Knex Bi-directional Cart V2

This cart drives itself both directions on a rail. The key differences between this design and my first design is:

1. The cart changes direction when something lands on it, rather than when the cart hits a barrier
2. The cart can power extenal machines using the gears that stick out of it

Here is a video of the car in action:

I haven't counted how many pieces you'll need, but here is a list of the special pieces that are needed:

8 small gears

I used 4 blue gears and 4 grey gears. They can probably be used interchangeably. Be aware that the grey gears have way more friction than blue gears, so if you use grey gears where I used blue gears you'll need to change the way their axel is connected to the rest of the car.

5 medium gears

I used 2 red gears and 3 yellow gears. I strongly recommend using 2 yellow gears in Step 2.

2 large gears (recommended)

These are the external gears at the end of the track. When the cart collides with them, the cart should stop moving and these gears will turn. You don't need large gears at the end of both tracks, but if you don't have them then the cart probably wouldn't be able to power external machines.

4 ball and socket joints (recommended)

2 of the ball and socket joints could be replaced with red connectors. If you don't have any ball and socket joints then there are other ways of attaching the gears that need those joints. I'll explain more in the step that they're used.

Motor

Different coloured motors run at different speeds. This can affect how much friction there is between the cart and the track. If you have many colours of motors and one of them isn't working for you, try swapping it with a different motor.

4 Wheels

Use the "medium pulley" wheels so the cart stays on the track

4 Snap Caps (recommended)

These are the small black pieces that go on the end of rods.

This step includes the wheels and the bottom small gears. Be aware that there are tan clips on only one side of the frame.

When you're finished building the entire cart you might run into some problems, which might be fixed by adjusting the gears or changing the side that the tan clips are on. I'll explain more at the end of these instructions.

The blue clips on the end of the axles can be substituted for regular connectors, snap caps, or gear caps. I recommend against using connectors because they could collide with things close to the track.

These gears will stick out of the cart so that they can mesh with external gears.

There are two ways of attaching the yellow gears with their shafts:

Method 1 (easier but slower):

1. Slide the shaft into one side of the frame from the outside
2. Add the pieces to the shaft
3. Push the shaft all the way through to the other side of the frame

Method 2 (harder but faster):

1. Add all the pieces to the shaft
2. Slide the shaft into one side of the frame from the inside
3. Push the shaft further into the side of the frame that it's already in. Now the shaft should be lined up with the other side of the frame
4. Push the shaft all the way through to the other side of the frame

At this point in the building process, the frame of the cart should still be flexible, so method 2 isn't as difficult as it usually is.

These extra gears make sure that the cart is travelling in the direction that has most recently been pressed on.

This is the most complicated step of the instructions. There are three shafts that need to be arranged in a triangle, and each shaft has 1 or 2 gears on them. This mechanism will be able to tilt, which changes which gears will mesh.

When you're done there should be 2 silver spacers on the middle shaft that could easily slide off. Keep track of them so you don't lose them.

The snap cap pieces probably aren't needed. If you're using grey gears then there should be enough friction to hold the gears in place. I found that this part is easier to build when I include the snap caps because it helps hold all the pieces together.

Make sure the silver spacers don't fall off the shaft. Also, make sure you put this in facing the correct direction.

Here are two ways of completing this step:

Method 1:

1. Remove both straight connectors (aka dark brown/orange connectors) from the frame
2. Put the straight connectors onto the shaft
3. Clip the straight connector back into the frame

Method 2:

1. Twist one straight connector so it's facing up
2. Slide the shaft onto that straight connectors
3. Push the shaft through the straight connector a little bit
4. Rotate the shaft so it's facing the right way
5. Push the shaft back through the other straight connector

I designed this cart for a knex ball machine, which is why I have added arms that can hold knex balls. You don't need to build ball holders for this to work, but you should build something that sticks out of the cart that can be pressed by external things.

This top section holds the motor and three of the gears.

I used ball and socket joints because red connectors wouldn't be able to fit around the motor. If you don't have ball and socket joints then you could probably use hinges instead. If you don't have hinges then you could probably put the gears on yellow rods and hold them in place using a setup similar to what is happening in Step 2.

Make sure the gears line up. One of the small gears from the motor (Step 7) should line up with one of the small gears from the middle gear (Step 4).

Build a track for the cart to go on. The track can be as long as you like.

If you have any gold rods from the original roller coaster set then I suggest using them to hold the tracks the right distance apart. Otherwise you can use red rods.

The reason why I used a bunch of straight connectors instead of red rods is because when I used red rods the track was too bumpy for the cart to drive over it.

There are small hooks to put on the end of either side of the track that can be used to help the cart push off when it changes direction.

On either end of the track you'll probably want to put large gears. This is so the car can power mechanisms on either side of the track.

If you are building this for a knex ball machine then you should add additional rods attached to the gear, that will scoop the balls out of the arms from Step 6.

I apologize for not making clearer pictures for this step.

Things might not go smoothly at first. If the gears are jamming then there's probably too much friction between the wheels and the track. If the wheels are turning but the cart isn't driving then there's probably not enough friction between the wheels and the track. Here are some things you can do to change this:

1. Go back to Step 1 and change which side of the frame the tan clips are on
2. Push one of the bottom gears so it's not driven by the motor

There is a blue rod sticking out the bottom of the machine (Step 4) and some hooks on the end of the track (Step 9). These exist because sometimes the cart changes direction but it gets stuck on the large gears (Step 10). I suggest testing if your cart can function without those parts, since in my opinion the cart looks better without that extra rod.