Cosmo's TRX-4M Defender Project

[CosmoM3]

TRX-4M Defender

This is my first journey into micro rigs as I was fascinated by the capability of the TRX-4M as I'm familiar with the Traxxas' house design. Coming from the TRX-4 Sport TRAXX project that I've been working on previous, I've decided to jump into a capable crawler out of the Defender despite is rear weight bias.

PSA: The Defender comes standard with the following spring rate setup:

Fronts: 0.072 Rate [TRA9757]
Rears: 0.155 Rate [TRA9760]

I feel as though that this isn't common knowledge and should be something people should be aware of when deciding on purchasing springs, esp for the rears. The Bronco comes with 0.095 Rate [TRA9758] on all four corners from the factory.

Anyways, I've done the following upgrades and this Defender is a crawling beast. I will get a scale to corner-balance the rig when I get the time, but stock weight distribution ratio was around 48:52 (F/R).

Electronics

• Traxxas Pro Scale LED Lights [TRA9784]
• LED Foglights (Orange)
• Injora LED Light Bar
• REEFS RC 99 Micro Servo x DSM Off Road TRX-4M Servo Mount
• REEFS RC SHORTY Micro Horn

Body

• Injora Roof Net with Accessories
• Spare Tire (Rear)
• Injora Tow Hooks (Front + Rear)
• Traxxas Lower Links (Steel) [TRA9749]
• Traxxas Hardware kit (Stainless Steel) [TRA9746X]
• Traxxas Steel Hollow Balls (Machined) [TRA7028X]
• Injora High Clearance Stainless Steel Links

Internals

• Injora Sealed Steel Bearings

Suspension

• Traxxas Shock Lower Retainer (Brass) - [TRA9761A] [On Backorder]
• Traxxas Shocks w/30wt OEM Shock Oil Mix
• Traxxas Springs - 0.125 Front [TRA9758] + 1 Clip / 0.155 Rear [Stock] (w/2x Preload Clips)
• Traxxas Steering Blocks, Brass [TRA9737]
• Traxxas Caster Blocks (Brass) [TRA9733]
• Injora Steering Link (Brass)

Powertrain

• Traxxas 7mm Wheel Hubs (Brass) [TRA9750X]
• Traxxas Driveshafts (6061-T6 Aluminum) Front / Rear [TRA9751-Gray]
• Traxxas Axle Shafts + Stub Axles (Hardened Steel) [TRA9756]
• Traxxas Metal Axle Gears [TRA9779]
• Traxxas Low Range Transmission Gear Set [TRA9776R]
• Traxxas Axle Covers, Brass (Front + Rear) [TRA9787]
• Injora 6mm Wheel Hub Extenders (Brass)
• Injora 24T/12T Alloy Steel Helical Gear Set [On Order]
• Treal Brass Extended Wheel Hubs 7mm*10mm Hex, Axle Counter Weight 17g/pc (4pcs) Wheel Spacer [On Order]

Wheels & Tires

• Traxxas Mickey Thompson Baja Pro X Tires [TRA9782]
• Traxxas Method 105 Beadlock Wheels [TRA9781]
• Traxxas Wheel Weights (Brass) Front and Rear [TRA9780]
• FubberStufferz V23 TRX SlymeBallz

Misc

• Jim's Bearings PTFE Coating for Axles Shafts, Stub Axles, Stub Axles, Transmission and Driveshafts
• Jim's Bearings Waterproof Grease for the Axle Gears and Transmission Gears

[DirtMerchant]

Nice. Are those SCX24 Bronco Maxtrax? The orange fog lights are pretty cool.

[B-MOW71]

First off, welcome to RCC!

Nice list of upgrades! Looks like you're building a beast!

Nice heads up on the rear springs. I have the Bronco body on mine and recently picked up the Defender unpainted body. I'll have to get an order in for some heavier rear springs if I see to much rear sag.

Have any pics of under the hood??

[CosmoM3]

Originally Posted by DirtMerchant

Nice. Are those SCX24 Bronco Maxtrax? The orange fog lights are pretty cool.

I don't believe I'm using anything from the Maxtrax. I got the orange fog lights from Etsy.

Originally Posted by B-MOW71

First off, welcome to RCC!

Nice list of upgrades! Looks like you're building a beast!

Nice heads up on the rear springs. I have the Bronco body on mine and recently picked up the Defender unpainted body. I'll have to get an order in for some heavier rear springs if I see to much rear sag.

Have any pics of under the hood??

I recommend running two preload clips on each shock in the rear, but it still doesn't solve the sagging or the torque flex issue. I've rebuilt the shocks with heavier shock oil (mixing the stock 20wt and the TRX-4's 30wt to get a 25wt mix) and it helps a little bit. I'm thinking of running double springs in the rear.

No pics under the hood until all the brassy goodies arrive

[CosmoM3]

Went out to do some shakedown tests on some rocks and dirt. It’s still a bit rear heavy but that should resolve itself soon.

[BREL]

Nice looking Trx4m Defender, can't wait to get one as a little brother to my 1/10 TRX4 Defender

[CosmoM3]

PSA: The hollow, plastic lower suspension links bend can bend under load where your tires may get lodged under load (i.e.) when your rear tires in wedged downhill between two rocks. This will compress your rear shocks, but at its limit, will bend the lower links from the load.

