DannyC
0
OK, you all know that I am a fairly recent "lathe-boy" and that of course "if you only have a hammer everything looks like a nail".
Paul recently sent me a Longstaff 2WD unit from an English trike so I could have a play with it.
Apparently people are discarding them because they have a very limited 6-speed set of gearing .
I compared it to one that I had made that can accept any modern 9-11 speed cassette or custom cassette.
My version was slightly longer but also 100gms lighter.
We then had a discussion about how such a 2WD unit could be made with the most minimal set of tools.
So I had a bash at "how" I would do that IF I did not have a lathe.
This what I came up with (apologies for the blurred image):
On the left is an "off the shelf" screw on freewheel, on the right is an "off the shelf" screw-in cassette carrier freewheel.
The pair are available from evilBay for <£20 combined.
Joining them together is 2-sizes of tubing that is welded to the "outer race" components of each freewheel.
The RH screw in freewheel has a 10mm hex machined in the end, but we cannot use it as a drive element because the axle section of the freewheel can only be 12mm OD and that is too small to create a 10mm hex from.
My proposal was to cut most of that threaded section of the RH freewheel off and weld a 6mm plate over the exposed end.
A square hole is made in the plate by drilling and filing to create a drive-plate for the squared-off end of a 12mm axle (again, just marking out and filing).
In the LH end we insert a standard BB cup with a plate welded over it and....guess what? That's right another 8mm square hole formed in it by drilling and filing.
In this way we have removed the need for a lathe and we have created a ratchet driven 2WD unit that drives 2 independent half-shafts.
As the drive unit sit in the middle it would be necessary to have inboard support bearings on the half-shafts, but that is probably easy to do.
So that’s it in a nutshell. That would probably be as small and as lightweight as I could make one without resort to proper tooling.
Making the drive dogs square means that anyone with access to a welder a set of files and a drill can form the holes/squared ends of the shafts and make this unit. The biggest square you can make out of a 12mm rod is an 8.64mm square. I looked up the shear strength of an 8mm pin and it is in the many hundreds of foot-pounds, so I think it would suffice as a drive-pin.
The bigger risk (i think) would be that such a small square pin manages to "round-out" the square hole it is inserted into, but it is always possible to quench harden the plate with the hole in it.
Anyway, that’s a pretty cheap 2WD unit IMHO.
Your thoughts/observations are much anticipated.
Paul recently sent me a Longstaff 2WD unit from an English trike so I could have a play with it.
Apparently people are discarding them because they have a very limited 6-speed set of gearing .
I compared it to one that I had made that can accept any modern 9-11 speed cassette or custom cassette.
My version was slightly longer but also 100gms lighter.
We then had a discussion about how such a 2WD unit could be made with the most minimal set of tools.
So I had a bash at "how" I would do that IF I did not have a lathe.
This what I came up with (apologies for the blurred image):
On the left is an "off the shelf" screw on freewheel, on the right is an "off the shelf" screw-in cassette carrier freewheel.
The pair are available from evilBay for <£20 combined.
Joining them together is 2-sizes of tubing that is welded to the "outer race" components of each freewheel.
The RH screw in freewheel has a 10mm hex machined in the end, but we cannot use it as a drive element because the axle section of the freewheel can only be 12mm OD and that is too small to create a 10mm hex from.
My proposal was to cut most of that threaded section of the RH freewheel off and weld a 6mm plate over the exposed end.
A square hole is made in the plate by drilling and filing to create a drive-plate for the squared-off end of a 12mm axle (again, just marking out and filing).
In the LH end we insert a standard BB cup with a plate welded over it and....guess what? That's right another 8mm square hole formed in it by drilling and filing.
In this way we have removed the need for a lathe and we have created a ratchet driven 2WD unit that drives 2 independent half-shafts.
As the drive unit sit in the middle it would be necessary to have inboard support bearings on the half-shafts, but that is probably easy to do.
So that’s it in a nutshell. That would probably be as small and as lightweight as I could make one without resort to proper tooling.
Making the drive dogs square means that anyone with access to a welder a set of files and a drill can form the holes/squared ends of the shafts and make this unit. The biggest square you can make out of a 12mm rod is an 8.64mm square. I looked up the shear strength of an 8mm pin and it is in the many hundreds of foot-pounds, so I think it would suffice as a drive-pin.
The bigger risk (i think) would be that such a small square pin manages to "round-out" the square hole it is inserted into, but it is always possible to quench harden the plate with the hole in it.
Anyway, that’s a pretty cheap 2WD unit IMHO.
Your thoughts/observations are much anticipated.