DIY Servo controller

[kreutz]

Hello Guys:

I am planing to finish the PCB layout tomorrow and send it to the fab next Wednesday. There are a few differences to the original UHU schematics, one experimental difference is my approach to torque control (it can always be bypassed by eliminating a few components if you want to keep the original peak current control).

Any Permanent magnet brushed DC motor is specified for maximum continuous torque and peak stall torque, which translates to maximum continuous current and Peak stall current. Usually the later is more than twice the former. If you adjust the peak current to the former, you are losing a short time reserve torque that could be more than double the maximum continuous torque. That can make the difference between a completed and a ruined job.

My approach consists in two different current limits; A short time limit is 2.1 times the continuous current, and a long time limit that is the maximum average continuous current. Since I like things simple, there is only one current adjustment: Average maximum continuous Current limit.

I know that many of you know about other commercial servo amplifiers, and would like to see if something like this has been implemented before. I haven't been able to find much information around.

[contactirfu]

Originally Posted by kreutz Hello Guys: I am planing to finish the PCB layout tomorrow and send it to the fab next Wednesday. There are a few differences to the original UHU schematics, one e............................................................................................................................................other commercial servo amplifiers, and would like to see if something like this has been implemented before. I haven't been able to find much information around.

Thats great news Kreutz, I have 3 more of the UHU chips and would utilize for them for the larger PS which I already have, with your PCB, Good to know that u are testing your circuit ...... your circuit might be the latest for the UHU, my suggestion would be that you offer the gerbers for a very nominal fee, after all the hard work u put into it. Also it might help your email inbox to have lesser mails than intended and only serious people will contact you. I would personally buy the PCB layout files from you and use them for myself.

I might be wrong here, if you have a different approach for the diy and dont want to charge any one for anything it probably is your happiness factor, but for the amount of great work you do for the CNC DIYer's ON CNC zone .............

I SALUTE YOU

Keep the great work goin on and on Kreutz.

Regards
IRfan

[kreutz]

Originally Posted by contactirfu Thats great news Kreutz, I have 3 more of the UHU chips and would utilize for them for the larger PS which I already have, with your PCB, Good to know that u are testing your circuit ...... your circuit might be the latest for the UHU, my suggestion would be that you offer the gerbers for a very nominal fee, after all the hard work u put into it. Also it might help your email inbox to have lesser mails than intended and only serious people will contact you. I would personally buy the PCB layout files from you and use them for myself. I might be wrong here, if you have a different approach for the diy and dont want to charge any one for anything it probably is your happiness factor, but for the amount of great work you do for the CNC DIYer's ON CNC zone ............. I SALUTE YOU Keep the great work goin on and on Kreutz. Regards IRfan

I won't charge for the schematics or Gerbers. I won't post them unless they are well tested.


Thanks,

Kreutz.

[kreutz]

Does any of you have the female connectors for the SEM MT30U4-31 servo?, only need them for a few weeks, I will send them back as soon as finished testing the servo. At least having a part number (for each connector) will help me a lot, I don't have much time available.

[lingdao]

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[kreutz]

Originally Posted by kreutz Hello Guys: I am planing to finish the PCB layout tomorrow and send it to the fab next Wednesday. There are a few differences to the original UHU schematics, one experimental difference is my approach to torque control (it can always be bypassed by eliminating a few components if you want to keep the original peak current control). Any Permanent magnet brushed DC motor is specified for maximum continuous torque and peak stall torque, which translates to maximum continuous current and Peak stall current. Usually the later is more than twice the former. If you adjust the peak current to the former, you are losing a short time reserve torque that could be more than double the maximum continuous torque. That can make the difference between a completed and a ruined job. My approach consists in two different current limits; A short time limit is 2.1 times the continuous current, and a long time limit that is the maximum average continuous current. Since I like things simple, there is only one current adjustment: Average maximum continuous Current limit. I know that many of you know about other commercial servo amplifiers, and would like to see if something like this has been implemented before. I haven't been able to find much information around.

