Chinese Ramps 1.6

[jeffeb3]

@ednisley

If you’re feeling adventurous, you can use one wire of the harness as a current-sensing resistor: measure the wire resistance, connect a scope across the wire, and the waveform will give you the current. For example, a 0.25 Ω wire will give you a 250 mV/A = 4 A/V waveform. Note that the wire has nothing in common with circuit “ground”: connecting the ground clip of a line-operated scope probe to the wire will kill the driver chip stone cold dead.

I just might. I have a cheapo scope, but I think I can run it from a battery…

@ednisley

The IR drop varies with the current, so it’s a minimum when the sine wave crosses zero and maximum at the peaks. However, when you’re looking for trouble, don’t start by minimizing the trouble. You’re not showing why something works, but why it might not; always expect reality to be worse than your assumptions.

Yeah, I might try to break it down for all 32 microsteps in my spreadsheet. Just to see how pecimistic this is. I’m guessing the worst step will vary with speed, but be closer to the middle steps.

@ednisley

Accelerating that huge mass hanging on the gantry requires more torque than cruising along at top speed, which means the acceleration limits influence the results. A sufficiently low acceleration may prevent the motor from reaching top speed during a short move, which will screw up all your calculations.

Those things are true, but they are problems on the otherside. Determining what torque is fighting the motor is different than maximizing torque output.

@ednisley

Basically, you cannot determine a hard speed limit from these simple models. What you can get is a better understanding of how speed, torque, and supply voltage interact, which is nothing to sniff at!

Yeah, I understand more than I wanted, for sure. Thanks for dragging me through this.

[vicious1 (Ryan)]

Sorry to butt in, Ed, Thank you for getting more pictures of my machine in the magazine again!

 

I am desperately trying to follow along with you two but you went over my head real fast. So I will just sit quietly while the smart guys talk, try to learn a new word or two, Glean some knowledge. It is fun seeing real engineers discuss an issue.

 

[bcdcmcnamara (BT)]

I’m with Ryan, but I just updated my contact list for really smart people to add Ed to the collection with Jeff and Ryan and … so many others!

[ednisley]

more pictures of my machine in the magazine again

Readers may not recognize it from the bug's eye view, but the middle assembly is definitely an impressive collection of plastic & bolts!

[ednisley]

If I plug in 900mA, I get the cutoff moved to 53mm/s.

Torque is proportional to current: at 0.9 A the motor produces only 60% = 0.9/1.5 of its rated 76 oz·in = 45 oz·in.

Power dissipation in the winding resistance varies as the square of the current, so they’re dissipating only 36% of their rated power. Even at 1.5 A, though, they’d dissipate only 5-ish W and shouldn’t get too warm for PLA.

[ednisley]

@bcdcmcnamara

contact list for really smart people

Nah, I’ve just managed to learn a bit from a whole bunch of mistakes … [sigh]

[vicious1 (Ryan)]

@bcdcmcnamara

I’m with Ryan, but I just updated my contact list for really smart people to add Ed to the collection with Jeff and Ryan and … so many others!

Well thank you but I am more of a persistent bastard, than a smart guy. If I can’t figure it out I just keep trying, a little finger crossing, some cussing, occasionally a plug and pray.

[banish (Jeff)]

OMG - my head just exploded trying to read the posts on page 2 of this thread… good god, there are some very large brains on this board!!

I’m gonna go back to drooling on myself now. lol.

[esis94]

I used this board for my 3D printer, and here the headaches come!
there is no Ramps_16 in marlin source list, so i tried any other boards in configuration but got nothing in the lcd. firmware compiles and uploads successfully via Arduino IDE. however i changed my Arduino board and lcd board (12864 LCD) and still nothing changed.

[Paciente8159]

Maybe the LCD connectors are inverted relative to ramps 1.4. I switched from ramps 1.4 to MKS gen l v1. It should be Pin compatible… But that turned out not to be the case. This video made my day

[SupraGuy (Dan)]

@Paciente8159

I switched from ramps 1.4 to MKS gen l v1.

I used one of those for my Primo. Yeah, the LCD connectors are keyed backwards as compared to most other ones.