In order to obtain the best possible wheel torque for crawling and climbing
ability, the object of the exercise is to try to achieve an approximately 3.0/3.5 MPH (or good walking pace) top speed for the truck.
The gearbox is positioned to use the 23 tooth pinion option (and the chassis motor mounting holes to match) because the ratio of the gearbox is a rather large
7.4 to 1, and this would give excessive overall reduction with any of the smaller available (19t, 21t) pinion sizes. To achieve the best possible wheel speed for crawling and climbing use it is likely that a 'SPEED TUNED' internal gear set will also be required to additionally compensate for the gearbox's large reduction ratio.
This pinion choice has the distinct advantage of mounting the gearbox as far forwards as possible. This positioning means that it is necessary to remove a lesser amount of plastic material from the rear (left-side and smallest) part of the main chassis in order to fit the new additional gearbox. This rear (left) part is one-half of the rear main gearbox compartment, and it is far easier to re-make and reseal this area to prevent otherwise damaging foreign object ingress when less material is initially removed.
There is plenty of tyre/motor clearance, in fact more than is found on any TL-01 fitted with standard touring car suspension arms, these including the Stadium Raider and Ford Lightning trucks. The next three pictures show different views with the gearbox and motor fitted (N.B. the suspension arm has been reversed - this gives the longest possible wheelbase when using only standard parts):
The next three photos show inverted views. The gearbox smoothly protrudes below the bottom of the chassis by about 6mm (1/4").
An additional advantage of this mod is that a motor guard/heatsink will now fit around the completely exposed motor. Previously, when the motor was buried in the chassis, a full size heatsink would not fit.
Three more views, showing the gearbox alone in the chassis. In the last one daylight can just be seen past the box. In reality the box is quite a tight fit in there, and becomes in part a longitudinal structural member.
The chassis only requires cutting of the left hand side, which is ordinarily constructed in two parts, whereas the right hand side is a single piece and does not need any re-working. These next two pictures show the material removed from the lower part(s) of the motor area. The lower of the two little 'fins' above the motor protector mount has been trimmed back slightly just to avoid contact with the motor itself:
These last two pictures mainly show the amount of material removed from the front (left) chassis section. The rearmost upper and lower screw locations remain unaffected:
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