Hi all. The thing I'd like to point out about induction heating systems is that they can be very fiddly - they need high quality capacitors and inductors and proper tuning to operate correctly. That being said, an advantage of this sort of technology is that you'd be able to heat the barrel from outside the insulation. The issue of getting high current leads to the extruder head can be partialby jbb - Plastic Extruder Working Group
Hi aka47 I can see the confusion about the 3rd wire, and I agree that screened cables should be treated with care lest one get the dreaded hum. A 2 wire connection would probably work OK, but will not be as reliable as the 3 wire connection... RS485 measures the voltage difference between two wires, A and B. In an ideal world, all a receiver cares about is the differential voltage (A-B), andby jbb - Controllers
I suggest a clone of the DT006, as discussed here It works fine with AVRdude for 5V chips, and with the addition of a few more bits and pieces I've had it going on 3V logic also. jbbby jbb - Controllers
Hi Ant If you port the soft USB port to another micro you will need to be very careful because the timing is tight. You will almost certainly have to code in assembler. Also, you may face some nasty timing issues: you will be trying to run three stepper motors & an extruder in real time (violate this and build quality goes down) and USB in real time (violate this and comms drop out). It mby jbb - Controllers
sudhir This isn't really the right place for this question - 150kg is way above anything RepRaps would handle. Your cheapest alternative is to buy an automotive winch - except that it will be of low quality and use a brushed DC motor and a speed controller. Alternatively, you will need a suitable BLDC and gearbox. Someone like Anaheim automation can sell you a nice big motor with gearbox, butby jbb - Controllers
Hi guys A few years ago I did a microstepping driver in C using an AVR. I've subsequently lost the code, but it turns out to be quite easy to do.... I ended up using an ISR and a few static variables. The basic idea is shown below (almost certainly won't work as is, though): flash unsigned int LUT [] = ; ISR() { static unsigned int step = 0; if (pos < target) step = (step + 1) %by jbb - RepRap Host
Hi again aka47: the article on getting more resolution out of a BLDC seems to be suggesting that you 'half step' it - much like a stepper motor. It would probably help with the resolution but I'm not sure how well the precision would fare. Additionally, I recall people around here saying that gearboxes are undesirable due to backlash etc. At the very least I know that a gearbox will increase tby jbb - Controllers
Hi guys It's good to see someone talking about brushless DC motors. They are a little trickier to drive than steppers but offer potentially excellent results. I'm now going to stick my oar in in a big way :-) The reason that BLDCs outperform normal (brushed) DC motors is that they have quite powerful magnets on the SHAFT, and the windings on the outside of the machine. This makes it easier tby jbb - Controllers
Hi all. I had a look around a while ago for a micro with an FPU, and they're not easy to find. If you move to bigger ARMs (ARM9, ARM11), you can definately get one but you end up stuck with a BGA (Ball Grid Array) package which is very difficult to deal with. Texas Instruments make some in their C2000 microprocessor range, but you need expensive software, programmer etc. In this case, I expectby jbb - Controllers
Hi grael I can recommend Bruce Eckel's 'Thinking in C' as a reference. Unfortunately it's really aimed at desktop computer programming, but it covers the basics well. Additionally, you will probably want to use some form of operating system which will make it much easier to keep your different tasks in line. There are quite a few available, and I'm by no means an expert but FreeRTOS may beby jbb - Controllers
Hi guys Another little problem I ran into: have you checked the coils for conductivity? If one of them's broken things won't go too well... Good luck jbbby jbb - Controllers
Hi guys The issue of the actual spec is important, we should have thought of it sooner. We should make an effort to calculate how many packets/second are passed during a build and do some calculations to specify latency - possibly it's as simple as feed_rate * max_latency < x. I would guess that the maximum latency will be the limiting factor, rather than basic throughput or average latencyby jbb - Controllers
Errr, two questions: 1) If you have a 'light' device that doesn't do data frames, how will it report back to the bus master what it is and what baud rates it can support? 2) How about using the same CRC check (I feel CRC16 would be best) for both stages - it will reduce coding effort and CRCs can be tricky to debug? jbbby jbb - Controllers
Hi guys Nophead is correct: a well-written table based CRC16 will take ~15 cycles per character on an AVR. If the CRC is updated as each character comes in by the UART receive interrupt then the latency drops right off. Calaculating the CRC at the end would, it's true, be slow (tens of microseconds). An additional point: if you elect to simply ignore any message with an error in it (and let tby jbb - Controllers
Hi Annirak Defining a comms standard now is a good idea - it's best to get a standard in place before there is a large code base to modify. I've got 4 comments: 1) A few years ago I cooked up some RS232 based hardware for use on a production line. I found that per-character (hardware) parity was not effective and would let bad characters through, and a standard additive checksum was likewiseby jbb - Controllers
