F103GT High Speed Car - Novice driver!

[ChrisRx718 4470]

Many moons ago I worked at Time Tunnel Models in Stevenage, Herts. This is where my affliction with Tamiya started. 

At the time I had a very small fleet - a TL-01 and a TT01D. When the F103GT chassis was announced, I was intrigued. I was really taken with the bright red kit box too.

For the unfamiliar, this is what an F103GT looks like:

Pretty cool, right?

Thing is, it was really hard to drive. Especially for someone ham-fisted and very impatient. It would regularly spear off towards the nearest kerb under my control.

So my F103GT sat languishing on top of my wardrobe for a long, long time. Over 13 years in fact (and a few different wardrobes )

Today, that changed. I retrieved the sorry car and began cleaning it up: 

That's 13 years (give-or-take) of dust 

What's that tucked away inside the motor cage?

No wonder it was a bit of a handful to drive!

I've put this motor away as it's a bit special, I'll put it in one of my older more appropriate cars...

For this car my objective is simple; fast, straight-line speed. Car park zinger if you will. The gearing means you can go a bit nuts on this, so I have. I also went a bit mad with the power, keeping it brushed:

It's an LRP GT2 11x2 brushed motor. 

The thinking here is that -

a] I already had this motor kicking around, from god-knows where

b] It should be fun, right?

Onwards with the refresh. You'll be pleased to know I gave it a good clean. I also finally found an excuse to use this stuff, which (much like the chassis) has been sitting in the bottom of my pit box for years and years. It's basically a sticky grease, which you install in a fine layer between the friction 'discs' mounted to the T-bar at the back of the chassis. The discs are then under adjustable pressure via two tiny springs. Allegedly this works - although I'm expecting all this will do is attract dirt. 

Because this is all about top-end speed I fitted the largest pinion I had (29T) and the smallest spur (93T) resulting in a final drive ratio of 3.20:1

The LRP motor has a manufacturer RPM of 41,600 (@ 7.2v, no load). Theoretically, I believe this gives me a top speed in the region of 97mph 

So all assembled, trusty Hobbywing 1060 ESC and HobbyKing radio gear, Acoms AS16 servo (I really don't want a fast servo in this, given the objective). Adjusted all the end points and got the tracking straight (as far as my 8 foot back-and-forth through my kitchen would show me anyway).

Now at this stage it really was bed time. But I had a fully-charged LiPo (2S) installed and that top speed calculated seemed pretty amazing. 

"I wonder what that would make the tyres look like under full throttle?"

Well I couldn't tell you.

As I mentioned earlier, I'm not exactly one for thinking-before-doing. I knew the tyres should have 'ballooned' out (who hasn't done this before?!!) 

Without second thought, I pulled that trigger to full-throttle

Within just a split-second of having done that:

BANG

The tyre literally exploded. 

A flying piece hit me smack on the ear (like being flicked reaaaallllly hard)

Cries from upstairs "What the badword was that? Are you OK?"

Of course once I explained what had happened I was promptly laughed at.

These were a nice set of Tamiya Reinforced 1-Piece Spoke wheels with M2 radial tyres and inserts. Not a cheap setup by any means, and not cheap to replace.

The moulded tyre reinforcement literally flew across the room and even now I don't know where the piece of tyre went that hit me in the ear.

So that was my evening pretty ruined.

Finally; I fitted the car with a bodyshell. This NSX will be slippery and I messed-up the paint job on it so I'm not too precious of it. It looks pretty good though don't you think?

Notice the rear wheels are now some old pre-glued HPI wheels and tyres I had kicking around. 

That rear spoiler isn't going to do much for aerodynamics either (it's a drift wing). 

 

What's the point in going fast if it doesn't look good? And at least this way if it ends in a barrel-roll it will look cool!

Next-up - Let's take it out on the currently-empty roads...

[ChrisRx718 4470]

High-speed testing didn't go that great.

I went into this knowing that the motor exceeded the turn limit on the 1060 ESC of 12T with my 11x2 LRP motor, but I thought that as this was a lightweight, 2WD 'pan' car effectively, not a 4WD touring car chassis, it would be OK.

However it also states a max. RPM of 30,000 and I already knew above that this motor is rated to 41,600 at no load, at 7.2V (and I was running LiPo 7.4v too)

So I got about 6-7 minutes of runtime before it overheated and refused to go anywhere. Motor was like touching lava!

 

Note I swapped out the rear wheels for some of the ones out of my TA05R kit, they were much more supple and sticky.

Still, it span out like ******* with me at the controls. Only once did it properly 'wipe out' and strike the kerb with a thud, but it wears its' scratches with pride.

The chassis FRP plates fared well too:

And yes that is a 3S LiPo in the last photo. I thought I would really push my luck and my god this thing went like a scolded cat at only half-throttle, before lasting about 2 minutes and inevitably overheating again!

So what motor shall I try next folks?

Tamiya SuperStock Type RR?

Team Orion 21x2 Method?

I have got a 19T and 15T motors but I'm thinking I'll start slower and work my way back up 

I also have one of those cheap-o Trackstar Gyro things in my M-06 and upon reading @speedy_w_beans RM-01GT project thread I'm thinking perhaps I'll try that, it might counter the spinning-out. Whereabouts in the chassis should it be placed though? Front, rear, middle?!

Thanks for reading!

 

[Problemchild 2149]

Wow - love this

you are like an old school engineer with a “let’s see what happens” wahoo

it’s like the bloodhound SSC - radial loaf on those wheels is 50,000 x gravity 

JJ

[Fabia130vRS 2098]

I dont know how this could happen, we have tried speed runs with F103s on f1 wheels, 3s 13T witht a FDR of 1,68... and nothing happend, and you go just out there with a brushed motor and 2s and BANG ahah cant believe it.

 

it happens to be I have the same LRP GT2 motor. 

[wolfdogstinkus 1893]

Never "test" anything close to bedtime.

Chances are it's going to break and you'll spend another hour looking for spares or trying to fix it. 

I attempted a speed run without glueing tyres, lost a tyre on a football pitch at 12.30 am and must have taken half hour to find it. 

Looking forward to seeing a video. 

Even if it's just 2 minutes of crazy doughnuts. Lol

[speedy_w_beans 4272]

I'd mount the gyro either up front or in the middle.  Avoid the rear pod and the steering servo due to vibration affecting the gyro.  Some foam tape or some other isolation tape would be good to minimize vibrations reaching the gyro.

[markbt73 5316]

Ah, another RCer falls victim to the "let's put a ridiculous motor in a pan car" idea... always a good time.

I can't offer any advice on tires, because my speed-run days were on standard pan-car foam tires on an RC10L. But I can say that you should make sure the tires/axle are balanced, or close to it. And true. Vibration and wobble are going to slow it down and make it harder to control.

Also: gear down. Smallest pinion and biggest spur you can manage. It sounds counterproductive to speed, but it will help your heat problem a lot. If it feels like it's maxing out, then gear up a little, but start out with nice low gears. And I would guess the 19 turn motor is going to end up being the sweet spot.

That NSX shell looks great, but it's not as slippery as you think. Biggest problem with on-road cars and aero is air getting trapped under the body. If you get rid of the ground effects thingy in the back, and cut out the back end of the body (bumper and taillight panel), you'd be closer, but I could understand your reluctance to do so. If you have another old touring car body, with no wing and no mirrors, try that instead, but cut the back out. And FYI: barrel-rolls during high-speed passes aren't a matter of "if," but "when."

Have fun!