Large Delta, small motors - Counterweights ?

Hi there,

I'm experimenting with delta's ... made a large one, and maybe the arms+effectors are a bit too heavy for the NEMA 17 + A4988 combination.

[imgur.com]

I cant make it lighter (actually, it will be come heavier), and i wonder if i can keep the costs + mechanics simple enough (no gearing)

Would using counterweights - and make slower accelerations to account for more inertia - help things out ? Has anyone tried ?

Cheers

Ram

Try the 8825 drivers!

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

yes, they're on their way, though, they might not be enough.
Bought a bunch of 80g fishing weights, will try :-)

I've used counter weights on an Ord bot before, since I converted it to belt drive. I used pretty heavy fishing weights myself. Here's a link to my page: [www.thingiverse.com]

I've run a 1000mm tall, 500mm wide delta with 50oz.in motors without problem.

It doesn't take that much effort to move the effector, notice that all three motors support the weight of the effector even while powered off. Higher torque will allow you to move faster and I highly recommend 76oz.in. for large format printers, but it's not required.


By the way, I would recommend putting the motors in the bottom since you have the room.
Not just for the wasted space, but you will have less wiring hassle (2 wires per end stop per tower rather than 4 wires per motor) but also, the top is less supported and that extra weight can make it swing like a pendulum when the effector gets moving. This is especially a problem since you are just using smooth rod, which doesn't really build a sturdy frame, and with your tiny clamps, it will be even less sturdy.

Looks good though.

Edited 1 time(s). Last edit at 09/26/2014 04:54PM by sheepdog43.

Thanks for the feedbacks.

Some clarifications on why it's built like that / what i want to do with it.

The effector will become much heavier, probably around 1Kg, as i intend to print with pastes (clay, etc) + will take some horizontal load due to the feeding mechanism. I expect somewhere around 1 to 2Kg of vertical load, and 0.5 to 1kg of horizontal load.

The idea of the counterweights is to cover about 50% of the extruder weight. I'm looking for delta design studies with forces evaluation. Found one, that used a soft to make a simulation, the guy says that forces on the carriages are quite low. I'm still looking for a study a bit more theoretical, identifying for example worst case scenarios for Z forces and XY plane forces on the carriages.

To start with, movements will be slow, and i hope that the counterweights inertia will not be a problem. The speed will be limited by the steppers holding torque (mainly inertia, because a good proportion of the gravity load will be taken by the counterweights)


Regarding the design, agreed, there are a few design enhancements to do, especially on the motor beds.Made a few choices though :
* Motors and electronics position : placed on top because i want to print with clay & other messy materials. So i've put them as far as possible from the base, where all the mess will endup :-)
* Rigidity / swing. The clamps are here to only prevent vertical movement, and i'll be using V braces for horizontal and torsional movements (hence the clamps to prevent the platform sliding when the cables will be tensionned). There will be a few changes on that, i fear that the clamps will not take the load.
* The carriages are relatively flexible, for dampening, and to accommodate of assembly imprecisions. If it doesnt work i'll glue wood plates behind them. Made that choice because what i saw on the i3's X axis.


runninfarmer - question, the counterweights are floating, so i guess they might balance no ? wondering if i can hook my counterweights directly on the timing belt or if it'll make them swing too much.

I have a delta with 3 extruders suspended from the top by 3 cables and counterweight system.

A video at [plus.google.com]
Printing perimeters at 30 mm/s infill at 60mm/s and travel at 120 mm/s

Motors Nema 17 - 70 oz-in


More pictures of the printer with only 1 extruder [deltaprinter.co.za]

Edited 2 time(s). Last edit at 09/27/2014 05:37AM by Xabbax.

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You only learn when you change your mind.
[www.deltaprinter.co.za]

nice !

Quote
ramkam
Some clarifications on why it's built like that / what i want to do with it.

For what you are doing, it all makes more sense now, particularly with the motor placement.

