Initial impressions of the HPI Bullet 3.0 ST Flux

This post is a bit of a departure from the usual fair on this blog, but I wanted to document my experiences as there seems to be a dearth of information around about the radio control car I recently bought — the HPI Bullet 3.0 ST Flux.  My wife Ang took this great snap of it in action:

HPI Bullet 3.0 ST Flux on dirt

I haven’t had an RC car since I was a teenager (I had a Tamiya Frog which I’d modified pretty heavily by the time I’d finished with it, and an ill-fated Mugen Mercury) so I’ve spent a bit of time “re-learning” with regards to maintenance etc.

For this post I’m not going to go over what’s in the kit — there are some good reviews already around for that.  Instead, over the jump I go into more detail on the learnings I’ve made in use, perhaps providing some insight into what other owners might expect if they get a Bullet Flux themselves.

Replaced parts

Overall I’m really happy with the car, though I have given it quite a bash meaning that I’ve already had to replace a number of parts — specifically:

  • 101208: bottom bracket snapped after accidentally hitting a tree stump
  • 101213: cracked the front left bracket after mis-calculating a turn and clipping a gutter
  • 101211 and 101238: popped after mis-landing a jump at the North Ryde off-road track (and I couldn’t find it anywhere around the track)
  • 101229 and 101231: these don’t need replacing just yet, but already are showing significant signs of wear (see below) so I’ve ordered replacements in case

Worn drive train part 101229

Maintenance tips

Given the repairs I’ve needed to make, and an ill-considered romp on a beach (note: don’t do this — I had to pretty much strip the entire car down within 24 hours to clean it and stop the corrosion/rust from a 30 minute stint) I’ve had to do a fair amount of work on it in a short amount of time.

Overall I think the layout is well considered — the entire car is pretty much designed around a series of semi-self-contained modules:

modules.jpg

  1. Front suspension and gearbox
  2. Rear suspension and gearbox
  3. Battery tray + radio receiver + ESC
  4. Steering servo
  5. Motor and main drive gear

This is especially helpful for the front and rear drive-train and suspension, as you can pretty much remove these to clean etc. without disrupting the rest of the car.  One thing I did learn when removing the front, though, is that the steering pins that are mounted to the chassis shouldn’t be removed — I went some way to stripping the screw before realising this is best done by removing the top screws — so remove these:

Correct screws for front module remove

Not these:

Chassis steering column screws

I also found that when replacing the top-mounted screws that doing these up too tightly would result in the steering mechanism to be too tight — so I’d suggest tightening them just enough to stay put and perhaps use a bit of thread lock to keep them in place (checking them regularly to make sure there are no unexpected losses).

Some other notes:

  • While the car is supposedly “Ready to Run”, the ESC needs to be programmed before use — make sure you follow the (unfortunately somewhat unclear) instructions before your first run.
  • I added an extra shim in the back shocks to tighten them up a little — I found the initial setup had these a little too soft/light for general use.  I haven’t tried any further changes to suspension setup.
  • I had an issue with an accidental “puddle run” allowing water into the receiver compartment — even though this seems fairly safe from water, I’d recommend double-checking the receiver compartment if you have accidental water exposure.
  • I have learnt a lot about how to use LiPo batteries etc. through lots of research and talking to the store — but I’ll post I have documented my learnings on that topic in a separate post.
  • I’ve been cleaning bearings using this method but replacing WD-40 with methylated spirits (denatured alcohol) — I found the local camera store was happy to part with their canisters, and a tip: grab the white/clear film containers, not black 😉  I’ve only used the WD-40 for hard to get at bearings that are reasonably well shielded from dirt (as a temporary measure — I’ll clean them properly in due course) and the odd anti-corrosion stop-gap.  (As an aside, last time I actively maintained an RC car WD-40 was the answer to all sorts of maintenance questions.  It seems that this is not the best solution in most cases — for bearings etc. it gets gummy and sticky over time, and generally attracts as much dirt as it repels.)
  • I get about 10–15 mins on 5000mHa 2S LiPos pushing it speed-wise in open areas (e.g. larger parks) and about 20–25 mins in smaller areas (such as the North Ryde track).
  • The battery case requires the body to be removed and three pins to be undone before the battery can be removed.  One of the pins also juts out too far and has scratched away a portion of the body paint (I just turn this pin up to avoid damaging the paint work).
  • The body also gets caught on occasion when hard turning — perhaps a bit of a trim or slightly alternate shape would solve the issue.
  • I’ve employed an old trick to keep the body and battery bay pins in check — I used to use fishing line/wire to tether pins together so they were easier to manage.  I’ve discovered that using wire and crimps from my wife’s bead jewellery kit to be a more durable option.  Tethering them this way also makes them easier to remove, especially for the battery bay clips.