SAFETY Note: This modified UHU board is specifically designed for High Power Servo motors > 80 Volt > 10 Amps. I will limit my tests to 150 volts, 13.5 Amps (continuous) 25 Amp maximum due to the used test motor's specs. Changing the Output mosfets will require extra modifications This board is not a plug and play servo test station, working at high power levels requires a safe and controlled environment (both, electrical and mechanically safe). I use an isolated 3KVA, 0 to 170 Vdc power supply (made specifically for this tests) and a thick lexan shield when powering the boards, exploding semiconductors could do a lot of damage to your face/body if you are still alive after the accident!! Please, be responsible.

[contactirfu]

Originally Posted by kreutz , working at high power levels requires a safe and controlled environment (both, electrical and mechanically safe). I use an isolated 3KVA, 0 to 170 Vdc power supply (made specifically for this tests) and a thick lexan shield when powering the boards, exploding semiconductors could do a lot of damage to your face/body if you are still alive after the accident!! Please, be responsible.

I myself use heavy High Voltage graded gloves and wear protective glasses now that you mentioned Lexan shields, I will add them on to my list of protective items to be bought on priority. DO u think the Lexan should be shaped like a Box with five sides or just a plain sheet protecting the face.

Thanks Kreutz

Regards
IRfan

[kreutz]

Originally Posted by contactirfu I myself use heavy High Voltage graded gloves and wear protective glasses now that you mentioned Lexan shields, I will add them on to my list of protective items to be bought on priority. DO u think the Lexan should be shaped like a Box with five sides or just a plain sheet protecting the face. Thanks Kreutz Regards IRfan

Mine is like a full body 1/2 inch (4 parallel sheets) vertical wall supported by heavy feet. The Lexan I use is the same sold here for protecting windows against hurricane force winds and high speed debris.

[kreutz]

A couple of more changes:

1- RS232 communication between the original UHU board and the PC is not isolated. When working with High voltage power supplies is is highly desirable to have electrical isolation between both of them, so I replaced the Max232 chip and associated components by a discrete opto-isolated Rs-232 interface that takes the PC side supply from the data lines. On the new design the -12 Vdc supply voltage, for the current limit comparator chip, is not necessary anymore (I also replaced the TL082 op-amp by the LM339 quad comparator).

2- There is no protection on the original UHU board against unconnected Encoder cable. When the encoder is left unconnected the motor will turn at high speed without stopping (once a step command is received from the PC). This behavior is a safety hazard. On the modified board if you left disconnected the encoder cable the board will be under Emergency Stop mode. There is a jumper on the encoder cable that feeds back information about encoder connection integrity. It is necessary to wire that jumper on the motor encoder side of the interface, as shown on the schematics.

[kreutz]

This is the time to ask

I am sure some of you have long encoder cables. Do you think that adding an independently adjustable +5 Volts supply for the encoder is justifiable? It will add a few components but will compensate for the encoder cable drop and will be short circuit proof.

Let me know your opinion, this is the time!!

[contactirfu]

Originally Posted by kreutz This is the time to ask I am sure some of you have long encoder cables. Do you think that adding an independently adjustable +5 Volts supply for the encoder is justifiable? It will add a few components but will compensate for the encoder cable drop and will be short circuit proof. Let me know your opinion, this is the time!!

I am in for it Kreutz, if it helps then why not, I particularly have long encoder cables as i am on a 4x8 router build.

REgards
IRfan

[LZ1TWB]

Hello kreutz,
I myself will have 6-7meters of cable till I reach the Z axis, some will say this is a lot I don't know. I was thinking about the voltage drop across the encoder line and that an encoder never takes much current, say will 0.1A do something significant? Most of the cases like me power is distributed across 2 or even 3 wires together for the GND and the +5V. Maybe you are right, because I haven't tried this yet.
I want to share another problem I faced recently. Is it normal that the motor heats up like a cooker even without moving?
I have one small and one big motor both 55Volt maximum. When I connect the small motor and turn it on /Using 65V/ it heats for about 10-15minutes like I cannot touch it. The big motor behaves much better maybe it cannot heat up that quick because it is much bigger a piece but sooner or later faces the same problem. This was quite visible when the weather was hot, say 30degrees in the room.
I blame this square wave which is double the voltage at the output. I think it should not be there when the motor is not moving. At first I thought 20Khz wont pass through the windings due to the inductance but maybe it is not the case. I was wondering why not put a D-class audio amplifier filter at the end? It will leave just the DC part of the signal. Just a suggestion. You will correct me if this is not possible with the project.

Thanks, Todor