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91
3D Printing / Re: MKS Gen L 1.0
« Last post by Reywas on April 22, 2019, 08:52:12 PM »
You are a wealth of knowledge jinx.  I may just order a couple of those to play with, although connecting the fan to the hotend fan is an acceptable (and easier solution).  On the subject of fans:  Are the ball bearing fans any more quiet than the sleeve bearing fans?
92
3D Printing / Re: MKS Gen L 1.0
« Last post by jinx on April 22, 2019, 12:54:04 PM »
Quote
I'm not sure what the Marlin folks had in mind by using that particular pin.

I think it not so much the marlin dev but stems from the RAMPS development the gen l board is a single board RAMPS setup/pin layout and basically you can buy a fan adapter for that set of pins on the RAMPS

              

     link to  ali https://tinyurl.com/y3mbxu4b  but am not sure you be able to plug that onto gen L board.... So hows your tronic skills to could make a simple vero board and tranny to do the switching.


update: just thinking out loud here you could get that adapter and use some short jumper cables  8)

PS:
  dont go just plugin a fan V+ onto the d4 pin   the current draw could destroy the pin!
93
3D Printing / Re: MKS Gen L 1.0
« Last post by Reywas on April 22, 2019, 12:01:15 PM »
Thanks for your reply jinx.  It really wasn't my idea to use that particular pin, it's just the default pin used in the Marlin config_adv.h file for the MKS GEN L Board.  That bit of code allows you to set the controller fan (main board cooling) to only come on when the stepper drivers are on.  That fan is by far the loudest thing on my printer at this point and it would be nice to have it run as little as possible.  I'm not sure what the Marlin folks had in mind by using that particular pin.  I should note that I have a tenuous at best grasp of the Arduino IDE and Marlin FW.
94
3D Printing / Re: MKS Gen L 1.0
« Last post by jinx on April 22, 2019, 10:17:56 AM »
Quote
My question is regarding the MKS GEN L so I thought this would be a good place to post it rather than start a new thread.  MarlinFW config_adv.h sets the Controller_Fan_Pin to 4.  Is that D4 as shown on the board diagram at the start of this thread?  If so I suppose I would need a 5V fan connected across D4 and GND?

that would be a way may require a current limiting resistor! but not total sure on that. BUT I got gut feeling that may not work as expected. you thinking of triggering the fan using a servo command, you be constantly sending a servo pulse to the fan, would that not pulsate the fan? how will that effect to gcode  data while sending the servo pulse ?... think if I was doing this, I attach a fan to the 12V line  "(depending on the fan voltage you say 5V most fans I came across are 12V)" with a switch and switch it on when needed see next to the X axis driver there a 12V line to tap into or attach to the Hotend cooling fan so when you start printing your board cooler would kick in at the same time,,, if that makes sense   
95
3D Printing / Re: MKS Gen L 1.0
« Last post by Reywas on April 22, 2019, 08:20:29 AM »
Hello All from North Georgia, USA:

This is my first post on this forum...lots of good reading to be found here.

My question is regarding the MKS GEN L so I thought this would be a good place to post it rather than start a new thread.  MarlinFW config_adv.h sets the Controller_Fan_Pin to 4.  Is that D4 as shown on the board diagram at the start of this thread?  If so I suppose I would need a 5V fan connected across D4 and GND?
96
Walking / Re: Meowth Abandoned
« Last post by Nemesis on April 11, 2019, 11:08:00 AM »
Very good summary of your work and what you have been through... This reminded me as well some issue I have/had with Animabot.
I'm sure you learned a lot with this project and you will continue to do so.

But I'm sure this robot is not finished, in few weeks/months you will start designing a new one ! Look at me, the last 3 versions of Animabot were supposed to be the last :D

Keep up the good work !
97
Walking / Meowth Abandoned
« Last post by BaldwinK on April 10, 2019, 06:35:48 AM »
As we are supposed to learn from our mistakes I have written up one of my failures.

The project was to build a bot, as cat like as possible, to sit and wave a paw, stand up and walk around.

 [ You are not allowed to view attachments ]

The activity started more than three years ago with an attempt to copy Boston Dynamics’ quadruped - Spot.  Believing the quoted torque values was the first mistake as the 55g servos could barely lift their own weight. The leg modules were later re-used for HybridTrotter and Scooter Boy where they provided the drive but the weight was carried on wheels.

Using a Picaxe micro, Hybrid Trotter was posted on their forum and the video shows a disinterested Meowth idly watching. A spirited American Ragdoll, he didn't live to see his namesake in action.


Much of my learning progress is posted in the Tutorial section. Firstly improving on the MG 995/996R servo performance and squeezing it into the legs. The fixing lugs were cut off and the electronics replaced by an Arduino Nano plus drive circuitry allowing all the motors to run directly from a 3S Li-Po supply.

Distributing the processing between a master and four slaves using an I2C bus required fast routines and short data packets. All processes had to be sync’d to a 15mS cycle time for the sixteen PIDs. Once again the MPU-6050 showed a disregard for protocol and had to be driven separately.

Three modes allowed for setpoint angles to be sent for direct action, or indirectly reached after delta time cycles. Inverse Kinematic values were converted into setpoint angles by sending x,y & w coords of the toes.

Sitting postures were held in lookup tables in the master and sent for indirect action. This proved harder than expected because of balance issues. Try standing up from a chair without moving your weight forward first.

Later development became too complicated and a PLX-DAQ mimic display was a great help.

It sometimes can happen that all four legs step correctly but, not wishing to scratch the table, the clip shows only two legs in action. This is stalking mode for a cat - a creep forward with only one leg lifted at a time.


