Stepper Driver to CIM

[eli2410]

This doesn't have to do necessarily with FIRST, but this seemed to be the best place to ask it. If I am trying to connect a couple of cim motors to a grbl shield (https://www.synthetos.com/project/grblshield/) what do I need to do? Do they hook up directly or is there something in between, since they are supposed to be stepper motors coming off of the grbl?

[Teamcodeorange]

That shield is meant for stepper motors, which CIM motors aren't. In addition, CIM motors use a vast amount more power than is available from that controller.

You'd be better off controlling it with a talon and some pwm code on your arduino.

Hope this helps.

[eli2410]

The thing is that I want to use CIM motors, but need to program it as a CNC device. I figured that the grbl shield was the best option, but can't figure out how to hook it up. I was thinking of doing it through the talon, but still, I'm unsure how to hook it up to the grbl shield. Any thoughts?

[Ether]

Originally Posted by eli2410

The thing is that I want to use CIM motors, but need to program it as a CNC device.

If you want position (or velocity) control of the CIM, you will have to have an appropriate sensor, and use that sensor to perform closed-loop control of the CIM. The CIM is not a servo; and it's not a stepper motor.

[eli2410]

Originally Posted by Ether

If you want position (or velocity) control of the CIM, you will have to have an appropriate sensor, and use that sensor to perform closed-loop control of the CIM. The CIM is not a servo; and it's not a stepper motor.

I've got the location problem already thought of using other means, though that could be a whole other problem hooking that up.

[wireties]

Originally Posted by Ether

If you want position (or velocity) control of the CIM, you will have to have an appropriate sensor, and use that sensor to perform closed-loop control of the CIM. The CIM is not a servo; and it's not a stepper motor.

Entirely correct! If it helps this is how a common CNC is done these days. They use DC servo motors that are servo-ing on velocity and/or current. Usually this servo loop is hardware-based and built into the amplifiers that drive the motors w/ tach output. The system servos on position using external position sensors, optical scales and such. The position servo is done in software or (in a more expensive setup) in a FPGA or a dedicated computing engine of some sort.

[Al Skierkiewicz]

Eli,
I have to ask how big you are planning to make this robot? The CIM motors are obviously capable of driving a full size 150 lb robot. I suspect what you want is something much smaller and not nearly as fast. While not a big fan of FTC motors, they do the job on that size robot every year and the hardware for driving them is available. Arduino support is also available on the net.
I seriously doubt that a CIM driven CNC would give you the accuracy needed or do a better job than stepper motors. The brush spacing won't give you the accuracy needed for precision machining.

[techhelpbb]

Originally Posted by Al Skierkiewicz

Eli,
I seriously doubt that a CIM driven CNC would give you the accuracy needed or do a better job than stepper motors. The brush spacing won't give you the accuracy needed for precision machining.

I will see you in 80 days from my trip around the world

Considering that you will gear down the CIMs significantly to achieve the target IPM feeds the brushes are not nearly as significant an issue as they would first appear.

I do not disagree that steppers driving directly into an axis are far more likely to produce the fine control easily that someone would desire for this application.

However even my Mitsubishi HC-KFS43K servo motor with encoders and controller are geared down on my machine.
These are no toy servos.

Especially if the axis in question is a lead screw you immediately gain gear ratio.

Besides I can easily demonstrate my point right now.
Find a really high precision X/Y table in a machine shop and turn the cranks.
Many of them require multiple complete revolutions to travel extremely tiny distances.
You don't even need nearly that level of gearing.

Plus you will be magnifying the trust of the axis by gearing down the CIM.
Put the encoders at the output side of the axis and they will move slower and you can measure where the output is.

[magnets]

If you gear your stepper motors correctly, you can use them for anything, including robot that weigh over 1000 pounds.

[Ether]

Originally Posted by magnets

If you gear your stepper motors correctly, you can use them for anything, including robot that weigh over 1000 pounds.

I guess that depends on your definition of "use them".

