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Thread: OS's SWB Yeti with trans swap

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Old 12-06-2017, 06:28 AM   #1
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Default OS's SWB Yeti with trans swap

I picked up a Yeti Score kit a few years ago, and it was a fun build. However, driving left a bit to be desired... The dump truck handling turned me off, the nosediving off jumps ripped the front bumper off after 2 battery packs, and it sat on a shelf after 2 outings.

Then I converted it to a standard Yeti... Added 2.2's and reworked the suspension. Still not happy with the handling, it's been on the shelf since.

Pulled it off the shelf and decided to give it one last go. With some tweaks of course...

Times for some mods and changes....

Here's where I started. Tires removed, dusty and unloved. Loved the look, just wish the performance matched.


Got a good base to start with, I added quite a bit of hop ups when building it up.


Original plan was to move over to an Exo chassis and build off that...


Scrapped that idea, and decided to work with the stock chassis. broke out the dremel and started hacking.


and boom! SCX trans installed.


Differences to the COG is obvious when side by side with the stock trans. Can even feel the difference just handling it.


Have to do a bit of trimming to the battery box. I wanted to leave plenty of room for a 550 so the trans is back pretty far.


Whoops! trimmed a bit too much and took off one of the bosses for the front brace. This was more of an experiment...I've got another chassis here I'll do a bit cleaner later on.


Shortened the rear suspension with Twin Hammers arms while I was at it. Figured this would help with weight balance (the Yeti is way nose heavy) plus I like the look..


New chassis layout


Went back to the stock Yeti body and cage for now, along with the TT tires. I like it, kind of has a Polaris Razr vibe to it. May invest in a new body later if I can get this thing dialed.


More to come..
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Old 12-07-2017, 06:18 AM   #2
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Default Re: OS's SWB Yeti with trans swap

Made a few more changes...

Had to grind out the chassis a bit to get full droop in the back. Not sure what this plastic compound is, but it tuned to black dust as I ground it. Messy messy!


I wanted to add a swaybar, and the stock swaybar mounts were making life difficult. I brainstormed a bit and this is what I came up with. Made a set of shock mounts to lower the shock a bit and used a wraith swaybar in the stock location.


Lower shock mounts moved to the axle and swaybar is now on the trailing arms. It was way too stiff on compression even with the shocks layed down, so I drilled the pistons a bit and went with 20wt oil. Feels great now - plush and plenty of travel. Should work out well.
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Old 12-07-2017, 06:58 AM   #3
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Default Re: OS's SWB Yeti with trans swap

Builds like this make me truly realise how much of a newbie I am. I am humbled, impressed and curious on the end result.
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Old 12-08-2017, 06:11 AM   #4
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Default Re: OS's SWB Yeti with trans swap

Test time! Tim to see if all the plastic dust sweat and tears were worth it. Glad to say they were! (mostly)

The biggest handling issue I had with the Yeti was how it nose dived - both on jumping and when decelerating. No matter what I tried with the suspension, I could never tune it out. Great for trails and rocks - no so much for anything high speed. Lowering the motor and shortening the wheelbase made a ton of difference. It no longer 3 wheeled under braking at all - just leaned in like a buggy would. It still wants to nosedive off jumps, but it's far better. Feel like I'm on the right track - further tuning to ensue. Also noticed it's much more agile overall - the shorter wheelbase really livens it up.

A bigger issue is that the SCX trans really lowered the gear ratio - kinda figured it would. With the smaller TT tires and with the biggest pinion I have, I'm still not even in the ballpark - it's basically running at 1/2 speed. Debating a few options - SSD high ratio trans maybe, or even dropping in an EXO style 1/8 motor mount.

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Old 12-08-2017, 06:26 AM   #5
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Default Re: OS's SWB Yeti with trans swap

My vote would be the Exo motor mount. Simple and easy.
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Old 12-09-2017, 07:12 AM   #6
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Default Re: OS's SWB Yeti with trans swap

Front suspension needed some serious love. Both front shocks were completely blown apart from all the nose first landings. Instead of rebuilding, I found a set of Zero shocks in my box that were the same length and fitted them with some stiffer springs. Much smoother!


In the rear, I just swapped out some softer springs. Shocks were still full and in good shape. 20wt oil inside and drilled pistons. Tweaked the upper links and swaybar also.