Hi there There's nothing wrong with testing stuff on breadboard, but a couple of holes I've fallen down in the past are: 1) a loose connection can cause really weird behaviour - try wiggling things if you have trouble. 2) because the L298s operate in switching mode, they will generate some high frequency currents. You showed a 100nF and 100uF capacitor pair across the 12V rail, which is good,by jbb - Controllers
Hi guys. If you have a look over at Oatley Electronics under the 'CNC' section they have a few kits and may have posted diagrams. One really important thing to bear in mind when using a PC to drive something directly is that it's really hard to get accurate timing, which will muck up your build accuracy or even cause complete failure to move. Also you probably won't be able to do PWM via theby jbb - Controllers
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. 2) You might want to put a small RC circuit (t = 300ns, say) between the current sense resistor and the current sense amplifier so that switching current pulses do not make it to the current comparator and cause prematby jbb - Controllers
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... That's a clever take on current mode control... one thing to look out for is that the time constant of the R-C filter on the PWM output may reduce your maximum control rates. I have two suggestions: 1) You're using dual opamp chiby jbb - Controllers
Woah there... lets not get personal. On the RS485: Annirak has a good point - you need tight timing on some of the master -> slave communications. Remember the RepRap gen 1 electronics had a synch line? This isn't about bandwidth, it's about predictable timing, which is essential if we want to keep the build quality up. Going to a two lane connection will indeed increase the cost a littleby jbb - Controllers
Hi there grael. I've thought for a while that instead of grudgingly moving up a single processor size whenever we hit a limit is not the best idea - the non-recoverable expenses aren't too hot. Moving to a nice big ARM will give plenty of elbow room for future development. I also suggest an RS232 port for debugging work - they have been very very very helpful for me in the past. Motor driversby jbb - Controllers
Hey, neat to see some crazy ideas bubbling away over here. Two things to say: 1) The choice between a master controller and a nodal architecture is really interesting. A central controller chip would be good for the motion control work (XYZ, R, theta...) because to get good motion all of these must be carefully synchronised, and comms lag could bite us badly. However, we don't want too manyby jbb - Controllers
Annirak To put the FETs on the high side seems fair enough, especially if you want to sense operating currents, but it makes things just a little more tricky. There are two approaches: 1) get an inverting gate drive chip (say the TC1426) and use a P channel FET. They have marginally higher on resistance and gate charge numbers, but with a 1A gate drive chip you'll have no trouble switching one.by jbb - Controllers
Looking pretty good! I have a few suggestions, but feel free to ignore them - it's your project. Power supply: How about a power ON indicator? Reverse polarity protection is a good thing - or are you using a polarised connector? Maybe you should include a trusty old 78L05 on the board? Something people have been talking about on these forums is that a PC power supply can have poor voltage reguby jbb - Controllers
It's good to see someone getting into it... on the software management side, the micro (PIC/AVR/whatever) can store a little configuration string which identifies it to the main board and hence the control PC. One comment I'd make, though: sharing a comms line with a synch line might cause trouble if your software does something weird - you could end up with your comms locked out. Would it beby jbb - Controllers
On components: buying a whole reel of bits is going to be expensive! Many distributors (I use Digikey) will supply 'cut tape' - i.e. a short length of tape with, say, 10 components on it. These short segments could be stuck down onto a base board to avoid having to develop tape dispensers.by jbb - General
That's a very interesting thought: building captured nuts, washers or even bolts into parts could be very handy when it comes to assembling things, especially for complicated structures. One thought on captured bolts: if you put a bolt in and it sticks up above the work, won't the extruder head hit it as it tries to fill the surrounding area?by jbb - General
Good thinking to suggest a custom tray, Enriquie - that way it will have precisely controlled dimensions. Bumping the components up against a guide to slide them into place is also a good thought thanks Freds - it might not let us get down toby jbb - Controllers
I know the feeling with SMD! It seems that all the cool toys are coming out in SMT packages now - either TQFP or (shudder) BGA. I've hand soldered of SOIC (rectangular with leads on 2 sides) and TQFP (square with leads on all sides) myself with OK results, but it wasn't exactly easy. Forest raises a good point: pick and place is hard and how many people will need it? As a community effort one cby jbb - Controllers
Hi guys. I haven't had any real PSoC experience but the people I know who have say they're pretty good but a little hard to program. On the thermocouple front, I have seen app notes which suggest using a good, high precision ADC to measure the voltage across a thermocouple directly - either with an internal preamplifier and moderate resolution (16 bits?) or a really high precision (say 24 bit)by jbb - Controllers