Post by xah on Dec 28, 2011 19:27:07 GMT -6
Hi all, I'm putting together some notes for our pack on some things they can do to improve performance (and very brief background on why each one works). I'd love some feedback 
I don't want it to get too technical or scientific, but I do want it to be accurate.
Thanks
edit: in case it's relevant, we're racing on the plastic supertrack (no center rail). Also, the aim is to cover only basic tricks, none of the more advanced stuff like 3 wheeling etc. For people at that level I will expect they will have done their own research and be beyond this basic guide anyway.
Pinewood Derby speed hints and tips
The rules are strict and don’t allow a significant improvement in any one area of your pinewood derby car, however there are a lot of small improvements that can be made which have the potential to add up, and make a big difference to the end product.
The goal is to make the most of the energy conversion from potential to kinetic, and remove anything that converts that kinetic energy into any other energy form.
The pack’s track has a steep downward curve followed by a long flat section. The car will convert the potential energy (the weight of the car) in to kinetic energy (movement) during the sloped part of the run (maximum speed is attained at the bottom of the slope), then the kinetic energy is depleted along the flat section. It will start to ‘run out of steam’ so to speak. Maximizing the speed at the bottom of the slope is based on the weight of the car, and minimizing the friction is what keeps the momentum going along the flat section.
Tools that will help in the construction of your car:
• Household drill
• Small metal file
• Sandpaper
• Coping saw for cutting the wooden block
If you don’t have any of these, other scout parents do, so ask around or ask the den leader.
Weight:
Fact: The heavier the car, the faster it will go.
Science: The stored weight (potential energy) is converted to motion (kinetic energy) by the downward force of gravity. It also means that the higher up the track the weight is, the more potential energy you start with (more to get converted to kinetic energy = more speed).
What to do: Get the weight as far back as possible. Get as close to the 5 ounce weight limit as you can without going over it.
Remember though: Not enough weight at the front will make the car unstable. Weight too high on the car will make it unstable. There is a tradeoff; an unstable car will bounce around the side rails slowing it down significantly.
Axles:
Fact: The straighter the axles, the faster it will go.
Science: Bent axles rub the wheel hub unevenly and cause friction, slowing the car down.
What to do: Get the axles as straight as possible. A simple way to check is to put the axle in the chuck of a drill and turn it slowly. Have a sheet of lined paper about 6 inches behind it, and focus one eye on the line. As you turn the axle, you should see the head remain in the same position. If it appears to go up and down, the axle is bent and needs straightening. The axles supplied in the kits are rarely straight.
Remember though: The axles are soft and quite easily bent with a hammer. It’s easy to make the problem worse by getting carried away. If the bend is slight, it’s probably best left alone.
Fact: The smoother the axles, the faster the car will go.
Science: Smooth axles have less friction. Friction is the conversion of kinetic energy in to heat (thermal energy). Converting the kinetic energy in to thermal energy is bad because it means there is less kinetic energy, which means less speed.
What to do: Make the axles as smooth as possible. Mounting the axle in a drill and removing the casting burrs (little lumps near the head) with a file, followed by polishing with a fine grit sandpaper will minimize the friction.
Remember though: A little lubrication will help reduce friction, but the rules are strict here.
Wheels:
Fact: Nice smooth round wheels will make the car run with more stability.
Science: Wheels which are not round, or which are ‘lumpy’ will cause the car to bounce around and be unstable. Any movement of the car that isn’t directly forward (for example bumping and bouncing) is using kinetic energy, which means there is less for forward movement.
What to do: Get the wheels smooth, by removing any inconsistencies on the surface with fine sandpaper. You can also polish the bore of the wheel for the same reason (the hole the axle goes through).
Remember though: the advantage here is small, and the inconsistencies in the wheel as supplied in the kit are usually too slight to even see. Concentrate on what you can see, and don’t get too carried away on this one. As the rules state, significant changes such as lightening or reshaping the flat area are not allowed.
Fact: A longer wheelbase (the distance between the front and rear wheels) will make the car more stable.
