Grégoire Saunier
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BearExxa V2 - Gearing
🕑 Added 2022-02-11 15:13:19 +0000 UTCHi all, I will share several posts in the coming days explaining features and design we have selected for our new extruder.
The new BearExxa will use a Bondtech 3:1 gear set, same one than in the BMG extruders. One of the reason behind it is because it is well known, compact, reliable, good teeth design and easy to source. Another advantage is that many already have it on their printer as they have upgraded their Prusa extruder to Bondtech extruders. And obviously, everyone has the Bondtech dual print gears.
As you know, we focus on reliability and want to reduce maintenance to minimum. Most of the time, this gear set comes with tiny and fragile bearings to support the drive gear. We have solved this by using larger bearings, same size than on the trusty PulleyBox (and one more part you can reuse!) made by Vertigo235. On the 2nd and 3rd picture, the left bearing is the Bondtech one, the right is the one used in BearExxa V2.
You may have heard that those Bondtech print gears are creating 602 issue (moire, wood grain, basket wave, call it as you like). We have tested this a long time ago by replacing the Bondtech idler gear with a bearing and it has not improved the 602 pattern. We have re-tested this recently with the Discord community and it we got the same results. To make it short, 602 is coming from the torque variation in the stepper (due to how steppers are rotating: by steps), a not strong enough hotend cooling and a little to warm stepper. I can make a longer post regarding this if you want to learn more. It is however true that the Bondtech gear distance vary due to the filament and impact the gear meshing. This can potentially add a little backlash but then it would only be a problem for retraction and this aspect has never been an issue on Prusa printers. Be reassured that with our new BearExxa is the 602 pattern is almost invisible.
Finally, this gear set offers some flexibility on the motor selection. The main BearExxa V2 will use and focus on a standard Nema 17 pancake motor for strong torque but this gear set allow us to explore lighter steppers like the Nema 14 rounded ones.
Comments
Grégoire Saunier
Yes not going to change that now hahaha :D
Emeric Bréhaut
The bearing you use will not change until the release ? if not, can you share the type of bearing please ? just to prepare the switch :D
Grégoire Saunier
I tried Orbiter V1 with the new cooler stepper used on V2 and the shaft/print gear was going too close too PLA melting temperature for my liking (similar issue than with stock Prusa extruder). The Orbiter V2 is still very interesting and I will continue to study this type of build more in depth.
Eric Moyer
Really like to see the Orbiter V2 part of the mix.
