Building a Tjet Screamer
by Brad Birdnow
I have a tan '67 Camaro that is my hottest Tjet. It has
Super II
magnets and a Blue Dragster armature in a chassis that was a super runner
to begin with. The rear gears are the Tuff Ones set with AJs screw on (jam
nut) slicks. The slicks are set out to the maximum span of 1 3/8" for more
stable cornering. Tuff Ones wheels are up front with 0.382" silicone tires
to lower the front a shade. (I used to sand down Tjet stock tires for this
purpose, but I got lazy when I found some silicone Tjet tires in the
smaller diameter.) Tuff Ones wheels are independent rotating, like AFX
wheels and they set the tires out to roughly the width of the body. For
brushes I'm currently running the old "hop-up" silver brushes. I really
like the new JB Thunderbrushes too. The pickup shoes are Tjet "hop-up"
silver shoes with a modified bend to place more shoe on the rail.
As I explain how this car was put together, you'll see that it
pays
off to have enough parts for about ten cars. That way you can use the
variations in these parts to your advantage and put together a chassis
that's really hot.
By starting with a chassis that was a good runner I was
reasonably
assured that there were no warped parts or misaligned holes for the
gearshafts and axles. Sometimes I will switch parts around to see if I can
improve a chassis. What I am really looking for is a chassis with a lot of
"coast". When you cut the power it keeps rolling for a bit.
Minimizing
friction is the key.
The Blue Dragster armature is alleged by some to be the hottest
arm
available for the Tjet. It is a hot arm, but is it the hottest? I'll
address that in another article. When selecting the arm for the Camaro I
started with several and measured the ohms across each pole. I set aside
all but the couple of them that were the lowest readings and matched on all
three poles. I took the two that made the cut and laid the shaft of each
one across a balancing tool. (A couple of razor blades stuck into an
eraser like miniature parallel bars - be sure to level them!) I rolled
them back and forth to check for wobble. In other words, the armature
poles need to be as perpendicular as possible to the shaft. If there is a
noticeable wobble it will slow the car down and increase wear and tear. (I
pitch wobblers in the trash.) They both passed the wobble test so I
checked them for balance. I let them sit on the blades to see if they had
a heavy spot. One of them would roll until one pole was at the bottom.
The other was OK, so I used it. The one that didn't balance was used in
another car after adding a little (very little!) solder to the tab across
from the heavy pole and rechecking the balance. Sometimes it's a little
tedious adding and removing solder until you get it right, but believe me,
it's worth the trouble. I have also balanced arms by filing a little off
the end of the heavy pole. I prefer the solder method. I can solder
pretty well and I like the poles to be nice and pretty. If I'm race
prepping a car for serious competition, I will resolder all three tabs and
then balance the arm. I had a wire come off a tab in the middle of a race
once and it really slowed the car down.
I tried a few different idler gears until I found one that fit
the
little plastic stub perfectly. I sanded both faces of all the gears with
100 grit, then progressed to 300 grit and finally 600 grit sandpaper. I
used a Dremel with a brass wire wheel on the teeth. I was super careful to
get the gear on the shaft nice and straight when mounting the arm in the
Tjet gearplate. Ditto the rear pinion gear when I mounted it. I also made
sure to mount the two gears on the pinion shaft so that just the minimum
end on the shaft fits into the hole in the bottom of the chassis. The idea
is to get it just deep enough to position the shaft securely against the
crown gear. The deeper you place it, the more friction. I also bowed the
gearplate clip slightly to make sure it was holding the plate securely
without touching the gear or its hub. When I assemble the gears on a plate
I will oil them a little too generously to make sure the oil gets
everywhere I want it to be. I take the gearplate assembly off the chassis
after a little running to clean off the excess oil. After that I oil
sparingly.
I started with several sets of Super II magnets. I made a
little
basket out of a Dixie cup, taped a big washer to the top, counted out a
bunch of six-penny finishing nails and played around with seeing how many
nails each magnet could lift until I had them all rated. The strongest two
magnets went into the Camaro.
A couple of other things I've done is to solder small wires from
each
pickup shoe to the rivet nearest each brush spring, and switch the pickup
springs to AFX springs. I put a drop of superglue on the wires in a couple
places to keep them up off the track. The AFX pickup springs help to
reduce the "wheelie" effect of a high torque motor and cuts down on
deslotting. While prepping the chassis, I cleaned everything thoroughly,
using a Dremel with a wire wheel on the electricals. I also bent the final
bend on the brush springs a little more to bring them up flat against the
brushes, keeping them just flush with the inside surface of the chassis.
Another electrical tweak is to rebend the pickup shoes so that the rear
bend is further back. This places more contact surface on the rail. BSRT
is now making "ski shoes" for Tjets. Ask Jim about them.
The body on this car is something I've had since I was a kid.
I
decided to use this body when I read an article on another website. The
author had had the opportunity and the equipment to weigh and assess the
center of gravity of the various Tjet bodies. He reported that the Camaro
body was comparatively light, well balanced and carried its weight low.
This one had radiused rear wheels when I got it, so I didn't have to worry
about ruining the value of a Tjet body by modifying it. I shaved the posts
to drop it down as low as possible, removed the front and rear bumpers,
leaving just the grill, and sleeved the ends of the screw posts with brass
tube. I super glued a Tjet rear guide pin (they're longer) into the front
of the chassis and test fitted it on a spare piece of track, trimming the
pin until it just clears the bottom of the groove. I leave the body screws
slightly loose to let the body rattle around just a little. This allows
the body to absorb some of the vibrations from the track.
This Camaro is way fast! It has so much coast that if you
get a long
enough straight to really open it up it takes 7 or 8 feet (without a
braking controller) to slow it down enough to make a 9" radius curve.