Sariel.pl

Model of Ken Block’s custom Mustang from Gymkhana 7 video. Features RWD, steering, suspension, lights and custom stickers.

Datasheet:

Completion date: 12/01/2015
Power: electric (RC unit)
Dimensions: length 53 studs / width 24 studs / height 12 studs (not including antenna)
Weight: 1.326 kg
Suspension: full independent
Propulsion: 2 x RC motor geared 1.4:1 from faster output
Motors: 2 x RC motor

Inspiration for a model can come from the least thing you expect – in my case, I was watching Ken Block’s excellent Gymkhana 7 video when it occurred to me that the rims of his custom-built Ford Mustang AKA Hoonicorn RTR look really good in this color, and that this color looks very much like Lego pearl gold. My next though was that this color is too rare for any Lego wheels to exist, but wait, I think I actually have a pair or two. Then it turned out I actually had four very rare pearl gold wheels from the 7784 Batmobile set, sitting at the bottom of my wheels chest, never used in any MOC. Once I found them, it was a matter of pure curiosity to calculate the scale of a model to see if it’s possible at all… and before I knew it, I had most of the chassis ready and good to go.

This model was designed first and foremost for performance, and then for looks. I intended to propel it with two RC motors and keep it as light as possible from the very beginning. I have actually experimented with using SBrick to save some weight, but it turned out that a regular battery box was unable to power the motors efficiently, and I had to resort to the Lego RC unit. I have also built and tested front suspension with rubber bands instead of shock absorbers to save some weight too, but in the end the model turned a little too heavy for it. Using the RC unit made installing AWD drivetrain impossible: there was no room for it, it would make the model much larger and heavier, and it would have no real use, just hurting the performance.

The finished model was suspended on four hard shock absorbers, which were all additionally pre-compressed and had their motion limited. The suspension thus created was very hard and had very limited travel – just like I wanted it to be. Two RC motors were installed crosswise in front of the rear axle, their faster outputs driving the differential inside it. The RC unit was installed in the center of the chassis, and it pretty much filled the entire model, serving as a bearing frame. The model was literally built around the RC unit, with very little spare space – and most of it in the trunk area. The steering was controlled by the RC unit’s steering output, connected to a custom-built steering mechanism which was compact, low and robust, but which also provided a rather limited steering lock. The RC unit’s auxiliary output was used for front and rear lights. This allowed to turn the lights on and off from the remote, which is why they are off in some parts of the video – operating them was simply too distracting on some sections of the track.

I wasn’t entirely happy with the look of the model, for two reasons. First, after I have carefully re-created the livery and all the stickers from the original Hoonicorn, I tried to have them printed on sticker foil, but I couldn’t find any solution to printing white, and the foil proved semi-transparent even when printed, making all decals fade and show model’s black body beneath. In the end, I had an entire array of stickers printed on a standard sticker paper, which wasn’t perfect in terms of quality. Second, since the model has no interior to speak of and had to weigh as little as possible, the entire body was made of a number of separate thin pannels – the sides, the rear, the roof, even the bonnet. Only the front end was more complex and integrated into the frame around steering system to better withstand head-on impacts. This has limited my options in shaping the body, which was particularly apparent from the trunk, which looked like a simple box, just attached to the car somehow.

I have tested and filmed the model at RCDriftPark track located in Warsaw, thanks to its friendly owner. As it turned out, the model was just about the size of hobby-grade RC drift cars, while being a little lighter and generally on par with performance. It was pretty fast with the right batteries – the RC motors performed much better with Eneloop AA batteries than with freshly bought Duracell ones – and it handled reasonably well, despite poor steering lock and despite its steering geometry being dead simple in comparison to that of the RC cars. Once I got the hang of it, I was able to make tens and tens of laps largely at full speed, with no collisions. For drifting, I have replaced rear wheels with solid plastic rims without any tires. This allowed to spin the car, but did not allow an actual drifting – according to the RC drift enthusiasts on the scene, it was because of the front wheels having too much traction. Sadly, spinning turned out to be harder to control than speeding and I have quickly crashed the model.

I was quite happy with the model – it wasn’t ugly, it looked authentic enough, and it performed nicely. I was only unhappy about paper stickers which were ugly and also difficult to remove – neither of which would be a problem if the car had light-colored body, allowing me to use foil stickers.

Photos:

Video:

Media coverage:

Bild (German), Legomanija (Lithuanian), The Lego Car Blog