Another Wraith Transmission Install

[supermoturd]

WARNING: Before you even think about converting to the Wraith transmission, there are some things you may want to consider. For starters, this transmission is built more for top end speed than low end torque when compared to a transmission like the RC4WD R2 which has a max advertised reduction of about 30:1. When you look at the gearing calculations in the backs of the Axial manuals, bear in mind that those ratios include the reduction at the differential. You need to divide those ratios by 2.92 to get the reduction at the transmission output. From my calculations, the very best gear reduction that you can manage with the Wraith transmission (motor to transmission output) is 25.1:1. And this can only be accomplished with a 32P 58T spur gear (available from Traxxas and the dust cover should still fit) and a 6T pinion (they do exist and you can get one from RC4WD.) With the stock 87T 48P spur gear and the smallest available 48P pinion, which is a 12T, you get 18.85:1. You can do a little better with the 48P setup by bumping up to a larger spur gear, but the biggest you can install without hitting the U-Joint on your drive shaft is 93T (unconfirmed) and with a 12T pinion you only get 20.5:1, which isn’t much of an improvement. Furthermore, with the larger spur gear, the dust cover will no longer fit. If you want to compare diameters of various gears, you can calculate pitch diameter (approximately the same as the total diameter of the gear) by dividing the number of teeth by the diametral pitch. Eg., an 87T 48P spur gear’s diameter is 87/48 = 1.8125 inches.

Just some food for thought. This is probably not a big deal to most of you since all you ever do is cry about how your rigs don’t go fast enough. But I like to crawl smoothly so it makes a big difference to me.

Anyways, after all of the trouble I went to to install my RC4WD R2D transmission, I ended up being very dissatisfied with it for reasons you can read about here RC4WD R2 Dig Install In R1 Chassis

After doing some research and getting a lot of helpful input from many of you, I decided to go with an Axial Wraith/SCX-10 transmission together with the Vanquish Products Hurtz dig. I hope it will be worth the effort because the installation is turning into a real headache.

I'm starting with the standard (plastic) Wraith transmission kit with plans to upgrade to the aluminum case that Vanquish Products makes. I may also switch to a 32P spur. Thus far I am pleased with the fit and finish of both the transmission and the Hurtz Dig Unit. I'm using my low profile Savox SC-1251MG, which fits nicely back between the upper links.





The fun ended when I went to install the transmission. I did a dry fit to see where I wanted to drill out the bolt pattern in my skid plate. I realized immediately that my main problem was going to be interference between the protruding ends of the wrist pin on the front driveshaft U-Joint and the big 87-tooth spur gear on the transmission. My solution was to install a shaft extension on the transmission's front output shaft; the idea being to shift the wrist pin portion of the U-Joint out in front of the spur gear.



This worked as you can see in the image above. However, it produced another problem. Namely, with the suspension fully extended/unloaded, the wrist pin on the U-Joint scrubs the rod end on the upper link.



I noticed that it was the same case for the rear.



I'm hoping that this will not be such a big deal since my suspension is rarely fully unloaded. I may try upgrading to JunFac shafts in hopes that their lower profile might buy me some clearance. However, I hate to do that since it will add undesired weight to the rig and strain to the drivetrain. What I am also worried about is the spur gear cover that I ordered. I doubt seriously that it will fit with the front U-Joint riding so close to the spur gear. I may notch it or something. I really need the cover because I crawl on sandstone a lot and my rig is exposed to a lot of grit.

Here are some more pictures for reference.

[cytogen]

I never has these clearance issue when I installed my wrath trans. However, info have the junfac shafts with set screws instead of the thru shaft screw. I'm running a 32p 58 tooth traxxas spur as well. I have about a 1.5 mm of clearance between the shaft and spur.

I'm actually surprised you are still running the plastic shafts. My yokes were popping out for the 5 mins of running them.

At least the shafts will be down low. I'll take some close up shots of my rig for comparison.

[supermoturd]

I looked very closely at your thread the other night and it prompted me to order a JunFac shaft for the front. I also have my upper front links mounted to the inboard-most mounting holes (there are two on each side.) I did this to increase my caster angle and I really like how my suspension is working so I don't want to move links. I also just ordered an 80T spur gear so that should buy me a little more clearance. What is the part number for your 32P spur and where did you get it? And I will certainly have to notch the dust cover. As far as the stock, plastic drive shafts go, I have not had any problems with them. They are holding up nicely and I like how light they are.

[supermoturd]

I installed the dust cover tonight and was pleasantly surprised to discover that it was molded with a slight indentation to accommodate the upper U-Joint on the front drive shaft. Thanks to the shaft extension that I installed on the front output of the transmission, the U-Joint fits perfectly against the dust cover. So, clearly, there is no need to install a smaller spur gear. As far as the U-Joints interfering with the rod ends on my upper links, my test runs revealed that this interference is negligible. And so far, the dig servo has no problem shifting in and out of 4WD and dig while the drivetrain is loaded, which was my issue with the RC4WD R2D. It will be nice to finally be able to shift into neutral and in and out of dig while applying throttle!

