The set uses the NXT set and the F1 set and no other parts – no wierd old chain link pieces this time. Once again there are three motors, two at the back (one driving the wheels and one driving the engine) and one at the front turning the steering.

I built the NXT into the F1 car as I built from the F1 set’s instructions. This means the front of the car is very similar to the original and still has working suspension. The back of the car is almost completely redesigned, due to the size and shape of the NXT and motors, and the need for strength to hold everything together. The rear suspension has gone because it would make it impossible to transmit the power to the wheels through the universal (bendy) joints.

As for sensors, the ultrasonic sensor is built into the front wing to avoid objects. The light sensor at the back is used as a brake light, but doesn’t actually do any sensing!

 You might wonder how it can detect collisions while going backwards with no touch sensors. The answer is that by writing the program to monitor the rotation sensor of the motor driving the wheels it can detect when it has stopped moving and can take evasive action. I’ve done this by having a loop which resets the rotation sensor, waits for a short time then reads it. If it is zero, a boolean variable is set to flag that the car has stopped. Other parts of the program can then pick this up and deal with it.

 The software is pretty simple otherwise, I’ve made it act as a remote control car using the Lego Mindstorms Mobile Application. Like the roadster the engine can idle and changes speed with the wheels, and as an extra bonus, the brake light comes on when stopped.

Bigger versions of the photos:

I have taken a slightly different approach to most of the cranes I have seen on NXTLog. Rather than focussing on lifting heavy loads and making a working crane, I have tried to make a good-looking model that looks as much like a real tower crane as possible.

Lots more details, photos and a video after the link…

Crane Actions

The first problem I faced was that in order to get the full range of movements (hook up and down, hook forwards and back, rotating the jib) I would need to mount the motors on the jib (the horizontal part at the top of the crane). This would then mean I would need to mount the NXT itself on the jib, so the cables don’t get tangled. All of this would be very heavy and the supporting structure would have to be very large. I simply don’t have enough Lego, or space in my house, to do that!

The solution was to only provide two motorised actions, which are raising/lowering the hook, and rotating the jib. This enabled me to move the motors to the base of the crane, so the jib could be kept as light as possible. One motor rotates the jib via a set of joined together axles running up the side of the mast with small gears at the top driving the turntable the jib is mounted on. The other motor directly drives a spindle which holds the string the hook is hanging from. This is routed up through the middle of the mast, through the hole in the turntable and along the jib.

The base of the crane, showing the worm gear drive to the jib turntable on the outside and the hook string spindle in the centre

The centre of the jib, showing the turntable drive gears and the hook string running along the jib

It is still possible to move the hook along the jib, but this action isn’t motorised. The trolley part can be moved by hand along the jib, and rests on the rubber pieces from the NXT kit to stop it slipping. 

The front of the jib, showing the adjustable trolley

Stability

Keeping a structure like this stable is very difficult. A real tower crane keeps upright by being bolted into a concrete slab in the ground. The closest I could manage with Lego was to use a large grey base sheet to spread the load, with studded beams attached to it. The base of the mast is attached to these beams (you can see this in the photo of the base above). Because the beams are longer than the mast is wide, and there are many points of contact with the studs, the structure is actually very rigid.

The second aspect to keeping the crane stable is the balance of the jib. The jib is held flat by the strings running to the triangle shaped section in the middle. These are the support strings from the crawler crane that have round plastic studs at each end. Additionally, the weight of the front of the jib, trolley, hook and load is counterbalanced by the weighted bricks from the crawler crane set. This is adjustable by sliding it back and forth along the back end of the jib, to match the change in balance when the trolley is moved.

The back of the jib, showing the adjustable counterweight

The final aspect of stability is making the jib move smoothly. The turntable that the jib is mounted on was not particularly smooth at first, so I disassembled it and lubricated it using vegetable oil. I used vegetable oil as it is less likely to damage the plastic than some other things such as Vaseline. This made a significant improvement.

Control

The crane is controlled with the NXT intelligent brick as a kind of wired remote control. I guess I could extend it to use Bluetooth from my mobile phone, but I didn’t really see much point in that since it doesn’t move at all!