Science: If car needs to turn a lot (like in karting) then a short wheelbase makes it agile and easy to turn. If the car doesn’t need to turn (like in drag racing) then the longer wheelbase helps prevent it from ‘wandering’ and becoming unstable. As we’ve already covered, an unstable car is a bad thing.
What to do: Drill new axle holes in the body. Make the front holes a little further forward, and the rear holes a little further back. You can use a 5/64 inch drill bit (common in most sets).
Remember though: If the holes you drill are not perfectly square to the body, you will effectively be adding ‘steering’ to the car. As the track is completely straight, you don’t want any steering. Remember to keep within the rules (the wheels cannot extend beyond the ends of the body).
Fact: A car that runs straight will be faster than one that steers into the side rail
Science: Should be obvious, that dragging down the side rails will cause friction and slow the car down.
What to do: Make sure the car runs as straight as you can get it. Take a smooth plank of wood, draw a perfectly straight line down the middle. Lift one end enough to make the car roll under its own weight (make sure the plank isn’t tipping to one side – use a spirit level if you can). A 6 foot plank should have one end raised 6 inches, 5 foot plank raised 5 inches etc. You want the car to travel slowly enough that you can see whether it is steering.
Place the car at the raised end, pointing perfectly straight down over the line. Let the car roll. Ideally it should reach the bottom still centered over the line. If it doesn’t, adjust the angle of the front wheels and try again. Keep going until it runs as straight as possible.
Remember though: the axles are soft, as are the wheels. Don’t use too much pressure when adjusting the steering, particularly if it’s only a little out of straight.
Body:
Fact: A large flat front increases wind resistance, making the car slower.
Science: A large flat front means the air can’t flow around the car as easily, instead the car has to push the air out of the way rather than cutting through it (like using a vertical hand to push through water instead of a horizontal hand to cut through it).
What to do: Make the front of the car thinner. Even a simple wedge shape is an improvement. You can do it by drawing a line along one side of the car, laying it on the opposite side, then sawing along the line.
Remember though: make sure you don’t saw where the axles go in to the body. Once cut, there’s no ‘uncutting’! Also, the aerodynamic advantage is very very small on pinewood derby cars, so don’t cut it so thin that the car becomes weak.
I don't want it to get too technical or scientific, but I do want it to be accurate.
Thanks
edit: in case it's relevant, we're racing on the plastic supertrack (no center rail). Also, the aim is to cover only basic tricks, none of the more advanced stuff like 3 wheeling etc. For people at that level I will expect they will have done their own research and be beyond this basic guide anyway.
Pinewood Derby speed hints and tips
The rules are strict and don’t allow a significant improvement in any one area of your pinewood derby car, however there are a lot of small improvements that can be made which have the potential to add up, and make a big difference to the end product.
The goal is to make the most of the energy conversion from potential to kinetic, and remove anything that converts that kinetic energy into any other energy form.
The pack’s track has a steep downward curve followed by a long flat section. The car will convert the potential energy (the weight of the car) in to kinetic energy (movement) during the sloped part of the run (maximum speed is attained at the bottom of the slope), then the kinetic energy is depleted along the flat section. It will start to ‘run out of steam’ so to speak. Maximizing the speed at the bottom of the slope is based on the weight of the car, and minimizing the friction is what keeps the momentum going along the flat section.
Tools that will help in the construction of your car:
• Household drill
• Small metal file
• Sandpaper
• Coping saw for cutting the wooden block
If you don’t have any of these, other scout parents do, so ask around or ask the den leader.
Weight:
Fact: The heavier the car, the faster it will go.
Science: The stored weight (potential energy) is converted to motion (kinetic energy) by the downward force of gravity. It also means that the higher up the track the weight is, the more potential energy you start with (more to get converted to kinetic energy = more speed).
What to do: Get the weight as far back as possible. Get as close to the 5 ounce weight limit as you can without going over it.
Remember though: Not enough weight at the front will make the car unstable. Weight too high on the car will make it unstable. There is a tradeoff; an unstable car will bounce around the side rails slowing it down significantly.
Axles:
Fact: The straighter the axles, the faster it will go.
Science: Bent axles rub the wheel hub unevenly and cause friction, slowing the car down.
