New member lots to learn

[AndyUK]

Hope you can see these pictures of my machine that i have attached.

*head in hands* My mother-in-law has the same rainbow drawers - just seeing them makes me nervous about what her next 'job card' entails.

Looks like you've made some serious progress there - and your workshop is far tidier than mine I can assure you!! What are the dimensions of the machine? Looks like its got a decent amount of Z clearance.

As Clive mentioned though, you may find that a single beefier motor (I'm thinking Nema34 > 8nm) will be more appropriate with the belt drive. If they're physically connected, you won't loose sync between the screws, and you don't want to get into a situation where the motors are fighting each other.

Dropping the slave motor potentially frees up an axis and saves you buying another motor driver - it might also make a homing routine less confusing!

[chillybo]

Z axis travel is about 130mm. I can adjust the clearance by sliding the assembly up or down the gantry uprights (the benefits of extrusion). Ive built it so I can either use a belt as you suggest or slave it without any new modification. I think your right about using the belt. Only issue is I've only got 4.6 Nm Nema 34's. I could give it a try and see if one can move the gantry ok. If not Id have to splash out on a bigger stepper motor and then id have 2 spare motors.

[chillybo]

BTW its a 4x2 foot machine (roughly)

[Clive S]

BTW its a 4x2 foot machine (roughly)

nema 23 motors probably would have driven the machine fine.

[m.marino]

From the original post you made the statement that 5mm pitch will give you slow rapids. What Voltage do you plan on running this at? As mine is running on slightly more than 60V and is capable of doing 27m/min rapids fully stable. I agree with the other statements that you use either a belt drive or two motor working in sync but never both. Good luck on the build.

Michael

[chillybo]

From the original post you made the statement that 5mm pitch will give you slow rapids. What Voltage do you plan on running this at? As mine is running on slightly more than 60V and is capable of doing 27m/min rapids fully stable. I agree with the other statements that you use either a belt drive or two motor working in sync but never both. Good luck on the build.

Michael

I'l be honest at this point. Electronics are my weak point when it comes to building this machine. I know that low inductance stepper motors can potentially run faster than higher inductance ones. As for what power to run the machine at Im guessing that depends on the power supply output voltage. I really need to build my knowledge around the electrics side. I have yet to purchase stepper drivers and a power supply, control cabinet limit switches etc so any advice would be really appreciated.

regards Chris

[m.marino]

Okay, time for me to pay a bit of my debt forward.

1) Stepper motors have a sweet spot on Voltage. In reality it is a sweet band of voltage that will allow it to operate at it's highest speeds while keeping accurate steps. The formula for that is one of two they are as follows (with examples):

A) \sqrt{I} * 1000. Where I = the inductance of the motor (normally in milliHenries) Which would look like this for an equation 3.2mH 0.032 \sqrt{0.0032}*1000. That equals .0565685 * 1000. Which gives you a rough voltage of 56.57V for optimum usage of the current that the motor will demand. Thereby avoiding coil saturation and the problems that is caused by that issue.

B) \sqrt{I}(ignoring mH) * 32 (interestingly very near the square root of 1000). That get you this \sqrt{3.2}*32. Which gets you 1.78885*32 and that in turn gives you 57.24V as a safety margin. Both of these equations where written to include safety margins. Studying the engineering texts of the 1920's to the 1950's is fun. Brain draining but fun. The electrical texts need a glass of wine or two for those who are not well taught in the various strangeness that is electricity. I hold a full permit from the UK government in amateur radio and still take a glass of wine ( The UK is considered to have one of the toughest amateur radio tests for intermediate and full license permits).

So the above will help you with the Voltage. Current is another issue completely. A motor is under it's heaviest load in two main conditions. First is when it is holding a position against other motion going on (Cutting a straight line and the non cutting axis holding it's position accurately). The other is when under full dynamic load. That area i will leave to someone who understand that side of the motor better than I. As it happens during cutting but not all the time during cutting and is something that I under the function of better then the physics of.

Limits switches and such should be shielded. Full stop. I have dealt with the nightmare of them not being shielded it is not worth it. Also if possible run at 12 to 24 volts (24V is better, as less chance of stray signal noise affecting the switches and giving a false trigger.

While you are thinking about this realize that your tooling expenses can easily reach to over half the amount you put into the machine and many times much more. Don't cut corners on quality with bits it will affect your finished product.

Power Supplies can be bought or built. RSGB (Radio Society of Great Britain) has a couple of really good books on building them and there are folks here who can help as well as well as diagrams on some of the build threads. While it requires safety and understanding it is NOT as difficult as many think it is. Link to their shop page here: https://rsgbshop.org/acatalog/Online...chnical_6.html

I hope this helps you and anyone else that needs a hand on setting things up. I had a lot of help from folks here and a few other sites and paying it forward is the best I can do.

[chillybo]

Okay, time for me to pay a bit of my debt forward.