Click below for a short video:

[DirtMerchant]

Originally Posted by CosmoM3

I don't believe I'm using anything from the Maxtrax. I got the orange fog lights from Etsy.

I was talking about the orange traction boards on the side window. They look nice. They look just like the 1:1 product from the company Maxtrax. Where did you get those?

[CosmoM3]

Originally Posted by DirtMerchant

I was talking about the orange traction boards on the side window. They look nice. They look just like the 1:1 product from the company Maxtrax. Where did you get those?

Gotcha.

I just grabbed them on Amazon.

[CosmoM3]

Some of the heavy hitting parts started to trickle in today (more on the way through the end of the month).



Since I’m not satisfied with the rear spring rates on the Defender (they’re the stiffest available @ 0.155 rate), I’ve decided to put together a progressive coilover setup from my track driving days with my sportscar by adding a helper spring to the shock:

• Stock OEM Traxxas Shocks
• OEM Traxxas Shock Oil [20wt/30wt Mix]
• OEM Traxxas 0.072 Spring Rate [Stock Fronts on the Defender]
• 2x Preload Clips
• OEM Traxxas 0.155 Spring Rate [Stock Rears on the Defender]

This would hopefully improve the torque flex and the rear sagging issue if you’re Defender is loaded with accessories on the roof:



During regular driving around, the top half (softer spring) will compress first while maintaining composure - these are the helper springs, while the bottom half of the shock will take on the heavier loads over bigger bumps and rock crawling.

I’ll do some additional testing and descide if I should go with a lighter setup for the bottom half like the 0.125 rate or the stock Bronco’s 0.095 rates.

For people wondering - this does not affect the overall shock shaft travel and full extension (51mm) or compression (it will still full compress).

[CosmoM3]

Weekend Update

Had some additional parts come in.







Promptly took it out to a local RC Hobby shit and did a shakedown test at their indoor crawler course and I'm happy to say that it floated by with no issues. The REEFS 99 Micro made a noticeable upgrade during those tight, off-camber corners when the weight was shifted heavily to one side.





They had a couple of the OEM Traxxas brass front-end parts in stock so I picked them up for the Defender. The Injora brass parts that are still in transit will go on my new Bronco when it comes in this week.



The brass parts made a huge difference as much as the brass weighted wheels.



The Defender now weighs around 740-750 grams and it seems to float by any obstacle at full speed with the low-speed gears.

Slo-mo video in action: https://i.imgur.com/Uzgc8YRh.mp4

[CosmoM3]

I replaced the roof LEDs with something brighter, adjustable, better mounting hardware and more robust that can handle falls.

I have her sitting on my desktop within my view so that I can plug it in and go for a quick over-landing or quick crawl over some slippers on the floor during work.

[AK KRAWLER]

Nice truck, but you had me at KEF...

[CosmoM3]

Originally Posted by AK KRAWLER

Nice truck, but you had me at KEF...

[Ynad]

Thanks for the research on the springs. I've also came to the same conclusion, it will need different rate of spring than provided. I'll try doubling springs on the rear.

Sent from my LG-V521 using Tapatalk

[B-MOW71]

Defender is looking good! Nice find on the Traxxas brass items! I have yet to see them hit my LHS.

Yeah and thanks for taking the time to figure out the spring problem! This will help me down the road!

[CosmoM3]

Since I had to take the OEM Method 105 beadlock wheels off to install my FlubberStuffers, I’ve decided to paint the faux beadlock rim with some leftover jar of titanium metallic paint from Tamiya.

I also weighed the wheel combo with the OEM brass wheel weights, Baja Pro X and Method wheels:







I went out to my local drainage pipe to do some testing:





The Defender performed incredibly well considering the size its size and weight. I’m very happy with its crawling performance and its ability to vertically climb over 50 degree inclines without breaking a sweat.

However, the O-ring gasket that holds the pin that connects the driveshaft and the CV joint peeled back and I had lost the pin during testing. I initially thought I blew the rear diff since the truck seemed to have lost power in the rear wheels, but sure enough, this was what I saw:



I’m going heat shrink this guy onto the CV to prevent future failures.

[CosmoM3]

Originally Posted by Ynad

Thanks for the research on the springs. I've also came to the same conclusion, it will need different rate of spring than provided. I'll try doubling springs on the rear.

Sent from my LG-V521 using Tapatalk

I’ve actually changed up the spring setup after doing some gates at an indoor crawl test.

Front: 0.125 + 1 Clip
Rear: 0.155 + 3 Clips

This is dependent on what you’re carrying on your rig, but this setup worked perfectly for a body that weighed over 250g, with a rear weight bias.

[CosmoM3]

Last pic with the stock plastic steering link before my Injora brass version arrives (taking around 2 weeks at this point).

[CosmoM3]

The Bronco finally joined the family thanks to Traxxas.



I used some heatshrink to seal in those annoying O-ring that are known to slip off during rock crawling session. If you lose those pins, they’re gone! You have to buy a whole new driveshaft assembly to get those pins.



Here she is now on her new throne, mostly done (with her new antenna).