Cheap gecko drives

[snowyskiesau]

News! Gecko (https://www.geckodrive.com) have just released a new stepper drive, the G250.
Introductory price until 3rd September is only $US29!

Specs on the new drive are:


3.5A 50VDC maximum
Optoisolated Step, Dir and Disable Inputs
Optoisolator Common is ground
3.3V and 5V logic compatible inputs
300 kHz maximum Step pulse frequency
Top settable Adjust trimpot
Power LED indicator
No user settable jumpers
20 kHz switching frequency
Mid-band resonance compensated
Microstep to full step morphing at higher speeds
Small size
Four layer PCB
Discreet all n-channel MOSFET full bridge design
14A rated power MOSFETs
2.5mm 2x15 header in either male or female

I've ordered mine :)

EDIT: Issues with gecko website listed wrong price

[Ch4iS]

What did postage set you back?

I was trying to work it out and only way to find out is to sign up and put a CC card up on file.

[snowyskiesau]

If you order and it's an overseas address, you get the option to request a quote - which is what I did. They seem to respond pretty quickly to email.

The other problem was that the price given on the website was different to that listed in the checkout, the checkout price was $46 instead of $31. I've asked about this too.

I've enquired of a few other US companies re postal charges. If they use USPS and go for the standard parcel size, it should be about $US39 for a maximum of 20 lbs weight.

[snowyskiesau]

In case you haven't been following the threads on cnczone.com, there is a G251 available shortly. This is slightly more expensive but includes screw terminals and a built in heat sink.

[Greolt]

Yeah just be aware that the G250 must be mounted on a heatsink and must also be insulated from that heatsink.

This is not for the uninitiated. Any electrical contact with the heatsink and the drive is toast.

The G251 is much better suited to those without this sort of experience.

Greg

[snowyskiesau]

Yeah just be aware that the G250 must be mounted on a heatsink and must also be insulated from that heatsink.

This is not for the uninitiated. Any electrical contact with the heatsink and the drive is toast.

The G251 is much better suited to those without this sort of experience.

Greg

The optional heat sink, hard anodised aluminium, for the G250 is only $4 and is probably worth it.
I plan to mount 4 drives on a single heatsink (http://jaycar.com.au/productView.asp?ID=HH8574&CATID=&keywords=heatsink&SPECIAL=&form=KEYWORD&ProdCodeOnly=&Keyword1=&Keyword2=&pageNumber=&priceMin=&priceMax=&SUBCATID=), providing I can get some suitable insulators. The anodising on these Jaycar heatsinks is thin and too easily scratched.

[snowyskiesau]

My Gecko G250 drives have arrived!
Ordered Monday, arrived today, damn good service.

These things are tiny, that's a 50c piece in case it's not that clear. :oo:

[Greolt]

I am going to get some G251s. How did the postage work out?

They don't have international postage set up on on their site.

Greg

[snowyskiesau]

I am going to get some G251s. How did the postage work out?

They don't have international postage set up on on their site.


Greg,
I sent an email and they provided a quote - $28 via FEDEX. Based in the size/weight of these things, it wouldn't make any difference how many you got! - provided they fit in the standard FEDEX small package.
It would have been a bit cheaper by USPS but not sure if they offer that option.

[rodm]

Ok my turn to ask the silly question.

What are these drives microstepping at when it states:

Microstep to full step morphing at higher speeds

What microstep do you set for motor tuning?

Just when I thought I was getting on top of this mumbo jumbo they have to go and do something like this. :-

[Greolt]

Rod

Gecko drives are ten microsteps. This is set and not configurable. Mariss says that more than ten is no advantage.

Microstepping becomes a liability at higher motor speeds and somehow the drive morphs to full step at higher speeds. Don't ask me how. :)

Also they have mid band resonance damping. Another thing I have no clue about. :)

Greg

[snowyskiesau]

The step setting on the G250/251 is 10 microsteps, there's no jumper option to set this.
No idea what they mean by morphing in this context.

As a new customer, I shall ask the question of Gecko.

Edit: Just checked cnczone.com and morphing is explained here (http://www.cnczone.com/forums/showthread.php?p=233614&highlight=morphing#post233614).
I'm still looking for an explanation of this explanation - more coffee required I think

There's a paper from Gecko that covers midband resonance. Find it here (http://www.geckodrive.com/upload/Step_motor_basics.pdf).

[rodm]

Thanks :2tsup:

[Greolt]

Wow that white paper is a bit much for this uneducated carpenters brain. :p

Greg

[snowyskiesau]

Just a heads up to anyone wanting to take advantage of the introductory low price on the G251 drives.
The special ends at 5:00 PM Pacific time which (according to this site) (http://www.timeanddate.com) is 10:00AM tomorrow local (Sydney) time.

The special price on the G250's has already finished.

[Greolt]

My G251s arrived today.

Three of them will be going straight into the Wigitmaster. :)

Greg

[snowyskiesau]

I think the $9 extra for the G251 over the G250 was more than worth it.
The screw terminal will have to make it much easier/safer to connect to.
Having failed to find any local heatsinks that are hard anodised, the $4 from Gecko would have been well spent.
I had to to rush in!

BTW, what motors will your G251's be driving?

[rodm]

Hi Geoff,
I know what you are saying - we all have a few of those rushed into purchases. :)
I'm sure your drivers will be fine and not like the components that hide in one of my cupboards. :-

[crocky]

Well I have ordered my Geckodrive 251's a few days ago too :)

I have a tracking number so they are on the way!

Now I'll just _very carefully_ build a new CNC controller over time and get some new motors etc :)

[Greolt]

I fitted three G251s to the little widgitmaster today.

