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Slash 4x4 LCG Stage 3: Prototype 1 and revision

Slash 4x4 LCG Stage 3: Prototype 1 and revision


Probably one of the most exciting parts about my work is receiving the prototype parts.  This is sort of where the “rubber meets the road” and especially exciting for a larger, multi-pieces project like the Slash 4x4 LCG kit.  When I received the FedEx box from our factory I immediately tear into it and start fitting the pieces on our brand new Slash 4x4 that was waiting.

As I was putting together the prototype, already I was thinking about improvements on it.  Mainly the chassis was what was bothering me the most.  Although it was narrower than the stock chassis, but it looks to be very wide and because we are machining 4mm thick chassis plate, the extra material of being wide also made the chassis heavier than I liked it to be. 


Often time with first prototype on a multi-piece project of this complexity we do not get to run the prototype.  There are sometimes tolerance and fit issues we have to address before we get a working prototype on the next try.  To be honest, this first prototype was no different, and while I was a bit disappointed that we were not able to put this first prototype on the track, it was still a very exciting start to finally see the first design in your hands instead of just being in the computer.

We went after a list of refinement for the next set of prototype:

1) Narrower chassis.  To prevent the now lower to the ground chassis from scraping and to save some weight, we have to figure out a way to narrow up the chassis

2) Moving the servo back.  This will straighten out the steering linkage movement making it parallel with the moment of the steering rack link

3) Extend the top motor screws lot.  This will allow the motor cam to slide out more for taller pinion gear for more gear ratios

4) Fix tolerance issue for motor mount.  The first prototype had the motor mount too close to the rear gear box and bind up the transmission a bit

5) Hole opening at the bottom of the chassis for steering linkage screw access.  Since the steering linkage from the servo to the steering bellcrank is secured from the bottom, a small opening would make this a lot easier of a process.

6) Wider upper deck.  Since we are moving the chassis post, to make sure there’s good support around the chassis posts new location, we widen the upper deck a bit and give it a better contour/shape. 

Our team went after these design changes right away.  In order to narrow up the chassis, we put the center chassis posts that also double as a battery block to keep it from sliding to the center shaft, now moved to the other side of the shaft.  To keep the battery from sliding into the center shaft, we used a low profile battery block that sits below the center shaft.  This narrowed up the chassis considerably on the battery side.  On the motor side, we basically kept the outside servo mount as the line and everything outside of this line stretched to the motor was cut and removed. 

(our design team went a tad too far in narrowing the chassis....not good for off-road with electronics hanging out, but might work for on-road GT-8 racing)

With these changes, we went from a 150mm wide chassis to a 125mm wide chassis, shaving off exactly 1 each worth of material.  This is a huge reduction in weight, and also improve the over look of the chassis kit.  It also pretty much eliminated the possibility of the chassis scraping the track during hard cornering.

However, a curve ball was thrown our way as we were trying to produce the second prototype.    The factory tried several attempt on bending the front kick up angle on this solid 4mm thick lower chassis and were not able to get consistent result for mass production.  So a new design had to be implemented for the front of the chassis.  The solution was to have a separate CNC machined billet aluminum front bulkhead with the kick up and this piece will "key" into the front of the lower chassis plate.  The whole front suspension and gear box assembly will sit on this aluminum bulkhead and held down from the top by the upper deck.  

While the machining and tolerance were not an issue for our factory, the durability of this area where the front bulkhead connects to the chassis would be where we focus on the most during prototype testing.  With all the refinements addressed, we look forward to the second prototype.  

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