Let the fun begin !!! ???

**njhussey** · 10-02-2015

The steppers will generally only lose steps if they're tuned too close to their maximum speed and acceleration from my understanding and reading of Jazz's posts. There's plenty of people on here using twin setups and not many posts to say they're losing steps and racking the gantry. I'm in the same situation as you regarding the twin vs single stepper and I'm leaning towards the single Nema 34 with a different driver. The AM882 will not drive the Nema 34 with any sort of speed, 240V drives are best for them but they are more expensive! I'm going to use my spare 3.1Nm Nema 23 stepper and driver for a 4th axis when I get the Nema 34....

**PAULRO** · 10-02-2015

that's good to know about the AM882 drive. originally i bought 4 nema 23 4Nm with the intention of using 1 each for the x,y,z and a spare for the fourth axis. but soon realized that i would probably need 2 for the x axis. ( 1 on each ball screw). maybe down the road i might just follow you down the road and replace the 2 23s for a 34, now that i know i will just keep going with the 23s and 60 VDC power supply. cheers for that.

**Clive S** · 10-02-2015

Paulro The homing with the am882 drives is a doddle all you need is two inductive switches like this : http://www.ebay.co.uk/itm/DC-3-Wire-...-/390880485798 mounted one each side and adjusted so that they both trip at the same time when the gantry is square.
Then set homing slaved axis in Mach3 X with A (ask how to do this nearer the time) what happens then is when the home button is pressed the gantry will move to the end with the switches on and trip the switches. Then the gantry will back off the switch until it trips again. You can adjust the gantry square by adjusting one of the switches a little.
The machine will then make sure the gantry is squared every time you home the machine.

When using the AM882 drivers you wire up the stall detect (fault) terminals so that if one motor stalls it estops the router and saves any damage by racking the gantry. Hope this helps. ..Clive

**JAZZCNC** · 10-02-2015

Clives answered the slaving question correctly but I'll give a little more detail.!
When the motors are slaved both move together towards each home switch. The first switch to hit a switch stops just it's own motor not both and reverse's off the switch. The other motor carry's on it's merry way until it hits the home switch and does the same.
Now in practice this happens so fast it appears as one motion. This is because if the gantry is setup correctly the switches should trip exactly at same time.
If your gantry is not quite square you can tweak it square by moving the switches slightly but all the same it still appears like one motion as the difference will and should be tiny.

Regards the Motors and single or twin motors then it's personal thing and close call in some respects. If using quality Digital drives with stall detect like AM882 then I wouldn't worry about it and it's far easier to setup and less messy on wide machines.

One thing I would suggest to get the best from the motors is that you use more than 60Vdc with 80v drives and if using toridal psu you'll easily get away with running 70vdc. The extra 10v makes all the difference and worth sizing psu to maximise the motors.

Regards the electronics then don't get carried away like Eddy current did because for home use it's really not required. YES safety is important and a decent emergency stop circuit is required but you don't have to go to lengths of using expensive safety relays like Pilz. Normal Relays will work just as well if sized correctly.
More important is that e-stop or safety circuit can not be reset unless any fault is cleared and that it removes power to any devise that might do you harm.
Limits I don't really class as emergency stop condition and more positional error so can be dealt with in a differant manner. Instead of killing Power to devices they can just inform the control software limit as been tripped so can halt G-code and at same time remove siganls to the drives by using the drive enable signal.
This should be done in such away that it halts the machine and won't allow reset until limit is cleared or over ridden but at same time leaves the drives powered and holding the motors under torque.
E-stop system should done in such away that it responds to outside events like Fault signals from drives, IE Stall detect, VFD/spindle fault or emergency button press. In which case power should be removed and again system not allowed to restart unless fault cleared.

Building a control box isn't difficult and doesn't need to be complex but it does need to be safe which is easily done using relays.

**PAULRO** · 11-02-2015

well i'm glad i held off with the purchase of the 60 VDC PSU. i must get a sketch of a psu organised and post it here. i remember reading a thread posted here about the grounding issues and potential for error if the power supply is grounded incorrectly . i think it was in relation to the main screw of the coil touching or not touching the base plate . i'll have to dig it out and give it a read again. the homing issue can be put to bed for the time being at least , i 'm clear in my mind following the info from you guys here. with regards to the safety relay i think i will leave it for now and get the baby to take its first step with a decent level of safety using the relays that i have . down the road i will tackle the safety relay when i get more familiar with the whole experience. as always guys ... the advice is first class, cheers

**JAZZCNC** · 11-02-2015

Originally Posted by PAULRO

with regards to the safety relay i think i will leave it for now and get the baby to take its first step with a decent level of safety using the relays that i have . down the road i will tackle the safety relay when i get more familiar with the whole experience.

That's the point you don't need a safety relay at all. You just need standard relay/s wired such that they create a latch and drops the latch if an E-stop occurs. Latch can only be reset via momentary button after fault is cleared. Very easily done and costs very little.

**Clive S** · 11-02-2015

i think it was in relation to the main screw of the coil touching or not touching the base plate . i'll have to dig it out and give it a read again.

Paulro I think what you are referring to is the bolt that holds the toroidal transformer through the centre to the chassis. What you must not do is connect an earth wire to the end of the bolt that is not touching the chassis. The reason of this is that it will give you a shorted turn on the transformer by connecting the bolt from the two ends to the same point ie earth. ..Clive

**PAULRO** · 11-02-2015

so i have a coil with 2 insulating rubber pads ( 1 per side of the coil) a steel dish washer to sit on top of 1 rubber pad and a bolt to secure the whole lot through the disc on to a metal plate that will be earthed anyway. so the steel disc will be earthed through the frame and if i put another earth at the top i'm creating a shorted turn. Standard Range Toroidal Transformers- CM0750225- 750VA 230v to 2x25v that is good to know , i've been searching the forum for a thread that explained the construction but couldn't find it . by the way is my understanding of how the coil is assembled correct or am i assuming the assembly incorrectly?