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making servo motor with DC motors

Tharukasf

New Member
hello, I am attempting to build my own servo motors out of dc motor and optical encoders and 3D printed gears. in this way I hope to reduce cost and make precise toque servos.
my question is what internal driver ICs are suitable for it, and what are best encoders. please suggest any other driver circuits. thank you.
 

shortbus=

Well-Known Member
Most Helpful Member
Servo motor is an over used term, one that means many things. You need to qualify it, are you meaning a RC servo or what?
 

MaxHeadRoom78

Well-Known Member
If this is motion control servo's for e.g., you need at least 1000 pulse/rev encoders, there are many makes out there, AutomationDirect is one source.
Max.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
What voltage and current is the motor rated for, what speed or angle range for the encoder?

For a small to medium DC motor, something like an L6203 would probably be a suitable driver:

For position, a TLE5012 may the simplest and best value.
All you need with one of those is a small magnet on the end of the rotating part & the IC directly over the axis of rotation.

It gives you a serial data interface that can read the position to about 1/100th of a degree, plus the other step or sequence signals.
 

MaxHeadRoom78

Well-Known Member
Depends if the OP wants to create something like a CNC positioning etc, for accuracy the 1k/rev encoder would be minimum.
Coarser ones are OK for RPM control only.
Max.
 

Tharukasf

New Member
What voltage and current is the motor rated for, what speed or angle range for the encoder?

For a small to medium DC motor, something like an L6203 would probably be a suitable driver:

For position, a TLE5012 may the simplest and best value.
All you need with one of those is a small magnet on the end of the rotating part & the IC directly over the axis of rotation.

It gives you a serial data interface that can read the position to about 1/100th of a degree, plus the other step or sequence signals.
Thank you. however I think there should be ICs that do more processing than bridge drive, just my opinion. and I am not sure if magnet sensor IC is suitable for precise motion control
 

MaxHeadRoom78

Well-Known Member
For precise motion control of a servo motor, you not only require a drive, but a trajectory controller of some kind that uses PID loop control via the encoder.
Max.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
Thank you. however I think there should be ICs that do more processing than bridge drive, just my opinion. and I am not sure if magnet sensor IC is suitable for precise motion control
That's the "power stage", in integrated H bridge.

The control is typically done in a microcontroller that has a suitable PWM module & analog / digital I/O for motor voltage / current feedback, the position feedback device and control system.

Other than that, you are looking at a ready-made servo controller, but decent dual-loop ones for CNC or robotics tend to be relatively expensive.


Those hall transducers are pretty good equivalents to a industrial CNC grade optical encoder - eg. if you are using 10mm pitch leadscrews with a 3:1 reduction from the motor, which is pretty typical, one micron of movement is around 1/3000 of a motor turn. A 2000 line optical encoder (so 8000 counts) gives better than that & the hall encoders are four times that resolution.

With 5mm pitch screws, you double the mechanical resolution for the same counts.

Or you could use something like this, an economy grade optical encoder; connect it to the driven end of the leadscrew with either a bellows or oldham coupling. With a 5mm pitch screw, that would give (5000 / 2400) roughly 2 micron increments, or 4 micron with 10mm pitch screw.

If connected to the motor before the belt reduction, you would get better than 1um counts with 5mm pitch, but with a slight loss of absolute position due to give in the belt.

For really high resolution, you are looking at something more like these - but don't get carried away, most cheaper ballscrew, ballnut and bearing combinations cannot get all that near 1um accuracy to start with.


Note that "brushless DC" motors and drives have near enough completely replaced conventional DC drives in machine tools and robotics now.
A new, good, servo drive to suit those is relatively cheap - and the motors inherently have internal position sensors, which are often made available on the drives to give position feedback to the CNC unit.

Example:
 

Tharukasf

New Member
That's the "power stage", in integrated H bridge.

The control is typically done in a microcontroller that has a suitable PWM module & analog / digital I/O for motor voltage / current feedback, the position feedback device and control system.

Other than that, you are looking at a ready-made servo controller, but decent dual-loop ones for CNC or robotics tend to be relatively expensive.


Those hall transducers are pretty good equivalents to a industrial CNC grade optical encoder - eg. if you are using 10mm pitch leadscrews with a 3:1 reduction from the motor, which is pretty typical, one micron of movement is around 1/3000 of a motor turn. A 2000 line optical encoder (so 8000 counts) gives better than that & the hall encoders are four times that resolution.

With 5mm pitch screws, you double the mechanical resolution for the same counts.

Or you could use something like this, an economy grade optical encoder; connect it to the driven end of the leadscrew with either a bellows or oldham coupling. With a 5mm pitch screw, that would give (5000 / 2400) roughly 2 micron increments, or 4 micron with 10mm pitch screw.

If connected to the motor before the belt reduction, you would get better than 1um counts with 5mm pitch, but with a slight loss of absolute position due to give in the belt.

For really high resolution, you are looking at something more like these - but don't get carried away, most cheaper ballscrew, ballnut and bearing combinations cannot get all that near 1um accuracy to start with.


Note that "brushless DC" motors and drives have near enough completely replaced conventional DC drives in machine tools and robotics now.
A new, good, servo drive to suit those is relatively cheap - and the motors inherently have internal position sensors, which are often made available on the drives to give position feedback to the CNC unit.

Example:
thank you so much for spending your valuable time to accomplish my task. now I hope to try something in fractical.
 

strik

New Member
Hi , i'm 64 yo Belgian allowed my self a membership to give you some simple answers . i used wheelshare motors , took the el-mech breack away and mounted a encoder on it :) Drivers are the German UHU's witch you can solder truehole . I made my cnc as a testplatform to lern about the mechanics and electronics . It's all about what YOU are wanted to use them for ... i am not in need for speed , for me it has to do what I tel him to do .
Maybe i can help wiht some questions ? Englisch is not my natif and being a member since 2004 in a German cnc forum its time to clean up my Englisch reading/writing . Due to the MS (multiplus scleroses) that i am been blest wiht since 15 years i need time to find writing mistakes sorry for that .

Grtz
rik
 

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picbits

Well-Known Member
If you can get hold of a car throttle body that uses drive by wire you can have some fun with them. This is a project I worked on for some engine testing. It used a TLE5206 if I remember correctly. The PIC produced a direction and PWM and used the 0-5v feedback from the throttle as a position sensor.
 

strik

New Member
There are manny kinds of encoders yours is one of them . 10 years ago i made a mini MB jeep for my grandson Mathias the throttel is one from a forklift :) the drive is an 4QD and has throwen a white towel Mathias does not fit annymore . Wheel share throttel have a zero point in the middel so watch out for them ! Encoders wil cost about 35 $ and can only be used ones ,, open them you breack them exept the ones i bought in Taiwan they have them whit a slider "honest sensor" www . For a cnc you better buy linear encoders so you have no backlash you connect them on your maschine not the motor thats 99% foolproof . --> Mb jeep and transaxel from a wheelshare ,,, what else :) Front wheels from a sit on lawnmower .
 

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