Why a 1/16 scale Traxxas transmission maybe good for your crawler .

So here is my reasoning .

 The 1/16 Traxxas transmission is a very small unit and is very compact .

 It has pretty much proven its self to be a strong and durable transmission as its quite common for people to buy a Traxxas 1/16th scale Revo or Summit and install 1/10th scale truck wheels and rubber and then install 540 or 550 brushless systems intended for 1/10th scale car's and trucks .

So what pushed me over the top and made it my must have transmission ? The gear ratio flexibility . The transmission is designed as a double gear reduction where the center gear(s) are not a idler like most transmissions in RC but acts as a jackshaft . Traxxas designed the transmission so that its ratio could be changed by swapping 2 gears shown in picture below circled in green .

The reason for this was because they have and are using  this transmission in several chassis configurations that use different size tires . So whats the transmissions ratios well you can choose 1.93 or 3.71 . OK so that doesn't tell you much . Here is a couple of examples showing the gearing extremes of this transmission vs a Axial AX10 transmission and the old Traxxas 272 magnum. the axle ratio listed is for a AX10 or HPI king axle and the motor is a generic kv rating for a 35 turn 3 pole 540 motor .    

Axial AX10 2.60	Traxxas 272 magnum	Traxxas 1/16 3.71 ratio	Traxxas 1/16 1.93 ratio
Low Differential Ratio: 2.92 Transmission Ratio: 2.6 Other Ratio: 1 Spur Tooth Count: 96 Pinion Tooth Count: 12 Total Voltage: 8.40 Motor KV: 1565 Tire Diameter (inches): 5. Top Speed (MPH): 3.22	Low  Differential Ratio: 2.92 Transmission Ratio: 2.72 Other Ratio: 1 Spur Tooth Count: 90 Pinion Tooth Count: 12 Total Voltage: 8.40 Motor KV: 1565 Tire Diameter (inches): 5. Top Speed (MPH): 3.27	Low Differential Ratio: 2.92 Transmission Ratio: 3.71 Other Ratio: 1 Spur Tooth Count: 55 Pinion Tooth Count: 18 Total Voltage: 8.40 Motor KV: 1565 Tire Diameter (inches): 5. Top Speed (MPH): 5.9	low Differential Ratio: 2.92 Transmission Ratio: 1.96 Other Ratio: 1 Spur Tooth Count: 55 Pinion Tooth Count: 18 Total Voltage: 8.40 Motor KV: 1565 Tire Diameter (inches): 5. Top Speed (MPH): 11.17
High Differential Ratio: 2.92 Transmission Ratio: 2.6 Other Ratio: 1 Spur Tooth Count: 72 Pinion Tooth Count: 30 Total Voltage: 8.40 Motor KV: 1565 Tire Diameter (inches): 5. Top Speed (MPH): 10.72	High  Differential Ratio: 2.92 Transmission Ratio: 2.72 Other Ratio: 1 Spur Tooth Count: 76 Pinion Tooth Count: 31 Total Voltage: 8.40 Motor KV: 1565 Tire Diameter (inches): 5. Top Speed (MPH): 10.01	High Differential Ratio: 2.92 Transmission Ratio: 3.71 Other Ratio: 1 Spur Tooth Count: 45 Pinion Tooth Count: 31 Total Voltage: 8.40 Motor KV: 1565 Tire Diameter (inches): 5. Top Speed (MPH): 12.42	High Differential Ratio: 2.92 Transmission Ratio: 1.96 Other Ratio: 1 Spur Tooth Count: 45 Pinion Tooth Count: 31 Total Voltage: 8.40 Motor KV: 1565 Tire Diameter (inches): 5. Top Speed (MPH): 23.51

Now you probably wont use the 1.93 ratio in a crawler but the flexibility would be nice to have (could throw some touring car tires on and go cruising around the local carpet track at a brisk pace )

So whats the down side ?

 I think the main reason this hasn't found more use in crawlers and other projects comes down to the output shaft size . Its small with a diameter of  4 mm  its smaller than the shafts most drive shafts attach to . Most drive shafts used in crawling have a hole designed for a 5 mm  or 6 mm shaft .   Now the final drive gear that attaches and drives this shaft has a 5mm hole and the shaft its self is 5 mm in the center and is machined down to 4 mm at its ends . The shaft has been circled in the diagram above . By replacing the bearings with 8x5 bearings and replacing the shaft with one that is 5 mm from end to end common drive shafts should be able to be used . I am currently looking for a shaft that will be a drop in replacement but one should be able to be made fairly easily .