The L293 is just a level translator for me. Check out my circuit. It uses current mode PWM without disable. To do this, it either drives or shorts the winding.by Annirak - Controllers
grael Wrote: > I think Annirak has some great ideas, I just hope > that he can see them as achievable on half duplex > RS485, you know my position on that. It would be a > shame to have that being the whole sticking point > on integration on a whole new generation of > reprap~ish CNC/deposition machines. > -------------------------------------------------- I'm not so arroganby Annirak - Controllers
Those are all points I want to avoid. Here's a driver for you: The cost was prohibitive for me, but you might be able to use it, or it might give you an idea.by Annirak - Controllers
While the full duplex argument makes sense to me, there has been significant resistance to it. So in an effort to maintain compatibility with other parallel development streams, I will have to set the orange pair to "reserved" and the green pair to tx/rx. If I run in to timing or bandwidth issues, I will revert my standard to full duplex.by Annirak - Controllers
Well, I think I know what I'm going to do. I'm going to write my protocol so that it can support fdx, but test it out completely in hdx. I'm going to maintain fdx cabling capability and use CAT-5E, mainly because of the existence of good connectors and widely available, cheap cabling. I suggest that we use the green pair as the hdx communication pair.by Annirak - Controllers
Hi Geert, That driver is exactly the kind of thing I was looking for. It implements approximately the same control method as I am trying for. It costs $21 per phase for the control device alone, and does 3A at up to 55V. Mine costs about $6 per phase and does 5A at up to 30V (the L293 is the limiting factor here, the FET's can take 60V). Scaling back power at low velocities shouldn't be an isby Annirak - Controllers
I don't know where to go on this. The price difference on the physical layer is sub-dollar. The coding difference is minimal, provided that a framed communication protocol is in use. I know we don't need a high baud rate, but it would provide for better timing. Of course, increasing the baud rate also means that half-duplex is more doable. I know why you're against CAT-5. I don't like its bby Annirak - Controllers
nophead Wrote: ------------------------------------------------------- > Yes more expensive drivers, more wires, more > software complexity. The wires aren't really an issue. CAT-5E is perfect for the job and has plenty of wires to carry both limited power and full duplex data. Software complexity isn't an issue: you don't have to make the logical link full duplex unless you need it to bby Annirak - Controllers
nophead: Is there a good reason to not use full duplex?by Annirak - Controllers
jbb, The only fix here is to get the thermal loading to be even given that the motor is actively moving. Let me know what you think. Brendanby Annirak - Controllers
> I'm not persuaded to your view yet. > *I still think that half duplex allows > synchronisation just fine, > *I recognise the advantages of full duplex, but I > think they are inconsequential in this > application, as there are far more effective ways > to ensure fast, synchronised response times. My > idea of a CPLD expansion port as an alternate > function of the LCby Annirak - Controllers
jbb Wrote: ------------------------------------------------------- > Another couple of thoughts on the way home... > > 1) You might want to leave a space on the board > for external antiparallel diodes on the MOSFETS - > the internal body diodes can suck. I don't think those are necessary. The fet's I've spec'd have a really good set of body diodes, 0.76V typical, 4A continuous.by Annirak - Controllers
Hi Randyy, I did consider that. There are four reasons I didn't follow through on it. 1) (the most important) I/O. check out the ATMega in that diagram. It's got very little I/O left. The design uses 2xPWM, 2xdirection control, 2xADC, 2xShut Down for each motor. It provides 2xoptional quadrature feedback pins (forgot to include it in the schematics), and SPI for optical position sensors (mby Annirak - Controllers
It seems to me that we need to decide on a cabling standard for interconnect. I think that everyone is agreed on the use of RS-485. There are a few remaining questions about whether to use half-duplex vs. full-duplex. There also remains the question of the type of cable to use. SATA: I originally was pretty happy with the option of using SATA cables, but the pitch and availability of the connby Annirak - Controllers
jbb Wrote: ------------------------------------------------------- > Hi annirak. > > I've done the microstepping thing with an AVR > before, and it tends to work nicely. How finely > you can microstep will depend on how good the > motor is... I'm not going to let motor quality limit my controller quality The only difference is really which PWM outputs I use anyway. Timer1by Annirak - Controllers