[cytogen]

Originally Posted by supermoturd

I looked very closely at your thread the other night and it prompted me to order a JunFac shaft for the front. I also have my upper front links mounted to the inboard-most mounting holes (there are two on each side.) I did this to increase my caster angle and I really like how my suspension is working so I don't want to move links. I also just ordered an 80T spur gear so that should buy me a little more clearance. What is the part number for your 32P spur and where did you get it? And I will certainly have to notch the dust cover. As far as the stock, plastic drive shafts go, I have not had any problems with them. They are holding up nicely and I like how light they are.

Mind you, the setup I have is still quite different then yours, the top links I use are stock (outer most mounting, but the bottom are wraith links which extend the wheel base. this also inherently gives me the caster upfront.

The 32P gear is a traxxas spur gear ( TRA3958 ), any LHS should have it.

I was contemplating on getting the gear cover on, but I wanted to have more of the weight towards the front, so there was no room for it. I figure I was never going to take it into any muddy areas so I decided against it.

I have a brushless system in mine so it might had contributed to the driveshafts popping. At least you got a set coming, so you got a spare.

[supermoturd]

I took my rig out for a test run this morning at a local spot and had a bittersweet experience.

The sweet part was that the Vanquish Products Hurtz dig works perfectly. This was my first experience with a functional dig system and pulling off some theretofore impossible lines put a huge smile on my face.

The bitter part was that my brakes were not working and I seemed to be stalling on stuff that I can usually power through. At first I suspected the slipper clutch, but I could clearly see the motor’s rotor spinning as the rig coasted down inclines. This led me to suspect the gear reduction. Based on the gearing chart in the back of the Wraith manual, I was supposed to be getting 35:1, which is even more torque than the RC4WD R2D’s 30:1 with an 8T pinion. I left scratching my head and when I got to work, I sat down to calculate the gear reduction myself. To my horror, it was an abysmal 12:1! I spotted my mistake instantly. When you look at the gearing calculations in the backs of the Axial manuals, bear in mind that those ratios include the reduction at the differential. You need to divide those ratios by 2.92 to get the reduction at the transmission output. My sigh of relief and accomplishment was short lived. From subsequent calculations and online shopping, I determined that the very best gear reduction that you can manage with the Wraith transmission (motor to transmission output) is 25.1:1. And this can only be accomplished with a 32P 58T spur gear (available from Traxxas and the dust cover should still fit) and a 6T pinion (they do exist and you can get one from RC4WD.) With the stock 87T 48P spur gear and the smallest available 48P pinion, which is a 12T, you get 18.85:1. You can do a little better with the 48P setup by bumping up to a larger spur gear, but the biggest you can install without hitting the U-Joint on your drive shaft is 93T (unconfirmed) and with a 12T pinion you only get 20.5:1, which isn’t much of an improvement. Furthermore, with the larger spur gear, the dust cover will no longer fit. Aside: If you want to compare diameters of various gears, you can calculate pitch diameter (approximately the same as the total diameter of the gear) by dividing the number of teeth by the diametric pitch. Eg., an 87T 48P spur gear’s diameter is 87/48 = 1.8125 inches.

Just some food for thought. This is probably not a big deal to most of you since all you ever do is cry about how your rigs don’t go fast enough. *grin* But I like to crawl smoothly so it makes a big difference to me.

[Dravpnir]

Oh, thanks for the information. Better start looking for some Traxxas parts then for my R1 build as I am planning to use an Axial tranny too.

[supermoturd]

Originally Posted by Dravpnir

Oh, thanks for the information. Better start looking for some Traxxas parts then for my R1 build as I am planning to use an Axial tranny too.

No problem. I'm thrilled to be able to give a little something back to this forum.

[supermoturd]

The JunFac drive shafts make a huge difference. They are much more compact than the stock shafts and they really are not very heavy at all. You can see in the pics that the CV joint does clear the dust cover and that I no longer need the shaft extension on the transmission output.

Also, if the 32P 6T pinion and 58T spur are not enough of a reduction, you can always go with an RC4WD Ultra Compact Gear Reduction Unit: 3:1 Ultra Compact Gear Reduction Unit for 540 Motor

But if you go this route, you'll have to raise the transmission a bit to keep the lower links in the rear from interfering with your motor can.

[maddogs1965]

Nice job on the Wraith tranny swap....

So i just purchased a Wraith for my sons 9th B.D. and in a day and a half he has already stripped out the 80 tooth spur gear . I was wondering if you new if there was a metal up grade for this gear, or should i just leave it plastic so it is a weak link and he does not start ripping other stuff up with the metal gear...

Thanks for any info...

Rick

[supermoturd]

Originally Posted by maddogs1965

Nice job on the Wraith tranny swap....

So i just purchased a Wraith for my sons 9th B.D. and in a day and a half he has already stripped out the 80 tooth spur gear . I was wondering if you new if there was a metal up grade for this gear, or should i just leave it plastic so it is a weak link and he does not start ripping other stuff up with the metal gear...

Thanks for any info...

