Senton 4S Kraton/Outcast metal spur gear in 3S Senton

[Just a Basher]

It looks like the metal 4S spur gear will fit in a 3S rig with minor modifications.

Looking at the exploded views of the 4S slipper and the 3S slipper assembly, the part numbers are different. I took a gamble that ARRMA wouldn't change the design too much and the metal spur gear should drop right into my Senton.

It looks like there are two different slipper pads ARRMA is using. AR310790 is the octogon shaped pad and ARA310908 is the castellated slipper pad (I think this is the new 4S pad and my 3S senton has it too, so maybe a design update for the 3S line?). Looking at the spur gear, it looks like it will take either pad, but I can only say it works with the castellated pads.

Arrma part number ARA310945. It actually arrived before my Senton.

I should have taken pictures before I assembled the whole thing, but I thought of this too late. The right gear is the metal 4S spur gear mounted, and on the left is the stock 3S spur gear. The metal gear is quite a bit thinner than the original.

Left on both below is the metal gear mounted. Right is the original gear that was removed from the Senton.

The entire slipper assembly went together without any hiccups (aside from what seemed to be an entire tube of blue threadlocker holding everything together).

Dropping the slipper assembly into the motor housing is where I had to start modifying. The new gear doesn't sit in the same spot as the old gear, I had to trim a bit of the housing to ensure it would clear without any issue. I did notice when held the way it was in this picture, something seemed to contact the plastic motor housing (possibly part of the slipper assembly or spur gear since it sits further forward or downward in the photo than the original). That did not seem to be an issue since the spring in the driveshaft pushing the entire slipper assembly towards the rear of the car, or up in the photo below kept it away from whatever it may have been hitting.

I had to get creative here. The pinion and spur didn't line up and I had to push the pinion closer to the motor (down in the photo). Flipping the pinion doesn't work, it will interfere with the housing then. Simply pushing the pinion further down on the motor shaft meant I couldn't access the set screw to tighten the pinion. To access this, you need to loosen the screws attaching the motor to its mount, angle the motor so you can tighten set screw in the pinion, reattach the motor to its mount, and reassemble everything.

Everything should go back together and viola, a metal spur gear in a 3S Senton. It even sounds like its bigger 6S brothers.

Enjoy.

 

[Yonic]

Just throwing an idea, i don't have the new spur so i'm not sure - but maybe you mounted the spur backwards? maybe if you'll rotate it 180 degrees it will be positioned more backwards?

 

[crimsonfancy]

Very cool. Now I want to hear how it sounds too.

 

[Just a Basher]

Just throwing an idea, i don't have the new spur so i'm not sure - but maybe you mounted the spur backwards? maybe if you'll rotate it 180 degrees it will be positioned more backwards?

I thought about that for a while. The gear itself is the same either way. The original was offset though.
One thing I didn't try was that there are two clutch disks on one side (the rear if I remember correctly) and one on the other. I think I reassembled it per the manual, but maybe I could try to flip it around. I am not sure how that would work with the center plate that has two flat spots on it to engage with the rear output. Pic below.

 

[Just a Basher]

For those that wanted a bit more comparison of the two gears, well now is your chance.
Its update time.

I got two packs through the setup and then the slipper started to loosen. I thought I had tightened it up enough (I followed the manuals 1.5 turns from full tight) so I pulled the adjustment screw out, cleaned the threads, reapplied blue loctite and cranked it down as tight as I felt it would go before stripping. Today I brought the Senton to work with a charged 3s pack with the intention of hitting up a skate park after work. It was packed when I went after work. I found a nice dirt lot to play in near my house. Again second pack it was coming loose again.

I took the whole thing back apart to diagnose. mmm... toasty slipper pads.

Closer comparison shots of the two gears.

Looking everything over. I was suspicious that something changed in the design. I pulled out my calipers and started measuring. I've got all of the measurements worked out and figured out where it all went wrong. I was at the adjustment limit of the entire clutch. Everything was brand new and unrun (metal gear went in before the first battery), so the metal gear is thinner where the clutch pads engage allowing you to bottom out the adjustment before its actually tight enough.

The thickness of the original 3S gear between the pad contact surfaces is 0.122" (just over 3mm for the rest of the world).
The thickness of the metal 4S gear between the pad contact surfaces is 0.075" (1.9mm).

So the entire thickness from slipper hub to hub is now short 0.047" (over 1.1mm), approximately 1 clutch disk (0.04" or 1mm).

So off to the 4S Kraton exploded view. Well...it has an additional clutch disk.

So if you want to upgrade your 3S rig to have a metal spur gear, you'll need the gear and another clutch disk for 4 total. Since Jennys just started selling 4S parts this week, I would recommend just ordering that assembly there. Part numbers on the housing are the same, so it should drop in and it would be cheaper than just the metal gear itself.

I'm not giving up yet on my experiment. I'm going to see if I can find a washer in the garage that I can modify to work as the new intermediate plate and would be a little thicker. If that doesn't work, I have a huge roll of gasket material I'll make another disk, I could even trim the inner portion of one of the hubs down to get a little closer...or just buy the 4S assembly.

