[FPV_GTp]

I would like to do the same as what truetex did , Converting an Ordinary DC Motor to a Servomotor http://truetex.com/servomod.htm.

BUT

Question ? - What hobby CNC servo driver will drive a 12volt Permanent magnet DC motors

I have had a look at a few variety 12volt Permanent magnet DC motors are typically used in automotive car industry. Wiper motors of cars , heater motors of cars , electri-window regulator motors , ABS motors of cars , electric fan motors of a car and some starter motors that are reduction drive units made by bosch Permanent magnet DC motors ( VERY STRONG MOTOR ) which all are 12volt Permanent magnet DC motors common found in everyday life . Very cheap and abundant.

There are 2 pole versions and 4 pole versions . Some have bushes and some have bearings supporting there armature , some are nice and compact and very strong motors.

By doing what truetex has done in his website , these motors would make a great cheap and affordable servo motor for small cnc-tables http://truetex.com/servomod.htm. Just add a encoder and you have a servo motor.

Does anyone know of any 12Volt servo motor drivers that exist or any driver that will control a 12volt Permanent magnet DC motors ????

Just list a link to a website in this thread please and any information would be appreciated.

I haven't been lazy i have been search the web and corresponded with a few manufactures but to no avail. So i thought i would try for some assistance in www.cnczone.com.

This is for a experimental small cnc table i want to make so i can carry it around with me . Want to keep the costs way down.

cheers

[Al_The_Man]

You probabally want to look into the RC and robotics products, http://www.dimensionengineering.com/Sabertooth2X5.htm
to get low voltage drives.
You can convert these to servo action, but they will always lack the true features that make a DC motor 'Servo Grade'.
Al.

[FPV_GTp]

You probabally want to look into the RC and robotics products, http://www.dimensionengineering.com/Sabertooth2X5.htm
to get low voltage drives.
You can convert these to servo action, but they will always lack the true features that make a DC motor 'Servo Grade'.
Al.

Hi

Thanks AL_The_Man , that is a interesting website .

Will this weekend put all those motors to a load test and see how much current they draw .

Maybe another method would be to control 12Volt high current relays to switch on the motors , Ok will loose a bit of time delay in switching process but maybe i can ofset that time delay in Mach3 software , not sure on this part.


What would be better a mechanical type relay or some form of a solid state relay ??

any information would be greatful

cheers

[FPV_GTp]

Hi

Does anyone know of any other DC 12 volt high current drivers ?


cheers

[epineh]

I would use something like this :

http://www.allegromicro.com/sf/3940/

This way you can build your H-bridge to suit whatever size motor you want, and adds some nice features.

Mechanical just won't cut it, you are looking at switching frequencies in the KHz.

What do you intend to use for the brains? Myself I am looking at building a hobby style servodrive, using a microcontroller to read the encoder, calculate PID loop and output the PWM locked anti-phase to the gate driver, but unfortunately it has to wait a while until I finish building stepper drivers for my router, and build a shed...and house (chair)

Russell.

[holbieone]

what is high current

some golf cart controllers go down to 12v

[WayneHill]

Heard somewhere that you should not take magnetic DC motors apart because it will weaken the magnetic field.

[FPV_GTp]

Heard somewhere that you should not take magnetic DC motors apart because it will weaken the magnetic field.

Hi

Waynehill that i would have to say is a wisetail myth in my books

cheers

[epineh]

I heard it was steppers you shouldn't take apart...

[PeteZ28]

Actually, they say it's any perminant magnet motor you shouldn't take apart.

True or not? I have no idea. But I have heard it is advisable to put some type of magnetic metal in there the same diameter as the armature or close to it. Either a thin tube over the arm before removal, or if you can take both ends of the motor can off, slide a peice of barstock in behind it as you are removing it.

Again, I have no idea if it's true, but an ounce of prevention...

[Al_The_Man]

Many of the latest high quality mag. materials do not require a 'keeper'.
So far I have never had a problem with ones I have overhauled.
Al.

