DavidH
Quarry Creeper
I went to the LHS a while back, with some birthday money to spend. I looked wistfully at the losi SCBE, but it was not cheap, and without a track nearby I would simply be using it the same way I use the yeti (trails).
The other thing I wanted to do was to convert my RTR score to the rock racer cage/tires/wheels; on the store shelf was a discounted (-CAN$100) RR kit, so I snatched it up. This would let me do the conversion for about the same as buying the bits individually, and would give me lots of spares and upgrades such as the HD gears.
I also had a bit of an epiphany; I was happy with how the yeti handled, from crawling to high speed, and the only breakage has been a spur gear, which I put down to the slipper plates getting rusty; the thing that would stop this truck dead is getting the rear pumpkin hung up on rocks and underbrush. While I give the nod to the live axle for the articulation (and potential crawling) advantage, crawling is not why I have the yeti, and I have no attachment to the solid axle scale appearance, so I would use the purchase of the kit to do a conversion to IRS/4WS for the yeti.
While my original conception was to simply 'back-half' the truck, removing the trailing arms and axle and bolting in an aluminum plate and requisite suspension and servo bits, a little voice in my head said to aim higher, and do a full chassis pan. Why not?
A stop at a local metal fabrication shop yielded some free aluminum. I marked it up, and started cutting. I picked a width of 100mm; in retrospect, I would have left another 20mm on each side to bend up later to both increase rigidity and form a guard for the servos.
Interestingly, the new pan was within a gram of the plastic tub.
Clearance for the bevel gears.
Bolting everything down. No fancy 3D printing here, just some sheets of 1/16, 1/8, and 1/4" ABS, and a scroll saw. These are the bulkheads for the battery tray and servo mounts. They leave the rear drive shaft clear for inspection and lubrication.
I filled the front and rear diffs with putty. I may switch to 500K or 1m in the front after I do some testing.
Rear shock tower. I decided to re-use the rear shocks, although the tower could be drilled to use shorter shocks. I believe the longer rear shocks will allow me to better tune the front-to-rear roll stiffness.
While I have only bent two hinge pins so far, I took the time to sleeve all four a-arms.
I fabricated a spacer to fit under the servo saver spring, to tighten up the rear steering (the front is using a previously purchased HR graphite setup).
Being new to RC crawler stuff, I had no idea that the factory 2.2 tires were so wobbly (I ran them prior to the conversion). I put some dual-stage foams in the front, and will test to see how that goes.
Just about done. I did fabricate a 1/16 skid plate to completely cover the bottom, but the exposed aluminum looks so cool. I may cover it with a vinyl film at some point.
The strategically placed shock towers poke through the yeti cage.
The hinged rear bulkhead allows for the cage to be flipped up with the removal of the two front clips. I will add the holes later for the score body posts so that I can mount the TT body. The rear hinge uses a front a-arm hinge pin.
I re-used the fuel cell for the rx and bec, adding some closed-cell foam to seal off the top when the body is clipped down. Two small drain holes have been added to the bottom of the cell.
Some droop.
Rear stance.
Rear droop. 3.5" of travel, limited by the axial universals.
Side stance.
Belly up. Only two holes drilled in the wrong place
but I was able to fix that without re-drilling. Not too bad for a first try, and not bad enough to warrant starting a new plate.
Wheels turned.
I almost forgot - the flex shot. The can is 170 mm high.
Biggest challenge: rear steering geometry - 1) getting the kick, caster, steering assembly to where they needed to be, because you cannot simply run it backwards and 2) dialling out the bump steer from the rear suspension. Yikes.
Now that the axle widths are the same f/r, I swapped the hubs from the front TT wheels onto the rear 2.2 wheels to keep the f/r track the same.
Stuff purchased for/before this conversion:
- Axial Yeti SCORE TT RTR $400
- Axial Yeti Rock Racer kit $270
- Spektrum DX4C four channel radio w/ waterproof rx (bought used $70)
- PowerHD 20kg servo waterproof $20
- Savox 1210sg servo waterproof $70
- Traxxas 2075 servo waterproof $20
- HR Graphite steering assembly with aluminum posts $40
- Axial 2-speed package $100
- Axial Front universals 92mm $35
- Proline 2-stage foams (1-pair)
- 5000 mah 3s lipo
- Castle BEC set at 7.4v and fan for motor $35
- servo extension cable for the front servo (10 for $5)
Besides the pan, I fabricated:
- front steering links
- rear servo saver spring shim
- a-arm sleeves
- toe blocks, front and rear
- rear shock towers and rear body hinge
- servo mounts
- battery tray and straps
- gaskets for the diff-case-to-chassis-pan interface
- full skid plate (not shown)
- ESC fan mount with 12v fan
Things to do:
- dab every new bit of metal on the truck in Corrosion-X, to stave off the rust typical of the axial fasteners.