Balance

This is always the main challenge when working with limited motor torque, thicker than real life limbs and limited sensors. Working with 2mm 4-ply is not the only reason the result can appear ‘wooden’.

Once you start using IK values and forget about individual angles, other techniques become simpler. If the bot were to step down onto a hump or into a depression, the riding height at hip or shoulder would need to change for the rest of the gait cycle. Just add a few milimeters to IKy to lower it, or subtract a bit to raise it.

On a flat table surely that won’t be necessary? Consider the leg construction: four motors are joined in line so that the bot is narrow at the hips. Like elephants hanging onto the output shaft of the one in front. Output shafts with end play and gearbox slop. Calculating trig functions to a fraction of a degree and millimetre is fine in theory but in practice the IK coords will end up somewhere near a centimeter circle on a good day.

So balance can’t be predicted because the feet will land in different positions each cycle. The MPU will report Pitch and Roll but the bot has four legs. You might spot in the video the bot straightening up just before lifting a leg. But the MPU cannot indicate where the centre of mass is before it moves. If we’re lucky the error might be recoverable by changing leg lengths on the fly. Or the bot might have been level on three legs and suddenly the most important one is too short and the bot must fall.

So the next creation must have a load cell for each leg to determine CoM before committing to stepping. Moving the balance point still requires flexibilty, mostly to move to the side. The design (which makes for a narrow body that can sit) has the lateral motors set a 40 degrees to the horizontal. Very tricky 3D IK and producing a non-linear roll/rotation. In practice the square foot profile provides more lateral stability than an active motor.


The MPU can derive a ‘falling vector’, different for each leg, that is sensitive enough to trigger an emergency foot down process. Here the motors can step wide quickly and stop a crash. A couple of retries are permitted where the leg straightens and lifts to the last postion before continuing. Each time the bot is tilted further over  to help. Again this is only guesswork without load cells.

Software is now working like a cars suspension to allow IKy coords to drift, within limits, from the theoretical. Placing a foot down is problematical anyway. Too heavily and the shock can tip the bot and upset the next cycle, too softly and the weight distribution may be wrong. Experimenting with a simple microswitch foot sensor did not obviously help. The slave loses a cycle to get the info to the master leaving little time to act. The next creation will need a shock absorbing toe and well designed sensor directly connected to the master.

Tilt Plane

We can derive from Pitch and Roll the amount by which each leg needs to change. This can be referenced to the next leg to lift. These corrections can be applied immediately as a feedback signal but the result is too lively. With four legs grounded the bot bucks and rears much like an animal but will eventually overshoot and topple. With the support body being nearly four times longer than the width, Pitch is dominant.

However, if a snapshot of Pitch and Roll is applied slowly, then the bot will settle into a level pose. Pitch is -1 degree and Roll is +1 degree in the graph referenced to HL.

 [ You are not allowed to view attachments ]

  Poff = 220 * sin(degpos[1]/57.296);
  Roff = 60 * sin(degpos[0]/57.296);

  //snapshot tilt plane values to make level 
  FLbal = -Poff;
  HRbal = Roff + 2;           //then add extra tilt
  FRbal = -Poff + Roff + 2; 
  HLbal = HLbase;     
  balTest ();                 //keep bases within limits

Stiction

Another issue causing intermittent toppling was my use of the classic PID code to control the motors.

We deal with static friction, or stiction, when driving a vehicle from rest. An extra touch on the gas pedal will ensure a smooth start and once rolling it will need less to run onwards. When controlling a wheeled bot we know that there will be a minimum voltage below which the motor will not turn.

Surely this must also affect a servo motor system. Tim Wescott in his blog puts the tricky maths around the problem. Since Tim has offered consultancy on this for 20 years it is unlikely there will be an easy answer.

Brett Beauregard wrote the library PID code and explains it well. However, it does assume a linear system - and a brushed electric motor with high ratio gearbox can be spectacularly non-linear.

MG996 with PID and PWM control can fail to move sometimes, like a joint with arthritis. Similarly Iterm makes no difference to performance.

I spent forever coding a State Machine form of PID controller. It failed the KISS test but clearly showed the problem. This bot still uses the classic PD code but the output is monitored and ‘kicked’ when it fails to move for a few cycles despite an error signal. Even stiction has a breaking point! The problem comes if it is pulsed too strongly as it has to be brought back under control by the next reversal. Iterm is now more a ‘nudge’ to move closer to the setpoint.

Conclusion

It is very hard to pull the plug on a long running project. So much time and effort invested, hopefully not all wasted. The next project is still to be decided but load cells must certainly be investigated.
98
General Discussion / Re: Bench Power: Help a rebel out
« Last post by jinx on April 03, 2019, 04:20:10 AM »
you get to the bottom of this
99
General Discussion / Bench Power: Help a rebel out
« Last post by ZeroMax on March 27, 2019, 10:00:53 PM »
I went about 5 years with the same inexpensive MPJA bench power supply, but it died on me last November so I upgraded slightly to a digital by the same manufacturer. That one died on me after about a month while I was putting 5v into the simplest CMOS oscillator you can make, so they sent me a replacement.  I’ve had it about three weeks now and tonight, while powering a RobotDyn ch34 mega clone which was rated for 9-12 on the Vin, it let the smoke out of the USB chip and stopped reading any current draw.

You all know I’m not new to this but it seems like ever since I turned my iron towards musical instruments I’ve been on a path of destruction.  Can anyone give me some pointers about variable V/I bench supplies, or Did I really get 2 lemons?  (The old one was V only.)
100
Introductions / Re: Just a short intro...
« Last post by MEgg on March 18, 2019, 05:49:28 PM »
A warm welcome.
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