[FPV_GTp]

Actually, they say it's any permanent magnet motor you shouldn't take apart.
True or not? ..............
Again, I have no idea if it's true, but an ounce of prevention...

Ok ,,, seems like there is some merit to pulling apart permanent magnetic DC motors.

Will ask a few guys in the industry who do repairs on motors and see what they have to say.

Sorry for doubting you guys , it just doesn't sound right.

These motors that i have pulled apart are just cheap every day units. I wanted to have a look at the different types and see how there armatures are made , there shaft and housing configurations and so on.. with no real intention of putting them back together again.

I was at a factory here in Melbourne the other day from memory and they assembled and made permanent DC motors for the car industry here like Ford and Holden and i seen motor parts scattered all over the factory.

There were tubs of parts where different people where performing different assembling processing of the motors and the , permanent magnetic field bodies that housed the magnets didn't have any special part in the center of them awaiting assemblying where the armatures sits normally.

And there were tubs of these permanent magnetic field bodies awaiting assembling.

Will do some homework on this part of the conversation.

cheers

[FPV_GTp]

link http://www.cnczone.com/forums/showth...highlight=dyno

Read post #9

This topic came up in another group. The stator acts as a magnetic "keeper" for the rotor.

Nothing like running an experiment to know if something is true or not.

I had a motor I didn't care for (MO62-FD04), so I ran dyno tests on it that showed 112 in-oz low-speed torque. I removed the rotor for 5 seconds, then replaced it and re-ran the dyno test.

The low-speed torque now was 70 in-oz, or only 62% of what it was before disassemby.

You may not notice the loss in torque but it is real and it is there.

Mariss

[FPV_GTp]

hi


D200 Model
High Power H-Bridge DC Motor Driver Board

specs : D200 Features:
Power Semiconductors: Four 110A MOSFETS
Rated Current: 10A Without Heatsinks
Max Current: 45A with Proper Heatsinks Installed
Board's Size: 2.5" x 2.5" (6.35cm x 6.35cm).
Components Type: 100% Solid State, NO Relays

On Board:
Filter Capacitors
VTS diodes
Snubber Circuit Ready

Voltage Requirements:
5 Volts for the Digital and MOSFET Bias Circuits
Any voltage up to 55 Volts for the Motor B+

http://www.tecel.com/d200/

[FPV_GTp]

Hi

Amazing some of the things you find on the net http://www.gearseds.com/curriculum/i...ures/Motor.swf

this site has a great deal of information on motors in the " M " section http://www.gearseds.com/curriculum/l...s.php?letter=M

and some very good test apparatus for testing motors

cheers

[FPV_GTp]

Hi

this site has some very nice h-bridge electronics http://www.modularcircuits.com/h-bridge.htm

Introduction
This µModule implements a 16A H-bridge with rich feed-back options to create a closed-loop speed-controller application. The module interfaces to the external world using the TWI interface that's common among all µModules. It also has an optional CMOS-level RS-232 interface. It can control motors up to 18V.


Features
Standard µModule TWI with optional RS-232 interface
Integrated 3.3V power supply, 5V operation is optional using an external power source
16A current limit
7 to 18V motor voltage
High-side short-circuit protection
High efficiency n-channel MOSFETs
Rich speed-feedback options for closed-loop operation
Back-EMF feedback for sensorless motion-control
PID control loop
Acceleration and deceleration limits
Traveled distance calculation
'Go-to-distance' support with trapezoid speed-profile
Braking and free-wheeling support
Parameters can be stored in permanent EEPROM storage
Duty-cycle throttling to limit torque
Per-cycle programmable current-limit
Servo controller mode with external position feedback potentiometer

[FPV_GTp]

Hi

Some interesting reading how a H-bridge works and constructing a h_bridge from scratch , H-Bridges: Theory and Practice http://www.mcmanis.com/chuck/robotic...rial/h-bridge/


This website has some very high current H_bridge controlling capacity for low voltage DC motor control and a very good explanation how it all works

h-bridge_secrets1 http://www.modularcircuits.com/h-bridge_secrets1.htm

h-bridge_secrets2 http://www.modularcircuits.com/h-bridge_secrets2.htm

h-bridge_secrets3 http://www.modularcircuits.com/h-bridge_secrets3.htm

Now that i have found some high amperage H_bridge DC 12volt motor drivers , need to find cheap encoders , how they work , how they are made and so on.