What to do: Get the axles as straight as possible. A simple way to check is to put the axle in the chuck of a drill and turn it slowly. Have a sheet of lined paper about 6 inches behind it, and focus one eye on the line. As you turn the axle, you should see the head remain in the same position. If it appears to go up and down, the axle is bent and needs straightening. The axles supplied in the kits are rarely straight.
Remember though: The axles are soft and quite easily bent with a hammer. It’s easy to make the problem worse by getting carried away. If the bend is slight, it’s probably best left alone.
Fact: The smoother the axles, the faster the car will go.
Science: Smooth axles have less friction. Friction is the conversion of kinetic energy in to heat (thermal energy). Converting the kinetic energy in to thermal energy is bad because it means there is less kinetic energy, which means less speed.
What to do: Make the axles as smooth as possible. Mounting the axle in a drill and removing the casting burrs (little lumps near the head) with a file, followed by polishing with a fine grit sandpaper will minimize the friction.
Remember though: A little lubrication will help reduce friction, but the rules are strict here.
Wheels:
Fact: Nice smooth round wheels will make the car run with more stability.
Science: Wheels which are not round, or which are ‘lumpy’ will cause the car to bounce around and be unstable. Any movement of the car that isn’t directly forward (for example bumping and bouncing) is using kinetic energy, which means there is less for forward movement.
What to do: Get the wheels smooth, by removing any inconsistencies on the surface with fine sandpaper. You can also polish the bore of the wheel for the same reason (the hole the axle goes through).
Remember though: the advantage here is small, and the inconsistencies in the wheel as supplied in the kit are usually too slight to even see. Concentrate on what you can see, and don’t get too carried away on this one. As the rules state, significant changes such as lightening or reshaping the flat area are not allowed.
Fact: A longer wheelbase (the distance between the front and rear wheels) will make the car more stable.
Science: If car needs to turn a lot (like in karting) then a short wheelbase makes it agile and easy to turn. If the car doesn’t need to turn (like in drag racing) then the longer wheelbase helps prevent it from ‘wandering’ and becoming unstable. As we’ve already covered, an unstable car is a bad thing.
What to do: Drill new axle holes in the body. Make the front holes a little further forward, and the rear holes a little further back. You can use a 5/64 inch drill bit (common in most sets).
Remember though: If the holes you drill are not perfectly square to the body, you will effectively be adding ‘steering’ to the car. As the track is completely straight, you don’t want any steering. Remember to keep within the rules (the wheels cannot extend beyond the ends of the body).
Fact: A car that runs straight will be faster than one that steers into the side rail
Science: Should be obvious, that dragging down the side rails will cause friction and slow the car down.
What to do: Make sure the car runs as straight as you can get it. Take a smooth plank of wood, draw a perfectly straight line down the middle. Lift one end enough to make the car roll under its own weight (make sure the plank isn’t tipping to one side – use a spirit level if you can). A 6 foot plank should have one end raised 6 inches, 5 foot plank raised 5 inches etc. You want the car to travel slowly enough that you can see whether it is steering.
Place the car at the raised end, pointing perfectly straight down over the line. Let the car roll. Ideally it should reach the bottom still centered over the line. If it doesn’t, adjust the angle of the front wheels and try again. Keep going until it runs as straight as possible.
Remember though: the axles are soft, as are the wheels. Don’t use too much pressure when adjusting the steering, particularly if it’s only a little out of straight.
Body:
Fact: A large flat front increases wind resistance, making the car slower.
Science: A large flat front means the air can’t flow around the car as easily, instead the car has to push the air out of the way rather than cutting through it (like using a vertical hand to push through water instead of a horizontal hand to cut through it).
What to do: Make the front of the car thinner. Even a simple wedge shape is an improvement. You can do it by drawing a line along one side of the car, laying it on the opposite side, then sawing along the line.
Remember though: make sure you don’t saw where the axles go in to the body. Once cut, there’s no ‘uncutting’! Also, the aerodynamic advantage is very very small on pinewood derby cars, so don’t cut it so thin that the car becomes weak.
