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HPI Bullet Flux ST - Bulletproof the Bullet

I hope you checked the short review of the Bullet Flux ST truck I wrote some time ago in the Articles & Reviews section of the website, as this one is going to be more like a show off of the all the new stuff I added or changed on the same car. It was the underline note in the review that made me want to do something about tghe car. If we were going to drive it on 3S, it would break some of its stuff most of the time, and while steering was largely improved by making the front diff less stiffer, the handling suffered. So, on to the new things...

 

The middle of the car
I'm going to start from the least obvious addition to the HPI Bullet I made - a center differential. It wasn't really huge issue, and although it required some modifications, I think anyone who's not with two left hands will be able to do it, given they have a dremel and the proper parts. And the "proper part" was the Hot Bodies Hardened Differential (HBC8084-1):

Hot Bodies Front or Rear Hardened Differential

Of course I've changed the gear with a Spur gear (50T), which will result a bit higher than I wanted gear ratio - I used to drive the original 54T spur and 12T pinion with 4.5 ratio and now it is a 10T pinion gear, resulting ratio of 5 . Thing is - since the central diff also redirects more power to the ground and the original ration of the Bullet is 54/10, I'm still more into the speed section rather than going for acceleration, and the motor should actually run even less warm than before. I still plan to buy 8T pinion for when I need even better acceleration though I'll use the 10T for some time to get accustomed to it.

HPI Bullet Center Differential HBC8084-1

You will have to grind some of the main chassis plate - else the diff gear will hit one of the walls, and a you can see on the picture - you will need some kind of top plate that connects the motor and diff mounts (mine sucks, but it will do until I make another one).

HPI Bullet Center Differential CD HBC8084-1 with 50T gear

As you see, I also changed the servo - I used Turnigy servo before and it was very good, but now I had to move it elsewhere just because it was a bit longer. I took the Blue Bird Champion servo out of my Savage truck (its steering is awful anyway) and I should say it is very fast and has very high torque, but it has a small problem - its consumption is a bit higher than needed. I can always change it so it will stick there for a while.

Oh, yeah - I took the receiver out of its box. If I need it to be waterproof I'll just make it waterproofed.

One of the main problems with these 1/8 differential is their joint cup size. The bullet uses very small drive shafts and these are huge. Since I had the aluminium braces on the body and they don't allow any flex, I made a fair trade - the drive shafts are now fitted with a small O-ring on the original front/rear differential joint cups (those that hold the bevel gear) and small ball bearings in the bigger cups on the center diff. This only leaves me with the problem of how to deal with the small pins the shafts have - which I decided to ignore for now. I added rubber boots to all cups and filled them with heavy lubricant - a mix of MC-1000 (which I think is the best grease I've seen) and some STP Oil Threatment for gearboxes (which I trust to protect almost everything in my cars), which should reduce the wear level a lot - I still suffer the backlashes from the pins having too much space, but I'll look at this some other time.

 

The back of the car
One of the main changes at the rear end of our car was adding a sway bar set for the Bullet. Combined with changing the shocks with two of these threaded aluminum alloy shocks (I kept the original shock springs though), I managed to make a good combination, although I'm still wondering if I have to add another shocks set (I still have two new plastic shocks and those orange boots protectors, so I might do that anytime).

HPI Bullet Flux ST with sway bar (stabilization bar) and Threaded Aluminum Shocks

Having threaded shocks is great as it allows easy adjustments of the shocks reaction, and the bullet also allows you to change the ball end position (when it attaches to the lower arm) just as easily. I considered getting two big bore aluminum shocks, but then I had to change the silicone oil in them (I still might have to do that, the shocks are stiff).

Rear Threaded Shocks HPI Bullet Flux ST

 

The front of the Bullet Flux ST
For a time I considered addint a stabilization bar to the Bullet's front as well, but the bar tickness is a bit more than one might need for the car's front, so I decided to to leave it out for now. The front was very easy to move with just a couple of shocks (seems that one couple was filled with much thinner shock oil), so I added another couple and left the front a bit higher than usual. If you wonder why - I have attached small aluminum protector on the front bottom (just below the differential case), and I needed as little play in the front while still having good dampening force - this helps the center differential a lot, you can literally see the motor power going to the front instead of jumping back to the rear differential. I have much more nose-diving when the car stops, but less play when it accelerates.

Bullet Flux front with 4 threaded aluminium shocks

The list of changes ends with what might be the best HPI Bullet Flux ST upgrade ever - couple of aluminum C-hubs and steering arms with rubber-protected ball bearings. Itl needed some modifications - for example I added universal shafts to the front (afraid of losing all the bearings and a dogbone if the upper arm fails).

Bullet ST Flux aluminum C-hubs and steering arms with CVD kit

HPI Bullet CVD with aluminum C-hub and steering arms with ball bearings

As you can see on the image - I broke a steering ball end on one of the steering arms, and I couldn't get it out. The screw thread is somehow different and I really couldn't get the exact screws, so I had to tighten them with force - which is not that hard, it's just boring and those should have been with the same thread as Bullet's screws.

 

A word on differential fluids
If you ever decide to add center differential to your car - consider google-ing something as "tripple diff basics". I've gone another way - I never liked silicone oils. They are not lubricants, they change with time and they do not protect gears. So I thought - why not use real car petroleum-based or syntethic lubricants? They mix well enough with each other while you cannot mix them with silicone oil (believe me, I've tried). If you get your hands on very thick oil - use it! Else you can try mixing greasy with fluids for just the exact thinckness you need, but it is try-and-pray thing. Anyway - I used grease in the CD to almost lock it and a a thinner fluid in the front diff (thinnest in the rear differential). Now I'll pray not to see blown tires :)

 

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