Blakbird

Moo!

I was going to say you posted the wrong picture because I couldn't see any minifigure in that image, but then I realized it was that tiny little speck next to the treads!

I've built both. The pony car is much smaller and more compact. They are both excellent, your choice would be based on what you are looking for. Since you already built the Predator, I'd recommend going with the pony car for something different.

Very well done! Looks like that base unit would be a competent trial truck.

I don't really know why they would do that. I don't own any of the (few) sets that ever included it.

That part actually exists in a form which has the pins permanently attached.

I liked the old 20:1 planet drives that could be added in series with the 4.5V motors. This made it very easy to adjust torque and speed as desired, and one of them even had a 90 degree output for driving car axles. Sadly, they only ever came in Supplemental Set 872.

The 8232 helicopter has exactly the function you are talking about. Take a look.

The next function is the anti-torque pedals. On most helicopters these would control the pitch of the tail rotor, but on a coaxial helicopter they must control torque on the main rotors. This animation shows the system. A pair of interlinked pedals (green) on the right and left side of the cockpit work in tandem. As one pedal pushes forward, the other comes back via a set of 8 tooth gears. A crank then drives the orange link which connects to an L-shaped crank at the aft end. A tie rod connects this crank to an axle with a 12 tooth double bevel gear. Movement of the gear lifts the purple rack assembly up and down. There are stops in the structure (not shown) to limit the motion. The down stop also supports the weight. A pair of yellow 16 tooth spur gears inside the purple bracket attach to the rotor shaft and lift the whole thing up and down. This results in the entire upper rotor head translating up and down. Since the upper swashplate is fixed, this changes the pitch of the blades. This closeup shows the pitch change in more detail. Note that the angle goes both positive and negative. This whole system is nearly, but not quite, like a real coaxial helicopter. The change of the upper rotor blades' pitch would indeed produce a torque differential and therefore result in yaw motion, but it would also result in a major change in lift which would have to be compensated by the collective. On a real coax, the anti-torque pedals simultaneously increase the pitch on one rotor while decreasing it an equal amount on the other. This still results in yaw, but the overall lift is held constant. The only thing left to animate is the cyclic which will be the most difficult. No one has replied to this thread for a while so I'm not sure anyone is still interested. If not, I won't spend the time on it.

Next I'll present the power system that drives the rotor rotation. Both rotors are powered by a single XL motor. The yellow and blue rotor shafts are concentric and counter rotating. The weight of the blue rotor is supported by the lower turntable. Rotational power is passed from the lower turntable to the rotor head via the vertical 1x8 plates shown. Rotational power is passed from the rotor head to the swashplates via the torque links (scissors mechanism). The weight of the yellow rotor is supported by a stop bracket at the lower end around the 16 tooth drive gears. The yellow swashplate is suspended from the rotor head vertically by 3 links and rotational power is passed through torque links. This closeup of the drive system shows how the counter rotation is accomplished. The orange drive gear powers the green and red axles. The green axle drives the ring gear of the blue differential. This diff passes through the turntable and is anchored to the upper half. The red axle drives the yellow rotor. The reason for using two gears is that the entire yellow axle translates up and down with the rudder pedals. The spacing of the red and yellow gears allows them to remain engaged during translational motion. An XL motor may seem excessive for doing nothing but rotating a shaft, but there are good reasons for it. Firstly, it has a low speed which eliminates the need for a lot of gear reduction. Most importantly, the turntables have a lot of friction so it requires considerable torque to rotate them. The new turntables would probably work better. Since neither the internal or external turntable gears are used, the new turntables could probably be dropped in with no modifications.

That's because Bricksafe has changed their IP address. Just change the IP to www.bricksafe.com and they should all work.

I just had to go pull out my copy of Need for Speed:Carbon and fire up my blue GT-R again. Thanks for the memories.

Very nice machine! I've built Nico71's machine, but while it is called a "braiding machine" it does not actually braid. Rather it twists. Your machine does a real braid. Now can you make it work on my daughter's hair?

The rechargeable battery allows speed control. At full speed, it is already way too fast for proper stability, so I would not advise adding any more speed. I found that there is great variation in the turntable friction. The upper swashplate barely worked in the first version I built. Then I changed to a different turntable and now it works great. I tried lubricating them but it didn't help much. The thrust load is low.

