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Topic: Start with CNC (Read 2 times) previous topic - next topic

polymorph

The TB6560 can do up to 2.5A per phase.

This and the A4988 are what are called chopper drivers. Basically, they are switching current regulators.

http://www.instructables.com/id/TB6560-Microstepping-Bipolar-Chopper-Stepper-Motor/

Some problems with generic TB6560 boards:

http://www.homediystuff.com/fixing-a-chinese-made-cnc-stepper-motor-driver-board-tb6560-chips/
Steve Greenfield AE7HD
CET Consumer Electronics and Computer
Please don't read your attitudes into my messages

Robin2

The Pololu DRV8825 seems to be a bit more powerful than the A4988 but not as powerful as the TB6560.

...R

daniellyall

do not get a TB6560 board they more than like will blow up as soon as they are connected. or it will arrive dead. made that mistake myself.
if you wont a machine that will run all day and night you need to spend the money on good quality stepper drives as you will regret it and will end up get them in the end.

polymorph

That's kind of a blanket condemnation. If someone bought an Arduino that "blew up", would you tell everyone to never by an Arduino from anyone?
Steve Greenfield AE7HD
CET Consumer Electronics and Computer
Please don't read your attitudes into my messages

Yaro

They are too expensive related to A4988.



You only miss steps if you try to get the motor to operate beyond its capacity. For example trying to move a heavy load with an underpowered motor or trying to accelerate (or decelerate) a load too quickly.

The A4988 (and similar purpose made stepper driver boards) have the ability to limit the current in the motor coil. The A4988 has a small preset potentiometer to adjust the maximum current. The Pololu website explains how to use it.

If you have the maximum current set correctly then regardless of the voltage supplied to the stepper driver board it will only allow the correct current to flow. Of course the voltage must not exceed the limits of the stepper driver board. And there is probably a minimum voltage for the driver board also.

The reason for using a high voltage is to overcome the inductance of the motor coils in order to reach the maximum permitted current as quickly as possible.

The voltage that is normally quoted for the motor is the DC voltage that would produce the maximum current in the coil based on Ohms law. For practical puposes the voltage number is irrelevant. The important number is the permitted current.

...R


If i have a motor with 1.5 ohm per coil and a rated current of 1.7A, i can put on A4988 a 35v power supply and it will not permit to fry my motor and will provide the current I need to motor? So the only limit of this module max 1 A per coil? If so, can you advice me a more powerfull motor driver that's cheap as A4988 or with similar price?

Otherwise, if I use an A4988 on a 1.7A motor I will use only 56% of it's motor power?


Someone can confirm my suppose?

Robin2


They are too expensive related to A4988.



Otherwise, if I use an A4988 on a 1.7A motor I will use only 56% of it's motor power?


Someone can confirm my suppose?


What max current are you proposing to use that gave you the number of 56%?
And do you mean power or torque?

...R

dave-in-nj


They are too expensive related to A4988.


what is the cost of failure ?

the a4988 only costs about $5 and you can drive your motor.

time to order the unit, install it and test it.

you are never going to find the answers on a web page, a data sheet or a forum.

the only place you will find the answer is on your device, in your shop.

would you rather use a $300 linear bearing with the lowest cooefficent in order to use a $3 driver because the $3.25 driver cost too much ?

what will you say if you put on the motor and find the $3.25 driver and motor have 5 times more torque than you need ?

the power of the motor is often used to overcome the poor design of the device.  the first mechanical iteration shows the possibility of operation, the second shows the refinement of both over design and under design.   be happy if version 5 works flawless.  be happier if your first design can actually be built and works at all.

sounds like you are an engineer who wants to know everything before actually doing anything.

and, in the end, if that $5 driver is wrong and underpowered, you will still find uses for it.  there are just too many times you want to grab something to try it out and use whatever is at hand.

if you truly only want to build it once, then buy the Gecko 201 vampire.  at $143 it WILL power your motor.  no questions.

also buy a matching power supply.   should not cost over $100.  but you are guaranteed that if a stepper can work in that application, that combination will drive it.

spending $5 on the driver you would be KNOW already.  this whole thread is really about a part that may cost $15.  without any actual measurements, no tests and unknown quantities. 