1) Stepper motors have a sweet spot on Voltage. In reality it is a sweet band of voltage that will allow it to operate at it's highest speeds while keeping accurate steps. The formula for that is one of two they are as follows (with examples):

A) \sqrt{I} * 1000. Where I = the inductance of the motor (normally in milliHenries) Which would look like this for an equation 3.2mH 0.032 \sqrt{0.0032}*1000. That equals .0565685 * 1000. Which gives you a rough voltage of 56.57V for optimum usage of the current that the motor will demand. Thereby avoiding coil saturation and the problems that is caused by that issue.

B) \sqrt{I}(ignoring mH) * 32 (interestingly very near the square root of 1000). That get you this \sqrt{3.2}*32. Which gets you 1.78885*32 and that in turn gives you 57.24V as a safety margin. Both of these equations where written to include safety margins. Studying the engineering texts of the 1920's to the 1950's is fun. Brain draining but fun. The electrical texts need a glass of wine or two for those who are not well taught in the various strangeness that is electricity. I hold a full permit from the UK government in amateur radio and still take a glass of wine ( The UK is considered to have one of the toughest amateur radio tests for intermediate and full license permits).

So the above will help you with the Voltage. Current is another issue completely. A motor is under it's heaviest load in two main conditions. First is when it is holding a position against other motion going on (Cutting a straight line and the non cutting axis holding it's position accurately). The other is when under full dynamic load. That area i will leave to someone who understand that side of the motor better than I. As it happens during cutting but not all the time during cutting and is something that I under the function of better then the physics of.

Limits switches and such should be shielded. Full stop. I have dealt with the nightmare of them not being shielded it is not worth it. Also if possible run at 12 to 24 volts (24V is better, as less chance of stray signal noise affecting the switches and giving a false trigger.

While you are thinking about this realize that your tooling expenses can easily reach to over half the amount you put into the machine and many times much more. Don't cut corners on quality with bits it will affect your finished product.

Power Supplies can be bought or built. RSGB (Radio Society of Great Britain) has a couple of really good books on building them and there are folks here who can help as well as well as diagrams on some of the build threads. While it requires safety and understanding it is NOT as difficult as many think it is. Link to their shop page here: https://rsgbshop.org/acatalog/Online...chnical_6.html

I hope this helps you and anyone else that needs a hand on setting things up. I had a lot of help from folks here and a few other sites and paying it forward is the best I can do.

Thank you very much Michael for explaining this.
The inductance of my nema 34 stepper motors is 3.4 mH and I have 3 of these (two will be slaved). I also have a 4nM nema 23 to move the z axis up and down this is rated at 3mH. As for the nema 34 motors using the calculation this works out at 59 volts. The closest voltage output of a power supply i can find is 60v

https://www.zappautomation.co.uk/ele...-ac-input.html

My question is would this be suitable to run the three Nema 34 steppers and will I need a separate PSU for the z axis?
Regards ...Chris

[m.marino]

Okay, Power supplies the other pain in the backside.

If you go with a switching PSU as you have in the link then you need to have between 150 to 200% of the required current for the motors available. This gets expensive rather fast and is one of the areas folks cut corners often and wonder why they have issues. On the other hand IF you go with a Toroidal transformer you can get away with as little 50% of the required current available (microstepping makes this an even more real option as the amount of current on demand rarely ever reaches full capacity). The other advantage of most unregulated Toroidal transformers is they handle back EMF much better then their switching PSU counter parts (which is one of the reasons for the increased current requirements).

60V will do just fine and you could get away with 48V with a huge loss in available torque. Which would bring the costs down on your PSU. If you go with 60V as your PSU it won't cause any issues as long as you are not pushing it extremely hard and just adding some passive cooling will help deal with the minor heat issue that might develop. I am no an EE and have built my own PSU's and more then a passing background in electrical equipment due to being in amateur radio (Full permit). So I would strongly suggest taking the time to sit down and read and learn a good bit before buying your PSU or building it.

Michael

[chillybo]

Okay, Power supplies the other pain in the backside.

If you go with a switching PSU as you have in the link then you need to have between 150 to 200% of the required current for the motors available. This gets expensive rather fast and is one of the areas folks cut corners often and wonder why they have issues. On the other hand IF you go with a Toroidal transformer you can get away with as little 50% of the required current available (microstepping makes this an even more real option as the amount of current on demand rarely ever reaches full capacity). The other advantage of most unregulated Toroidal transformers is they handle back EMF much better then their switching PSU counter parts (which is one of the reasons for the increased current requirements).

60V will do just fine and you could get away with 48V with a huge loss in available torque. Which would bring the costs down on your PSU. If you go with 60V as your PSU it won't cause any issues as long as you are not pushing it extremely hard and just adding some passive cooling will help deal with the minor heat issue that might develop. I am no an EE and have built my own PSU's and more then a passing background in electrical equipment due to being in amateur radio (Full permit). So I would strongly suggest taking the time to sit down and read and learn a good bit before buying your PSU or building it.

Michael

Thanks Michael. Ive started my research by watching this
https://www.youtube.com/watch?v=lTtYkofw-Jg
The search continues for an unregulated toroidal PSU
Regards Chris