Feb 19 2017

CakeSpinner

Category: Lego,TechnicsSpiller @ 02:58


I was looking through my Lego folders and found this 5 years old creation. I don’t quite remember why I made this, but it was probably to improve my earlier large turntable design to 8 wheels instead of 4. The small Technic turntables just aren’t strong enough to balance a huge construction, so using wheels was a good and simple solution.

It is a rotating design where all 8 wheels are powered. I quite like it, but since the 42055 Bucket Wheel Excavator introduced the perfect part for large turntables (and quite a few of them) I will probably use that in the future. (And that was an amazing set, especially at 50 % off.)


Of some reason I though of making a rotating cake plate would be funny, so I added a flat top and this ended up being the result.


May 04 2015

6×6 off-roader

Category: Lego,Mindstorms,TechnicsSpiller @ 22:17

I have been meaning to get this out a long time ago, but this model was characterized by delays, long delays.
Alternative front view Back view
This was supposed to be a quick attempt on making a 6 wheeled vehicle with steering on both front and back wheels, and all wheels having power. My initial model is a clear indication of my ambitions with this project:
First prototype
Somewhere along the road I decided to try to add pendular suspension and it slowly turned into a full blown project. Then I started delaying the project, with me not even touching it for periods of up to 6 months.

The steering module is the most important part of the build, with steering and drive being controlled from each side of the axle it suspends on. I tried to keep it small and strong, while including a differential. I tried to figure out how to get the power through the steering, but I didn’t manage to find a solution which was small enough, so I ended up using those Universal Joints. It is not a good solution, as only a little bit of friction actually holds the wheel in place.
Pendular module with steering Steering
To improve the amount of distance the suspension can work with, I made the connection to the spring so it can detach when the spring on the other side is being pressed together.
drop suspension Suspension example, diagonal view
Suspension example, front view Suspension example, side view

To keep the overall height of the model down, I placed the NXT motors between the modules, which worked rather well. As a side effect it also gave the build a very low center of gravity. One thing which required special attention was to keep a smooth surface to prevent the modules getting stuck on the motors.
The modules and motor drive
I do really hate the shape of the NXT motors though, it makes them nearly impossible to incorporate them into a space-efficient model.

All in all, I can’t really say I’m satisfied with the build. While the entire model is very robust, the wheels can easily pop off making the strength of the rest of the model kinda pointless. Also the suspension on the middle wheels should really have been something else than pendular suspension, as it causes the front or back wheels to lift off the ground.
One of my goals with the project was to learn how to do wireless bluetooth communication in C++ from my computer to the NXT. I did succeed, but I never got it polished up with joystick support as I wanted…

No webgl

Download LDraw file here


Feb 16 2013

Headphone stand

Category: Lego,TechnicsSpiller @ 17:31

The wires on my headphones kept breaking, so I decided to buy a set of wireless ones. The I bought the Sennheiser RS 160 which uses a portable transmitter, instead of the larger stationary RS 170. However the RS 170 transmitter duals as a headphone stand (and charger) and I would like to have some way of safely storing my headphones, so I built a stand in Lego Technics.

I had two ambitions, to make it look a bit more fancy than what I usually build and to mainly use pieces that I rarely use (as otherwise I would probably disassemble it if I needed them). When I noticed that large box with angled beams I never use, it seemed perfect for this.

Headphone stand made with Lego Technics

In the end it just became two plates with 4 straight beams built using angled beams, but I still think it gives it a nice touch.

The beams are not locked and are free to move, which should make the stand very unstable, however it is not. Partially because of the friction pins, but mainly because the beams are each placed at a slightly different angles than the others. So when the top plate wants to move in one direction, one of the beams will restrict this movement as the angle is slightly off. It is not perfect, but as long as you are not rough with it, it stands.

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May 01 2012

XOR gate

Category: Lego,TechnicsSpiller @ 09:08

As I mentioned in Mechanic NOR gate I was working on extending the NOR-gate to a compact XOR-gate and I finally succeeded in making a prototype of it.

