3/20/2017, last updated
|When I was in the early
stages of this project Dick McCloy dug out an old set of
wheels with axel. He said that they came
off a switcher locomotive. The were
a good match to pair with the 4" wheels on the arch
bar truck I had. The wheels are press fit and
held in place with thin nuts.
I believe I turned the ends
slightly to fit R10 bearings: 5/8" ID, 1 3/8" OD and
The next step was to make journal boxes and
rails for the axel. (File:
Journal) The rails are machined
from 1" square bar stock. The
Journal Boxes are machined from a 2"X2" aluminum
bar stock. Everything is
straightforward except the 1.375" hole for the
bearing OD is made a few thousands large so the
bearing can accommodate one box being higher
than the other.
|This drawing shows the
installed rails and journal box. The
truss straps are bent from 1"X1/8" bar stock.
The retaining plate below the journal box is
also made from1" X 1/8" bar stock.
In another part I suggested that this area is
very tight. The suggestion was that
the angle in front of the axel be moved forward
|These are the springs used
for the rear axel- McMaster #9657K374. We
should be prepared for a maximum of 300 pounds
on the rear axel. For 4 springs that
would be about 75 lbs per spring leaving margin
to absorb a bump.
|This shows an installed
journal. The top outside of the
rails were ground round to match with the fillet
in the angle. The rails were secured
with at least one screw and then welded in
place. The truss straps are secured with 10-32
studs and Nyloc nuts. Three 5/16" bolts
with the heads cut off were screwed into the
journal boxes to provide center posts for
three springs per journal. With only two
springs per side the center position isn't used.
|Early on in the project I
went looking for suitable motors. I wanted
a motor that would fit between the wheels and
was as big as possible. I was shooting for
about one HP (~750 watts). The real
requirement is that the motor be powerful enough
to make the wheels slip before the motor stalls.
Stalled motors can overheat and be destroyed.
This AmpFlow G43-500 was the best I could find
at 6.5" length including bolt heads on the back
the shaft out the front. It comes with a
11 tooth sprocket for #25 chain. The 500
is the rated power ---500 watts or about 2/3 HP.
The motors are a little less than $100 including
shipping and tax. They are heavy so
shipping can run up to $20.
This drawing gives you all you need to know about
the physical aspects of the motor.
|These curves provide insight
into the motor electrical characteristics when
operating at 24 volts (full power) The
torque is pretty much proportional to current.
The speed is fairly constant at about 3000 RPM
independent of load, so
how fast will we go at full power?
|The largest readily
available sprocket that is smaller than the 5.8"
wheel diameter is the 60 tooth model shown on
With a 11 tooth sprocket on
the motor and a 60 tooth on the axel the maximum
wheel RPM is 3000 X 11/60 = 550.
wheel has a 3.14 X 5.8 = 18.2" ~ 1.5'
circumference. The 550 RPM then translates
to 550 X 1.5 = 825 feet per minute or about
49000 feet per hour and with 5280 feet per mile
we get about 9 mph.
That's about 72 scale mph which is
what I'd expect for an overpowered bus going
downhill with a tail wind.
Definitely don't need a greater top speed
and since this 60 tooth sprocket is the largest
we can use with the 5.8" wheels we'll go with
it. (The 60 tooth sprocket was
later replaced with a 70 tooth sprocket.)
Many of the small
locomotives use two motors. So, should I
use one or two? There was room (barely)
for two so two it was. Later I tried
running on one motor and it performed like the
prototype probably did --- slowed down on the
hills. I wanted a "muscle bus" so stuck
with two motors.|
The motors and chain
drive must be secured to the dive axel so that
the chain tension and alignment don't change
when the axel tilts. I used the
inexpensive pillow blocks on the right to secure
the motor mount to the axel.
