With the width of the vehicle worked out, it is time to make it drive like a crawler.
To slow the Slash down to believable crawler speed I actually kept the stock gearing in place (19.23 Final Drive Ratio for the brushed 4×4). Then I added a RC4WD 1:3 Gear Reducer, which would change the final drive ratio to almost 60:1 – a popular ratio amongst crawlers and close to the TRX-4 low-speed setting.
The gear reducer is normally a bolt on part, but there were some tweaks I had to do to get it to fit the Titan 550 motor. First the receiver hole in the gear reducer is too small fo the 550’s standard 13mm bearing enclosure (the part that sticks out right before the motor shaft). Which is strange because the age-old Tamiya 540 motor also specifies 13mm for this part of the motor.
But I made quick work of it by removing the gear reducer plate and enlarging the hole with a 17/32″ (13.5mm) drill bit.
Also the 550’s shaft is a bit long, so I cut off about 3-4mm from the end using a dremel and a 409 cut-off wheel.
The included pinion gear needed to be installed very close to the motor in order for it to engage smoothly. So I used the same cut-off wheel to extend the flat spot of the shaft almost up to the bearing.
A quick aside – something I found out later is that the pin that holds in the reduction gear… it worked its way loose and into the vent holes of the Titan 550 within the first hour of running – ruining a brand new motor 😔
So I bought a new Titan 550 (and performed all of the aforementioned modifications) and put the gear reducer back together but added a piece of silicone tape to keep that shaft from wiggling loose again. Silicone tape is the same stuff powder coaters use to mask metals – it will withstand high temperatures. Anything that can stand reasonably high temps should do.
The gear reducer doesn’t include mounting screws as they’ll vary by installation. For it to fit the Brushed 4×4 Slash I needed two 4x25mm tapered head screws to fasten the motor plate, gear reducer, and motor all together in a stack.
The endbell of the Titan 550 barely cleared the driveshaft cover. If it didn’t I was prepared to remove it and cut some plastic, but I had about 1mm to spare.
To make sure the power would keep all the wheels moving at once, I purchased a $2 egg of Silly Putty – the cheapest part in this whole build. I removed the grease from inside the diffs using Simple Green and re-assembled them, adding Silly Putty in layers. They feel extremely locked, but hopefully will provide just enough give to relieve stress from the rest of the drivetrain. They’ll likely loosen up as the gears slowly push the putty out of the way – then I’ll add more putty 😂
For traction I found some old-stock Pro-Line Trencher SC M3 (soft) tires – the ones that have some tread on the sidewall. I’m sure Pro-Line removed the tread from the sidewall because track racers found it contributing to traction roll at high speeds. But I wanted the soft rubber and extra tread for climbing.
I mounted them up to a set of Pro-Line Bead-Loc wheels that were made for the front of a Slash 2wd. That offset keeps them from rubbing the front shocks at full steering lock. I like these wheels because they can use any Pro-Line short course tire with the bead lock system which requires no glueing – so I can change tires easily later.
For the tire foams, I used open-cell soft HPI 103335 Short Course foams. I kept the included closed-cell Pro-Line foams to maybe run in the rear if they need more stiffness.
To complete the power package, I needed a speed controller that has a drag brake. This is helpful when you need to stop on a steep incline or decline without your rig coasting down the hill like a runaway tractor-trailer. The HobbyWing WP1080 “Crawler” ESC is popular among locals and it’s available for less than $50. It’s a waterproof 80A ESC with tons of features for both crawlers and brushed racers.
I mounted it up front to add a little nose weight. I’m excited about it – it’s the first ESC I’ve purchased that I didn’t have to rewire the battery connector on. The future is now!