V0.2r1 Double Shear AB Drive MGN7 + MGN9

well, where to begin…

This was kind of a dream and to be honest I didn't expect it to work given the size it had to work in…

After the usual staring at the PC with ideas of what / how and what not to do, I just went for it and allowed the creative to flow.

What this has turned into a very capable AB Motor Mount that should help you eek that little bit more from your V0 without stressing the Motors.

For those wondering what double shear is…

your standard setup has the pully above the motor and its bearings. (see pic)

• the blue rectangles represent the bearings (two in the motor)
• the red represents the points of stress and direction of force applied to that point
• the green is the direction of the force from the belt

so this would mean that we have a bending force applied to the motor shaft.
also the further away from the bearing the force from the belt is the more bending force we have on the shaft.
now we add even more force from the belt when we accelerate and decelerate the motion system.
this can lead to a number of problems but I wont go into it as its a bit of a rabbit hole.

now for a double shear setup has the pully mounted between two supporting bearings. (see pic)

• the blue represents the bearings (two in the motor and one above the pully)
• the red represents the points of stress and direction of force applied to that point
• the green represents the direction of the force from the belt

the first thing to note is that we have changed the type of force on the motor shaft.
it is no longer a bending force but now a shear force.
the motor shaft is vastly stronger in handling this type of force applied to it than the previous setup.
also the motor bearings and the top bearing now equally share the force between them so stress is reduced.
the motor shaft now is held securely in place so acceleration and deceleration moves of the motion system do not effect the motor shaft as before.
this reduction in motor shaft force means that a higher belt tension can be attained without stressing the motors too much so we effectively remove the back lash on the belts.

ok, enough with the engineering science lesson…
lets get to the good stuff!

INSTALATION

you will only need to change two types of fixings to install this mod…

8 off M3 x 30 BHCS (for the motors - these replace the M3 x 35 BHCS)

2 off M3 x 14 BHCS (for the umbilical attachment - these will replace the M3 x 10 BHCS)

you will also require…

2 off 625 (ZZ or RS) bearings

now that you have these, print off all the files (pre laid on a V0 bed)
I've labelled each side A and B for easy install (and to remind yourself what side it should be on)

the actual installation as fairly easy, as with the standard setup i have kept all the original fixing points and as many fixings as per the original too.

the heat set threaded inserts go into the Lower AB Motor Frame as before but all of them flush. (4 off Threaded inserts per motor mount - 8 in total for both sides)

now its just a case of building up the bearing stacks as per the manual.
taking the Upper AB Motor Frame and building upside down

next insert the bearing into the Top Tensioner Bearing Housing
this must be flush with the top.
it will be a good press fit (I turned the bearing housing upside down and pressed down with my palm on the table until it was flush with the table)

this should now just klick onto the top of the Tensioner

after that insert the Tensioner into the Lower AB Motor Frame and add the Tensioner Nut to hold it in place. align the Upper and Lower parts and fit together.
add in the 2 off M3 x 35 BHCS and 2 off M3 x 30 BHCS screws.

now add the AB Motor Plate to the bottom.

at this point you can re-install it back onto the printer (hopefully you haven't knocked the nuts out of place)

now this is where the real fun begins!

once back on the frame and secure (remember not to over tighten the bearing stacks though) add the 4 off M3 x 30 BHCS screws for the motor.

the Motor has been raised 5mm into the AB Motor Frame so we need to lower the pullies by 5mm down the shaft.
it's ok to leave them loose if you want.

now get you belt and loop it into the Motor Frame and push it right to the back of the tensioner!

this is the tricky part…

with the belt looped at the back slide up the motor making sure to get the looped belt over the pully and slide the motor shaft into the top bearing!

once you've successfully done that loosely tighten down the motor to hold it in place.

now get yourself a cup of tea - you deserve it!

all that is left is to run the belts as per the manual and tension.

also don't forget to make sure your pullies are tightened (don't want to have headaches trying to figure out why your printer isn't working properly later)

warning - when I installed this I found I needed and extra 2 teeth on each belt.
I can only assume that this is because the motor shaft is not deflecting under load anymore.

I'm not going to recommend a tension here because there are many factors that will change what you may end up using, but I will tell you what I'm running.

so, i have…

• MOONS motors running at 1.1 Amps
• tension is set to 138Hz
• Fushi Bearings
• motor temp (after 3 hours print time) was 10 degrees less than on standard setup.
• travel speed of 800mm/s @ 30k accel before motor stall

I did play with tensions up to 185Hz but found that the motors got hot and my sweet spot was 135 - 140Hz for my V0.
but I would start with the 110Hz recommended by Voron and go from there.

on the standard setup I had travel moves of 600mm/s @ 25k accel before motor stall so a marginal increase of performance has been obtained.

I can not however guarantee that you will also get the same performance increase as it depends on your own setup and tuning of your V0.
But I wish you the best of luck and I hope you also benefit from this mod.

I'VE NOW ADDED AN OPTION FOR THE POPULAR MGN9C RAIL !!!

Please Follow the Voron Print Settings

4 perimeters

5 top / bottom layers

40% infill

material - ABS / ASA

any feedback is welcome and i hope you enjoy this mod!

Happy printing!

Full Credit Goes to the Awesome Voron Design Team for Creating This Brilliant Little Printer and making it Free for us to MOD!

you can find the GitHub repo here
https://github.com/Driftrotor/Voron-V0.2r1-Double-Shear-AB-Motor-Mounts/tree/main