Hand Ergometer

**irving2008** · 22-07-2013

Originally Posted by FatFreddie

Hi Irving,

Sorry I've been quiet - took a while to get the printer going again and I've been busy - the new firmware needed all the accelerations and speeds sorting as well.

Where do we go from here? Two options I think -

1. I've got a very simple set of gears working which I can send you to have a look at (I gave up on the idea of destructively testing them, the originals weren't far off requirements and these are a lot better). PM me an address if you want to do this.

2. I can just build some gears to your spec - should have some time on Tuesday. If you want to do this, could you send me the latest drawings.

Mark

Hi Mark,

Sorry not got back to you sooner, hasn't been a good few days given the heat (people with high-level spinal cord injury can't regulate body temperature easily).

I'm trying to finalise drawings for the gears and have beefed them up by increasing thickness as well as making the ring gear even more substantial to try avoid needing a seperate ally support, but will retain fixings for that in case. Overall assembly needed a rethink as can't get gearbox and magnets on same side of rotor without much more complex magnet carrier so going for magnets on one side only. Fortunately 3 x speed increase plus reduced torque requirement introduced by gearbox means can use smaller magnets anyway. I'll post that up shortly.

Also doing a 3-gear planet carrier to reduce gear tip loading. Going to make the carrier boss more substantial and have 2 grub screws at 90 deg so will give it a go in PLA. Worst case it'll do for testing and I'll get one made in ally later if need be.

Hope I'm not imposing too much.

**FatFreddie** · 23-07-2013

Originally Posted by irving2008

Sorry not got back to you sooner, hasn't been a good few days given the heat (people with high-level spinal cord injury can't regulate body temperature easily).

Makes my whingeing about being a bit hot seem rather pathetic.

No rush on any of this from my perspective but I'm away for the middle two weeks in August and will be busy in the run up and I don't want to become the bottleneck.

Originally Posted by irving2008

Also doing a 3-gear planet carrier to reduce gear tip loading. Going to make the carrier boss more substantial and have 2 grub screws at 90 deg so will give it a go in PLA. Worst case it'll do for testing and I'll get one made in ally later if need be.

Worth a try with the carrier - as you say, you can always fall back to ally.

Originally Posted by irving2008

Hope I'm not imposing too much.

Not at all - it's been a very useful exercise and I've improved both my understanding of the process and the printers hardware and software and am now able to produce much better prints more easily.

Mark

**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 ?