My original idea to make it smaller failed, however after trying to think outside the box for a bit I finally made a breakthrough. Keshav Saharia made an AND-gate by surrounding an OR-gate with NOT-gates. I realized that this can be achieved by modifying an OR-gate slightly. Instead of enforcing the output to be true when one input is, you can get the AND-gate result by enforcing that the output is false when at least one input is too. Instead of pushing the output beam on true inputs, you pull it on false input like shown in the example AND-gate design below:

AND gate

With this much smaller AND-gate it becomes a whole lot easier to create a compact XOR-gate. My prototype as shown below contains two layers, one layer contains 2 AND-gates and one OR-gate while the bottom layer is a single NOT-gate.

Top view of XOR gate Bottom view of XOR gate

The reason I call this a prototype is that it contains the same flaw as Keshav Saharia’s XOR-gate, it does not reset its internal gates when a state updates. This could be solved by using rubber-bands like I did with my NOR-gate design. However I believe this approach to logic gate design is flawed and since it is difficult to do add this without increasing the size (and work well) I wouldn’t even bother.

The issue is that friction will continue to build up in the system when you start combining the gates, and those rubber bands makes it much worse. (I also fear that the rubber bands in one gate might affect another gate.) It is limited how much force these gates can function with. Small inaccuracies in how much the axles extend will also propagate throughout the system.

All those issues limits the amount of gates you can chain together and I don’t think it would perform well enough to complete a 4-bit adder (using half/full-adders).

So I want to try a completely different approach using continually rotational power as inputs and using gears to create the gates. One of the advantages is that gears can handle much much larger power throughput than the axle-beams approach. Secondly, by making it continuous you can more easily supply more power by embedding motors in the gates. The big disadvantage however is that it will use much more space and therefore also pieces. However if I can get it to work and I believe it will scale well I will try to get the gears/parts required.


Jan 30 2012

Linear 4-finger grabber

Category: Lego,TechnicsSpiller @ 20:02

I originally made this design for a small scale pneumatic robotic arm which included a multiplexed pneumatic control station. I here present you a revamped version of it:

Photo of grabber

(LDraw file available soon, my Brickshelf account is under maintenance apparently)

This design works with both with pneumatics and linear accumulators. The tubing will be a bit tight for the pneumatic version, but if you are worried you can just remove the axle which is in the way. It might also work with the small pneumatic piston which would create a very compact design however I don’t have one of those so I can’t try it out.

In the design each finger is a section of its own and every section is completely the same, just rotated 90 degrees each. I like it as it is something I rarely see in Technic models; mirroring is quite common however rotating is much less seen.

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Jan 29 2012

Mechanic NOR gate

Category: LDraw,Lego,TechnicsSpiller @ 19:20

Several years ago I tinkered around with making mechanic logic gates, so the LEGO Answers question: Is it possible to build simple logic gates with LEGO mechanics? caught my interest.

Keshav Saharia blog post Mechanical computation from Lego bricks was interesting, but I was not quite satisfied with his NOR gate. First of all the OR gate in it looks rather shabby in my opinion but most importantly it does not reset its state. It starts out in the TRUE position, but when an input becomes TRUE and the output becomes FALSE it will stay FALSE even it the input changes back to FALSE again. So I wanted to try making my own version based on Keshav´s design and the result is shown below:

Top view of my NOR gate  Bottom view of my NOR gate

(CAD file available, I just can’t upload it to WordPress and Brickshelf appears down at the moment.)

My version is a bit smaller as the frame is 6×8 instead of Keshav´s 6×10, but it does use a few more pieces. I’m not quite satisfied with my OR gate either as I’m not sure how much force it can transfer before becoming unreliable.

A rubber band have been added so the gate properly resets itself however it does create a new problem, more force is needed to go through the input in order to operate the gate. This is not a problem with just one gate, but imagine 10 of these stacked together and this force will become rather large.

So I believe that the axle approach will always be limited with that, because while most gates pushes, insert a NOT gate and it will start pulling which could pull the axle out of what might be connecting it.