Sorry if I seem abrupt, but this thread is going around in circles and has been answered WITHOUT any actual data.

what is the load ? what is the MEASURED force needed ? how are you driving, belts ? gears ? screws ?

what PROBLEMS with your device are you EXPERIENCING ?

it started on June 27 and it appears that no project is being built and the same questions are being asked.  what is the force needed to drive your machine ?

by this time, parts could have been ordered, arrived, the device built and troubleshooting underway.

if your machine is ever going to be built, then build it, tie a string on the pulley and add weight until it moved.  calculate force and you do not have to keep others guessing about what is the color of a flower in a room without light.


steinie44

Quote

it started on June 27 and it appears that no project is being built and the same questions are being asked.  what is the force needed to drive your machine ?

by this time, parts could have been ordered, arrived, the device built and troubleshooting underway.

if your machine is ever going to be built, then build it, tie a string on the pulley and add weight until it moved.  calculate force and you do not have to keep others guessing about what is the color of a flower in a room without light.

Agree 100%
This is a ARDUINO FORUM
SEE REPLY #3

Yaro

I don't understand why you enrage. Before do any order i need to know if the piece is suitable to my purposes to not loose money(no matter if 1$ or 100$) and time(ship is very long) and the only method is to asked opinion to people that may have experience with this products and modules.

I asked ELECTRONICS things and not mechanical things and this is related to this forum since i use arduino to control them, so, if you don't know what are we talking about, please stop enrage.

Now i'm talking about motor and its torque NOT related to any cnc mechanics or load.

Since i have not experience with motor driver modules and i don't want to fry or buy wrong module/motor, i asked:
I have a stepper motor 1.5 ohm per coil and a rated current of 1.7A, i see there is a trimmer on a4988, is this used to regulate current? So with an 35v power supply i can regulate to 1,7A per coil(2A per coil max for A4988) and the motor will not fry, that's right? Or is regulated by circuit?

Otherwise, if I use an A4988 with 1A per coil on a 1.7A motor(1A is 56% of 1.7A) I will use only 56% of it's motor max torque(is approximated excluding alot of factors)?

polymorph

Yes, the trimpot is to adjust the current. For some reason, Pololu designed it so that you are only using part of the trimpot travel.

http://www.pololu.com/product/1182

Quote
Another way to set the current limit is to measure the voltage on the "ref" pin and to calculate the resulting current limit (the current sense resistors are 0.05?). The ref pin voltage is accessible on a via that is circled on the bottom silkscreen of the circuit board. The current limit relates to the reference voltage as follows:

Current Limit = VREF × 2.5

So, for example, if the reference voltage is 0.3 V, the current limit is 0.75 A. As mentioned above, in full step mode, the current through the coils is limited to 70% of the current limit, so to get a full-step coil current of 1 A, the current limit should be 1 A/0.7=1.4 A, which corresponds to a VREF of 1.4 A/2.5=0.56 V. See the A4988 datasheet for more information.


You can also read VREF by simply attaching a cliplead to the screwdriver you are using to set the trimpot, as the metal body of that is also connected to the wiper, which is VREF. And you don't need to have the stepper connected while adjusting it this way.

Note that the regular A4988 board is rated for 1A, but says 2A with extra cooling.

I'm putting small heat sinks on my chips, using fans to force cooling, and replacing R5 with a 56k resistor. Heatsinks meant for VGA RAM are the right size and some come with heat conductive doublestick tape, here are the ones I'm using:

http://www.amazon.com/gp/product/B007XACV8O/ref=oh_details_o03_s01_i00?ie=UTF8&psc=1

The Black edition has more layers in the PCB, so it should run cooler at higher currents. Same ultimate limit of 2A with heatsinks and fan cooling

http://www.pololu.com/product/2128

In any case, if you run your steppers at 1.7A, the full rated current, they will get too hot to touch. That is normal, but I prefer to run mine cooler. Either with less current, if torque limits permit, or fan cooling.