Time to finish my drink.
Enjoy.

tldr - buy the 4S clutch assembly from jennys if you want a metal spur gear in your 3S rig.

 

[bicketybam]

I don't mean to throw cold water on your experiment but you don't need a metal spur. I've been running the same spur since September. I even went to 4s with the BLX185 system and it was fine.

 

[Just a Basher]

I don't mean to throw cold water on your experiment but you don't need a metal spur. I've been running the same spur since September. I even went to 4s with the BLX185 system and it was fine.

I kinda figured.
I just wanted to mess around with it. I'm not sure its possible for me to leave something alone.

To add, the gasket material worked wonders. I put it between the forward most disk and spur gear. There wont be any rotation of it, so I think it should last a long time. And I doubt the clutch will get hotter than a car engine, so it should be fine heat wise.

 

[ndoppes]

It looks like the metal 4S spur gear will fit in a 3S rig with minor modifications.

Looking at the exploded views of the 4S slipper and the 3S slipper assembly, the part numbers are different. I took a gamble that ARRMA wouldn't change the design too much and the metal spur gear should drop right into my Senton.

It looks like there are two different slipper pads ARRMA is using. AR310790 is the octogon shaped pad and ARA310908 is the castellated slipper pad (I think this is the new 4S pad and my 3S senton has it too, so maybe a design update for the 3S line?). Looking at the spur gear, it looks like it will take either pad, but I can only say it works with the castellated pads.

Arrma part number ARA310945. It actually arrived before my Senton.

View attachment 38353

I should have taken pictures before I assembled the whole thing, but I thought of this too late. The right gear is the metal 4S spur gear mounted, and on the left is the stock 3S spur gear. The metal gear is quite a bit thinner than the original.
View attachment 38354

Left on both below is the metal gear mounted. Right is the original gear that was removed from the Senton.
View attachment 38355
View attachment 38356

The entire slipper assembly went together without any hiccups (aside from what seemed to be an entire tube of blue threadlocker holding everything together).

Dropping the slipper assembly into the motor housing is where I had to start modifying. The new gear doesn't sit in the same spot as the old gear, I had to trim a bit of the housing to ensure it would clear without any issue. I did notice when held the way it was in this picture, something seemed to contact the plastic motor housing (possibly part of the slipper assembly or spur gear since it sits further forward or downward in the photo than the original). That did not seem to be an issue since the spring in the driveshaft pushing the entire slipper assembly towards the rear of the car, or up in the photo below kept it away from whatever it may have been hitting.
View attachment 38357

I had to get creative here. The pinion and spur didn't line up and I had to push the pinion closer to the motor (down in the photo). Flipping the pinion doesn't work, it will interfere with the housing then. Simply pushing the pinion further down on the motor shaft meant I couldn't access the set screw to tighten the pinion. To access this, you need to loosen the screws attaching the motor to its mount, angle the motor so you can tighten set screw in the pinion, reattach the motor to its mount, and reassemble everything. View attachment 38358

Everything should go back together and viola, a metal spur gear in a 3S Senton. It even sounds like its bigger 6S brothers.
View attachment 38360

Enjoy.

nice write up, question for you guys.I just ordered a Hot Racing metal Spur, will i need to run an extra clutch like you are saying? Do you think it would be wise to run an adjustable motor mount as well?

 

[Just a Basher]

I doubt you will have to run an extra clutch disk with the HR metal spur gear. It was likely designed around the 3 disk pack that ARRMA had before the 4S line came out. Plus that part is specifically designed for the Mega and 3S line.

as for the adjustable motor mount, if the pinion and new spur gear have a good mesh together I would leave it alone. If you wanted to start changing to a bigger pinion, or one that the stock mount doesn't have a bolt pattern for, I would change it out. But changing it out just gives you a new failure point you didn't have before, not setting the mesh correctly.

 

[ndoppes]

I doubt you will have to run an extra clutch disk with the HR metal spur gear. It was likely designed around the 3 disk pack that ARRMA had before the 4S line came out. Plus that part is specifically designed for the Mega and 3S line.

as for the adjustable motor mount, if the pinion and new spur gear have a good mesh together I would leave it alone. If you wanted to start changing to a bigger pinion, or one that the stock mount doesn't have a bolt pattern for, I would change it out. But changing it out just gives you a new failure point you didn't have before, not setting the mesh correctly.

well thats kind my issue..... I just posted a few days ago about this problem I am having. https://www.arrmaforum.com/threads/pinion-to-spur-lash.12517/ I tried to leave a link to my post but Im not sure if it worked. Long story short my senton 3s ate two spurs in 8 packs.

 

[FordFalcon]

Same problem here with the metal spur. Had to crank the adjustment screw all the way down to even get it to move. I see now adding an additional slipper pad should hopefully help with that situation. So far pretty disappointed with the 3s. One spur gear gone, both bearings, and now the bearing in the motor just exploded, only had it for a month.