It's been a while since my last post.
Here, as if there's not enough projects here to keep some of us busy.
I found this http://members.shaw.ca/swstuff/dspic-servo.html
haven't tried it yet tho, doing something else for the moment.
If any1 ever build this please post result.
"This is intentionally left blank."
There is some further development on this project under way.
I have a working prototype of a higher current version that uses two op-amps in parallel to increase the current capacity of the drive.
I have some larger motors that I would like to use that require more current than a single op-amp can provide.
Also, I am building a version that uses two op-amps as an H-Bridge to give me higher voltage capability. Hope to have a working prototype in a few days...
There is a U-Tube video of the servo drive in action.
I have been looking over this project and am quite interested. Do you feel there is much work required to get this to work with a HBridge????
The present design relies on the op-amp power stage to look after current limiting. The dsPic controller outputs a pwm signal which is filtered to a voltage proportional to the required output current.
The new design uses 2 op-amps as an h-bridge. The design should be capable of up to 60 volts and 7 amps, which are the op-amp specs.
I have not fully tested the new design but initial test look good.
It runs the servo and didn't let the smoke out of anything.
perhaps check out some of these op amps
perhaps a few lm3886 gain clones ($6.00 each)
e_mail recieved about lm3886
Cool, glad you liked it!
Yes I think the National chips would make great servo drivers. Not that the
LM1875 I had in the drawer ever got used for that. Just treat them as an
ordinary opamp and as long as you run them with a high enough gain (above
10 to be safe) and good power supply decoupling they should work as
expected without stability problems.
One thing I noticed though is they don't like a lot of reverse current
(regenerative braking), as this places maximum stress on the output devices
(I think). I think they are protected to an extent but it would pay to run them
well below their power limit and with really good heatsinking, or at least drive
one hard and see if it survives whatever mode of operation you want to throw
at them. A really well protected chip will run without a heatsink, it'll just cut in
Best of luck!
Last edited by smarbaga; 03-05-2008 at 01:27 PM.
A PIC 30F4012 is used in this controller
Can I use an alternative PIC instead of this one ? like the 16FXXX to do the same job ?
The 30F4012 has built in provision for the quadrature input and hardware counter for the input from the encoder.
the 16F pics do not have this.
I am interested in trying this and using the PWM drive signal and direction signal, converting this using logic into PWM and NOT PWM and feeding this straight into a discrete H-Bridge.
Any thoughts would be appreciated.
Nice work so far btw.
I'm (slowly) working to convert the output routine to h-bridge operation compatible with a hip4080/81 bridge driver so I can make some with only junk box parts.
The way it's put together should make it really simple to convert, it already does the PWM by itself so it's just a matter of getting a "direction" signal out of the PIC, coming up with a way to limit the current, and making sure that the deadband operation is OK. I think all of this stuff is in a single function in the code.
kudos to Lawrence/Tom for putting together and sharing such a well documented and great project.
I think at some point I read that someone else was doing the exact same thing, but I lost track of it?
Last edited by ladzhari; 06-03-2008 at 07:11 PM. Reason: said wrong chip!
I would be interested in how you go, I have put together a board, and logic to use the output from the DSPIC to drive a discrete bridge, but I think the PWM output needs to be inverted, as 4.75 V is zero current and 0V is full current from the original Op Amp configuration, I got distracted and have not been back to try again. I also couldn't get any serial comms so there were other issues with my board, I don't think I set the clock configuration correctly.
I have a friend that used the DSPIC servo with a different op amp (smaller) to drive +- 10V industrial drives and it works very well, just have to get it working with discrete's.