Longs 3 axis CNC kits - are they suitable for Bridgeport Series 1 conversion?

[john swift]

with stepper drivers like the dm860a that has its own input opto-isolators



you don't need a breakout board with output opto-isolators like this supplied in the kit-


these two BOB's only buffer the printer port outputs and only opto-isolate the 5 inputs -

a breakout board like this found in some of the ready made control boxes


the closest available on ebay is something like this


note it does not have the 5V DC/DC converter found on the TX14175 and requires another power supply

the least expensive change will be the breakout board but it may not make any noticeable
difference when using the original motors and drivers


As I don't have the longs kit to test, I don't have a definitive answer but
problems the original breakout board will only show up at high speeds
the original motor / driver combination may limit the maximum motor speed first

without going through all the stepper motors , stepper drivers and power supplies on sale

its not easy to say which is the most cost effective change

using a higher voltage supply & stepper drivers verses replacing the motors with lower inductance motors

John

[heb-cnc]

As I don't have the longs kit to test, I don't have a definitive answer but
problems the original breakout board will only show up at high speeds
the original motor / driver combination may limit the maximum motor speed first
without going through all the stepper motors , stepper drivers and power supplies on sale
its not easy to say which is the most cost effective change
using a higher voltage supply & stepper drivers verses replacing the motors with lower inductance motors

John

A very informative and educational reply! Allows me to analyse motor and driver specs with a little more knowledge than I had yesterday. Thanks for taking time to explain things in such detail.

[m_c]

It's worth highlighting the main reason opto-isolators are added to BOBs is for protection.
Using a parallel port, get something wired wrong, or have something short and connect power to pins they can't withstand, then more than likely your PCs parallel port (and likely entire motherboard) will be dead.

With newer motion controllers, the path of destruction from a wiring problem isn't likely to be as long, but it's still potentially a couple hundred pound controller that could be releasing it's magic smoke.

It's a calculated risk not using them, but at slow speeds, they shouldn't cause any problems. I certainly wouldn't be searching out a BOB without them, unless I was really going to be pushing pulse rates.


Regarding suitable motors.
A good starting point would be to try and find out the torque for the existing motors, or even a datasheet with torque curve (it's surprising what a google for the model number turns up).
You can then run a few figures and see how the various options compare. You'll likely find some suitably geared NEMA23/4s provide better performance than NEMA34s directly coupled, especially when running from lower voltage.

[Boyan Silyavski]

I would Not retrofit a precision metal cutting machine with an Open Loop system , given prices of new cheap servo motors and drives, used servo motors and drives and closed looped steppers which i dont like much pricewise

[john swift]

adding more detail to post 7 for any one wanting to use a BOB with opto-isolated outputs and stepper drivers with opto-isolated inputs


the problem with the BOB supplied as part of the kit is ue use of the slow PC817 opto-isolators used for the outputs


I would expect the DM860A stepper drivers would have a PC817 on the enable input and a high speed isolator like a HCPL2531 for the step and direction inputs
as used on this Tormach driver input



the diagram is from
https://www.cnczone.com/forums/torma...ml#post2107952


if I used a breakout with opto-isolated outputs then I would look for a BOB like this -

https://cnc4you.co.uk/resources/Brea...ard%20HG08.pdf

or this

http://www.electronics-lab.com/proje...r-cnc-routers/

they are just two of example found


John