SLAMStepper/Bob purchase questions...

[racedirector]

Hi

I am looking at going with the SLAMStepper drivers for my machines, love the idea of opensource I have a question or two for those in the know as I plan my purchases this month.

Currently in my shopping cart I have 4x SLAMSteppers and various parts for the 4 axis BOB. I wanted to check I have what I need on terms of going from PC to the motors....

The BOB parts I have are:

1x PCB kit (416012)
1x 5v Power Kit (416025)
1x Parallel connector & cable (416036)
1x 4way cable (416014)

Is this what I need to do the job? Am I missing anything?

I would also like to turn the router and the vacuum on with my software (either Mach or EMC) so would like to use relays but there isn't a relay kit available yet. So what would I need to integrate them into the BOB?

And lastly, I plan to use either 387oz-in or 425oz-in motors initially with a 48V power supply. Are these going to be a problem?

Any help would be very much appreciated.

Cheers
Bruce

[doorknob]

I don't have direct experience with the SLAMStepper, however apparently it is based on the Allegro SLA7062M.

If I am reading it correctly, it looks like the datasheet for the SLA7062M states that the absolute maximum voltage rating is 46 volts, while the recommended maximum voltage is 44 volts, and the SLAMStepper web page refers to 40 volts. So applying 48 volts to the circuit may be flirting with disaster and smoke.

[racedirector]

Ah crap, missed that. I planned to start with 48V and then increase as funds became available. Looks like I will have to forgo the open source route and buy commercial

Cheers
Bruce

[James Newton]

doorknob is right.

I'm just amazed that you need 48volts. What on earth are you driving.

[racedirector]

Originally Posted by James Newton doorknob is right. I'm just amazed that you need 48volts. What on earth are you driving.

Ahhh what is so amazing about 48V? Look around the forum, there are a ton of people driving their setups with 48V and more.

I admit I am still learning about all of this and taking my cues from those who have already "been there done that". I am seeing posts & threads that talk about getting the most efficiency from their motors by driving them with more volts. Please do tell me if I am wrong in assuming this information is correct.

As a starter this is what I want to do with the gear.....

My next machine will probably be a Joes2006 or a Lionclaw LC50B. While these are not a big routers, in the future I am building a Joes 4x4 Hybrid (bought the plans the other day). I want to cut anything from wood to acrylic to aluminium eventually and want to "futureproof" my electronics as much as possible hence my looking for controllers to work a 4x4 Hybrid cutting the materials above.

I have seen that monster CNC that uses SlamSteppers to cut surfboards but that is foam. Your surprise at needing 48V makes me think that 36V running 3xx oz-in motors could handle what I want to do in the future, please correct me if I am wrong as I will duly bow down to superior knowledge and continue researching commercial controllers.

Cheers
Bruce

[James Newton]

Well, first, just because people are doing it, doesn't mean its necessary or even wise. Higher supply voltage allows faster changes to the current and field strength in the motor coils and so faster rotation. But there is also a balance; at higher PSU voltages the motor will get hotter (because of increased wattage) and it will jerk faster from step to step, so you get more resonance and more problems with stalling. A higher voltage can actually stop the motor getting through resonance bands.

The rule of thumb is: Watts = IPM * Lbs / 531 where Watts is Amps * Volts and IPM is Inches Per Minute. And so with a 100 watt drive you can easily push 40 or 50 lbs of axis load around at 1000 IPM. 3 amps @ 40 volts is 120 watts.

Now, that does not count the pressure caused by the cutting head, but if the head is sharp and the spindle isn't vibrating and the feed rate is reasonable, that really should not be a huge "back pressure". If you start missing steps when you cut, something else is wrong. Yes, you probably need more force to cut steel than you do to cut foam, but it isn't /much/ more. Or at least that has been my experience, I will admit that I haven't done any work in steel and not much in aluminum for at matter. But when I did, the problems I had were with the cutting bit, not the mill. LOL...

I'd put my money into bigger motors, so they will run cool at lower than rated current and voltage, and then get the smallest driver and set the lowest current and voltage that moves the load reliably. That will avoid heating the motors and loosing power after an hours operation just when you think it's all going so well...

