Stepper Driver to CIM
 

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?

Re: Stepper Driver to CIM
 

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.

Re: Stepper Driver to CIM
 

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?

Re: Stepper Driver to CIM
 

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.

Re: Stepper Driver to CIM
 

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

Re: Stepper Driver to CIM
 

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.

Re: Stepper Driver to CIM
 

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.

Re: Stepper Driver to CIM
 

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.

Re: Stepper Driver to CIM
 

The DRV8818 stepper drivers from TI used on the grbl sheild are for stepper motors and are not compatible with brushed motors. Stepper motors are electrically and fuctionaly different from brushed motors (like a CIM). Closed loop speed control with talons and encoders are the way to go.

Re: Stepper Driver to CIM
 

This topic confuses me.

Driving a CIM open loop is easy with existing FIRST motor controls.
Get a Talon, Victor or Jaguar and the power electronics are done.
Arduino can easily produce PWM.
Most servo CNC controls use PWM on the low end anyway.
They close the loop with encoders, potentiometers or other sensors in the control system.

Driving a CIM closed loop could be done with a Jaguar alone but that would hybrid part of the control into the Jaguar.

I use steppers to drive non-FIRST robots all the time.
Position in the environment exceeds the sort of sensing most CNC controls do.
That is why CNC machines can be very dangerous.
They do not 'see' hands in the work area.
There is no reason you can not use a stepper to drive a robot at all.

I know this post is 60 days old but I just came across it.
I am more confused why you would want to drive a robot around on G-code or M-code.
I doubt Mach 3 or BobCAD support a driving milling machine :)
Then again a router on wheels has been done an I doubt the software would know either.

I have considered using a FIRST size robot to haul around loads but at low speed and not under CNC control.
Bolt the milling machine to the robot frame?
That is a strange way to look at a portable machine tool.

Kidding:
Hey the driving milling machine needs some flood coolant.
Drive it through the locker room showers!
No...no...stop milling Lexan in the hall way now you need to tow a vacuum.

Not kidding:
I want to build a FIRST motor based CNC system.
I may even try to use the Talon or Victor for that purpose.

It only makes good sense when you think about it:

Every year we accumulate more CIMs and motor controls (drivers in CNC parlance).
We have the ever growing pile of parts.
A CIM is a 100+A 12V motor. That's plenty big enough to drive a CNC axis.
You need to control the speed of the CIM which we do all the time.
You need feedback and that's a concept we basically teach all the time.
All the community needs are viable plans and a working example.
It's not like we couldn't use a CNC machine in the competition!
So why not part the never ending pile as an act of technology recycling?

We could use but don't need fancy linear bearings.
You can use a piece of black pipe or even 80/20 extrusion as the linear system.
Just use skateboard bearings or whatever you can find.
You can gear down the axis with the cogged belts which is common for servo systems anyway.
You could probably use AndyMark gear boxes but the backlash would increase.
You don't need fancy ACME or roller ball screws, you can pull with belts or rack and pinion.

If you sit and think about this for a while you'll realize that you are sitting on a mountain of CNC parts.
Every year you participate you could be building a robot to make building more robots easier.

Parts required to make this work:
1. A computer to act as the control system.
3D printers can use G-code and M-code but I doubt the Arduino CNC controller has the power to drive a larger CNC.
There are plenty of PC based CNC control systems: EMC2 (Linux), Mach3 (Windows), KCAM (Older Windows), TurboCNC (DOS).
2. A suitable interface between the computer controller and the FIRST motor controls.
This for the most part already exists off the shelf.
I suspect the FIRST control system could be rigged to do this if you did not want to buy or build this.
3. Plates to put the CIMs on the machine with the necessary gearing to drive an axis at acceptable velocity and thrust.
This is perhaps the part most likely to require machine tools already to make.
4. A machine design for a gantry router.
I already have a pile of my own and other people's designs for this purpose.

Re: Stepper Driver to CIM
 

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.

Re: Stepper Driver to CIM
 

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.

Re: Stepper Driver to CIM
 

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.

Re: Stepper Driver to CIM
 

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

Re: Stepper Driver to CIM
 

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