2 speed mid-drive build

[LegendLength]

Original 6 speed: 5.4kg
New 2 speed: 1.8kg
Saving: 3.6kg (66%!)

Wow that's really impressive. I figured that throwing out some of the gears would save a few 100 grams.

Please add more updates to this if you get a chance. I know there are many anti-transmission people on this forum but I think a lot of them don't think about off-road riding and the types of hill climbs that are done regularly.

 

[ksithumper]

Thanks for the encouragement!

Hoping to make a little more progress this weekend and put some more photos up.

 

[toolman2]

Original 6 speed: 5.4kg
New 2 speed: 1.8kg
Saving: 3.6kg (66%!)

Wow that's really impressive. I figured that throwing out some of the gears would save a few 100 grams.

Please add more updates to this if you get a chance. I know there are many anti-transmission people on this forum but I think a lot of them don't think about off-road riding and the types of hill climbs that are done regularly.

True that brother, its nearly 3 years ago now that i built this bike https://www.youtube.com/watch?v=qfJT0Ww3tdc (with a 2 speed gearbox) but due to the shame it would bring to me and my family, i dont talk about it here.

 

[ksithumper]

Love the vid, Toolman, that looks like way more power than we are going for - how many kW?

We'd hoped to have the motor running submerged in the gearbox oil, both for noise isolation and cooling, but Astro aren't comfortable that the cable grommets will seal long term. We'll therefore amend the design a little, to keep the motor in air. I bought a Hall sensor kit from Bertie, that now becomes an option again if we think we need it.

We also widened the 'box a little, to leave space to include a 3rd gear later, if needed.

Locking the belt drive wheel to the input shaft won't be simple - I fear the torque will overcome any reasonable shrink fit. A key will be better but the shaft is too hard to machine. We need some sort of grinder.... the poor little Dremel is gonna get some abuse again!... just need to think what to do, then how...

 

[toolman2]

Love the vid, Toolman, that looks like way more power than we are going for - how many kW?

Thanks, 11.2 kw output at the tire. So about 30kw peaks, measured as per the ES test standard. :wink:

 

[recumpence]

Love the vid, Toolman, that looks like way more power than we are going for - how many kW?

Thanks, 11.2 kw output at the tire. So about 30kw peaks, measured as per the ES test standard. :wink:

Power is a funny thing. You can measure peaks from the pack, continuous output after electric losses, or power at the rear tire. Each has its place.

Matt

 

[macribs]

*subscribed*

Nice craftsmanship and ingenuity skills. Like your approach to try solving the holy grail of e-bikes - how to go steep hill climbing/technical riding yet still have top speed. I surely like your idea here, and the endless possibilities to swap sprockets to find the correct gearing for your use will ensure you will avoid riding a lot "in between" gears. The size and the weight seems perfect. Can't wait to see what you come up with for shifting.
A solenoid and a handlebar button would look sweet. Solenoid might add too much weight compared to wire gear change?

Keep up the great work and be sure to update this thread.

 

[ksithumper]

We've made some more progress, mostly mundane stuff like spacers and circlip grooves and bearing caps to keep the shaft end floats correct.

The pics below show how we cut a groove in the shaft to hold a half-moon key (we Brits call them Woodruff keys) to locate the input belt pulley.

First pic is just starting the grind, the second pic is the finished groove,





(Those with eagle eyesight may spot that we changed the grinding wheel - that's because the first one wasn't running very true).

Next job is to bore the pulley accurately, then cut the matching internal keyway...may have to make a special tool for that... unless our cheater plan works! Watch this space

 

[rodgah]

[youtube]yQcgLDZLMsk[/youtube]

used this method with a few times works great. Slow and steady though.

 

[ksithumper]

Nice vid Rodgah!

That method (broaching in the lathe) is exactly what we're planning, I've done that successfully before to cut a keyway on a steel motorcycle flywheel, and so an aluminium pulley should present no problem. It does need to be a tight fit though, or will just fret and wear quickly.

That's why we need to grind up a cutter to accurately match the key width - we do have a sneaky 'plan B' to try first though, as it may save a bit of time!

After all, what can possibly go wrong?

 

[tahustvedt]

I recommend covering the slideways of the lathe with some protective plastic or fabric when you grind. The abrasive dust is harmful to the slideways and gets everywhere.

 

[DanGT86]

Nice vid Rodgah!

That method (broaching in the lathe) is exactly what we're planning, I've done that successfully before to cut a keyway on a steel motorcycle flywheel, and so an aluminium pulley should present no problem. It does need to be a tight fit though, or will just fret and wear quickly.

That's why we need to grind up a cutter to accurately match the key width - we do have a sneaky 'plan B' to try first though, as it may save a bit of time!

After all, what can possibly go wrong?

Your resourcefulness is making me feel guilty that I have lost my machining creativity completely. Nice work so far with the grinding wheel solutions. That being said, have you priced out buying a cheap broach to push through with an arbor press? Seems like it would save you tons of time and energy as well as come in handy in the future since it would be a common size for shafts at ebike power levels. I suspect some of your parts are too hard for that but if not it might be a good investment.

Anyway I can't wait to see how this build turns out. I know there is always debate about the need for gearboxes on electric vehicles but that doesn't make their use any less beautiful.

 

[kfong]

Nice work, looking forward to the finished gearbox