The rover platform (kit):
RC4WD’s Killer Krawler is a crawler kit which comes without any electronics, wheels, cables, simply nada.
Just the bare chassis with axles, gearboxes and 2 pinion gears.
My decision was mainly influenced by the fact that it is of 1/5 scale and all the parts are crafted (CNC’d) from aluminium, no plastic parts.
All the parts fit nearly perfectly so the manufactoring process quality is high.
The main features:
CNC Machined Killer chassis
CNC Machined Killer axle
Heat treated stainless steel spool gear
Max volume adjustable piggy back shocks
Killer angled suspension arms
Front and rear billet bumper
Full metal steering kit
Full ball bearings
1/4 scale servo mounts
Gear ratio: 30:1
Length: 546mm/21.5 inch, Width: 510mm/20.47inch, Height: 250mm/9.84inch, Axle ground clearance: 70mm/2.75inch, Middle ground clearance: 150mm/5.90inch
Wheel base: 22.4″ (570mm) wheels on-center
Includes standard 1/10 scale servo mounts
The kit is available from their site only, for 700$.
NOTE: this is a 2008 year model and already discontinued, so spare parts would not be get so easily,
on the other side, any part of the kit can be recreated If one has a good connection to a CNC expert.
Wheels, wheel hubs and tyres:
The KK kit comes with 23mm hex wheel hubs by default. The problem with this is that there are not so many
wheels which fit this size. Fortunately, RC4WD offers 24mm conversion hex hubs, around 30$.
By using these, I am able to use any wheel with 24mm hexes.
I searched primarily for HPI Baja 5 type wheels and finally ended with cheapo aftermarket Rovan wheels&tyres.
These are 195mmx80mm with offroad pattern and will hopefully offer anough drag. They cost me around 140$.
For the electronics, I wanted to buy some relatively cheapo but reliable parts, so I decided for HobbyKing.
(I know some says the reliability is not common with Hk parts but after 100+ orders I still have good experience with them)
The manufacturer suggests 540 sized brushed motors with the crawler.
Many of the guys use quality Novak brushed motors for crawling but they are too expensive for my application.
Plus, I did not want to do the regular maintanance of the brushed motors after a few runs.
Present year is 2013! So I went for brushless, of course.
As my rover has 2 axles I decided to use 4WD, instead of just 2WD, that means 2 motors, one for each axle.
This allow more power for rough terrain.
As the final gear ratio comes to 1:166 with the factory 9P pinion gear I wanted a slow kv brushless motor
and because of the capability of slow speed it had to be sensored, to avoid any cogging.
I had to find a motor which is not bigger that a 540 size brushed one, so the upper links can move freely.
Although RC4WD offers 750 size motor mount I am not sure how can these fit not to block the upper link movement.
As my factory pinion gears are for 3.175mm shaft the motor has to have the same.
And the winner is the HK’s Turnigy TrackStar 21.5T Sensored Brushless Motor 1855KV.
I was a bit afraid of the fact that its maximum power usage is only 150W but it seems to do the job well.
NOTE: the motor cables are not interchangeable, they have strict positions to fit in the esc,
when using a sensor cable.
As the maximum drain of my motors is only 22A any 45A sensored ecs would be enough but for future
upgrade plans I went for 80A escs.
I chose the HK Turnigy Trackstar 80A Turbo Sensored Brushless 1/12th 1/10th ESCs. They only need to get calibrated
and are ready to go.
Many more features can be programmed but only by a specific card which is in BK all the time. So I am using the default values.
As my wheel diameter is 195mm and width is 80mm I bet I would need high torque servos.
Most of the guys use >20kg servos for this beast so I decided around this value.
Again, a cheapo solution from HK: BMS-L530DMG Digital Servo (MG) 19.8kg / .15sec / 140.5g
Plus, I have ordered some heavy duty alloy servo arms.
Unfortunately, the HK Post is unable to deliver the servos for more than 3 weeks so I could not test them yet.
I am using the T9X with Frsky telemetry capable module, with factory firmware.