This graphic shows the entire drive. (File:
Drive) The motor mount
consists of of a 6"X9-1/4"X1/4" aluminum base, a
4"X9-1/4"X3/8" aluminum vertical and 1/8" aluminum angle
stiffening plates on each side. The four pieces of
the mount are screwed together. The motors are
attached to the vertical with a pair of 6 mm screws
each. The motor on the front side (left side
on drawing) is against the
stiffening angle and rests on the base. This motor is
fixed. The rear motor rests on the base but slides to
adjust the chain tension. The chain tension is tricky
and very small movements can change the chain from too
loose to too tight. I finally tapped a 10-32 hole in
the side of the aluminum nose of the rear motor in line
with the shaft and horizontal. A mating hole was
drilled in the stiffing plate, and a 10-32 screw was
inserted to make a fine tension adjustment. The
attachment screws can be loosened, the tension adjusted
with the 10-32 screw and the attachment screws
The drive assembly is a tight fit in the frame with
only 1/8" clearance at the front and at the back.
In the Frame section it was noted that the batteries can
be slid 5/8" to the front to give more room for the
drive. The extra space could be used by
adding 3/8" to the dive and 1/8" clearance to the front
and the back.
|There is one problem
with the floating drive, what keeps it from
spinning on the axel.? There is a lever
added to the lower rear of the motor platform---
the part resting on the flashlight in the photo
on the right.
vertical part of the motor mount looks
like Swiss cheese. One excuse
is that the holes are for ventilation. The
truth is that the mount went through several
iterations and as long as there was a place for
new mounting holes I kept using it.
At the end there is a suggestion for an
improvement. If I do that I'll have to buy
a new piece of aluminum.
The socket head of the tension adjustment
screw is just visible on the back in line with
the drive sprocket.
|This photo show shows how
the drive lever is attached to the frame --- in
the upper right. It is attached with
a 5/16" bolt through oversize holes in the
lever and the frame channel and secured with a
Nyloc nut using washers under the head and nut.
An extra axel spring is used between the lever
and channel and the nut is tightened to the
point where the drive is level when at rest.
This single point swivel attachment permits each
end of the axel to move up and down independent
of the other side.
dreaded brakes next. The brakes in fact
work great and are needed at the speeds I race
around the track. I had some shoes left
from the truck project, drawing on the right.
A better design is to
split the hanger and shoe so the pressure
applied to the wheel is uniform across the shoes
surface. Maybe next time.
|This drawing shows how the
shoes fit on the drive. The square bars
are held off the motor mount platform with 1/2"
spacers. The rear bar attaches to the
platform directly whereas the front bar is
|This photo shows the rear
spacer and offset for the front is visible just
in front of the sprocket.
The top screw in the lever on the rear
round bar is 3/4" above the round bar and
the bottom screw is 1-3/4"
below the round bar.
The linkage rods are 1/4"
diameter. Note that the rod between the axel and
motor mount platform appears to be scraping the
axel. That happens when the brakes are
applied and the lever at the back rotates
quite a bit. That doesn't happen if the
brakes are properly adjusted.
photo shows the arrangement at a different
angle. This is an early photo. After the
shoes wore in a little linings made of strips of
auto serpentine belt with the ridges sanded off
were glued to the shoes using epoxy adhesive.
The linings significantly increased the brake
Linings cut from 3/16" X 1" brake lining
material purchased from McMaster were just
installed on the front but no test yet.
This photo was taken from the rear but rotated to
fit better on the page. The brake cylinder has a
3/4" piston and
is reverse acting.
The brake compressor and associated plumbing is covered
in the Accessories section.
|The controller mounts
above the drive on the cover pictured on the
right. The cover is made of 1/4" PVC.
It is slightly out of position in the photo; it
fits between the two frame outside angles.
The cover serves to seal
the inside of the railbus from mice.
The second use is a platform to mount the
controller and associated electronics.
This photo was taken early
in the project. The cover now looks like
Swiss cheese similar to the motor mount.
The drive assembly has worked well over the two
summers of operation. However, experience
can always lead to improvements. (File:
Improvements). Dan Staron early
on told me that it is bad practice to connect more then
two sprockets, especially two motors on a single chain.