I tried making an AND gate where the NOT gates are combined with the NOR gate (in order to make it smaller) but I didn’t succeed in making up a good design for the combined double NOT and OR gate. But inspiration have struck me and I have an idea how to make a XOR gate which will end up being about 6×12 and about 5-6 stud high. This will be my next goal.

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Jan 28 2012

9392 Quad Bike – review

Category: Lego,TechnicsSpiller @ 20:38

One of the new Technic sets, the 9392 Quad Bike, looked rather interesting to me since it has 3 springs, chains links and that the price is low as it is a small set. So I went ahead and bought one.

Assembled Quad Bike

Building

The build was fairly straightforward and if you know what you are doing it shouldn’t cause much trouble. If you are new to Technic it might be a bit tricky at times I guess, as the chassis is constructed of angled beams in an way which isn’t straightforward and there are sub-modules which again isn’t always straightforward to combine with the main model. The instructions are however clear about these areas and does also at times include extra clarifying illustrations of the assembly to make sure you did it correctly.

I don’t like how the pieces were sorted in the backs though. There were a lot of cases were I thought it should be in one bag, but it actually was in the other. For example, the 3m Technic pin was not in the same bag as the 3m Technic pin with Stop Bush, which makes no sense at all. There were 3 bags and they were NOT ordered.

The unboxing and construction of the main model took just under a half hour.

The model’s construction

I was positively surprised of the construction of this model. I have previously been a bit disappointed with Lego’s newer models which just feels weak in my opinion. This model only contains 182 pieces (+26 chain links), yet it manages to impress me. I really like how the chassis is constructed by angled beams and how those angles are used to add details to the construction. I also like how the front is made, it manages to get a cool looking suspension with steering while keeping the piece count down.

There are a few things in the construction which isn’t optimal though. The motor block is rather loose but most importantly, the chassis hits the ground before the front suspension is fully compressed. While I could live with the first, the latter is definitively a flaw in the design.

At times the part usage appears a bit weird, for example a 4m axle with stop is used where a 4m axle without stop actually would have been better, but I guess it is to make the available parts better.

But all in all I like it as it packs a fair amount of features using only ~200 pieces and looks rather nice at the same time.

Parts

This sets contains a lot of angled beams, in fact it nearly doesn’t contain any straight beams at all. I rarely don’t use those parts though, in fact I have a whole box of them which I never touch.

The tires, springs, motor block and chain links are a good plus, but it would be nice if there had been 4 springs instead of 3, as this would have made it possible to create a fully suspended car.

The rest is pretty much just normal pieces, but most of them are only in the 1-3 amount so there is a great variety, including some more special pieces.

Conclusion

While there are a few flaws this is definitively a good set and worth buying. The model is cleverly constructed and packs a decent amount of features, at the cost of being a bit more tricky to build. There are about 210 parts in it which are rather varied which makes it a good buy if you have a few sets already and want to spice your collection up.

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Dec 20 2010

Small Technic walkers

Category: Lego,TechnicsSpiller @ 18:28

In Computer Science class we have a course about robotics and we where given the task to build a walking robot using Lego Mindstorms (with a 2 hour time frame).

Due to the limited amount of parts available we settled on a 4 legged design. However after 2 hours of struggle we went home empty-handed. Being annoyed that it didn’t work out, I continued at home to build a simpler Technic model. Two hours later I had this:

4-legged walker

[youtube=http://www.youtube.com/watch?v=GCmyogVerC0]
(Sorry for the bad lightning)

Balance showed to be crucial to the walking performance, the two round 2×2 bricks sole purpose is to balance the walker as without them it became (even more) unstable. It was probably also the issue with the failed NXT model as it had a lot more weight and fell over all the time. (The motor speed might have been too high too though.)
Interestingly enough, the surface had an effect on how the model should be balanced.

6-legged walker

I have previously build another small walker similar to the above but with 6 legs. It showed to be a much better solution than the 4-legged version as the stability is much better.

[youtube=http://www.youtube.com/watch?v=KpDoNH0Ibnc]

There is also a CAD file, I will upload it to brickshelf or something later…

Bonus

Made this for fun, a motor and battery box is inside making it able to drive. It is not that great though since the motor connection is pretty weak.