Both the belt and spur gear versions (in my post on Oct 17) were 3D printed using an SLS nylon process.
Conclusions from this 1st prototype run:
- The large SLS spur gear is slightly warped, so look at using an injection moulded gear. Meshing is very good. SLS printed nylon MOD1 gears are good in general with a low tooth number.
- The surface detail of the SLS belt pulley isn’t good enough to ensure a nice fit with the GT2 belt.
- Concentrate on the spur gear variant due to easier-to-source spur gear parts and lower part count. (K.I.S.S.)
I’m now looking at using a Delrin injection moulded large gear, and either an SLS printed small gear or a steel small gear. I’ve also adjusted the ratio from 14:60 to 12:60.
I’m now waiting to receive the 2nd prototype run from the SLS printer, which is a tweaked version of the spur gear design with 12:60 ratio and different bearings.
I’m moving from flanged bearings to ordinary 608 bearings, allowing me to use the awesomely high quality SKF E2 bearing range (608 size is among the cheapest of SKF E2 bearings, but still double the price of chinesium bearings… worth every penny).
The reason for moving to the higher quality bearings is that the chinesium flanged bearings run really rough with a lot of friction when under preload. Tests with the SKF E2 bearings show that they run beautifully smooth under high preload.
A note on preloading; preloading is used to eliminate any wobble in the bearing (thus shaft wiggle). Adding preloading in this design is very easy with a spring between the bearings. I’m aiming for a fairly high preload (for this size bearing) of 25N +/- 5N.
On the electronics front; I’ve been made aware of a new contender, the VESC:
Particularly interesting because the designer is going to release a new version within the next few months with the intention of turning it into a fully fledged open source project. Interesting video on the new design and software here:
With any luck, around the time that I finish the mechanical build, the VESC 6 design will be ready for use…