- Radio endpoints tuning; the rear wheels won't turn as far with this body, compared to the TT body (done)
- Sort out the foams
- Install internal mud flaps
- Change the front diff fluid (maybe)
- Install bumper/guards for the servo arms
- Install kit's HD gears in the front diff (I am still running the RTR set in there)
- Chassis brace, bulkhead-to-bulkhead. Right now the pan is stiffened by all the stuff bolted to it, but a high speed tumble may tweak it.
- install rear bump stops (nitro fuel tubing) on the rear shocks so that the chassis and the suspension bottom out together.
- paint the body. There is just a plasti-dip-type film applied to the inside of the lexan at this time. I will probably keep with the blue.
- another savox 1210sg servo to replace the powerHD in the front. The savox currently runs the rear steer, as that is where the fastest and tightest response is required.
- aluminum steering rack, for the rear (the plastic rack may be the weak link at this time)
- fabricate a rear bumper
- lights
- replace bendy servo arms with aluminum.
I think the TT RTR spring rates are ok for now, but the rear shocks will need heavier fluid. A quick check has the truck at 8 lbs 5oz with a slight rearward bias with its 3s 5000mah battery installed. The side-to-side weight balance is only a few grams off, even with the battery to one side; I hypothesize that this is the result of new narrow pan that keeps the battery close to the centerline.
I never measured the lateral CoG on the original chassis, but then that is so dependant on the ride height. I suspect the CoG is now a bit lower with this design, at the sacrifice of the greater potential break-over angle of the live axle rear.
As I did with my previous 4WS conversion, I will have the ability to toggle the feature on/off, and when on it will use a 100% expo mix that only engages the rear wheels to turn when the front wheels reach their endpoints. This way the 4WS does not upset the chassis stability at speed when making minor corrections.
And as I look in my freshly stocked spare parts bin, I'm thinking... bomber 6x6?
The other thing I wanted to do was to convert my RTR score to the rock racer cage/tires/wheels; on the store shelf was a discounted (-CAN$100) RR kit, so I snatched it up. This would let me do the conversion for about the same as buying the bits individually, and would give me lots of spares and upgrades such as the HD gears.
I also had a bit of an epiphany; I was happy with how the yeti handled, from crawling to high speed, and the only breakage has been a spur gear, which I put down to the slipper plates getting rusty; the thing that would stop this truck dead is getting the rear pumpkin hung up on rocks and underbrush. While I give the nod to the live axle for the articulation (and potential crawling) advantage, crawling is not why I have the yeti, and I have no attachment to the solid axle scale appearance, so I would use the purchase of the kit to do a conversion to IRS/4WS for the yeti.
While my original conception was to simply 'back-half' the truck, removing the trailing arms and axle and bolting in an aluminum plate and requisite suspension and servo bits, a little voice in my head said to aim higher, and do a full chassis pan. Why not?
A stop at a local metal fabrication shop yielded some free aluminum. I marked it up, and started cutting. I picked a width of 100mm; in retrospect, I would have left another 20mm on each side to bend up later to both increase rigidity and form a guard for the servos.
Interestingly, the new pan was within a gram of the plastic tub.
Clearance for the bevel gears.
Bolting everything down. No fancy 3D printing here, just some sheets of 1/16, 1/8, and 1/4" ABS, and a scroll saw. These are the bulkheads for the battery tray and servo mounts. They leave the rear drive shaft clear for inspection and lubrication.
I filled the front and rear diffs with putty. I may switch to 500K or 1m in the front after I do some testing.
Rear shock tower. I decided to re-use the rear shocks, although the tower could be drilled to use shorter shocks. I believe the longer rear shocks will allow me to better tune the front-to-rear roll stiffness.
While I have only bent two hinge pins so far, I took the time to sleeve all four a-arms.
I fabricated a spacer to fit under the servo saver spring, to tighten up the rear steering (the front is using a previously purchased HR graphite setup).
