A simple question that is not covered in places i looked. (JD - junction deviation) I want to clarify how movement start from stop position. With JERK (without JD) marlin just start with speed of JERK and then continues accelerating to set speed (assuming final speed is more than JERK) How does it work with JD enabled? Does it start from zero and uses acceleration or does start with MINIMUM_PLAby ArtemKuchin - Firmware - Marlin
I know, but don't you think that this topic already has too much irrelevant text?by ArtemKuchin - General
"RRF calculates when the motor should have moved by an amount corresponding to one microstep" Even if it know full system inertia it still cannot know when it moved or not, because the nature of microstepping itself is such that a due to manufacturing differences the ustep may or may not happen. So, i don't understand this statement. the delta in my example is usual acceleration, How else any fiby ArtemKuchin - General
Aha, i figured the equation already, not in the differential form, but same stuff eventually. Yes, JD is still jerk in 3d printer sense. On the other hand, what is NOT jerk? Really, even when you accelerate the motor you have to change the speed from zero to v1 and then to v2=v1+delta then v3=v2+delta, so, delta is jerk. At what threshold would you start calling this delta not acceleration buby ArtemKuchin - General
What you say it is true, but it is very generic. "up to 1 step", "reach 2full steps" - that's possible maximum conditions, but not real life conditions. As i said, i am sure, from real world experience, that lag is far less and that's exactly i need to know - the real lag. Marlin has S curve and Junction deviation. They may be turned on or off (back to usual jerk stuff). When JD is used the jerkby ArtemKuchin - General
What does it have to do with jerk in a sense used in 3d printing firmware?by ArtemKuchin - General
I don't know about reprap software, but marlin seem to use jerk as starting speed from zero. Yes, it is a threshold speed. For speed below JERK acceleration is not used, for speed = or > JERK acceleration is used. Again, i am talking about marlin firmware, sorry. So, if motor starts at JERK the firmware pulses to drivers STEP input at frequency which will result in JERK speed (taking into accby ArtemKuchin - General
My point is i am not looking for step skipping conditions. I am looking for forces during normal operation, when there are no shifted layers of skipped steps.by ArtemKuchin - General
If 2 full steps lag would really happen normally in real life that would casually cause problems with fine details. For example, you have an indent of 0.1mm and the step delaid by 2 full steps, so, it just neve happens, because their is only 1/2 of full step there. But i don;t see any reports of such things. So, it seems like it applies only for high load applications like CNC. Still, did not seeby ArtemKuchin - General
with 20t pulley 1 full step is 0.2mm, 2 full steps is 0.4mm If jerk take place in 2 full steps and it would be impossible to print details less than 0.4mm Which is clearly not the case, i can show you test print with details as small as 0.025 mm, crazy huh? (need 16t pulley though and good geared extruder). Microstepping does rise resolution and microsteps do move things around. For me "jerk hasby ArtemKuchin - General
That's funny Alrighty. There is nothing instantaneous in the world. Nothing to be at stop position and then in no time at some speed just because it would require 1) infinite acceleration 2) infinite impulse So, the real picture is in many aspects unknown for now. 1) JERK speed is a constant speed, that is defined 2) SPEED for stepper is defined by period between STEP pulses to driver 3) Pby ArtemKuchin - General
I fully and deeply (to the source code of marlin) understand what is jerk and how it works and why it exists. What i don't understand is what really physically happens when jerk is applied. It really does not matter if it is applied from stop position or from movement, the real acceleration and forces will be there.by ArtemKuchin - General
Continuing talking to myself. Rotor moment of inertia is 47 g*cm^2 = 0,0000047 kg*m^2 Speed needed 20mm/sec, that 2000 pulses/sec 3200 pulses per revolution, 2000/32000 = 0.625 part of one revolution which is 2*pi*0.625=3,925 rad This is needed angular speed Available torque per microstep is 0.04 torque = moment of inertia (MI) * angular acceleration (AA) angular acceleration =angular velocityby ArtemKuchin - General
Alright, figured our the static friction numbers. There is engineering reference with coeficients for each type of friction and each type of material. Steel on steel is takes as 0.1 and that's for flat surfaces. We usually roll So, 0.1 will cover all cases. Now, let's take my stepper and calculate incremental torque. Thfs=0.4 Nm SDR=16 microstepsstep/full step Tinc=Thfs*sin(90/SDR)=0,04 Nmby ArtemKuchin - General
I think i have another aproach at the problem! We can get calculate incremental torque produced by each microstep. That easy. Then i can calculate inertial of the load (+stiction) and calculate what toque is needed to overcome the load and count number of microsteps when the needed toque is accumulated and count total pulse time. That will give me the acceleration and force acting on the belt. Wiby ArtemKuchin - General
