to wire them up lol ). Not much of an increase over the Hobby board at 2.15nm but im hopeing just enough to stop it from stalling. If not then il replace the Z axis motor once i find one that matches the amps , which as you say Compfanon finding motors to match to get the most torque in the Uk is not proving easy. If i dont pay tax then i still think it will be a good buy .... but ive got the feeling il be getting a bill soon , the goverment needs more of my cash.
Heres hoping the bill gets lost in the system somewhere. The thought of "additional" charges put me off. My plan is to get (3) of the same motors from Zapp and drive with PM752's, all housed in a nice tower case perhaps along with the control pc.Quote:
Originally Posted by Buba b
My guru is helping me sort out appropriate power supply.
Good luck with your project.
HiQuote:
Originally Posted by Buba b
I am using a Powerpac 34 frame series wound stepper and it only draws 3.3 amps for 845oz-in on a z axis and it runs plenty fast enough.
Terry
one thing you need to remember is it is not the holding torque you need but the torque at a given speed.
In most cases the holding torque is totally irrelevant.
Also if you under rate the current this will only really effect the torque at the lower speed range, and will have little effect at the higher speeds as this will be lower than the torque you would get at lower current.
Dont forget the lower the current means the higher the inductance and that means you need more volts to force the current through the copper. So spending more money for a 3.5A motor will in most cases give you less performance than using a 4.2A motor and running at 3.5A.
Without the volts you are choking the driver and you will not get a good performance.
People always forget about volts, and with a stepper system it is very important.
Well i didnt get away with the tax so thats another £43 to add to the £189 for the Gecko , so if id checked around and wanted the hassel of conecting drivers and break out board up , the price wouldnt have been much differant than buying the gear from Zap in the first place. As Gary says i dont think the performace will suffer as im going to use 48v 7.3 amp power supply , its just that youv,e paid for the motor holding torque and would like to use the full spec of the motors. Its for a mini mill so i think it will make enough speed for what i want ..... time will tell .
well you haven't really, you will never get close to seeing the holding torque in practice whatever driver you have. Where the Gecko scores over any other driver is the clever stuff Mariss has built into them, resonance damping, step morphing, etc.Quote:
Originally Posted by Buba b
Remember that below the motors corner speed the torque is essentially flat except for resonances (which is where the gecko scores over other drivers which can show marked troughs in the torque at low revs). Above the corner speed the torque is inversely proportional to speed less the detent torque. A bigger motor will have a higher detent torque. the corner speed is related to inductance and drive volts and is independent of drive current. Once above the corner speed a smaller motor at higher voltage can produce more torque than a bigger motor driven at the same voltage as the bigger motor will often have higher inductances - this is despite the fact the bigger motor might have a higher holding torque.
The one particular stepper I'm using is Pacsci rated at 845 oz in at the rated current of 3.3 amps which is what I set my drive at. It is a 4 wire series wound and has a phase inductance of 8.3 mh.
Experts seem to all agree that low inductance is required for the best performance and I have found that this is not the case.
Unipolar drives are also said to be inferior, I have been using such a drive on a small lathe set up for a production contract and had no problems at all.
Also, I have never been able to get the type of rpms from a stepper that are discussed on forums either using high or low inductance motors, unipolar or bipolar, series, parallel. I'm talking rpms that that are actually useful to drive anything.
I have purchased high end drives and quality new steppers over the years and never been able to get they speeds I read about, then again i'm a microstepping fan.
Regards
The fact of the matter is that a higher inductance motor has a lower corner speed and therefore you are more likely to be in the downward torque slope region than the flat region at operating speeds. How that plays out depends a lot on the motor and what it being asked to do. Even two seemingly identically spec'd motors from different suppliers can behave very differently under load.
Having said that, you are right that there is often a big difference between the theoretical and the practical. It all depends on the situation so there is no 'one right answer'. I have some motors that according to their spec sheet should go to 900rpm. In practice I have never been able to get them above 300rpm even on a 48v supply and a range of drivers. I think a lot of people underestimate the impact of inertia and acceleration in their designs. Big leadscrews (20mm+ diameter) of any reasonable length have huge inertia and this is rarely factored in most designs leading to stalling and/or lost steps well below the revs that might have been expected. Of course, turning down the acceleration may allow you to creep up on those speeds... The other key issue is resonance. Most designs have no idea of their resonant frequency (its not easy to work out) and often a motor will stall out well below the expected revs simply because torque has vanished at that point and all the power is being absorbed by the resonance. Adding damping mass to the motor shaft can, non-intuitively, increase the maximum revs or sometimes lightly gearing the motor (1.1:1 say) to allow it to turn slightly slower can produce a better overall result without unduly affecting other parameters.
I have come to the conclusion that no matter what the drive, within reason, a look at stepper manufactures torque/speed curves is the most reliable indicator of what can be expected and they all look pretty much the same.
I have several Parker OEM 750 drives with many features yet they do not do any better that an inexpensive Allegro SLA 7044m based uniplolar drive I've used for several years.
I have not found steppers inaccurate or too slow, but I have never been interested in super fast G00's or air machining
Well in the end I opted for a local driver, coupled with some nice steppers and a home brew power supply. All in all a made to measure solution
In case anyone else stumbles upon this thread when searching for Gecko G540 info, here's an update to a previous post;
At the time of writing this (September 2011), the UK, (European?) distributors of Gecko gear, including the G540 is listed on the Gecko web site as being;
Charter Controls
6 Hayland Industrial Units.
Maunsell Road.
St Leonards on Sea.
East Sussex. UK. TN38 9NN.
Website: www.charter-controls.com
Phone: +44 (0)1424 850660