This is in part due to the leverage effect ( well its something to do with torque = force times distance )
The diagram below shows a hub motor and its axle , bike tyre and part of the bike frame. On the bottom right I've drawn a closeup of the axle
Torque Arms and Torque Washers
"For every action there is an equal and opposite reaction"..................Isaac N.(?)
{ off topic : (way off topic!): "when two personalities react each is
completely and irrevocably changed" Sigmond F.....I just like it}
All of the motors on this website come with a torque arm. It is 100%
necessary to install the torque arms!! (except on P2a motor) Why use torque
arms and torque washers?........glad you asked!
The axle on the hub motors have two flat sides which slide into the slots of
the bike frame (the slots are other wise known as drop outs). The axle of every
hub motor are designed to remain stationary (i.e they do not rotate , the motor
rotates around the stationary axle). Because most of the motors can develop
quite high torque it is very possible (almost inevitable in fact) that the axle
will eventually start to rotate in the slots (dropouts) due to this very high
torque..
This is in part due to the leverage effect ( well its something to do with
torque = force times distance )
The diagram below shows a hub motor and its axle , bike tyre and part of the
bike frame. On the bottom right I've drawn a closeup of the axle
think of it this way: lets say you try and stop the motor rotating by holding
the wheel with your hand, it will be hard to do but likely you can stop it
turning. Now imagine the motor has no spokes or rim, you use your hands to stop
the motor rotating just by holding onto the motor, you haven't got a chance of
stopping it!!
The force is much higher the smaller is the circumference of the turning circle.
The radius of the turning circle at the outer edge of a 26" tyre is 325mm,
the radius of the turning circle where the axle touches the bike frame is only
6mm, so the force is huge in the order of 50 times the force at the outer edge
of the tyre. Hence you really need to use torque arms!!!
What happens if you don't use the torque arms:
1. at some time is very likely the axle will turn inside the bike frame even if
you have it in their very tightly.
2. when the axle gets to a point where is going to rotate in the frame it
usually happens very quickly. When it happens the axle rotates and the wires
coming out of the axle wrap around the axle very quickly and get wound up like
wire on a fishing
reel. The wires will either pull out of the motor or break somewhere else.
It means a very big repair job either way, so it really is worth the time to
install the torque arm (s) in a very secure fashion.
How to Install the Torque Washers and Torque Arms:
1. Torque Washers:
Below is a picture of a torque washer. Every motor I sell has torque washers on
either side of the motor. The torque washer is quite thick steel and has a lip
on it. This lip sits inside the dropout slots and provides some added protection against the axle rotating.
Usually it will be necessary to bend the lip over to 90degrees to make the lip
fit neatly into the dropout slot. You'll need to do that with a big hammer and a
vice. So one washer should be used on each side of the axle. (I've recently
discovered you can on some motors put two torque washers on each side, one on
the inside of the frame and one on the outside of the frame but one torque
washer each side is sufficient).
2.Torque Arms
Below are some pictures of the torque arms I supply. These are the type commonly
available in china.
The central hole which goes onto the axle has a flat section on each side for
to hold the axle in place firmly. Most hub motors have a 12mm diameter shaft the
flat sections being about 10mm across.
How to install the torque bars:
Because bike have many different angles at which the dropouts (slots in frame
where axle goes) are aligned it means there may be some diy work to install the
torque bars. Heres a few ideas of how to install them.
This is Brian of Melbournes method, I think this is an excellent method, this
system could be used to make a torque bar which would adapt to most rear bike
frames (something I'm hoping to be able to offer at some stage in the future,
something similar to this).
Below I've joined the torque bar to the vertical arm of the rear carrier
which a hose clamp, it was necessary to grind out a recess so that the hose
clamp wouldn't move up or down.
Neddie in Sydney made his own torque bar using the pre-existing threaded
holes in the bike frame to keep it in place.
The torque arms can also be used on the front forks. It requires the use of
hoseclamps to keep in place and some bending of the torque arms is necessary to
get them to sit nicely next to the front forks. They are 4mm thick metal
so require substantial force with a hammer to change their shape.
A More Technical Method of Installation of Torque Bar
Heres a method (in detail) for the more technically minded. It requires some
cuting and welding of the torque arm but gives a nice result which will suit
your particular frame.
Installing the torque arm. The torque arm is a necessary part in order to
assure the axle will not rotate in the bike frame. If for some reason a torque
washer does not work correctly then the torque arm is an added precaution.
This is only a suggested way to install the torque arm. Because there are many
variations in rear frames its quite difficult to get a torque arm that would fit
any bike frame, so heres my solution to the problem. (requires a welder).
Cut the torque arm ( with hacksaw) into two pieces as shown below.
Install the flat piece onto the axle as shown below .
Note all pictures below show the bike frame upside down except for the last two
pictures at bottom of page)
Place the other part of the torque arm so it sits next to the bike frame where
it will later be held on by hose clamps. It will be necessary to make a
spacer tube so that the two pieces will line up for welding later. Two views
shown below.
Cut the end of the torque bar which is sitting along the bike frame in the pic.
below (on right in pic below) so that it will join neatly to the torque bar that
is sitting on the axle.
Place some tape on the bike frame to protect it from scratches. Using plastic
cable ties or similar to hold the horizontal torque bar in place so that it sits
right next to the torque bar on the axle. Then just do a tack weld to hold them
together.
Remove the torque bar and make a weld to join the two parts together as shown
below (dont weld while on the bike the paint might be damaged).
Picture below shows torque bar back in position after being welded off the bike.
Make sure the weld is a very strong one. Hit the weld with a small metal hammer
numerous times to remove slag and relieve stresses inside the weld (this will
also test to see if the weld is strong!).
The finished weld shown below (a bit rough!), two hose clamps the same as you
find on radiator hoses will be required (dont use aluminum type hose clamps they
are very weak, use steel ones).
Put the torque washer, spacer tube and torque arm on the axle with the nut. Note
the torque washer can also but put on the inside of the frame between the motor
and bike frame, this will move the wheel axis over by a few more mm towards the
centre line of the bike.
The finished torque arm with the bike turned up the right way on its wheels.
Note the torque washer is not really visible in the pictures below as I placed
it on the inner side of the bike frame to move the wheel centre over just a few
mm more (the tyre was almost rubbing on the bike frame on one side).
Postscript: have recently become aware that there are some errors in my
torque calculations, will need to go over all my torque graphs and fix,
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Copyright 1998-2006 by Brett White on all images/text/information and
graphical materials on this website.