Being new to RC crawler stuff, I had no idea that the factory 2.2 tires were so wobbly (I ran them prior to the conversion). I put some dual-stage foams in the front, and will test to see how that goes.
Just about done. I did fabricate a 1/16 skid plate to completely cover the bottom, but the exposed aluminum looks so cool. I may cover it with a vinyl film at some point.
The strategically placed shock towers poke through the yeti cage.
The hinged rear bulkhead allows for the cage to be flipped up with the removal of the two front clips. I will add the holes later for the score body posts so that I can mount the TT body. The rear hinge uses a front a-arm hinge pin.
I re-used the fuel cell for the rx and bec, adding some closed-cell foam to seal off the top when the body is clipped down. Two small drain holes have been added to the bottom of the cell.
Some droop.
Rear stance.
Rear droop. 3.5" of travel, limited by the axial universals.
Side stance.
Belly up. Only two holes drilled in the wrong place
but I was able to fix that without re-drilling. Not too bad for a first try, and not bad enough to warrant starting a new plate.
Wheels turned.
I almost forgot - the flex shot. The can is 170 mm high.
Biggest challenge: rear steering geometry - 1) getting the kick, caster, steering assembly to where they needed to be, because you cannot simply run it backwards and 2) dialling out the bump steer from the rear suspension. Yikes.
Now that the axle widths are the same f/r, I swapped the hubs from the front TT wheels onto the rear 2.2 wheels to keep the f/r track the same.
Stuff purchased for/before this conversion:
- Axial Yeti SCORE TT RTR $400
- Axial Yeti Rock Racer kit $270
- Spektrum DX4C four channel radio w/ waterproof rx (bought used $70)
- PowerHD 20kg servo waterproof $20
- Savox 1210sg servo waterproof $70
- Traxxas 2075 servo waterproof $20
- HR Graphite steering assembly with aluminum posts $40
- Axial 2-speed package $100
- Axial Front universals 92mm $35
- Proline 2-stage foams (1-pair)
- 5000 mah 3s lipo
- Castle BEC set at 7.4v and fan for motor $35
- servo extension cable for the front servo (10 for $5)
Besides the pan, I fabricated:
- front steering links
- rear servo saver spring shim
- a-arm sleeves
- toe blocks, front and rear
- rear shock towers and rear body hinge
- servo mounts
- battery tray and straps
- gaskets for the diff-case-to-chassis-pan interface
- full skid plate (not shown)
- ESC fan mount with 12v fan
Things to do:
- dab every new bit of metal on the truck in Corrosion-X, to stave off the rust typical of the axial fasteners.
- Radio endpoints tuning; the rear wheels won't turn as far with this body, compared to the TT body (done)
- Sort out the foams
- Install internal mud flaps
- Change the front diff fluid (maybe)
- Install bumper/guards for the servo arms
- Install kit's HD gears in the front diff (I am still running the RTR set in there)
- Chassis brace, bulkhead-to-bulkhead. Right now the pan is stiffened by all the stuff bolted to it, but a high speed tumble may tweak it.
- install rear bump stops (nitro fuel tubing) on the rear shocks so that the chassis and the suspension bottom out together.
- paint the body. There is just a plasti-dip-type film applied to the inside of the lexan at this time. I will probably keep with the blue.
- another savox 1210sg servo to replace the powerHD in the front. The savox currently runs the rear steer, as that is where the fastest and tightest response is required.
- aluminum steering rack, for the rear (the plastic rack may be the weak link at this time)
- fabricate a rear bumper
- lights
- replace bendy servo arms with aluminum.
I think the TT RTR spring rates are ok for now, but the rear shocks will need heavier fluid. A quick check has the truck at 8 lbs 5oz with a slight rearward bias with its 3s 5000mah battery installed. The side-to-side weight balance is only a few grams off, even with the battery to one side; I hypothesize that this is the result of new narrow pan that keeps the battery close to the centerline.
I never measured the lateral CoG on the original chassis, but then that is so dependant on the ride height. I suspect the CoG is now a bit lower with this design, at the sacrifice of the greater potential break-over angle of the live axle rear.
As I did with my previous 4WS conversion, I will have the ability to toggle the feature on/off, and when on it will use a 100% expo mix that only engages the rear wheels to turn when the front wheels reach their endpoints. This way the 4WS does not upset the chassis stability at speed when making minor corrections.
And as I look in my freshly stocked spare parts bin, I'm thinking... bomber 6x6?
Last edited:
