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Bruiser (clone) build: Automating the 3-speed gearbox

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I was tempted to do that initially but thought I'd see if the standard configuration could be made to work properly. The standard setup also has an advantage that the turnbuckle going to the steering knuckle is longer and less angled than when you do the front servo mod, which gives less bump steer. Ideally the servo should be mounted exactly where the standard lever pivot is, and that just isn't possible.

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This week it was time to replace the toy-like bumpers and side sliders/steps

i got these generic steel side steps from ebay. The main square section extended past the step part and had mounting holes at either end. I cut these off and drilled two new holes underneath the step so I could utilise existing chassis bolt locations for mounting.



Up front, I made an aluminium part which ties together the 6 bolts that the standard bruiser bar mounts to

This allows a steel front bar to mount securely, and the chassis probably won't get bent if I accidentally bulldoze a small country. The front bar is the same as an RC4WD Trail Finder bar, but it's a cheap knockoff / factory second or some such that I found on ebay. The quality is not A1, some bars are off by a mm to two, but it's good enough for my purposes. I had to bend the steel plate section of the front bar a little as the bruiser chassis has a downward slope towards the front - I guess if I have a hard crash this is the part that is going to bend. There's a spot for mounting a winch on the plate section of the bar - I decided to put an LED light bar there instead.



Down rear is another knockoff RC4WD bar. It turns out the bruiser body is about 1cm wider than the trailfinder body around the rear tail lights so the bar wouldn't fit. Fortunately, I was able to tilt over each corner/taillight section with the persuasion of a hammer so the top bar sits out 5mm wider than the bottom bar - as supplied top and bottom bars were equal width. I was worried the welds (or brazes?) would crack when I tried to do this, but they held up. Some paint cracked at the joints, but I just gave it a touch up with a brush and you'd never notice if I didn't point it out ;). The bottom bar sits underneath the body so it doesn't need to be wider. Another aluminium mounting solution mates it to the bruiser chassis.

More black paint keeps things stealthy and factory looking

Ready for a body - that's the next post!

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So, the body. The body was sprayed with TS-38 Gun metal. The idea is that it is close enough to the black plastic that if it scrapes through it won't be overly noticeable. This was my first time painting a hard body so I made plenty of rookie mistakes. Minors runs, dust and dirt, that kind of thing. Also made the mistake of spraying the cab and tray separately from different angles so the metallic flake doesn't match up where they meet. No matter, the aim here is that if it looks cool from a metre away, mission accomplished. I think the bruiser's 'sleeper cab' looks ugly as sin so I built the body as a single cab ute instead. Of course, there is no back window supplied with the body so I laser cut one at work out of two pieces of 1.5mm acrylic. The interior was painted in TS-46 Light Sand, with some matte black and silver brushwork for the floor, dashboard and steering wheel. The dash decals were pre-applied to the interior tub and not easily removable, so I just painted around them.




Aluminium tape inside these light buckets improves their realism


Some choice decals from the sticker sheet were applied, I might get a white tailgate logo as I didn't think the included red logo would go well with the gun metal.






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Progress is currently slow as I've been side tracked with other projects, but I did draw up two 40x50mm circuit boards, which together with the receiver form a stack which should fit inside the Bruiser's electronics box. Could probably be made a little smaller with a tidier layout but this will do the job for now. 
These boards will contain both the gear shifting controller and a lighting controller. The lighting controller will have full access to the motor sensors and all outputs of the receiver so the lighting can be semi-automated as well: brake lights, reverse lights, turn signals, etc.  

The top board has all the connectors for lights, power, servos, esc, sensored motor and the receiver. There's also a voltage regulator which provides constant +7.5V and +5V needed for the LEDs and microcontrollers, even if the battery voltage becomes as low as 4.5V. The bottom board has the two microcontrollers and eleven constant current drivers for LEDs: ten 20mA drivers for pairs of 3 or 5mm LEDs and one 100mA driver for the front light bar. Each LED output will have the ability to be dimmed in 13 increments, performed by pulse-width-modulation at 600Hz, which is chosen as it is a multiple of all the common video frame rates (24, 25, 30, 50, 60, 120Hz) so the lights won't be flickering in videos.



Had the first hiccup with the gearbox - one of the ball bearings in the selector mechanism jumped its track and jammed up the whole mechanism. After tearing it down and un-jamming it's working again as normal but I'd like to avoid that happening again. I put it down to too much torque from the servo so I reinstalled a servo saver, however a much better one than standard. I put in my go-to for 1/10 TC steering servos: A tamiya high torque with a 3racing aluminium horn. I've only done some initial testing but this seems to work well with the saver spring engaging while the gearbox isn't synchronised and then snapping into gear once it is. 

I upgraded the 12kg steering servo to a JX Servo PDI-6221MG 20kg and ditched the servo saver for an aluminium horn. I took the opportunity to chase the threads on the turnbuckles with some M3 dies as they weren't cut very well - the die used at the factory was blunt. I already had a rod end pop off the steering linkage and chasing the thread seemed to fix it by increasing the bite on the plastic rod end. I had to order a left hand die so I could do both ends and it turns out that not all dies are the same outer diameter. When you order the cheapest one off ebay it'll be the smallest possible size <_<. I made it work though :P



The steering is more than strong enough for my needs now and the steering servo doesn't groan and creak constantly like the old one did. Also changed the Tamiya TBLE02S ESC for a Trackstar 80A Turbo ESC since it has the option to run 16kHz switching frequency which eliminates annoying whining/ringing noises when crawling.

Little vid running the steering servo through its paces indoors as the weather is miserable:

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