It causes the sprockets and chain to wear quickly.
His experience is with large machinery. The
sprockets show wear but I don't know if the wear is
After sprucing up the
original drawings it became obvious that I could install
a second large sprocket on the axel and point one motor
each direction as shown in the drawing above. An
advantage of two chains is that one can make it back to
the shop if one chain comes off thus avoiding the
humiliation of being towed.
If there is a motor
pointing each direction then if the axel is centered on
the mount (slid toward the back 1") then the same size
chain can be used on both sides. This is a
slippery side as the journals must be moved (OK on new
construction) or the batteries must be moved still
further toward the front. Different size chains
don't look so bad now.
Another concern is the
load on the chain. McMaster says that #25
chain has a working load of 88 lbs. The
earlier graph on the motor indicated that the maximum
torque is about 1.5 Newton Meters that converts to ~13.3
inch pounds. The 11 tooth sprocket has a pitch
diameter of about 7/8" so the lever arm is 7/16".
Thus the 1.4 NM torque converts to 13.5/0.4375 = ~30.8
lbs. The total for two motors is a little over 60 lbs so well within the 88 lb chain working load limit.
The wheels usually start slipping at about 25 amps per
motor which corresponds to a about 1.5 Nm
torque so chain load is far from an issue.
The new drive has been tested for about 10
miles. The larger sprocket caused no
problems. The greater reduction btween the
motors and the wheels had the desired effect of
noticeable increase in torque/decrease in
Changes(updated May 10, 2017):
After some track experience with the new
controller I decided that I wanted a
greater reduction between the motors and
the wheel. The 11-tooth
sprocket on the motor end is the
smallest that will fit on the motor
shaft. The original sprocket on
the wheel axel was 60 tooth.
I replaced that sprocket with a 70-
tooth sprocket that has an OD of 5.72",
just less that the 5.8" wheel diameter.
The sprocket and chain may ride on high
guard rails and frogs but they are turning
with the wheel so that shouldn't be a
presented the opportunity to replace the
holey plate that holds the motors as
shown on the right. The motor on
the left (front motor) is fixed and the
one on the right slides to adjust the
chain tension. The smaller holes and
slots are for the motor attachment
bolts. The larger holes and slots
are for motor ventilation.
Note that I
decided to continue to gang the two
motors together on one chain.
shows the motor side of the new plate.
The brass cylinder with screw on the
left fits over one of the attachment
bolts of the motor to adjust the chain
tension. A nut on the end of the
screw pulls the motor to the left for a
fine adjustment before the attachment
bolts are tightened.
The big slot for
the right motor is to permit the motor
with sprocket to clear the top of the
wheel and then drop down into position.
|The drive assembly
is all ready for installation here.
|This is the
non-chain side of the drive.
Note that the back of the motor on the
right is slightly rotated --- the bolt
holes on the other end are aligned.
Never noticed that before but it really
showed up with the fenders.
|This shows the
chain side of the drive installed in the
frame. The fender (inner
fits between the
wheel and sprocket. The
purpose is to prevent water from the
wheels getting into the motors.
This fender is attached with three
screws into the top of that motor mount
plate. The fender is easily
removed to reinstall the chain --- which
is not so easy.
|This is the fender
on the side opposite the sprocket.
The fender is attached to the fixed
motor. The rotated holes show up
here with a sloping fender top.
The frame is blocked up with the wheels
hanging down to the lowest position
which causes a rotation of the drive
increasing the slant.
|The new drive
presented the opportunity to replace the
old holey cover box. That is
1/4" thick plastic of some sort that I
purchased for some other project.
This time I decided not to fasten the
cover down. Instead, it floats
between the batteries at the front and
that aluminum plate at the back.
Side-to-side motion is restricted by the
aluminum plate (the cover sides extend
to the back of the plate.
The cover is only partially
complete at this point. The cover also
serves as the mounting surface for the
controller and associated components.
More details in the Accessories Page.