Overall impressions

I really dig this car — I’ve given it an absolute beating since I’ve gotten it (both intentional and some less intentional) and it’s held up extremely well considering.  Most of the issues with parts etc. can be traced to driver error (or over-enthusiasm!).  I ran the car yesterday at the North Ryde track and it ended up on its back more often then not as I learned how to handle the various jumps etc. and only popped a steering arm (and inflicted a bit of body shell damage which is to be expected).

Speed wise it’s certainly got plenty of go from my perspective and I disagree with some appraisals of the car as being under-powered.  On a track I barely get past half-way on the throttle, and on open areas it can definitely outrun the local dogs! Besides, I think it’s clear that the limiting factor is the drive-train durability, not the motor.

There is a lot of slop/play in the steering mechanism and front suspension which was a bit of a surprise to me, but as a “backyard basher” this isn’t a serious concern for me — however I would expect this to be a bit tighter in general.  Handling is ok — I will be interested to see how I go with the a higher-powered servo (see “Planned upgrades” below) and if that improves things in due course.

While I’ve not had recent experience with RC cars, I’ve found it easy to maintain and the instructions reasonably easy to follow (except for the ESC programming component).  The spare parts listing in the back has been very useful, and the staff at RC Hobbies have been exceptional in their patience with me both ordering part after part, but also sharing their knowledge on LiPos etc.  (I also found Familyland a good option for some parts when RC Hobbies have been out of stock.)

If I was to make suggestions to HPI for improvements to the car, they would be:

  • Improved instructions for the ESC programming — I wanted to increase the default threshold for LiPo auto-cutout and it was hard to work out how to change options and determine if I’d done the right thing. But even for the basic setup the directions aren’t all that clear.  Either that, or an easier to program ESC would do the trick — I know there is likely some limitation to achieve pricing etc.
  • Higher default auto-cutout for LiPos — from my research it seems that the cutout should not occur any lower than 3.2V per cell, and as far as I can tell the default is 2.6V per cell (this is the first setting in programmable mode and seems to be what the instructions advise).  As a user I expect the default to be the “safe” option, with the more aggressive options only available for those that know what they’re doing.
  • Strengthen the main drivetrain components — the amount of wear on the 101229 and 101231 parts is excessive in my opinion given the amount of use that the car has had.  Simply these should be stronger.
  • Higher torque default servo — given what I’ve read (and my experience), this servo should be a higher-torque model (such as the HPI SF-2).

Planned upgrades

I found that the servo that comes with the car, the HPI SF-1 wasn’t performing that well — it seemed to struggle to stay turned under power.  After a little bit of research it seems that it is considered underpowered for a car of this size.  I’ve just purchased a replacement from local store RC Hobbies — the DYS0213MG, which is overkill, but given the price was just AUD$4 than the more appropriate 10.5KG/cm model made most sense.

I also intend to grab the CVD shaft set (front and rear) at some point — though probably only as a replacement to the dogbones once they wear down.

I’ve also painted up a new shell for it based on the HPI Ford F350 shell for the HPI Nitro MT.  While it’s not a direct replacement, it fits pretty neatly (and was dirt cheap, part of clearance stock at RC Hobbies for AUD$10) and I think looks pretty good, even with a simple paint job:

Ford F350 Nitro MT shell on HPI Bullet chassis

5 thoughts on “Initial impressions of the HPI Bullet 3.0 ST Flux

  1. Pingback: LiPo battery primer

  2. thanks for the information really helpful, can you tell me what all the programmable mode settings mean!!!!

    Thanks

  3. Thanks Gary – glad it was some help. I worked out a couple of the more obvious ones, but I suspect I’m in the same boat as you… Figured I’d work them out when I needed to 😉

  4. Wow Grant
    I love your blog! Just enjoyed your movie reviews (mostly agree) and then this. I know little about modern RC cars but so want to relive my childhood and get one. You’ve got my interest piqued – bring it in to the office so I can take it across to Hyde Park and give it a whirl, wont you? 😉

    Cheers
    Tony

  5. Heh — I hadn’t thought about bringing it in… it’s a bit quick to run when there are lots of people around, but might be worth a shot at some point…

Comments are closed.