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January 9, 2006
Principal Embedded Systems Engineer
Logic Product Development
Schmalz Haus LLC
Product ROB-11876 |
about a month ago
I’m really sorry to hear you had problems with the BED. It sounds like it’s best that you try other boards to see if you can get your system to work. Many people have constructed CNC systems using BEDs with no problems in the past- I’m very confident in the design itself. These little Allegro chips are quite sturdy. But because of the big powers involved, it is easy to make an innocent mistakes that can cause damage to the driver.
The resistor change was due to the need for reducing the power and voltage lost across the sense resistor. The smaller that sense resistor value, the more power goes into the motor, and the better we can make the microsteps at a lower input voltage. You are correct - if you crank the pot up high it will try to tell the driver to use more current than it’s able to dissipate. What happens in this situation is simply thermal limiting - the driver chip rapidly cycles on and off, which will keep it’s die temp down, and will produce a chattering or stuttering of the motor. This protects the driver chip. So you can’t hurt the driver by turning the pot up too much. Note that the actual max current you can get will depend on your input voltage, current pot setting, motor coil winding and inductance and ability to remove heat from the board. So some people max out at 1.5A, and some max out at 2.4V or above.
It could be. Do the Q13) checks on http://www.schmalzhaus.com/EasyDriver/index.html and see if you have any errors there. That should help you determine if you have a bad driver chip or not.
I have seen a couple of people with this problem in the past. Sometimes it’s a problem with their Arduino code (check your DIR pin with a volt meter or scope to make sure it’s going all the way high and low) or grounding between the various pieces of the system.
You can heatsink the driver chip on the top of the board, or you can heatsink the boar itself on the bottom of the board. Putting the heatsink on the driver chip itself will allow you get more heat off of the chip (since you’re not going through the board), but if you have a large metal surface that you can attach the board to (with a properly electrically insulating thermal pad between) you may get even better dissipation.
Yeah, the Big Easy Driver and the Gecko are in completely different worlds. Not only are their prices very different, but the Gecko can drive much larger motors much faster and much more smoothly than any little Allegro based solution like the BED. Totally different class. If you need to move big motors, don’t use a BED, you’ll be disappointed. If you need to move NEMA 17s or some of the smaller NEMA 23s, this should work out just fine. I’m really sorry that your BEDs died - but in almost every case that people have brought to my attention, some type of user error or mistake was found that likely caused the problem, not a bad board from SparkFun.
Unfortunately, the A4988 driver chip has a maximum voltage of 35V. Using 36V might work, but you would be beyond the ‘absolute maximum rating’ as per the datasheet.
Unfortunately the board sizes are quit different. If I made a version of the BED that could fit into one of the Polou pinouts, you couldn’t have them as close together as many of the RAMPS boards do. Sorry-
Yes, I’ve seen many people solder in the 3.5mm pitch screw terminals. They work great. I’ve also done it a lot too.
Product ROB-11876 |
about 4 months ago
You can try that. And depending on the coil resistance of your motors, the torque you need, and your input voltage, it may work. However, that will present a lower coil resistance to the driver board, which may or may not be a problem.
Another way to do it is simply take two BEDs, have each one power a motor, and run the same step/dir lines to both drivers. I’ve used this before to ‘gang’ any number of stepper motors.
No public wish lists :(