Full Option Ultra Hotshot

[LongRat 616]

Been racing and upgrading my Hotshot for a while now, and most of the changes are now complete.  The intention is to make the Hotshot as good a track racer as possible, without detracting from what I believe are its identifying characteristics and aesthetics.

There are several durability and handling issues well known to Hotshot runners.  Many were addressed in the later models in the HS series to a greater or lesser degree.  From a racing perspective, front end durability was my biggest problem.  The first time I touched a track marker it ripped apart the front gearbox.  This was simply addressed with some aluminium front pin braces, which also call for new steel hinge pins and e-clips.  I'm not a huge fan of e-clips but in this case the space available was limited.

Here you can see the top pin brace and there's another similar one bracing the main wishbone pivots as well.  Since fitting this car has seen some pretty hard tumbles and I haven't broken a gearbox yet.  An unforeseen benefit was much more positive feel in the front suspension.  Without bracing, the gearbox mounting points and arms themselves actually flex quite a lot, which takes up some of the suspension movement that should be transmitted to the monoshock.  With this flex removed, the whole front suspension feels a lot less spongy.  Which brings us to handling issue #1 - the monoshock.  I feel this is an essential part of the Hotshot and it just looks cool.  Unfortunately, its implementation could barely be any worse.  Way too soft to have any effect at absorbing jump landings, lots of friction from the flexing parts, mount points are well away from being inline with the damper shaft so large side loads are present on the shaft guides and seals, leading to rapid pollution of the oil with metal particulates, and the final killer - zero roll stiffness.  Yes, there is an anti roll bar, but it's completely ineffective flopping around everywhere and failing to couple the two sides of the car with any real capability.  To remove this problem I ditched the ARB and made up a torsion bar system to independently spring the left and right sides, using the existing ARB mounts on the upper arms and a load of custom carbon and aluminium.  This gives stiffness in roll, meaning there is balance in grip front to rear giving way more confidence in turns.  No more digging in at the front, causing either the rear to step out or the car to roll over.  It adds to the wheel rate in bump when both fronts compress, giving better jump landing.  The damping is still all in the monoshock - I added Schumacher 100wt silicone oil which seems to do a reasonable job.  Inline shock mounts would remove all of the stiction in the mono unit and improve the oil damping but that's something for later maybe.  All in I'm pretty happy with the torsion unit, of course it has adjustable spring rate simply by clamping the torsion bar at one of the alternative positions on the block.  Also ride height is infinitely adjustable by rotating the collar on the torsion bar clamp.

At the rear, while I really liked the clever 2-into-1 design of the kit monoshock, it was just too stiff, and didn't have enough travel.  I'm not a fan of the Supershot style rear mounted shocks, plus when racing they are very vulnerable to rear hits.  I much prefer the Hotshot II style system.  I did some rock sold aluminium mounts and a 6mm carbon tower that winds its way through the apertures in the roll cage without shouting too much about its presence.  This allows the fitting of long Pro-Line Powerstroke shocks which allow the chassis to bottom out on the ground before the shocks do.  Obviously these beautiful shocks are butter smooth too and I love the dual rate springing and Ti nitride shafts.  The rear suspension arms are custom out of Delrin.  It's the same material I used for the Jamie Booth Egress replica kits.  Same width as standard but with much needed 2 degrees of toe for improved grip and stability under acceleration.  I added adjustable top links made with 3Racing titanium turnbuckles and Traxxas rod ends.  I love the Kyosho Le Mans motors so had to include one on this - the Le Mans 480S.  Soft winds across pretty much the whole series though, that would not cut it.  This is running a hand wound Orion 9x2 armature.  Sounds like it would be too much, but the weak magnets in the Kyosho motor really limit the torque and violence this would otherwise have so it isn't too savage.  RPM is good though.  I have been running brushless on boosted 10.5 until now so we'll see how it goes.

From the top you can see my new roof part machined from aluminium sheet.  I extended it back to fit a Baja-style roof fan to cool the engine... er, speed controller.  I have a KO VFS-2 mounted behind the driver's head which is great for getting air to it (no chance of that in the standard radio box) and keeping wires short.  It is a very small ESC which allows placement here.

You can also see the custom mounts I did to allow large brick style LiPos to easily be fitted.  Loosen one grub screw and the carbon side plate can be slid out to change packs.  They are quite heavily engineered, shall we say, which should protect the motor from side-on hits.  I almost forgot, the first thing I did before anything else was sort out the bump steer in the horrible standard system.  There are large stand-offs on the steering knuckles to align the drag links properly and a carbon double bell crank system squeezed in to the chassis internals.  It's a tight one, but there is some breathing space now I have relocated the ESC.  This pic shows the Novak Kinetic I was using before.

Looking forward to racing this car.  Please post comments and observations or any other tips or upgrades that might be useful for HS runners/racers!

[kontemax 1725]

Excellent job, as usual!

I realized some years ago a similar steering linkage using some Egress steering links and steering plate.

I also agree on Hot Shot 2 rear damper configuration. I believe that the rear shock tower is a piece of art, like the front torsion bar.

