Setting up an FRC Slot.It Challenge car

Tips to help you get your cars to run better
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gordon
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Setting up an FRC Slot.It Challenge car

Post by gordon »

FRC's Slot.It Challenge class is formulated to use Slot.It Group C cars and components, configured to make it easy to prepare a competitive car. Here are the basic requirements:

For Slot.It brand Group C cars only
  • Body: See Eligible Cars below. Body must comply with General item 2. Windows may not be tinted - interior must be visible.
  • Chassis: Standard for the particular model.
  • Interior: Standard for the particular model and must comply with General item 3.
  • Digital Chip: Slot.It brand only.
  • Motor: Standard Slot.It orange-endbell 21,500 RPM motor.
  • Gearing: Gears may be changed however axle gears must be Slot.It.
  • Motor Pod (where applicable): Motor pod may be changed but must be inline Slot.It.
  • Magnets: A single currently-available standard Slot.It "non-race" magnet (the one with the grooves) which must be positioned in any of the standard locations on the Slot.It motor pod.
  • Wheels: May be changed but must be Slot.It.
  • Axles: Standard for the particular model.
  • Tyres: May be changed but must be Slot.It.
  • Guide Flag: Free.
Looking at these stipulations, on the surface there's very little anyone can do to a standard Slot.It Group C car to improve its performance. However when you look at each area in more detail, there are things that certainly will result in a quicker, better-handling car. Let's look at each component listed in the regulations above.

Body:
There's really nothing that can be done to the body itself, however you can try loosening the two body mounting screws slightly so that there's a little "roll". This can help the handling in any slot car where magnet downforce is not very high.

Chassis:
Quite often a plastic chassis may be slightly warped, causing one wheel (usually at the front) to not make contact when the car is placed on a perfectly flat surface such as a tech block. If you want to test this without a tech block (you should invest in one, BTW), be sure to remove the guide flag.

If you find the chassis warped, you'll need to flatten it. This involves completely stripping it down to the bare chassis and following these instructions:

http://slot.it/Download/FAQ_PDF_en/1-Ar ... sis.en.pdf

Once straightened, take your time to re-assemble everything carefully.

Interior:
Nothing to do here. The car must retain the stock interior. Ultra-light Slot.It or other interiors are not permitted.

Digital Chip:
The class only allows Slot.It chips which is just as well since these are currently the best available.

Motor:
Motors generally benefit from a break-in period before running flat out. I have been through just about every method of motor break in, from underwater, underwater/alcohol mix and others. My current method is to run the motor at 3v, 6v and 9v, each for ten minutes. Be sure to put a tiny drop of oil on both shaft bearings before starting. Be careful on the end-bell side though - you don't want any oil getting on the brushes and commutator.

Gearing:
This is where fine-tuning can make a difference. Group C Slot.It cars generally ship with a yellow 28-tooth (28T) crown gear and 9T pinion, giving a 3.11:1 gear ratio (the rear wheels turn once for every 3.11 turns of the motor). This is actually a good starting point as far as gear-ratios go - its right in the ball park, however because there's a change you can legally make on the next item which involves a new crown gear, please read on.

Motor Pod:
Some Slot.It Group C cars ship with an inline motor pod with 0.0mm offset (part no CH13b). This means that the centreline of the motor shaft is exactly in line with the centreline of the rear axle when the car is viewed from the side. There is a change which you can make here that's perfectly legal which will result in the most significant performance improvement to Slot.It Challenge cars - replacing the standard motor pod with an offset pod. With an offset pod, the axle is pushed up higher than the motor shaft and the two centrelines mentioned above will no longer be aligned. This brings the motor pod and the magnet closer to the track, increasing the magnetic downforce on the car and thus improving cornering speed. Its similar to running smaller diameter rear wheels which may not be possible because most of these cars already ship with 15.8mm rear wheels and you really can't go any smaller because the crown gear may touch the track.