jbb, CAT5 is definitely viable for this job, but it doesn't bend nearly as well. It might take the repeated mechanical cycling better, however. Brendanby Annirak - Controllers
Theory of operation: The PWM serves two purposes. It sets the maximum current threshold of the output and it drives the clock of the motor PWM circuit. The flipflop, U1A is initialized to 1, driving the #Q output low. This means that the XOR gate, U2A, passes DIRA through. Both pairs of MOSFETs, IC4 and IC5, drive to the same level, so there is no voltage across the motor winding, J3. Whenby Annirak - Controllers
Well, here are the first generation of schematics. I still need to clean them up quite a bit. Please forgive the overlapping values, particularly on the capacitors. I needed part numbers rather than values so that the bill of materials would come out nicely. (c) 2008 Brendan Moran, Released under the terms of the GPL v2 (http://www.gnu.org/licenses/gpl-2.0.html)by Annirak - Controllers
I've been attempting to design a new stepper motor controller. My design is different from what's been done before in several key features: 1)Drive current. My solution delivers 5A per phase. 2)Current limiting. I use a PWM driven current limiting circuit. 3)Stepping. I use microstepping (At least 32 microsteps per step) 4)Controller. I'm using an ATMega48 as the controller, rather than a deby Annirak - Controllers
grael Wrote: ------------------------------------------------------- > Annirak Wrote: > > The L298 is over double the price of the L293. > My > > plan is to use the L293 as a MOSFET driver. > > - > p-4ch-w-diodes-16-dip-l293d.html > > ll?Detail&name=497-1395-5-ND > Surprisingly, the higher current chip, is actually > cheaper, even in the multiwatt pacby Annirak - Controllers
grael Wrote: ------------------------------------------------------- > 2. I've used the L293D before on the printer I > designed.(inbuilt diode version) I don't think the > L298 are much more expensive, but they are double > the current, and it's nice to have more, rather > than less, than you actually need. I was thinking > that for serious power, to have an add-on board > tby Annirak - Controllers
Graham, I have a few comments for you which I hope will be useful. 1) Instead of eagle, if you have a linux box available, try gEDA. I haven't had much chance to play with it yet, but it seems to be a very full featured, completely free electronics CAD package. It has import capability from a lot of other tools, so you might even be able to pull in the work you've done. 2) Stepper control.by Annirak - Controllers
Hi Andy, This is the core of it. Actually connecting it to a counter, etc. isn't so bad. The CPLD code, likewise, would be pretty easy to handle. Let me know what you think! Brendanby Annirak - Controllers
Eh, I'm going for aluminum C channels with skate bearings. I need the flat aluminum surface for position tracking and maybe drive.by Annirak - Mechanics
SATA has dual differential shielded channels, with optional locking connectors on the cables. It's perfect for RS-485 and widely available.by Annirak - Controllers
I've been trying to figure out what to use for linear slides. While this doesn't really suit my end goals, it makes so much sense to me that I can't pass it by; someone might be able to make good use of it. Why not use drawer rails as linear slides? These look nigh-on perfect:by Annirak - Mechanics
I'm working on a stepper driver design. It will use SATA cables to attach to the main board, and handle a minimum of 5A per phase in bipolar. I'm considering adding a boost converter so that the drive voltage is 30V. Each channel will be current limiting, and they'll support microstepping. Obviously this will cost a little more than the existing design, but I think the payoff will be worth itby Annirak - Controllers
Hey Andy, Hand-wound linear induction motors are on my list of experiments once my cartesian frame is built. This is part of the reason that I've started work on rebuilding the stepper motor controller. I could see it being used to drive a 4-phase LIM provided that it can deliver higher currents. Brendanby Annirak - Controllers
The price was $15.86 from digikey. For the largest LPC23xx (LPC2388), it's $11.65. Quick feature comparison: LPC2388/STM32F103VBT Program memory: 512kx8/128kx8 RAM: 98kx8/20kx8 I/O: 104/80 Core: ARM7TDMI-S/ARM Cortex M3 Speed: 72MHz(64MIPS)/72MHz(90 MIPS) A/D:8x10b/16x12b D/A:1x10b/NONE USB: Device,Host,OTG/Device Ethernet: MAC/NONE UARTS: 4xUART/3xUSART SPI: 1+2xSSP/2 *Note: SSP's are liby Annirak - Controllers
grael, If you read through my thread on toolhead controllers, you'll notice a few important points that you may have missed. Just because two toolheads are both subtractive doesn't mean they need the same control system: Take milling vs. EDM, for example. For milling, you spin a tool quickly and it cuts. You may also spray lubricant onto the piece you're milling. For EDM, you charge up a cby Annirak - Controllers