I'll start my review of the functions by reviewing the collective mechanism. In any helicopter, the collective lever "collectively" changes the pitch of all the rotor blades which has the effect of increasing or decreasing lift. In a coaxial helicopter, the pitch of the blades on both the upper and lower rotors must be adjusted together. The orange lever sits between the seats. The blades have a neutral pitch (zero lift) when the lever is down. As the lever is lifted, it moves the orange mechanism. At the ends of the mechanism are a pair of 12 tooth double bevel gears. These gears lift the entire yellow collective gimbal assembly as shown. The blue parts of the lower rotor head rotate counter clockwise, and the red parts of the upper rotor head rotate clockwise. The dark colored portions (dark red and dark blue) translate up and down with the gimbal assembly while the other portions remain fixed. As the swashplates go up and down but the rotor heads remain in place, the links change the pitch of the blades. You can see the pitch changing from neutral to positive. The torque links between the swashplates and the rotor heads cause them to rotate together. Here is a closer view of the collective motion without the rotor rotation making it easier to see the blade pitch change. Feel free to ask any questions about the function. Since I'm sure there will be questions about how I made the animations, suffice it to say that this is the most work I've ever put into such a project. I derived all the equations of motion for each moving part by hand as a function of time, then used POV-Ray to animate one complete revolution. In some later posts, I'll discuss some of the more difficult math involved for anyone odd enough (like me) to be interested.

That was just the IP address of Bricksafe which has since changed. Sorry about that. I've corrected all the links in the original post.

I'm glad everyone is pleased about the instructions! I had been waiting to build this model for a long time. It is one of the best representations of a functional rotor head in LEGO that I have ever seen. The cyclic, collective, and pedals are all fully functional. Technically though, it is still not a fully articulated rotor head because the blades cannot flap or lead/lag, they can only feather. A fully articulated head can pivot on all three axes. The lower swashplate is supported by a 2-axis gimbal and is therefore quite stable. The upper swashplate does not have a central spherical bearing support and therefore it can "orbit" slightly. The instability is more noticeable at high speeds. The upper rotor is just held by an axle so it is not very stiff. However, as a demonstrator everything works fine. I built this model last weekend to test the instructions and I must say that I love it. It is huge, technical, and impressive. It is a wonderful way to show novices how a heli rotor system really works. This is a topic that is very hard to convey in words, but becomes much easier when you can see it with your own eyes. Over the next few days I will be posting some pictures and technical explanations of how the model works. I'll start with a global overview: The yellow parts rotate in one direction and the blue parts in the other direction. The red parts comprise the 2-axis gimbal which drives the swashplates. When using the red collective lever, the entire assembly goes up and down. When using the green cyclic levers, the swashplate tips either fore-aft or sideways. The orange pedals lift the entire yellow central drive assembly. The white XL motor powers it all. Everything you see in the image are moving parts. Ruminate on that whilst I prepare the next pictures!

Sadly, those rear wheels and tires are unique. There is nothing else to match them in size and width, and they are perfect for F1 models (in fact that's what they were made for).

Very nice! What size tires does it use? Is it as big as your Kenworth 953 oil field truck?

I suppose it couldn't hurt to try! I even thought of stuffing the inside of the tire with something to prevent it from squishing and effectively increasing the diameter.

Fantastic video. Makes me wish I was there with you!

I taped the paper to the table to keep it flat and watched closely when the wheels were over the edge. I didn't see any problem. I removed the 2x4 Technic plates and old 8 tooth gears that you were using for wheel spacers and replaced them with standard 1/2 bushings. This only makes about a millimeter of difference on each side, but what a difference a millimeter makes! The curve is much closer to joining properly now, however you can see that the wheels are still slightly too far apart. Sadly, there is no way to move them any closer together because they are already right against the main frame. I observed the model very closely while it drove and I noticed that the wheels pry apart noticeably at the bottom which effectively adds more space between the contact patches. I'm not sure how to counteract this. Ideally the tires would have a somewhat lower friction coefficient.

That's odd, I did not find my copy to be very fragile except for the mud guards. Your model and video look wonderful though!

Last night I finally managed to get my machine to draw the entire curve. This was made possible by the map which allows me to know where in the curve I am starting. The picture below shows the results. As you can see, it didn't quite work. There was a significant gap between the starting and ending points much larger than what Alexander got with his machine. If you look at the predictions of what will happen if the angles are slightly off, you can see that my curve resembles the result with 88 degree turns. This implies my wheels are too far apart. I tried pushing them inward and drawing again (the orange curve), but it is still not right. So how far off am I? In a previous post I said: According to LDraw, the outer diameter of the tire is 204 LDU which is about 81.6 mm. (This isn't quite right because the tire deforms, but it is good enough for comparison). This means the spacing between the tires should be twice this or 163.2 mm. If we solve for the spacing for an arbitrary turn angle, we get W=PI*D/theta. When theta is 90 degrees (PI/2 radians), then things cancel out and we get 2D. But what if I use 88 degrees? Then the spacing would be 166.9 mm. This implies my spacing is wide by about 3.7 mm which is not a trivial amount. Alexander was very careful to impose a certain spacing, so this result surprises me. Why is my model off? It is possible that it is my paper. I am using a relatively "sticky" paper which has some texture. This provides a lot of traction for the model which may change the pivot point in unexpected ways. Tonight I will swap some parts to change the spacing and see what kind of difference it makes.

I've made a slightly updated version of the PDF instructions and posted them here. I replaced the tires with the correct version, added a cover page, and added the "road map". Having built this model from the instructions, there were a couple of things that were not ideal about the build order or step view but it was good enough to build the model which is all I was going for. Enjoy!