supermoturd
Quarry Creeper
Don't know why I even post on this forum anymore. Aside from Dravpnir's Wrapter thread (which is awesome), this forum is as quiet as the grave. Kind of makes you wonder if anyone is buying/building/driving Gmades anymore.
Even after everyone pooped on the idea of using the ring and pinion (differential bevel gears) from the Sawback to affect an underdrive in the rear of the R1, I just could not give it up. The Sawback bevel gears (GM52106) are only about $8 a set so I took a chance and ordered them.
Installing the Sawback ring and pinion in the rear differential of the R1 turned out to be a lot more work than I expected. However, it was not an unreasonable amount of work, and the amazing results made it worth while.
As you can see, the Sawback pinion is much thicker than the R1 pinion and the ring hub on the Sawback ring gear is shorter than that of the R1 ring gear.
I had to file the Sawback pinion down to the same thickness as the R1 pinion to get it to fit and mesh properly with the ring.
As for the rings, both the Sawback and the R1 rings are the same diameter and have the same number of teeth (32). However, the hub on the Sawback ring is shorter than that of the R1 ring. This turned out to be advantageous since it gives you some play with which to adjust the position of the ring and ensure proper mesh with the pinion. I used washers at each end of the ring hub to shim and position the ring.
The shorter hub on the Sawback ring allows the axle shafts to be inserted further with the undesirable result that the outer ends of the shafts (especially the left shaft) don't quite reach the outer support bearings in the portal housing. To fix this, I had to drill and tap (M3) a hole (for an M3x0.5 the recommendation is a 2.5mm drill bit, but I have used a 7/64 inch bit with good results) through the center of the ring hub and install a set screw that could be adjusted to prevent the shaft from being inserted all the way. You can see the set screw in this picture. (Edit: A better solution would be to use cytogen's HD locker solution http://www.rccrawler.com/forum/g-made-crawlers/495412-poor-mans-hd-locker.html. This will remove slop from the drivetrain and will provide you with the ability to precisely adjust the locations the diff output shafts relative to the ring carrier.)
And here is an image and explanation of the adjustment.
With the pinion filed and the ring adjusted, the mesh is perfect.
Test drive revealed a marked improvement in turning radius and lowered and stretched suspension as expected. I can't wait to test on the rocks. My calculations indicate that for each turn of the transmission output the front wheels travel 0.5 inches (~12mm) further than the rear wheels. There is no discernible spinning of the front wheels or dragging of the rear wheels except in sharp turns. The drive ratio front-to-rear is a little greater than that for an Axial Wraith with underdrive. However, it is less than that for a Wraith with both overdrive and underdrive installed.
Even after everyone pooped on the idea of using the ring and pinion (differential bevel gears) from the Sawback to affect an underdrive in the rear of the R1, I just could not give it up. The Sawback bevel gears (GM52106) are only about $8 a set so I took a chance and ordered them.
Installing the Sawback ring and pinion in the rear differential of the R1 turned out to be a lot more work than I expected. However, it was not an unreasonable amount of work, and the amazing results made it worth while.
As you can see, the Sawback pinion is much thicker than the R1 pinion and the ring hub on the Sawback ring gear is shorter than that of the R1 ring gear.
I had to file the Sawback pinion down to the same thickness as the R1 pinion to get it to fit and mesh properly with the ring.
As for the rings, both the Sawback and the R1 rings are the same diameter and have the same number of teeth (32). However, the hub on the Sawback ring is shorter than that of the R1 ring. This turned out to be advantageous since it gives you some play with which to adjust the position of the ring and ensure proper mesh with the pinion. I used washers at each end of the ring hub to shim and position the ring.
The shorter hub on the Sawback ring allows the axle shafts to be inserted further with the undesirable result that the outer ends of the shafts (especially the left shaft) don't quite reach the outer support bearings in the portal housing. To fix this, I had to drill and tap (M3) a hole (for an M3x0.5 the recommendation is a 2.5mm drill bit, but I have used a 7/64 inch bit with good results) through the center of the ring hub and install a set screw that could be adjusted to prevent the shaft from being inserted all the way. You can see the set screw in this picture. (Edit: A better solution would be to use cytogen's HD locker solution http://www.rccrawler.com/forum/g-made-crawlers/495412-poor-mans-hd-locker.html. This will remove slop from the drivetrain and will provide you with the ability to precisely adjust the locations the diff output shafts relative to the ring carrier.)
And here is an image and explanation of the adjustment.
With the pinion filed and the ring adjusted, the mesh is perfect.
Test drive revealed a marked improvement in turning radius and lowered and stretched suspension as expected. I can't wait to test on the rocks. My calculations indicate that for each turn of the transmission output the front wheels travel 0.5 inches (~12mm) further than the rear wheels. There is no discernible spinning of the front wheels or dragging of the rear wheels except in sharp turns. The drive ratio front-to-rear is a little greater than that for an Axial Wraith with underdrive. However, it is less than that for a Wraith with both overdrive and underdrive installed.
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