On your counterweights, The weights will help hold the effector up, and lessen the torque needed to lift and move the effector. However, they will do nothing for the effect of it swinging weight as they move perpendicular to each other. Unfortunately there is no easy fix for this other than a stiff frame and slow speeds.

Properly balanced, your motors will work, no problem. And yes, just clamp right to the belt. This was (sort of) how SeeMeCNC did it on the Part Daddy.

I would consider reinforcing your carriage, there will be quite a bit of force on them pushing out from the center of the bot, especially with what all you plan on doing with it. You are likely to get several pounds of force against them. I think vertically in this aspect you are fine, but horizontally, a bit weak. I don't know if they would do well in the event of a head crash, which will happen at some point.

Hey sheepdog43,

i'll probably get some swinging because of the inevitable little offbalance of the weights and build not so rigid (the belt alone gets a little bit of swing), will post a pics/vid with the mod. will find a way to dampen it. thinking of something like a roller that will tension the belt, and dissipates energy for dampening, more to come...

regarding the headcrashes, already had a few while testing, the carriages resisted quite well. probably because of their flexibility, the forces are being better spread / redistributed on the 4 bearing, hence better use of the material. But yeah i'm not happy with these, it was a fishy idea late at night and me wanting to have the carriages printed as fast as possible.

will update them after understanding how to calibrate things nicely (the movement on a fixed Z are dome like, and the dome center is slightly offset from the build center).

speaking of which, it's a bit of a headache to choose the right marlin branch / variant. I'm using RichCatell's version. looks like it provisions for more adjustments than other versions.

also, until now i have only ventured in the configuration.h ... now, i need to get a better understanding of the code. I made a quickref of the files found in the different versions of marlin (made it public, open for mod), to help me out figuring what's where. if it drags interest, i can setup something so that we get an opportunity to make a real specification doc.
the link: [docs.google.com]

Hey,

I have just had a thought.

You could run 2 motors on each axis. One at the top, one at the bottom.

A Ramps can handle 2 motors on each axis as it can do 2 on the Z axis.

With x2 the power it may make it work?

Thanks

Hi Ayouden, i think the limitation is more from the stepstick, than from the motor (apart from heating).

I've done a quick try on the counterweights, i'm not sure it changed much, maybe i should retry more thouroughly.

then tried the DRV8825's on 32x microstepping, these guys put a lot more torque than the A4988's (it's lifting and moving 800 grams without any issue at slow speed),

but they do heat quite quickly (after 10min of operation, sticks at 74°C for a vref of 0.4; and steppers at 40°C) and i wonder if it's sustainable on a say 8hrs print

also, the arduino is lacking the crunching power to handle the 32x microsteps, it happens sometimes (probably buffer issues ?) when speeds is set beyond 60mm/s, and other times, the build is handling 600mm/s (shaky though)

so i'll go with the DRV8825's as my primary intent was to move slowly. i've got some doubts though, as some say they handle the waveform less smoothly than the A4988's, and are notorious to skip steps at high torque.

also, i'm getting other issues, when doing homing after playing with M220 Sxxx - but that's probably related to either bugs in repetier, or in the variant of marlin

i'll put more infos on my choices / what i found best

You will get more torque with lower microstepping values. Maximum torque with no microstepping. As for the temps 74 degrees is fine. Silicon can handle well over 120 degrees. On most devices maximum junction temperature is 150 degrees.

Edited 1 time(s). Last edit at 10/04/2014 05:17AM by AndyCart.

Quote
Xabbax
I have a delta with 3 extruders suspended from the top by 3 cables and counterweight system.

A video at [plus.google.com]

Wow, that thing is a monster! I remember seeing your thread with the tri-color extruder, but seeing it all together combined with the hanging Bowdens and coolant tubes makes it look intimidatingly complex (and at the same time, dangerously fragile, the way it all shakes and rattles around in there).

It looks right for a mad scientist's lab.