Now to the trans...this was from an Integy trail roller I traded for a long time ago just to see if it was a huge POS as listed (it held togther pretty well actually). The motor mount was bent so I replaced it with a stock plate for now. Internally, the steel gears were in perfect shape so I re-greased them and called it good. I couldn't get the gearing I wanted with the stock Axial parts unless it was 48p, so I swapped in a Traxxas slipper set-up which opens a much larger range of gears in either 32p or mod1. Think I can get the gearing in the ballpark without swapping transmissions...I had a 19t pinion and 54t spur in my parts boxes, so on they went.


Cut up the spur protector...just in the way and wouldn't fit over the incoming pinions anyway.


Mounted back in there.


Test driving with the new changes, the suspension is much better, but I still need more gearing. My EXO has a FDR of 12.7 with the same tires and it's pretty much perfect, so that's my goal. I started at 35.2:1 so I was way off. Top speed of 9mph or so. Now I'm at 25:1 so I'm getting closer. Got a few pinions and spurs and a set of OD gears for the diff coming for further mad scientist experiments.
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Old 12-09-2017, 07:19 AM   #7
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Default Re: OS's SWB Yeti with trans swap

Quote:
Originally Posted by Brake Weight View Post
My vote would be the Exo motor mount. Simple and easy.
That was my plan ....would solve all the gearing issues, but space might be an issue. It's much longer overall than the SCX trans footprint. I'm keeping an eye out for one in any case.
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Old 12-09-2017, 08:06 AM   #8
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Default OS's SWB Yeti with trans swap

The Exo tranny has a diff on the back of it giving a center diff. Mine is 2part epoxied to a spool so rendered useless.


Edit: saw you have an Exo. Check out the Thunder Tiger Jackal tranny. It looks like the SCX10, with a Yeti motor mount, and has a taller ratio. Plus metal gears but in a plastic case. It is 5 in to 4 out whereas my SCX is 13 in to 5 out.

Last edited by Brake Weight; 12-09-2017 at 08:13 AM.
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Old 12-09-2017, 02:16 PM   #9
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Default Re: OS's SWB Yeti with trans swap

The Exo tranny has similar dimensions L x W but is a little shorter and the motor mounts lower. I had mine broke down to its individual bits but I don't remember how easy it'd be to attach a driveshaft to one end of it.
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Old 12-13-2017, 06:40 AM   #10
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Default Re: OS's SWB Yeti with trans swap

So then this happened...Took the body off my unsed Emaxx and found it fit the wheelbase pretty good. So after some hacking and drilling, the Yeti has a new look! While I like the look of the stock body better there's a tremendous performance benefit from swapping over to a body that's less than 1/2 the weight.

Still waiting on my gears and what not..delivery times are a little iffy right now!

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Old 12-13-2017, 08:20 AM   #11
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Default Re: OS's SWB Yeti with trans swap

Great job!
Be sure to keep the battery away from that spinning spur
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Old 12-13-2017, 08:53 AM   #12
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Default Re: OS's SWB Yeti with trans swap

Looks great.

Is that an Orion ESC or just the fan? They make expensive stuff! And what brand is the motor?
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Old 12-13-2017, 12:25 PM   #13
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Default Re: OS's SWB Yeti with trans swap

Orion ESC and motor. ESC is a rebadged Hobbywing 60A, not sure on the motor. It's only a 2400kv - great torque, but not a lot of RPM's on 2S. Imagine I'll be swapping in something else eventually or trying 3S.
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Old 12-13-2017, 12:40 PM   #14
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Default Re: OS's SWB Yeti with trans swap

Ah yes Orion did rebadge HobbyWing ESCs back in the day before they started making their own. Awesome system!
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Old 12-27-2017, 09:15 AM   #15
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Default Re: OS's SWB Yeti with trans swap

Moving forward with the Yeti...

OD gears replaced the kit gears. Decided to give RC4WD gears a try. Steaming pile of junk. Didn't fit the front housing or the rear axle. No idea what these actually fit in, but in any case an utter waste of money. Ordered some Boom Racing gears, and they dropped right in no problem.



Rear axle is open with a diff...used a spring for a limited slip action similiar to the front. Works very well! Snapped a pic while I had it all apart.


I decided to try the VP mount - I'm sure this is nice for U4 and crawling, but didn't care for it from a go fast standpoint. I want the chassis to slap the ground first, not put the pressure on the shock mounts. Plus, lost some travel with the upright shock setup. Again, not the hot ticket for a go fast setup. Put in the parts pile for the eventual trail rig conversion


Got the gearing in - currently running 23/50. Found some other gears though, so more room for sure to gear up if needed. With the OD gears in the axle, now at a 14.86 FDR - in the ballpark for sure.


