Quite an Unusual one

[Clive S]

I would always expect encoder feedback to go directly to the driver, you don't way any delay introduced, it should go directly to the summing junction that should also exist in the driver.
If feedback does go via the bob on any system, I would steer clear of it.

Or perhaps to the motion control board (driver) .. Clive

[EddyCurrent]

Or perhaps to the motion control board (driver) .. Clive

Clive, sorry I'm not sure what you mean ?
To clarify, by driver I meant motion control board. Feedback should go to that and not via the bob.

[Clive S]

Clive, sorry I'm not sure what you mean ?
To clarify, by driver I meant motion control board. Feedback should go to that and not via the bob.

You are 100% correct of course, I was just trying to differentiate between a simple BOB and a full blown motion controller (driver) type.

Sorry for any confusion. ..Clive

[EddyCurrent]

You are 100% correct of course, I was just trying to differentiate between a simple BOB and a full blown motion controller (driver) type.

Sorry for any confusion. ..Clive

I thought I'd had too many 'old speckled hens'

[Jonathan]

Clive, sorry I'm not sure what you mean ?
To clarify, by driver I meant motion control board. Feedback should go to that and not via the bob.

There's actually a lot of debate on this topic when using LinuxCNC. Since LinuxCNC is real-time, you can implement the PID controller within the computer (instead of the motor drive), and have the computer output speed instead of position (step/dir) signals. That can work well, especially if you use a PCI card. Some people consider that better as then the computer is always tracking the following error... but just saying that is really oversimplifying the situation so if interested, Google it.

[Bart]

P [W]
Stands for maximum (instantaneous) mechanical power of a motor when going at full speed and utilizing full torque.
This wont happen in real life as with stepper motors you'll have a safety margin of 1/2 so you will get only half of that power from a stepper motor. It's also important to bear in mind that you will utilize half of this power only in two instances. First instance, when you're accelerating to full speed at full allowable acceleration during fraction of a sec just before reaching max speed. Second, when cutting at full speed with full allowable force. Otherwise you're using only fractions of that power.

Cutting a steel is done between 1 and 2 m/min so if your Vmax is 10 m/min than you will use only 10-20% of Pmax and only if the gantry had to be pushed with full allowable force which is unlikely to happen.

In a cell where you input a torque of motor it was required to input a combined torque of motors for given axis. Now you just input a torque of motor and number of motors.

I also see that you are interested in power of motors, so I've attached one more spreadsheet inside to calculate various mechanical powers of motor, as well as some information on power and current drawn from power supply - to help choose PS.

Attachment 11075

I don't know much about application of servo motors but from what i briefly read, the most important feature of a Servo Motors is a possibility to overload them up to 10 times which is not possible with stepper motors due to the nature of a driver.

If this overloading feature is possible than consider following.

For a 400 W servo motor that you've selected (assuming an overload factor of 5) you can get as much as 2000W for a fraction of a sec.
Now, if you open my spreadsheet (the new one) all the data there are for my design.
Equivalent Gantry Weight 290kg
Motors: 2x 1,5Nm -> maximum power of 150W per motor but steppers have to be used with some safety factor so as not to loose steps.

I've taken 1/2 so I'm Using only 75W of each motor. With that torque/power I can accelerate 290kg gantry to 10m/min (393 inches/min) in 55 mili sec. That's quite fast but with your servo and 2000W you will be able to accelerate it to the same speed in as little as 4,5 ms over a distance of 0,38 mm, ceteris paribus.

So what I want to say is: don't over-invest in motors.

Best regards

[Boyan Silyavski]

After reading these days a lot of motion control manuals, i think i have it more clear. The majority of them have their own brand daughter boards and that's the main reason it seems that they can close the loop directly on the board, for servos and steppers. Also most of the expensive ones have possibility to input 2 encoder signals on 1 axis, so they can control backslash this way. Also it seems connected to some external servo drives, even if the servo drive closes the loop, it can transmit it to the board at the same time, for the previous reason or for some extra functions.

Now i just cant believe how little choice there is for 5 and up axis BOBs and combinations, especially to work with mach3. I almost discarded the Galil. Read in forums there is no support at all if you don't buy it new. Which is crazy for a product that is worth thousands. Also 99% at ebay sell them on As Is basis, but not for As Is money. I dont see my self paying hard earned cash for a board that is not guaranteed at least a week from the sale. Also read that many of them are possibly tweaked for a certain customer, so even less support. And later to have problems with the Mach3 plugin...I was tempted. And still i am.


Its unbelievable how poor the choice of BOB is today. Couldn't be that more clear what is needed:

-USB or Ethernet board,small sized, mach3 plugin, on board spindle control, on board 220AC/transformer, opto isolated inputs and outputs, 6-8 axis,4 relays,...

Combining all of these is almost impossible and starts to get expensive. Same price as second hand motion controller

[JAZZCNC]

Its unbelievable how poor the choice of BOB is today. Couldn't be that more clear what is needed:

-USB or Ethernet board,small sized, mach3 plugin, on board spindle control, on board 220AC/transformer, opto isolated inputs and outputs, 6-8 axis,4 relays,...

Combining all of these is almost impossible and starts to get expensive. Same price as second hand motion controller

If you don't need slaved motors and using steppers then have a look at the Csmio-IP-M controller or the Csmio-IP-S if you need slaved motors or using Servos with high count encoders and want the full package. Here CS-Lab - CSMIO - CNC Ethernet Controllers- inexpensive solutions - CS-Lab CNC controllers CNC Machining CNC software.