I resolved the flex of the front end using two braces, up and down, between the front arms and I decided to have an inline mount front mono shock. I replaced the Boomerang/Hot Shot 2 front plastic damper mounts with carbon ones. This reduced the general flex in the front end. I made another modification, that I suggest you. Replace with some delrin part the two plastic plates that accomodate the ball connector of the front hubs. You have the experience, the materials and the machinery to make a good job. This will reduce the slop and the flex of the front hubs.

I really love the rear arms with the toe in, obviously.

I will remove the rear dummy resistors, they are useless and hide the piece of art of the rear tower adding useless weight.

I will think to a rear anti roll bar.

 

Max

[matman 1499]

Well , this looks like a peace of art . Love it !! . 

So when are the parts going to be avaliable   . 

[LongRat 616]

Thanks guys.  Max, some good advice there.  Currently my standard front arms with ball connectors have absolutely zero slop.  Perhaps an improvement over the vintage Hotshot, or maybe I haven't run my car enough in dirty environments?  However, to balance the colour of the arms front and rear, I do have the tooling necessary to machine duplicate front arms from solid Delrin to match the rears.  I could then make carbon plates to attach the monoshock.  I'll be honest, I was going to do that only if I smash the front arms up, and so far they have been durable.

Matman - no plans to sell parts, just enjoying doing something for my own cars this time.  But maybe later.

[matman 1499]

It would look great with the blue arms as well , So go on enjoy building the new arms & get more out of the hotshot

performance & that would make the look even better , A matching set .   . No pressure here !   .     

[shenlonco 1156]

Cool hot shot!

[kontemax 1725]

If you make the new arms don't do them straight but bent in the middle, like the Bigwig.

This will avoit to touch them inside the rims when the damper is full extended.

 

Max

[Hidalgo 0]

Awesome mods. Love the changes you have made.

 

[Buggyjam 144]

Did you make all those parts? The front anti roll bar looks amazing. So much engineering you've put into that. Is it CNC type stuff?

[LongRat 616]

Yes, I made everything on this that is custom.  One of my other hobbies is CNC machining and machine building.  By the way, the bar at the front isn't an anti roll bar (unlike the stock Hotshot), it is actually a pair of independent torsion springs.

[VagabondStarJXF 350]

2 minutes ago, LongRat said:

Yes, I made everything on this that is custom.  One of my other hobbies is CNC machining and machine building.

Awesome. Do you/Would you take requests?

Just kidding (I think... or maybe just half kidding! lol). I'd wanted to take up machining back at the beginning of the millennium, my other hobby is paintball marker building/customising, but I couldn't afford the machinery. Don't have the money or the space. 

I gotta say, your work looks really clean with no obvious tooling marks. Is everything you've made milled out of aluminium? And was everything polished and/or anodised?

[LongRat 616]

None of the stuff on this car was polished or anodised, pretty much all of it is straight off the machine.  The surfaces are decent, that's down to the machine being good, basically.  And I have quite a bit of experience with using it.  I make stuff in all materials, aluminium alloys, steels, titanium, lots of carbon fibre and also machined plastics.  I am almost finished building a 3D printer which I will use to make ABS and nylon parts for my cars too.

I do make parts for lots of people.  Can't at the moment because I am building a new workshop, but plenty of members on here have bought my stuff.  Check out the Jamie Booth Egress thread, that was the biggest project I have ever done.  17 full kits of parts, with all screws and hardware also included plus instructions and box.  I'm unlikely to do anything that ambitious again.

[Buggyjam 144]

Awesome skills. I'm already thinking of the projects if I had those skills. Let's see, full size Donald Campbell bluebird replica jet boat, top gear style rocket. The list is endless 

 

i did did a bit of machining during a failed career attempt as a merchant navy engineer cadet. Can't remember much of the skills as it was twenty years ago. Got shown milling by hand, lathing, tap and die on a lathe, grinding all that. I made a fully functioning socket ratchet with attachments. All from scratch using the various machines around the engine shop. Since been lost 

[LongRat 616]

It's very liberating to be able to make anything you want.  I wouldn't want to be without that ability, I was lucky because I was introduced to this from an early age and encouraged to improve and develop my skills.  It's helped me hugely in my 'real' job too.  Anyone who is serious about making stuff could get into it, you can buy a perfectly decent lathe and mill for the price of a high-ish end RC kit each.  Maybe some reasonable tooling for another kit's worth.  Small benchtop machines which would not be a problem space-wise for anyone who has a dedicated bench space for building RC cars.  The cost barrier is not that high, space and practicality are issues for more people because of shared living, flats etc and actually having the time and perseverance to develop the techniques and skills is probably the biggest hurdle.

That said, with some common sense most people could make usable car parts within a relatively short time.  It just takes longer to get to grips with some of the more complex processes and honing the set up to get really good-looking results.

[Scouser 83]

Just spotted this thread. That Hotshot is absolutely fantastic.

One of my favourite aspects of the hobby is taking a car and making it more than it was designed to be (if that makes sense?)

I just love what you have done to the car, makes me want a HS and have a crack at it myself. Brilliant work.

[LongRat 616]

Cheers Scouser.  Here's a shot of it racing in the 2016 Revival.  Unfortunately multiple motor issues meant I qualified nowhere but a clean run in the final would have been good enough for a high placing in the A if I had managed it in qualifying.