Wishlist for the next drive (describe your dream drive!)

[LeeWay]

I would like to see a drive that is like a Xylotex that has a built in breakout board, but for a single axis. Use a ribbon cable or even the printer cable directly to this board. The add extra drives by simply plugging them into the end. Need three. Buy one main and two solo's. Need 4, buy one main and three solo's.
Even better would be a USB connector to control the drives. I know this is relatively new, but that would be very nice especially for the hobbiest. You could also add board with relays, charge pumps, etc that plug into the other side of the Main axis card.
I do think this could be done quite easily and you would have a pretty good market simply because of the ease of installation and repair. Board #2 goes bad, simply unplug it and plug in a new one. Now thats a dream drive(s) system.

By far the most trouble I have seen from people is making all the correct connections to every possible type of drive and breakout board out there. Now there are some very nice systems already. The more you design something that is both large capacity and easy to install and maintain, the more attractive these are going to look to buyers, Pro's and Hobbyist alike.

[Xerxes]

Good ideas, Hunserv and Lee!

Analog monitor output could be really useful for some people but I'm afraid there is no enough pins left in the DSC I'm using. However, since VSD-E has some extra digital I/O, I'm planning to make user selectable functions for them. At least some kind of follow error warning output will be there. It is possible to inspect torque etc. by reading data from SPI bus.

Lee, it is a very nice idea indeed. I think same level of user friendliness can be achieved by making separate inexpensive breakout board with direct ribbon cable outputs to drives. It's been alredy done for VSD-A (see http://www.granitedevices.fi/assets/...akout_rev2.zip). Same will be done for VSD-E.

I almost once started designing a fully integrated drive with 3 or 4 servo axes, integrated power supply, PC connection etc. Just add transformer and motors and you have CNC. However, it would take more compromises than I would like so I thought separate drives with inexpensive support boards is much wiser.

Separate power stage output idea is tempting. Maybe I some day figure out a nice way to do it.



Oh, and happy Christmast to everyone :-)

[hunserv]

on the VSD-A I have seen the tiny DSC... what brand it is? quite unfamiliar to me (not PIC, not Atmel...)

Maybe for the next generation (modular control+power circuit) you should consider a bit larger one with more pins

Yes, Merry christmas, indeed

[Xerxes]

VSD-A has 48 pin Freescale 56F8322 DSC. VSD-E already has a larger 64 pin chip and there are two digital I/Os left.

Maybe we some day make a small run of powerstageless drives and see if they have a market. Perhaps some third parties would make compatible power stage modules for different size of motors (what do you think?).

[Episs]

I think it is great Idea of powerstageless drives and such design offers capability to support different motor types steppers, servo, 3phase AC, I think there are lot of people who has knowledge of how to design power stage, but don't have programmer skills.
do you think to make single motor or multiple motor powerstageless drive?
I think that multiple motor drive would be cheaper, but then there is question about your freescale DSC processing power will it be enough to drive 2 or even 4 motors ?

I checked your freescale DSC and it has 12bit ADC. Does so high 12 bits resolution give some advantage over some 10bit resolution ADC in motor driver application ?
I am asking because I checked in digikey your DSC price and it is little bit higher compared to other chips maybe this is because of 12bit ADC, other cheaper DSC has 10 bit resolution ADC

[Xerxes]

Episs, it's probably possible to control 2 DC servos in one DSC without compromises in control quality but 2 AC servos would require lots of code optimizations. I think these are the practical limits.

12 bit ADC gives lower current sensing noise which can be heard from reduced motor hiss.

[hunserv]

Well, on my side I'd be happy with a lower-cost VSD-A alike (but upgraded with outputs) powerstageless unit, outputs could be optocoupler driving ones, for firing high and low sides of IGBT inverters (3 high 3 low) and then the end user (me) could fit whatever he wants. Of course some input(s) would be needed powerstage-wise for current sensing as well.
Current sensing would be standardised, and the fitter of the power module would be responsible for the correct scaling of the current signal towards the controller.

[Xerxes]

Yep, that's what I have been thinking. There could be also few inputs to identify power stage properties like switching freq and required deadtime. These inputs would make power stages 'plug and play' and no user coniguration would be needed. Sounds like interesting project.

[hunserv]

I just thought of a power stage with its own microcontroller (in case it is not a discrete single chip powerstage) then this uc could accomodate the simple plug n'play communications. Well, at least on my side I could handle the programming of such interface (bridge control, and some data send to the servocontroller)
But maybe this is overcomplicating the issue, parametrization can be done directly in servocontroller, with care.
Discrete single-chip powerstages have built-in dead time generation and shortcircuit preventing logics (does not allow same high and low side IGBT-s to open simultaneously)
If a large powerstage is needed then these features (plus communication) can be done with its controller, but if a discrete one is enough then a communicationless method would be needed, too.

or the trick could be done on any custom powerstage boards with a few DIP switches, or even resistor arrays (configuration matrix) so user will not have to bother with setup.

[Xerxes]

Microcontroller for that purpose is unnecessarily complex. I can use ADC to read resistor values that set power stage properties.

Maybe following options would be enough: 10, 15 and 20 kHz switching freqs, 0, 500, 1000 and 2000 ns deadtimes.

[hunserv]

And how would you handle current sensing? DC bus voltage could be monitored, too. If we want "plug and play" alike feature then we should consider at least these, too.
e.g. an additional resistor which the ADC reads, and from its value the current-scale can be determined, and another one for the DC bus-voltage.

[Xerxes]

Voltage & current sensing will of course have inputs. Current sensings scale setting is something I didn't think of. Current could remain in arbitrary scale so user would just enter current limits by looking correct values from some lookup table. You have a very good point that scale could have also a setting resistor in power stage.