G-Rex Questions

[UKRobotics]

I want to start building my CNC electronics soon but I'm not 100% sure how to proceed. Previously I had my mind set on using a parrallel port break out board but there seems to be increased talk about this "G-Rex" so I was hoping that somone with a little more experience of using one could explain the pros and cons.

What are the main advantages of using a G-Rex over a parrallel port break out board such as the ones from soundlogic and cnc4pc ?

Does the G-Rex work with rutex drives and will it be significantly more difficult to get it to interface with a rutex than a gecko ?

What is the difference between the G100 and G101 appart from the $200 price tag ?

Has mach 3/4 Reached a stage where the G-Rex is actually safe and reliable to use for anything other than testing purposes?

I was watching some of the Mach video tutorials yesterday and Art mentioned how there were all sorts of bugs with things going out of sync and loosing steps. - Even if the g-rex turns out to be the best thing since sliced bread it would be no use to me if I couldnt trust it not to take chunks out of my workpiece or table if left unattended for a few minutes.

Is the configuration for the G-Rex in Mach much harder than setting up a parrallel port equivilant ? Is it still a case of point and click or would I have to write vast ammounts of VBScript before anything moves?

[ger21]

The advantages of the G-rex, are that it can output pulses much smoother and faster, 4,000,000 steps per second vs 45,000 max from a parallel port. You also get many more in puts and outputs.

The G101 is for developers, it's not complete. The G100 is for end users.

The drives just get the step and direction signals from the G100. Any step/direction drives would be connected the same way.

Mach4 is no more. I'd expect at least a few more months for a fully functional G100 running in Mach3.

Setting up a G100 in Mach3 is pretty much the same as a parallel port.

[UKRobotics]

Thanks ger21.

To put things into perspective, would using a new pc parrallel port system with mach3 & rutex be able to produce the same (or better) level of speed and smoothness as the 20year old Bosch/heidenhain system ?

[ger21]

No idea.

[JerryFlyGuy]

UK, I'd venture to guess "YES". Most likely the components on your old system are not as accurate nor as fast as todays [ Think back to computers 20yr's ago.. ] The G100 [Grex] will take in a encoder signal [ quad] at over 1Mhz and output up to 4Mhz [ step's per second] I think the limit on most older system's was down in the 500 [or less] line encoders [if they used encoders at all.. most had resolvers] while today we could run a 5,000 line encoder [ do they make them that high?] on a servo at 3000rpm before we'd tap out the G100 [ at 1Mhz ] we could use 6 encoders [1 for each axis] at this same speed all at the same time.. and just be reaching the potential of the G100. If we had a perfectly zero backlash system [ in reality it rarely happens.. and if it is.. you've paid for it ] w/ a 5:1 reduction on a ball screw w/ 10TPI and w/ these 5,000 line encoders have a resolution of 0.000002"--in quad [ in reality.. why even bother.. but for illustration..] I don't think there is a 20 yr old system that can resolve or read down to this level. Since today we can, we know that the steps will be smoother and more precise than they were from years ago, simply because we can use a higher [ maybe not 5,000 line encoder .. but a 2-3000 would be fine..] count encoder to get better control of the machine's movements.

my 2 cents..
Jerry [check my numbers.. ya just never know when Mr. Murphy comes calling.. ]

[ger21]

He said a 20 year old system vs a PARALLEL PORT system, not vs a G100.

[JerryFlyGuy]

True, he did.. i had my head in the original Grex question.. Even so, however.. w/ 45Khz on the parallel port, your going to see an improvement over the older equipment. Personally, if your going to buy a decent parallel port card, I don't know why you'd not just go straight to the G100, a typical board from some of the more established resellers your looking at 50-75% of the price of a G100 w/ 1/2 the I/O, if you get a second board so you have more I/o's you might as well have bought the G100 from the start.

I started out w/ a B/o board and then decided to move up to a G100 after they came out [wanted the increased speed as well as the option for the "Un-Stallable stepper --> which is still in the early stages], I wish I'd just started w/ it in the first place, it would have saved me several hundred dollars from the get-go..

Jerry