Rick

There are steel upgrades for all of the gears in the Wraith transmission. Robinson Racing makes them. You may also try switching to a 32-pitch spur and pinion. The Traxxas TRA3958 spur gear is a 32-pitch 58-tooth that will fit.

You may want to loosen the nut on the spur gear shaft so that the slipper clutch will be more effective in preventing stripping of the spur gear.

[maddogs1965]

Originally Posted by supermoturd

There are steel upgrades for all of the gears in the Wraith transmission. Robinson Racing makes them. You may also try switching to a 32-pitch spur and pinion. The Traxxas TRA3958 spur gear is a 32-pitch 58-tooth that will fit.

You may want to loosen the nut on the spur gear shaft so that the slipper clutch will be more effective in preventing stripping of the spur gear.

Thanks for the info......

I am sure it will be a chain reaction, if i up grade to the metal spur gear, then i will need to upgrade the 3 gears inside of the tranny to metal, then i am sure he will be tearing axles and ring and pinions out

and how do i know this....25 years of wheeling Rubicon, Sierra Trek & Moab, i guess the apple does not fall far from the tree

[IMG][/IMG]

[supermoturd]

Originally Posted by maddogs1965

Thanks for the info......

I am sure it will be a chain reaction, if i up grade to the metal spur gear, then i will need to upgrade the 3 gears inside of the tranny to metal, then i am sure he will be tearing axles and ring and pinions out

and how do i know this....25 years of wheeling Rubicon, Sierra Trek & Moab, i guess the apple does not fall far from the tree

[IMG][/IMG]

*laugh* I hear you! That is some insane articulation on leaf springs! Did you say it was an 80T spur? If so, you may try going to an 87T and maybe even going to a smaller pinion at the same time. The truck won't go as fast, but it will reduce the stresses in the drivetrain. If you want to stick with the 80T, I have one that I will never use. I'd be happy to mail it to you for free if you PM me with your mailing address.

[supermoturd]

I spent the evening upgrading to the 32P spur and pinion. I went with the Traxxas TRA3958 58T spur and the RC4WD 6T pinion. I ran into trouble straight out of the gate. For starters, the hole pattern on the 58T spur gear didn't quite line up with the hole pattern on the clutch disk. I had to ream out the holes on the spur gear and break off the outermost tabs in order to achieve a good fit.


The 6T pinion is oddly shaped (tapering from base to tip) and extremely long; so long that I had to fab a spacer to put between the motor and the mounting plate in order to achieve proper mesh and alignment between the spur and pinion. I made the spacer out of a couple of sheets of polystyrene. It's ugly and I plan to make a nicer one later. You can see in the photo below that I had to notch the dust cover in order to prevent interference with the rod end on the lower link. This was not necessary before. The reason that it is necessary now is because the Traxxas spur gear is about 1mm thicker and a little larger in diameter than the Axial 87T spur. As a result, the spur scrubs the inside of the dust cover. The solution was to put some spacers in to push the dust cover a bit further forward, away from the mounting plate so that the spur wouldn't scrub. This ended up pushing the dust cover into the rod end, hence the notch.

[supermoturd]

I am pleased with the 25:1 reduction from the 6T pinion/58T spur combo. My motor stays cool, I have plenty of torque, and I'm back to getting about an hour and a half of crawl time out of a 3S lipo. However, in my test run, I could hear the spur gear grinding against the inside of the dust cover. I removed the dust cover, inspected the inside, and found that the spur was scrubbing against the little dimple that is produced by the indentation that provides clearance for the CV joint on the drive shaft. I decided to ditch the cover for the time being, went crawling without it today, and nearly met with disaster when a twig jammed between the spur and pinion. Fortunately, I released the throttle before any damage was done. Frighteningly enough, my reason for releasing the throttle was not the twig. I only spotted it when I leaned in to reposition my rig.

The first thing that I did tonight was to grind down the dimple on the inside of the dust cover. The spur no longer scrubs. But as I was reinstalling the transmission, I found that the dust cover was coming into contact with one of the tubes on the chassis over on the motor's side. I've had to notch the dust cover to prevent this contact. Everything fits now. I'm ready to button her back up and be done with this transmission swap.

[supermoturd]

Drilled out a new skid plate tonight. Did the counterboring with a forstner bit. You can see where I put the bolt pattern in the images.



In the following image, you can see where I had to notch the dust cover to allow clearance for the tube on the chassis.


And here are some pictures of the installed trans.

[cytogen]

I am now waiting on your knuckle weight thread!

I have a bar stock of brass that was going to machine as a sleeve to go around the circumference of the knuckle with a grub screw. Similar to what you have there.

[supermoturd]

* laugh* I was wondering if anyone would notice. That is my prototype knuckle weight.

[supermoturd]

This has been one of the best upgrades/mods that I have made to the R1. The dig shifting is silky smooth, even under heavy torque loading. The transmission is holding up under abuse and has not required any maintenance work in the 20 or so hours that it has been run so far. The 25:1 reduction is more than enough of a reduction. The motor and ESC run cool and almost cold and I get between 1 and 2 hours out of a 3S lipo when crawling at a slow, steady pace.