Cycloidal speed reducers

[Solcar]

Cycloidal speed reduction looks like a potential way to get high speed reduction. The harmonic method looks simpler than the cam or roller bearing methods. I'd like to see the harmonic method used with nylon gears.

http://machinedesign.com/article/sometimes-it-pays-to-be-eccentric-0518

My original thought was to use a cam-driven push rod to advance a ratchet gear one tooth per motor revolution. It would give high gear reduction with just one stage. It would automatically freewheel, but tend to vibrate badly due to unbalanced rotation of and forces on the motor shaft.

 

[Miles]

Welcome solcar!

Efficiency around 90%?

So, a bit more efficient than a worm gear but with vibration/noise?

 

[Solcar]

Thanks for that welcome, Miles!

My present gearbox reducer uses plastic helical gearing, but is bigger than I like. I would like to replace it with a plastic worm gearbox, but I was wondering about other possibilities, too. I need less than a few hundred watts of assist on the cheap.

 

[Miles]

How much reduction do you need?

 

[Solcar]

At least 20:1. I use a Pittman servo motor that I bought over a decade ago. It has a plain 1/4 output shaft.

 

[Miles]

Two stage epicyclic?

 

[Solcar]

I've seen some planetary gearboxes that might work, but they are so expensive. Some might require me to grind a d shape onto my motor shaft.

 

[Miles]

You know this site, I guess?
http://www.matexgears.com/

 

[Solcar]

It looks very familiar! I'll check it out.

 

[Solcar]

Found a little more related information:

http://www.eurekamagazine.co.uk/article/2448/Wobbling-gears-achieve-high-ratios.aspx

 

[kfong]

That is unique; I haven't seen that design before. Would be interesting to see how it holds up in the real world or even see it in a product.

I picked up a harmonic gearbox from HD systems, but found the output torque to be less than a Neugart planetary spec. wise. I think it has to do with the flexible shaft. There isn't as much bite or tooth making it the weakest link in the design. They have none or very little backlash due to the design making them great for precision stuff. I dropped the idea for using it on an ebike and instead will make a rotary table for a 4th axis on my CNC. The Neugart drives look really solid. 70, 80, or 90 gearbox look plenty tough for the task. I plan to put one of those on an RC build when I have the time. I picked up an 80-8:1 an a 70-25:1, due to the extra stage needed for the 25:1, it’s a little longer than I wanted so you need to keep that in mind as well.

Found a little more related information:

http://www.eurekamagazine.co.uk/article/2448/Wobbling-gears-achieve-high-ratios.aspx

 

[Solcar]

It's good to get some feedback on the harmonic drive gearbox for ebike use. My drive assembly, including the motor weighs 8 pounds right now, and I'd like to reduce that by half or more. Getting more reduction from a single stage will go a long way in getting to that goal.

We could greatly benefit from more speed reduction/torque multiplication options that give smaller size, lighter weight, more simplicity, as well as easier mounting.

 

[kfong]

Depending on your application, if it’s strictly for road bike use on mostly flat conditions. A small Neu motor and planetary gearbox would be possible with current limit imposed to protect the gearbox. I have such a setup, but it's been put on the back burner since I haven't found a need for such a commute. It was initially planned to be put on a road bike, but I find I really dislike riding them. Too use to mountain bikes and prefer bikes with full suspension these days.