They are very high quality Ethernet Motion control units with industry standard 24V differential digital I/O so very good at handling electrical noise also come with very High quality Analogue spindle output built in. (Sorry to say this Eddy but those Spindle 4 boards are very erratic with speeds jumping around all over the place, used a couple now and not impressed.)

No BOB or external Spindle board is needed all mounts on industry Standard Din rail with separate quality Din rail connectors. Simple to fit and install plus very very neat.

I've used just about every Motion control card now in the Diy range so Sub £300 and I can tell you 100% these knock the spots off any other.

I've fitted 2 now but only on new build machines so couldn't compare same machine performance against other Cards but unfortunately and very very frustratingly for ME that's just changed.!!
The Russian PLCM E3P I've been using on my own machine has just gone faulty, doing strange things and tripping with noise issues from VFD, either using USB or Ethernet connections.

Couldn't have happened at worse time has I've been flat out chasing my arse between Family health issues and getting stuff done plus now every where is closed for Xmas. Just lent my spare ESS smooth stepper to a friend who isn't answering his bloody phone, just sold the spare spare USB SS has never used it. . Arghhhh . .(PLCM E3P is now smashed into 1,0000000000000 bits.!!! and NO it gave me no satisfaction other than to vent.!)

No way was I going back to Parallel port, plus laptop doesn't have PP. So I've got Csmio-IP-M which was half fitted into a control box destined for machine currently !!.Trying.!! to finish but needs must so out it came temporarily until I can get another Card.

WOW . . . 20mins later it's wired up, software installed and working with full spindle control.
Worked Straight off Copy of my Old Mach3 profile with just a quick Plug-in swap and pin assignments with very little tweaking of motor tuning required. . . In fact this is what really impressed me has now can tune the motors much higher even thou the PLCM-E3P and CSMIO_IP_M are both supposed to be 100Khz.

I haven't had or got much time to play and don't need the speed anyway but the first dabble took my My Y axis from Max 11mtr/min & 950s/s Accel to stable 14Mtr/min at 1200s/s and that's with 5mm pitch screw direct drive on 3.5Nm Nema 34 motor at 75v. That's 2800Rpm from Nema 34 motor.!!!. . I was quite impressed with 2200rpm the PLCM allowed.!!

The Motors so sound very sweet even at these dizzy heights and the pulses are clearly very smooth has the movement is excellent even at very low feeds.
Wouldn't ever run at that speed has I don't need it but it just shows not all Cards are Equal and I'm positive this speed increase is down to the quality of the product has it's the only thing that has changed on my machine.! . . .Very impressive and I won't be coming off any time soon so I better get another ordered ASAP.

. . . . . HAPPY NEW YEAR EVERYONE. . . .Keep smiling.

[Boyan Silyavski]

Lately spend too much time on choosing the BOB, motors and drives, which delayed my order for the ball screws and the rails. After all that talk, last night saw 2 interesting Galil listings on fleabay and something made me push the button and send best offer, thinking that if one accepts, will cancel the offer to the other.
Well, after i woke up this morning i found my self the happy future owner of 2 galil BOBs. i thought of excusing myself to one of them, then decided and payed them both. With the idea if one not working to use the other, or at least to see which one i like best. the other goes later for next machine or whatever.

So i bought the GALIL DMC-1880 PCI 8 axis Optima motion controller and the Galil DMC-2183 Ethernet/RS232 8-Axis Motion Controllers & 2 ICM-20105 Opto I/O .
Both seem to work with the Mach3 plugin / yes i checked before sending the offers/ .

I have some feeling that i made the right decision with these. What do you think?

Now i have to decide on the drives and motors. First of all now i can run steppers with encoder and servo motors directly closing the loop at the motion controller. Which in fact can lower the price of the build, implementing servos only for moving the gantry and steppers on the Z if i decide so.

No i am looking at a Galil AMP-19540 at ebay which coul drive directly 4 dc servos up to 500w each, costs only 100euro and connects directly to one of the BOBs i bought - the DMC-1880 . It seems this purchace can save me a lot of money on other drives and cheapen considerably the project, sourcing only the motors.

However i understand nothing of these type of servo and drives for me the description is like Chinese, i only see 500W :-) , here is from the description:

Galil's AMP-19540 is a 4-axis amplifier for driving brush or brushless motors up to 500 Watts. By interfacing directly to Galil's DMC-18x2, DMC-18x0, or DMC-18x6 controllers, it provides a cost-effective controller/drive solution for multi-axis applications. The AMP-19540 contains four transconductance, PWM amplifiers for driving brush or brushless motors. Each amplifier operates at 18V to 80V dc, up to 7 Amps continuous, 10 Amps peak. The AMP-19540 gain setting is easily configured with jumpers. The PWM switching frequency is 60 kHz.

The AMP-19520/40 is a brush/brushless trans-conductance PWM amplifier. The amplifier operates in torque mode and will output a motor current proportional to the command signal input.

Input Voltage: 18-80 VDC
Continuous Current: 7 amps
Peak Current 10 amps
Amplifier Gain 0.4, 0.7, or 1.0 A/V (jumper adjustable)
Switching Frequency 60 kHz (up to 175 kHz available--contact Galil)
Minimum Load Inductance 0.5 mH (low inductance option available)
Communtation Angle 120o (60o option available)

So, can some one help here please:

Can i find easily BLDC motors suitable for the drives, with hall sensors as far as i understood, new from ali express or from ebay? Are these drives any good, mean in 2014? And for my build?

[EddyCurrent]

Silyavski, I know this is not what you are after but may be of use.

Got one of these the other day, great little unit and great price.

5V 1/2/4/8 12V 16 Channel Relay Module W/ LED Indicator Light For Arduino | eBay

also these spindle boards work good and not too high a price
System4