Slot.It models from 2012 onwards are supposed to ship with a 0.5mm offset pod, however you can install one which has a 1.0mm offset to get the magnet as close to the track as possible (part no CH24b). This is the pod I would recommend you use. One caveat (this is where my reference under "Gearing" above comes in): once you go to a 1.0mm offset pod, you'll need to use offset Slot.It gears. The number of teeth on offset gears are not differentiated by different coloured gears, they're all white. I use a fine-point marker to write the number of teeth on my offset gears. Another advantage of offset gears is that they all have aluminium hubs instead of brass, reducing unwanted inertia and car weight.

Finally, as with the body, you can try slightly loosening the four motor pod screws so there's a little "rock" in the motor pod. This may or may not help. You'll have to test it both with tight and loose screws to find out.

Magnets:
Although you must use the standard "non-race" magnet with grooves, you can choose whether to put it ahead or behind the motor (as it ships). Most people will want it in the standard position behind the motor. Also, all magnets are not created equal. It may help to buy a few and test which has the most downforce.

Wheels:
In most cases, the standard wheels will be fine. However, if your car has 17.3mm rear wheels you may want to consider going to 15.8mm, again to bring the magnet as close to the ground as possible. Slot.It also makes 16.5mm wheels so you have some options to get the ride height just right.

If you're one of those always looking for the most competitive edge, you can install ultra-light Slot.It magnesium wheels and you can also look for the widest rear wheels that Slot.It makes. Remember, front wheels are only there for stabilisation, so you don't need extra-wide fronts.

Axles:
Nothing to do here. You are required to use the standard axles.

Tyres:
You must use Slot.It tyres and for the rear I would recommend silicones which seem to be best for Scalextric Sport track like FRC's. Slot.It makes two silicone tyre compounds, S1 and S2. Some people like S1s, others prefer S2s. Both are also available in different sizes:

S1:
PT06 10.0x18.8 (approx. 19mm tall)
PT03 12.2x19.8 (approx. 20mm tall)
PT29 12.4x20.4 - These are for F1 wheels only. Not suitable for Slot.It Challenge.

S2:
PT1214S2 8.4x14.6 (approx. 15mm tall - very low-profile)
PT1167S2 10.5x17.8 (approx. 19mm tall)
PT18 10.5x19.9 (approx. 20mm tall)

I suggest you get one set of approx. 19mm and one of approx. 20mm. This will allow for fine-tuning the car's ride height (and gear ratio). I'll leave the compound choice up to you. Be sure that the tyres sit flat on the wheels and there are no high and low spots. Once seated properly on the rims, silicone tyres do not need truing.

Front tyres on a slot car are just there for stability and to make the car look more realistic, the reason why they are compulsory at FRC. The things you want to aim for with front tyres are minimal contact with the track surface and reduced drag. When placed on the track, try to have the front tyres just making contact with the track surface. Slot.It provides ways to adjust the front ride height using spacers or grub screws (or a combination of both). I like to use grub screws since they can be easily adjusted to raise and lower the front axle.

When it comes to the front tyres themselves, be sure that they sit perfectly round and flat on the wheels. There should be no high and low spots when you hold the car upside down and spin the wheels. If there are, either change the tyres or true them till the spin flat. Finally, although Slot.It make "zero-grip" tyres, you don't have to use these. You can easily coat the front tyres with clear nail polish after they are mounted to produce a friction-free rolling surface.

Guide Flag:
The standard guide flag is fine, however I tend to prefer one that screws in instead of the press-fit one that ships with the standard car. I particularly like Slot.It's screw racing pickup (part no CH85). When it comes to braid, I use and recommend Slot.It's tin plated copper braid, available in a 1.0m roll (part no SP18).

There you have it. Now go rebuild your Slot.It Challenge car to get it running as fast as possible!
RameshB
Posts: 599
Joined: Tue Jan 15, 2013 12:30 pm

Re: Setting up an FRC Slot.It Challenge car

Post by RameshB »

Thanks Gordon , you did a real good job with those setting up tips , its was very detail and informative which can add value to any slot car builder wanting to improve , thanks .
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