[techhelpbb]

http://www.cncroutersource.com/stepper-vs-servo.html

Steppers are great for applying lots of force at low expectations of speed.
You can gear a stepper up to get more speed from the resulting output.
This works because the stepper pours torque in while moving slowly.

Other kinds of motors generally need to be geared down.
They produce power and speed in varying characteristics.
Most motors for CNC need to be geared down they move too fast.
Gear a motor down and the output torque increases.

Upside to a DC motor on CNC if you are cutting fast under power you can get there by gearing down.
Upside to a stepper on CNC if you cutting slowly you can move accurately easily and cheaper.

Gantry mills are typical for working over largish working areas.
A 4'x8' sheet of plywood for example.
How long would you like to wait for the stepper to do that job?
If the load is light like a plasma cutter that is one thing.
What if you are pushing around a 1/2+HP router with a big face mill on a deep cut?
A stepper will finish the job and you can even close the stepper loop with a sensor but is your CNC control smart enough to advance a missed step or microstep? Many are not. A detected error will just cause a stop.
On the other hand with a DC motor as noted the resolution of movement is never taken for granted.
A DC motor can take a heck of a beating as FIRST motors do and like FIRST motors they can be operated overloaded.
A DC motor will maintain the torque even as the rate of movement increases.

There is no magic 'right answer' to this.
My point stands: you have CIMS and a way to drive them.
An equivalent servo control and motor would be many hundreds of dollars per axis.
FIRST teams build gearing systems all the time.
Where as more hobby people with no tools, way to fabricate anything or idea how to make or program controls will undoubtedly start with steppers a large percentage of FIRST teams are not faced with those limits.

[daniel_dsouza]

So say that you do decide to use CIMS...

What would your electronics setup look like. Do you have a specific set of encoders in mind? What board will interface between the motors and PC CAM software?

There was someone who used CIM motors to make a 3D printer that printed concrete...That was some time back.

Your posts are like poetry...take it or leave it.

[Teamcodeorange]

Originally Posted by eli2410

The thing is that I want to use CIM motors, but need to program it as a CNC device. I figured that the grbl shield was the best option, but can't figure out how to hook it up. I was thinking of doing it through the talon, but still, I'm unsure how to hook it up to the grbl shield. Any thoughts?

You would be much better off just using a stepper motor in my opinion. CNC machines typically use stepper motors and they aren't that expensive.

[eli2410]

Originally Posted by Teamcodeorange

You would be much better off just using a stepper motor in my opinion. CNC machines typically use stepper motors and they aren't that expensive.

Reason why I was avoiding stepper motors was that the design I want to do is less of a CNC machine and more of a Roomba that only does certain paths instead of covering every spot of the area. Want to make it easily programmable, so I figured making it act like CNC machine would make that easier. Steppers, as far as I knew, wouldn't be able to drive something like a robot.

[Chris is me]

Originally Posted by eli2410

Reason why I was avoiding stepper motors was that the design I want to do is less of a CNC machine and more of a Roomba that only does certain paths instead of covering every spot of the area. Want to make it easily programmable, so I figured making it act like CNC machine would make that easier. Steppers, as far as I knew, wouldn't be able to drive something like a robot.

This is definitely an application for closed loop speed control, and not a stepper motor + stepper motor driver. Stepper motors and drivers allow for open-loop position control when there is no chance of the motor stalling (skipping steps) or slipping. In a Roomba like scenario, the robot is driving on carpet indoors, and could potentially find itself running into solid objects that would either stall the drive motors or spin the robot's wheels in place. With a stepper here you wouldn't be able to maintain reasonably precise positioning in these scenarios.

As others have said, you can't drive a CIM with a stepper motor controller, nor can you recreate the accurate open-loop positioning of a stepper motor with a CIM.

I think the simplest way to accurately do something like this would be to use undriven follower wheels hooked up to encoders for position feedback. Properly done, these will allow for decently precise position information across a variety of different floors, and if your drive wheels slip (e.g. hung up on a small object, driving into a wall) you won't lose any precision since the follower wheels would not be moving.