Aha, i see why in multiplies of 4! Because one full electrical cycle take 4 full steps. If step is missed the driver will need to repeat the electrical cycle to pickup the rotation and continue. Alright, that's clear. However, that does not apply to microstepping. If you miss a full step then your are done, it is missed. Microsteps, as i see it, are not missed. Just the accumulated energy may noby ArtemKuchin - General
Can you elaborate on your test with skipping and step lagging, do you have some desrcription of tests, videos? I would like to see that how you arranged that and original collected data. Very interesting. So, about lagging. Do i understand correctly that if there is not enough torque to make a step then motor will accumulate more energy for the movement UP TO to the next 2 full steps and when thby ArtemKuchin - General
M566 X600 Y600 Z30 E20 ; Maximum jerk speeds mm/minute what is this then?by ArtemKuchin - General
I'll give another superextreme example which has nothing to do with reality. Marlin can do quad-stepping up to 40 000 HZ of steps. Let assume we have 100 steps (pulses)/mm So, one step takes 25us and move the belt 0.01mm The belt were at test, the driver received the pulse and move the belt 0.01mm in 25us (just imagine it for now). Let's consider the movement evenly accelerated. So, X=X0+V0*T+ (by ArtemKuchin - General
I am building a a new corexy printer and considering some math (at least some very simple physical model) for picking the correct parts and arranging mechanics. I don't understand how jerk is really applied. By "really" i mean " in reality". As it is used in marlin it is Instantaneous change in velocity. For example: Let it be 30mm/sec (not ^3!, it is not jerk in physical sense). Now we haby ArtemKuchin - General
Hmm.. maybe it is related to a note in TMC2100 datasheet: Attention microPlyer only works perfectly with a stable STEP frequency. Which is far from truth in case of marlin. Then At 16 MHz system clock frequency, this results in a minimum step input frequency of 16 Hz for microPlyer operation. A lower step rate causes a standstill event to be detected. Which means if we go too slow on extrby ArtemKuchin - General
Um.. i don't know. Need to test that. I also plan to test with TMC2208 (currently TMC2100). Th pattern is exactly vertical now, i don't think it will change. The chamce that i just randomly hit some current that generate exactly vertical pattern is negligible.by ArtemKuchin - General
QuoteMCcarman If it was the extruder i would have expected it to be in both directions. Yes., i agree on that. QuoteMCcarman Does it change with print speed? Yes it does, with HIGHER print speed it is greatly reduced and almost invisible. Strange, huh? The scanned model i posted is made on 20mm/s. If print at 40mm/s hard to see at all. Even faster - non visible. I estimated the amplitude ofby ArtemKuchin - General
No, does not seem to be relates to full step. The pulley is 16 teeth, 32mm perimeter, the motor is 200 steps (1.8 degree), so, 32/200=0.16mmby ArtemKuchin - General
But can you explain why i cannot print everything with 1mm nozzle?by ArtemKuchin - General
I think such question has been asked many times but i cannot find a definitive answer for my case. Moving table (Y-axis) printer. TMC2100 drivers, 16 microsteps. MK8 direct extruder DRV8825 drivers with 32 microsteps 0.4 nozzle. 2GT belts, pulleys, etc. When i print a test cube on sides along Y axis (perpendicular to X axis) i see the ribs show in the attached image, The period is about 0.by ArtemKuchin - General
I always thought that extrusion width should be more than nozzle size, optimally like 1.2*nozzle size, but actually a little different for each material. I also thought that i can extrude wider, until the width more than nozzle end width (hole+walls), so, the filament is still ironed by the nozzle. I was sure that extruding less than nozzle width for normal shells will result in some kind of probby ArtemKuchin - General
As seen from the table the number in front is not pitch. 2GT belts can be 2,3,5,8mm pitch. So, nobody knows what this number actually means. But 2GT belts are circular H -type, and curvilinear Gt2 type are named MR2. Arghhh. God, help us all. It says " MR is a curvilinear profile and is compatible with PowerGrip® GT® 3 from Gates. MR is GT® and vice versa GT® is MR." However, from the textby ArtemKuchin - General
From what you say the correct way to name a belt would be 2GT2 - 2mm pitch GT profile 2nd generation belt. Yes, profiles for GT2 and Gt3 are the same, i have read the misumi and gates notes on that. Profile for original GT is different. However, E3D in its blog specified that profiles for their 2GT belts and GT2 belts are different. How different - no info. So, either 2GT is really GT1 - 1st genby ArtemKuchin - General
Hello! Recently i've seen many 2GT belts on ebay and alixpress. Then found 2GT belts and pulley from GATES on e3d site It seems like profiles for 2GT is a little different from GT2, but i am not sure. Maybe someone already dug this issue and have an answer how different or similar GT2 and 2GT.by ArtemKuchin - General