The controller 

The arrow buttons on the NXT are used to raise and lower the hook. The motor attached to the side of it is used to set the desired position of the jib. The program reads the rotation sensor on that motor and uses that to work out how many turns the jib motor has to go through to match it.

Finally

There you have it. The final version of the crane has a metal hook from an old Technic crane so it swings less, and the crawler crane’s cab is attached upside-down to the jib for the finishing touch!

 The driver’s cab

Here is a video of it in action

Typically my models are built over very long periods, in my free time. Spending extra leisure time learning how to work Lego CAD, cataloguing parts and producing genuinely useful photo sets to describe how to build something really isn’t my idea of fun. Similarly, the programming is nothing particularly special and I tend to just hack it together – I don’t want to have to spend more time making it suitable for public consumption as I spend quite enough time in front of a computer doing programming when I’m at work!

For me, the most fun that can be had with Lego is the process of creating something new. Starting with an idea and gradually turning it into a reality. Putting the bricks together is only a very small part of the process. I might even go as far as to say that the end result is relatively unimportant. After all, you don’t really need another Lego model!

I suggest that those of you who are interested in building a model like one of mine, or anyone else’s you see online, use these resources as inspiration for you to create something truly original and creative for yourselves. You’ll enjoy it, I promise!

 If you do get inspired by anything you’ve seen here, please let me know in the comments!

I’ve spent far too much time on this…

One of the things I wanted to do with the NXT before I even bought it was to build a working Lego car with proper rack and pinion steering, a differential to split power to the rear wheels and an engine that moved proportionally to the car’s speed.

My first attempt started with the 1:10 scale Ferrari F1 car (view on Peeron) and I tried to bodge the NXT and motors into it…

It was ok for a first attempt, but it looked rubbish and didn’t work very well. The design of the F1 car simply wasn’t strong enough for the weight and torque of the motors and the engine in its original position was completely obscured by the NXT brick. The engine also had the drive to the rear wheels going through it and the crank was very prone to coming apart.

I abandoned the idea for a while until I was reinspired by this post at The NXT Step Blog. It seems someone else had managed to build a very nice looking coupe from the NXT kit and the same F1 car. I started by building a rolling chassis with the features I wanted (proper steering, differential and working engine). The photo below shows it during disassembly.

I took some liberties by using other parts that I still have from before my Lego “Dark Ages”, notably the chain drive for the engine.  The engine is driven by a separate motor to the drive motor to reduce the stress on the crank.

The sensors used are the ultrasonic sensor at the front for collision avoidance, and a touch sensor at the back as a bumper. Additionally there is a sound sensor at the back. I couldn’t think what to do with that so it acts as emergency stop if I shout at it!

The bodywork started off as an attempt to cover up the workings, but gradually the thing started to turn into a sportscar.  The end result is below.

I created two programs in NXT-G for the roadster, one to automatically drive around and one to be controlled by my mobile phone using the Lego NXT Mobile application. The latter is much more fun and I’ve added various embellishments to it like a Ferrari badge on the screen, an engine startup sound and a horn.

Both programs use the same startup calibration routine for the steering, which turns slowly to the maximum extent in both directions until the motors stall, then uses the number of degrees between the two extremities to set the mid-point and maximum deviation for the motor. The steering is then controlled using a MyBlock to request a signed percentage value, with right being positive and left being negative.

The engine speed is controlled in a similar way, with a MyBlock that takes a percentage power and applies that to the rear wheels and runs the engine proportionally between idle and 100%. The engine can also be stopped, in which case the engine power MyBlock does nothing.

You can see video of the car in action under Bluetooth control below.

More photos…

Now, it doesn’t actually fetch the biscuits, but it does produce them on demand. Once the hopper at the front is filled with biscuits (digestives are particularly effective) then you need only reach forward for a delicious snack and the perfect accompaniment to a cup of tea will be pushed out to your waiting hand.

It is likely though, that this convenience could be taken for granted and the biscuits will run out quicker than expected. For this reason, the light sensor on top of the biscuit stack will detect the presence of suitable confectionery. When the Biscuitron’s stock is depleted, it will not dispense anything and will apologise for the inconvenience.

Extra photo and video after the link…