[racedirector]

Thanks James, explained so even people like me can understand

Just to clarify, a combo of, say, 425/495 oz-in steppers coupled with, say, SlamSteppers powered by 36V would be a better option for longevity of motors and my sanity...?

Cheers
Bruce

[ger21]

425 and 495 oz Nema 23's may be a bad choice, imo. They are high inductance motors, and not ideal for higher rpm operation.

Most people here use G540's and the majority use the lower inductance 381. The reason, is that at higher rpm's, they'll have more torque than the 425 and even 495 oz motors.

Having said that, what's even more important is that you match the motors to the application. If the motors won't be spinning over 400-500 rpm, then the 495 oz motors may be a better choice. But if they'll be spinning at 1000 rpm or more, than the larger motors are probably not the best choice.

If you plan on using the same motors for multiple machines, chances are that they won't be ideal for at least one of them.

[racedirector]

Now I am even more confused. I really appreciate the fact that there are some very knowledgeable people on here with regards to cnc machines and their makeup but now I have one saying go bigger motors and one saying smaller motors are the better choice.

Is there an absolute noobs guide to selecting the right components, surely there is more people like me starting down the road of cnc. In my case my tight budget doesn't allow buying 20 different configurations to see what is best. The G540 for example is $250 - $300 here in Aus yet I can get get 4 slamsteppers for example plus bob for around U$170.00. That $50 to $100 or so dollar difference is huge in my case and it could be applied somewhere else like software.

I am not trying to be difficult here, I am just trying to understand how to select the right combination of things.

Cheers
Bruce

[Bob La Londe]

I've got two machines running g540s and 382 oz stepeprs. They are ok, but they definitely are not fast. I get a very reliable 45 IPM out of both of them in XY & I turned down Z to 30. It is my understanding the limitation here is partly my using an LPT and putting all the timing load on the PC processor, but...

Originally Posted by ger21 425 and 495 oz Nema 23's may be a bad choice, imo. They are high inductance motors, and not ideal for higher rpm operation. Most people here use G540's and the majority use the lower inductance 381. The reason, is that at higher rpm's, they'll have more torque than the 425 and even 495 oz motors. Having said that, what's even more important is that you match the motors to the application. If the motors won't be spinning over 400-500 rpm, then the 495 oz motors may be a better choice. But if they'll be spinning at 1000 rpm or more, than the larger motors are probably not the best choice. If you plan on using the same motors for multiple machines, chances are that they won't be ideal for at least one of them.

[ger21]

I am not trying to be difficult here, I am just trying to understand how to select the right combination of things.

Choose a machine design, then choose your performance goals, then select motors and drives that will allow you to achieve those goals.

When you're talking about using them on more than one machine, and you're not sure which machine, that makes choosing more complicated.
Whether you're using screws or rack and pinion makes a difference. If you're using screws, the choice of screws makes a big difference.

Choosing the absolute best choice is very complicated.

For router users, The G540 and 380 oz motors work for a very diverse group of machines.

It looks like the SLAm drives are similar to the hobby CNC. Many people have used those drives successfully for many years, before the G540 became available. Note that because they are unipolar, you only get about 300 oz of torque with a 425oz motor. The 425 oz motor is actually a good choice for that board.

The G540 can supply more current, and can run at about 35% higher voltages. But it costs more.

If your on a budget, the SLAm drives and 425oz motors should work OK for you.

[racedirector]

Thanks for that Gerry, I was just about to ask about the whole bipolar/unipolar trip as well.

Bob brings up an interesting point. I have no idea if it is his machine or the motor/controller combination but compared with what I am reading on two different forums his speeds are slow. There are those that toute 200, 300, 500 ipm on their machines but say they are using G540's etc. All I know is that running Mach3 without a machine connected at 40 -50 ipm looks painfully slow and I would want to be running a little faster that that. Have I thrown another spanner in the works?

Machines: I am currently building one whose sole purpose in life will be to cut out a Joes2006 or Lionclaw LC50B as mentioned above. The screws of my bitza will be used on the next one and they are 1/2 6tpi 1 start acme. For the hybrid at a later date (need to save heaps for that one) I will probably go with either 16mm ballscrew or r&p depending on availability and budget.

So in the immediate future is a skate bearing/pipe 1/2 acme 6 tpi 1 start machine...

Cheers
Bruce