It uses a SmoothStepper for pulsing rather than a printer port. This had then hooked up to a Xylotex stepper driver board, but that has been passed on to jb2060 (Jason)

The G251s went on to a custom made heatsink. Piece of ally scrap :U

Same power supply. 24v linear.

Previously I had it set to 3000mm/min rapids. Now it will rapid at 6500mm/min. Scary fast. :o

Too fast for such a small machine so I set it at 4000mm/min. That's plenty quick enough for me.

One motor used to growl at a certain slow speed. Not lose steps but make noise. G251 has a trimpot adjustment for this.

Made this adjustment and now that motor is smooth and quiet all through the speed range. So it does make a difference.

So far I think these are a very nice drive for up to 3.5 amp motors.

Outstanding value at the introductory price. Shame that was not for very long. Still good value at full price I believe.

Greg

[rodm]

Useful information Greg. :2tsup:
Be good to know what screw pitch the Widget is running. I can then calculate the RPM of the steppers. Xylotex seem to peak out at 300 RPM for good aceleration and usable torque.
I am going to use the Kelling style drivers on the new machine but are seriously thinking smoothstepper. I use one computer (console) for all my machines so do you see any problem with using a parallel port on one setup and smoothstepper on another with the same computer?

[Greolt]

Rod

10 tpi acme lead screws. So by my reckoning 2.54mm pitch. 4000mm/2.54 = 1575rpm

I should test that with the dampers removed. They made a huge difference when still using the Xylotex.

No problem at all using one computer with either the LPT or SmoothStepper.

USB 2.1 is good but will work with USB 1.1

Just do what you most likely are already doing, have a Mach profile for each machine.

OK I just went and did some tests with the dampers removed.

When using the Xylotex the dampers made an enormous difference. Anything over about 350rpm and the motors would stall with mid band resonance.

For those who don't know, the dampers are like a small flywheel with some sort of rubber component to them. Bit like the harmonic balancer on the front of your car engine.

Anyway with the Xylotex and dampers fitted that motor speed went up to about 1200rpm.

With the G251s I can not tell any difference with the dampers fitted or not. Runs smoothly right through the speed range either way.

So I guess Gecko's claim about "mid band resonance damping" being built in to their drives must have some merit.

Greg

[rodm]

Thanks Greg,
All the figures look like it is fairly predictable. Geckos are the go then and I will visit here when I fit the Kelling drivers and add some more information. I don't expect as good a performance from the Kelling drivers as the Geckos but hopeful of better than Xylotex.
For the new builder this is not a bagging of the Xylotex as IMHO they are still the best entry level bang for bucks you can get. For performance Geckos are your choice.
Thanks for the info on smoothstepper - I can't afford to do three at once so at least I can trial it on one machine and move the rest over if it warrants it.

[crocky]

They sure are SMALL :) mine are here :)

Power supply and an isolated bob board will be the next items I would like to get but which one??

I am looking at maybe the Keling Inc KL-600-48 48V/12.5A $139.95 for the power supply.

The bob will probably be the Probotix http://www.probotix.com/breakout_boards/pbx-rf_isolated_breakout_board/

Then there is stepper motors.....

[Greolt]

Just in case any readers are thinking about these drives it is worth mentioning the G540.

The cheap introductory price which started this thread was short lived and no longer available. :(

The standard price for G251s is $69US. So 3 x 69 = $207US or 4 x 69 = $276US. Plus postage of course.

If this purchase was to go into an existing setup that already has a break out board (BoB) then this is likely all you have to spend.

If these were to go into a new controller setup then you probably need to add a BoB.

Or if replacing a Xylotex then same applies. Probably need a BoB.

I say probably because strictly speaking a BoB is optional. However it makes things a lot easier and helps with hooking up limits, home or other inputs.

Also much easier to drive outputs like spindle relays etc. Another advantage is it makes electrical noise easier to deal with.

So when you add the cost of a BoB, say like the one Crocky reffered to above, then it becomes, 3 drives and BoB = $253US or 4 x drives and BoB = $322US

The G540 is four drives exactly the same as the G251 including a BoB all in one easy to mount package for $299US

When you add it all up with ease of setup it makes it a pretty good option.

http://www.geckodrive.com/product.aspx?c=3&i=14469

Greg

[snowyskiesau]

The G540 will also add over/reverse voltage protection, short circuit protection and a charge pump detect to the G250s.
Having bought the G250's, I now have to make up a suitable connector and, as Greg pointed out, buy a BOB, all an added expense.
Still, this is all part of the fun!

[I have the circuit diagram of the G540 and plan to use it to make a poor mans version of the real G540. If I do end up getting a real G540, at least I'll have plenty of spare G250's should I need them :)]

[Frankmc]

Hi Guys

Im probably doing this ???? about face , but with limited funds at the moment i thought i would start accumulating stuff for my future cnc router and am thinking of sourcing the drive controllers first ...I was going to get the gecko 251s but just had a look at the g540 as Greg mentioned and am thinking maybe i should get that one....At this point im hoping to use Alans design (if he doesnt mind) as he will have his build im sure before i will...so im hoping someone can indicate that the G540 wil be suitable for that sort of design...Also what stepper motors are suitable for those drives...?

Thanks
Frank

[rodm]

For the unititiated a BOB is not your uncle it is a break out board. This is a cuircuit board that makes it possible to connect the driver boards to the parallel port of your computer. You can usually connect other things like limit switches to the BOB.

[crocky]

Hey Greg,

There is a guy on cnczone in the Gecko area asking for any pictures of a completed assembly with the 251's. It would be good if you could put some up so we can all see what sort of a job you have done too :)

I have ordered the PSU, Steppers and BOB from Keling yesterday and it will be sent today :D

Yesterday I reloaded the CNC computer too :)