Yes, that is probably a good approximation, running them at 1A will give you 1/1.7 = 59% torque.
Steve Greenfield AE7HD
CET Consumer Electronics and Computer
Please don't read your attitudes into my messages

polymorph

BTW, I'm planning on making a small laser cutter, something probably using a 10W blue laser to cut solder paste stencils. To move the gantry without racking, I have not decided yet if it is easier to use a shaft to carry torque to leadscrews on both rails, or to simply use two sync'd steppers. I plan on using something like Makerslide and NEMA 17 motors, 60oz-in or thereabouts.
Steve Greenfield AE7HD
CET Consumer Electronics and Computer
Please don't read your attitudes into my messages

Yaro


Yes, the trimpot is to adjust the current. For some reason, Pololu designed it so that you are only using part of the trimpot travel.

http://www.pololu.com/product/1182

Quote
Another way to set the current limit is to measure the voltage on the "ref" pin and to calculate the resulting current limit (the current sense resistors are 0.05?). The ref pin voltage is accessible on a via that is circled on the bottom silkscreen of the circuit board. The current limit relates to the reference voltage as follows:

Current Limit = VREF × 2.5

So, for example, if the reference voltage is 0.3 V, the current limit is 0.75 A. As mentioned above, in full step mode, the current through the coils is limited to 70% of the current limit, so to get a full-step coil current of 1 A, the current limit should be 1 A/0.7=1.4 A, which corresponds to a VREF of 1.4 A/2.5=0.56 V. See the A4988 datasheet for more information.


You can also read VREF by simply attaching a cliplead to the screwdriver you are using to set the trimpot, as the metal body of that is also connected to the wiper, which is VREF. And you don't need to have the stepper connected while adjusting it this way.

Note that the regular A4988 board is rated for 1A, but says 2A with extra cooling.

I'm putting small heat sinks on my chips, using fans to force cooling, and replacing R5 with a 56k resistor. Heatsinks meant for VGA RAM are the right size and some come with heat conductive doublestick tape, here are the ones I'm using:

http://www.amazon.com/gp/product/B007XACV8O/ref=oh_details_o03_s01_i00?ie=UTF8&psc=1

The Black edition has more layers in the PCB, so it should run cooler at higher currents. Same ultimate limit of 2A with heatsinks and fan cooling

http://www.pololu.com/product/2128

In any case, if you run your steppers at 1.7A, the full rated current, they will get too hot to touch. That is normal, but I prefer to run mine cooler. Either with less current, if torque limits permit, or fan cooling.

Yes, that is probably a good approximation, running them at 1A will give you 1/1.7 = 59% torque.


Nice answer, do you think that more voltage will cause more heat even i'll use low current(less then 1.7A)? Do you think that the gain in motor speed worth this?

polymorph

No, more voltage shouldn't cause more heat. Not appreciable amounts. Actually, more voltage means a shorter duty cycle for the chopper, so it may mean -less- heat.
Steve Greenfield AE7HD
CET Consumer Electronics and Computer
Please don't read your attitudes into my messages

daniellyall

A lazer machine can be quite light smaller to a 3D printer, if you look up force calculator or Nm/OZ calculator there are a few on line they work well, you input weight and speed and how many Nm the stepper motor is and if its wrong you will get a negative number in return.
also look up the gecko site the have a very good paper on stepper motors.
you need to work out the required stepper to use to know what stepper driver to use.
if you do this it will make life easer knowing you have the correct size stepper makes it easy to choose the stepper driver because you will know what you need.
the TB6560 boards are bad there is a lot of post on cnczone and mach3 forum about them they can be fix but this is only a temp fix as there are made on the dirt cheap, the Tb6560 chips are good it just the board they are attached to.

polymorph

Build your own TB6560?

http://www.instructables.com/id/TB6560-Microstepping-Bipolar-Chopper-Stepper-Motor/
Steve Greenfield AE7HD
CET Consumer Electronics and Computer
Please don't read your attitudes into my messages

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