Epicyclic ball drives

[modeng2000]

Does anyone have experience of epicyclic ball drives please?

They have been used in radio equipment where they provide a slow motion control, often there is a ratio of 6:1. I have in mind something a bit larger than the 1/4" shaft type, possibly using balls of about 15mm dia. How much torque before slipping etc is what I am not sure about. I guess it depends on how tight the three balls are when secured in the frame.

Any info would be useful before I embark on what might be a fools errand

John

[havoc]

No idea what your application is, but if you need more power than to turn a tuning cap maybe an epicyclic gear can help.

[modeng2000]

Havoc,

What I had in mind was trying to avoid making a ring gear with the internal teeth. However I'm not sure I could cut the teeth with the kit I have.

john

[steam4ian]

G'day John.

Depending on size you could look at the gear boxes on battery drills. I pulled a cheap drill apart to make a cross drilling attachment for my lathe. I found a neat two stage epicyclic gear box. The first stage had nylon pinions but the last stage had brass pinions. I was pleasantly surprised by the quality considering it was a cheap drill.
Alternately you could fashion the ring gear as a cage but cut the sun and planet wheels in the usual fashion. Some moons ago I came across professional gear boxes which used this approach. The outer ring had slots milled in the inner face with rollers inserted to form the teeth; it was rugged, used in the steel works.

Regards,
Ian

[SteveW]

John,

In a similar vein to above I found a similar little gear box in a cheap battery screwdriver a while back. Certainly cheaper than a battery drill.

[modeng2000]

This reply is along the lines of "Why didn't I think of that". I have a defunct battery drill so that could be the answer. The cage idea would not be too difficult to make so that will be the second choice.

I have not said anything about the application in case it turns out to be a lemon, I'd like to put something together to see if it is practical before committing myself. If I can use the idea it will make some of the machining I do much easier.

John

[modeng2000]

My defunct battery drill had a conventional gear box so that is of no use for this idea but I found a two stage epicyclic in the screwdriver. Only problem is, the screwdriver is still serviceable.

I'll look around for an old screwdriver to cannibalise.

John

[SteveW]

John,

I've just completed another pilgrimage to the local Maplins shop. For under three quid (if I remember correctly) you can get a little pack of gears, see also: www.maplin.co.uk/Module.aspx?ModuleNo=30962&criteria=gears&doy=21m7

With a bit of thought you could produce what you want as long as it hasn't got to be epicyclic based. Even then it might be possible to do something along the line of concentric in/out shafting.

[modeng2000]

Thanks Steve, I have given the project much thought recently and in the light of the replies have decided to use conventional spur gears. Another look at the present arrangement has led to different approach that will do the job and would be much simpler as well.

So thanks to you all for helping to rationalise my thoughts.

John