Bell B30D with tracks . LEGO model of the Bell B30D Articulated Dump Truck with tracks. This is another model in the scale 1:17,5 to fit my other models. It features: 3 sets of PF light units, XL powered drive, M motor powered articulated steering, M motor powered dumping and M motor powered air pump to operate the tracks. Of course it all operated remotely with a PF remote control except for the pneumatic switches which are operated manually.
. It was on a nice day in spring that I was out on my bike when I ran into this amazing piece of machinery. This Bell B30D articulated dump truck (ADT) with tracks realy caught my eye. With a little research I found out that this is only a prototype that is developed by the well known South African company Bell Equipment and the Dutch company Fuhler BV. That is all I know so far but that is enough to start building a model. From the very beginning I laid eyes on these Bells I knew I had to build a model out of LEGO one day. So I went back to those machines, there where two of them, this time I was equipped with my camera and I took as many pictures as my camera could hold.
The most inspiring on these machines where the tracks and the hydraulic system that goes with them. Let me start with it since this was realy challenging and this is what makes this model unique.
First thing I started to get into where the tracks. With the build of the excavator in my mind I knew it is not that easy to get a track system that runs smooth with the new LEGO tracks. From the very beginning I incorporated the turn table to make the tracks able to tilt. I use the Technic Turntable Large Type 2 a lot also to install wheels since this is a very strong solution to simulate hubs.
The pneumatic cylinder is used to tilt the tracks but also acts as a dampener. If the track would be free floating it could tilt unwanted when running into an obstacle.
Both front tracks act as a couple as both rear tracks do. With this I can tilt front tracks differently from the rear tracks and visa versa. I'm not sure whether similar real life dump trucks have all four independently operated tracks. To be honest if so I would not have installed this since there is not enough space anyway. To operate both pairs of tracks I have installed two pneumatic switches. The main switch is used to open or close the pneumatic system. The pump is operated remotely, but the switches are operated manually.
In real life both front and rear tracks are equipped with a single cylinder. Because of the use of air in LEGO pneumatic systems in stead of the use of oil like in real life hydraulic systems I ran into some issues. I started with a single cylinder on all four tracks as well and what happened is that the rear tracks started tilting and the front tracks didn't respond at all. This is not hard to understand since the front end of this model is way much heavier then the rear end.
To overcome this I installed double-acting cylinders on both front tracks. Building with LEGO is sometimes all about being lucky and I was. With a minor correction and the use of a small amount of parts I achieved a huge improvement. The system is quite slow since a lot of air has to be compressed, but it all works just fine.
With the limited space of this model in my mind I came up with this. Why not using the cabin to store stuff in. It is there anyway, it is quite large and can hold quite a lot of parts that I need to operate the tracks. I also wanted the cabin to be open and spacy like the real ones are. As you can see on this picture I located all three pneumatic switches around the drivers seat. At the last minute I came up with a nice detail. With all of its functions the operator needs dials and gauges to monitor all of this so I installed some.
Some people may have noticed that I have been working on an articulated dump truck before. The one I worked on back then had wheels and it never realy happened to be honest, but that is not what I was about to tell. I realy had issues building the dump with its tapered and wedged shapes allover and I sort of gave up. To be honest that was a good thing to do back then, I had so much to learn first. With the build of this model I realy had to get the dump going. So I started with the bottom since it's easy to start with. As you can see the picture shows a little detail of the studs I used to get angled shapes of the dumps walls. I used a bunch of modified tiles 4 x 6 with studs on edges and the old type of hing plates.
What I achieved is a quite strong and even light weighted tapered and wedged dump that is almost studless. To be honest, I'm proud of it!
Another very important issue to me is to get the dump angle for dumping the load as close to reality as possible. Seeing ADT's in action I always noticed the steep angle of the dump when dumping. This angle is 70° in real life so there was the challenge. Real life dumpers have long cylinders which are not available in LEGO so how do I achieve this, that was the quest. I came up with a solution that works quite well and I'm happy with the 62° dumping angle.
Two major keys to this success together with a load of luck again of course were: I geared down the M motor that powers the Technic Linear Actuators quite a lot and I installed two hard spring shock absorber 6.5L. By gearing down I was able to use a M motor, which was good since there is no room for a XL motor. The use of shock absorbers is a different story, I use gravity as a friend. When the dump is lowered the gravity will help it to compress the shock absorbers. The shock absorbers will help the actuators to lift the dump, I tested with and without the shock absorber and it realy makes a difference.
One more challenge for was the articulated steering. Again I want to get as close to reality as possible and of I go. Real life dump trucks of this type have two double-acting steering cylinders. The articulated steering angles with a 45° steering angle.
First designs worked with pneumatic cylinders, but that was a pain in the bud. It looks great when installed, but it works realy crappy.
Next step was to install Technic Linear Actuators since I noticed people using these for steering. I gave it a try for only one minute, but man are these things big. As mentioned before, this model appears quite large, but there is not much room. I've seen people using a single actuator in stead of two, which is a great ides, but for me not an option since this is not realistic.
So one option was left, using the Technic Linear Actuators Mini, but are those strong enough? Since I was running out of options, this one realy had to work. As you can see I came up with a very compact solution. I realy like it and yes it is strong enough! As with all linear actuators that I use I geared these down as well. This gives the actuators more power and a more realistic feel to it.
One little detail I realy like to share and realy helped me to get the job done. Where on earth do I put the M motor to power the steering system. It is behind the drivers seat right up, it's there but you won't even notice.
This image gives you an idea of how I managed to build a model of the Bell ADT. I am realy happy with the results, both looks and functionality, compare it yourself and let me know what you think of it.
I set my self some goals to achieve with the build of this model next to the challenges that are already there with the build of a LEGO model. The most challenging parts where the dump with its wedged shape, the tilting angle of it too, the tracks with there pneumatics, the angle of the articulated steering and of course where do I put all that is needed to make it actually work. This model appears quite big, but there is not much room to actually install and hide all its functions. One nice example is where to hide the IR Receivers...
Building my first truck back about 5 years now I came up with the idea of a limited slip solution for differentials. Unfortunately I never had to chance to implement it till now. To be honest did I use in a 6 x 6 truck before I build back then, but I never took any pictures of it or what so ever. So basically this is the first model with the use of this limited slip system that I have on display. The system is simple but quite effective. Both outgoing axles of the differential are connected using rubber belts with a single axle. So if one wheel start to free spin it helps the other wheel because the rubber belts forces the system to transfer power to the wheel with traction. The more rubber belts added the more the slip is limited, but this also increases the friction in the system.
With this image I do like to share a little on how I start on planning a model. As you can see this is the Bell B30D ADT with wheels. There are no official documents on the tracked version of this type. No problem at all since both the one with the wheels and the one with the tracks are exactly the same. With the pictures I took and the info on the wheeled version I had enough info to get it started. This image was used to determine the measures and as you can see I transferred it into studs, the numbers in brackets. For example the dumps length is 5318mm this is 304mm in the scale of 1:17,5 I work in and that equals about 38 studs. This is repeated with all important measures.
One note, since the tracked version has more ground clearance all vertical measures are related to the wheel hubs.