On ford and holden vehicles we use " ENCODERS " hall affect sensor type and optical Light emitting diode and receiving diode types. Will pull apart a few car units to see what is actually inside a rotaory counter

VL commodores here in Australia have a optical counter ( encoder ) with a disc that has 360 slots cut into it and another 6 slots which tell the cars ecu what position and how fast the engine is running. so it can make a calculation and inject the right amouty of fuel and advance or retard the ignition timing. I wander if i could couple one of these encoders onto a DC motor , it will have 360 counts the system needs 12 volts to run it Hmmm ????

Then there is the other option Ford Falcons have a hall affect sensor that runs 3 wires into it , 12 volts positive power ( RED ) earth 12 volts negative ( BLACK ) and a signal wire ( GREEN ) depending if it is a 6 or 8 cylinder it will have either a 6 or 8 chopper blade wheel that interupts the hall affect sensor and makes a zero to twelve volts square wave form. The choper plad can be modified ( make a new one ) with more windows in it like 200 or ant number and we have the counts. We can apply any voltage to get what ever signal we require , ie apply 10volts on the hall affect senors we will get a zero to ten volt square wave form. MMMMM ???

It is amazing the prices some of the instrument place are asking for the encoders.

Lets see what i can dig up on making some cheap units.

All i want to do here in this thread is use every day type 12 volt DC motors and fit a encoder on the end of the motor shaft and make a small cnc router table 12in by 12 in using materials that are not expensive and generally available around the home or junkyard or garage sales.

This is purely for just experimenting at this stage.

cheers

[ejkoeze]

Have you turned the shaft yet. You'll clearly feel "steps" in the rotation. This prevents a cheap motor from being used from what I have read. It will start to oscillate. Besides that, the lower the voltage the higher the peak current.
For the UHU servo controller we prefer 40 to 70v motors not just to keep the peak current down.
The heat produced by the h bridge is also depending on the current that flows through it.

IMHO a small simple cheap cnc router is best suited with a stepper solution. Smaller steppers are sold new for relatively low prices. Encoders alone are quite pricey.


Erik Jan

[Al_The_Man]

need to find cheap encoders , how they work , how they are made and so on.
It is amazing the prices some of the instrument place are asking for the encoders.

Lets see what i can dig up on making some cheap units.

This older link may help in explaining some of the encoder issues.
http://cnczone.com/forums/showthread...ighlight=moire
Al.

[NC Cams]

Regarding motor disasembly: it depends on the motor magnets.

Some magnets, especially the earlier non-oriented ceramic type were less resistant to demaging upon disassembly, hence, you were discouraged from disassembling them.

It should be noted that an early trick to eliminating the cogging problem in some motors WAS to INTENTIONALY pull the armature 1 or more times. This would smoothe out the cogging to make the motor perform better at low rotation speeds or under reduced linear terminal volts.

Today, especially with the newer "wet oriented" ceramic magnet and/or rare earth magnet motors, the old axiom of not pulling the armature is no longer 100% relevant.

Re servo driver: just about ANY servo driver with an adquate current capacity H bridge driver will drive the DC motors that the original member is looking to drive. It is the H bridge circuit that counts mostly and not the control circuitry per se.

If you do some searching through the Unitrode/TI website, at one time and I"m pretty sure they still do have a number of servo driver IC's. The associated tech briefs also showed you how to make the necessary amplifier that the servo chips could excite to drive a DC motor of virtually ANY size, including the ones originally pictured/described.

This very topic has been discussed along with the links to the websites where the IC's can be found - I know so as I looked up and subsequenlty posted the links (but don't have them handy on this PC or I'd do it again).

Careful and proper use of the 'Zone's search engine should uncover them quite readily.