Hand Ergometer

**irving2008** · 01-08-2013

Not been a great week what with heat and other issues but trying to get back on track.

Been prevaricating over how to retain bearings in the planet gears The revised gears are 10mm thick and the bearings I'm going with are 3 x 9 x 4. The planet carrier has a 3mm boss and with a 3mm caphead screw as an axle the bearing will be centrally located in the gear against a recess. but that doesn't stop the gear sliding off the bearing. Normally you'd have some sort of bearing retainer but the only way I can see to do this with a 3D printed gear is either a groove 'not printed' to take a circlip which means an overhang (do-able but not ideal) or some sort of printed protrusion which will deform enough to allow the bearing to be pressed into place (is this possible?).

Thoughts?

**FatFreddie** · 02-08-2013

Originally Posted by irving2008

Been prevaricating over how to retain bearings in the planet gears The revised gears are 10mm thick and the bearings I'm going with are 3 x 9 x 4. The planet carrier has a 3mm boss and with a 3mm caphead screw as an axle the bearing will be centrally located in the gear against a recess. but that doesn't stop the gear sliding off the bearing. Normally you'd have some sort of bearing retainer but the only way I can see to do this with a 3D printed gear is either a groove 'not printed' to take a circlip which means an overhang (do-able but not ideal) or some sort of printed protrusion which will deform enough to allow the bearing to be pressed into place (is this possible?).

Thoughts?

The bearings should be ok on a press fit but a small ring could be glued in place. I've been using 5 x 11 x 4 bearings for the planet gears and they press in quite firmly.

**mekanik** · 11-08-2013

Hi M8
Just been having a look @ your project and although you have expended considerable man hours on the prototype, i was wondering if you had given any consideration to using a Shimano/sram geared rear hub ?
Just a thought.
Take care and i sincerely hope your circumstances improve in the near future.
Regards
Mike

**irving2008** · 11-08-2013

Originally Posted by mekanik

Hi M8
Just been having a look @ your project and although you have expended considerable man hours on the prototype, i was wondering if you had given any consideration to using a Shimano/sram geared rear hub ?
Just a thought.
Take care and i sincerely hope your circumstances improve in the near future.
Regards
Mike

Mike,
Great minds etc... it was one of my first ideas. Sadly the maximum ratio on a Nexus hub is 1.5:1 and I need at least 3:1, plus the hub is too wide @ 110mm

regards,
Irving...

**mekanik** · 11-08-2013

Would the ring gears on the e-bay links not be better than plastic ?
those listed are cheap enough.
Could you use two spur gears with the correct ratio ?

**irving2008** · 11-08-2013

Originally Posted by mekanik

Would the ring gears on the e-bay links not be better than plastic ?
those listed are cheap enough.
Could you use two spur gears with the correct ratio ?

Epicyclic gears have very specific relationships. To get 3:1 the number of teeth on the ring is 2 x teeth on planet + 1 x teeth on sun gear. Without knowing the number of teeth, circular pitch and tooth form of the Nexus ring gear the chances of finding other gears to suit off the shelf is diminishingly small...