Took it out for a test drive...gearing is much better! Almost have some speed now. I think if I drop in a 3800-4500kv motor, it'll be perfect. The 2400kv just doesn't have the RPM's to get any speed. Putting the lighter body on made a noticable difference as well, though removing the weight off the back brought back the "donkey kick" effect. I'll have to retune the rear shocks (again) to compensate.

After run pic..too damn cold to get any action shots. Mud was even frozen!
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Old 12-28-2017, 12:32 PM   #16
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Default Re: OS's SWB Yeti with trans swap

Quote:
Originally Posted by OSRC View Post
Rear axle is open with a diff...used a spring for a limited slip action similiar to the front. Works very well! Snapped a pic while I had it all apart.
You mind explaining this a bit? What size spring, how it works, etc?

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Old 12-28-2017, 04:17 PM   #17
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Default Re: OS's SWB Yeti with trans swap

Found the spring in my parts box, no idea where it came from. It puts pressure on the spider gears and makes them more resistant to turn. All the gears are coated in Tamiya AW grease which slows things down as well.

It's like a poor man's silicone diff for when you can't seal things up. Old trick from my on-road days. The rear diff feels about the same as the front which has about 10k diff fluid in it.
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Old 12-28-2017, 04:24 PM   #18
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Default Re: OS's SWB Yeti with trans swap

Itís worth a try on my Twin Hammers.
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Old 03-23-2020, 10:55 AM   #19
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Default Re: OS's SWB Yeti with trans swap

"Been hiding out and laying low, it's nothing new to me. Well you can always find a place to go. If you can keep your sanity!" - W. Axl Rose

Been finding way to keep busy during the shutdown. Actually have less time to wrench lately since the kids are home, but I've been picking at projects here and there.

Had some bits sitting around for my Yeti that's collecting dust for 2 years now - now as good a time as any to get building. I tried this truck as a Score - meh. Tried it as a go fast rock racer - meh. Wants to nose dive constantly in pretty much any go fast situation. Since it's nose heavy anyway, sounds like a good crawler project. My twin hammers scaled up rocks like velcro, hoping this will eventually do the same.

First thing - lower the COG. The stock trans puts the motor way up high for some reason. Never understood that...so I picked up a Chinabay SCX trans and decided to swap it in.


First thing I did was put it apart and check it out. All metal, though the tolerances weren't great of course. Greased, shimmed, and reassembled it. Feels decent, we'll see how it does. It's certainly smooth.


No slipper pad. Hmm.... That's interesting.


Initially, I started with an old 'Boochi 5 pole 550 I had laying around.


Installed in the truck. I milled the chassis flat in the center a while ago, getting rid of all the ridges and what not so the trans sits flat on the chassis. I had an SCX trans in previously (though the pics were lost) so it dropped right in.


Had to fab a super long driveshaft out of WB parts, E6000, and hope. I have no idea how long this will hold up.


Started re-assembling the rest of the chassis. OD gears with a HR clamp style locker up front, and UD gears with an FI spool out back.


Chassis done. Some TSX Xl's should give good grip out in the wild. Back to a std. wheelbase as well.


COG is much lower now, can see where the motor now sits in relation to the chassis. I run 2200 packs up in the std. location.


Hacked up an old Raptor body and left the rear cage exposed - I thought it looked better this way.


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Old 03-23-2020, 10:59 AM   #20
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Default Re: OS's SWB Yeti with trans swap

And took it out to play... I swapped the motor and ESC to a TRX ESC out of my TRX4 and a Holmes 12t torquemaster. It did really well! The servo sucks and I need to play with gearing but it crawled around very well. I've got 10wt oil out back and 30wt up front which is super light. The entire truck is underdamped and the suspension is very active. It bounces and rolls a bit, and hunkers down in the back under acceleration. I like it.




It's just fast enough to bounce around the yard a bit, though I think i'm going to gear it down. The 12t isn't ideal for low speed work unless it's geared low. and things were getting warm in there. Not the best motor, but it's what I have for the moment.


So far, this is the best iteration of my Yeti, bar none. I'm thinking of dressing up the body a bit with lights, adding rear steering, and swapping in some better servos on a BEC.
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