Hello everyone!
Since TLG released 76023, I had been waiting for affordable Technic set which includes so-called Tumbler Tires. So I jumped at 42050 Drag Racer. I also bought some extra tires separately, then revived old project which had failed three years ago.
Avtoros Shaman 8x8
Weight: 2550g
- 4x L motor for 8 wheel drive
- 2x Servo motor for 8 wheel steering
- M motor for switching steering mode (AWS and crab)
- M motor for winch
- 3x LED for front and rear lights
- 2x SBrick powered by 2x 8878 rechargeable battery box
- Independent suspension for all wheels
- Working steering wheel
- Openable hood, doors and roof hatch
Back in 2013
As you may know, real Shaman is Massive Russian ATV which can go through almost any kind of terrain. It has three steering modes and can scale 45-degree incline. On top of that it is amphibious. Seeing pictures and videos, I instantly fell in love with it.
When I started the project, I was too ambitious to realize all features above. Sadly I could not build even steering mechanism while keeping all wheel drive and independent suspension. So I changed the project to building another 8x8 vehicle. It ended up as my Tatra 813 Trial Truck, but that is another story.
Focus on characteristic features
Two months ago, I suddenly came up with an idea that enables both normal AWS and crab steering. In the case of four-wheeler, you can do it by switching rotation of second Servo motor for rear axle. But in eight-wheeler like Shaman, you should change turning radius of second and third axle.
In normal mode, the steering angle of inner two axles is smaller than outer axles.
But in crab mode, all axles should be steered at the same angle.
This is the basis of steering idea. I used the way of fixing/moving pivot of steering linkage.
A: There are two 7L steering racks connected to 7L beams. Front rack is connected in the middle of beam, rear is one stud backwards. Both ends of beams are connected to steering arms of each axle.
B: In normal mode, rear rack is fixed by 12T bevel gear. So the fixed pivot of 7L beam is its 5th pin hole. Which makes front end of beam moves twice as rear end does. That means the steering angle of 1st axle is twice as 2nd axle.
C: In switching crab mode, 12T bevel gear moves one stud forward and fix front rack. Fixed pivot is 4th pin hole of beam. Which makes both ends of beams move equally. That means the steering angle of 1st axle is the same as 2nd axle.
And there is one more twist.
D: I put main steering rack (moved by pinion gear) on one stud forward of 7L beam's front-end (which means 9L beam’s front-end). Seeing from the pivot point, this rack is connected to farther than the point of front steering arms connected. So front steering arms always move slightly shorter than main rack does. When Servo fully turns 90 degrees, pinion gear moves the rack in one stud sideways. Steering arms move less than one stud. This was necessary for keeping CV joint (connected to steering hub) rotate smoothly even when fully steered.
Challenge and compromise
First of all, this MOC is NOT amphibious. It is too heavy to float. And because of driving motors of low position, chassis is not waterproof at all. So it is not recommended driving it through even shallow water pool. My aim was to achieve decent crawling capability. But I had to lower the bar because there was no room left for portal/planetary hub reduction. Without them, heavy load from 81mm tires directly goes to 12T half bevel gears.
First attempt was using two XL motors geared 25:9. I put each motor for left/right side of axle. The result was unsatisfied. Even when climbing over small obstacles, bevel gears often slipped and got damaged.
So I replaced them with four L motors geared 3:1. Each one drives a pair of half axles. Thanks to their good speed and smaller torque, new drivetrain proved to be more reliable. Although bevel gears were still slipping a bit, I accepted overall performance.
The picture above shows two L motors for driving right side of axles. The power functions switch for changing rotation of rear Servo motor is synchronized with moving steering pivot mechanism. In crab mode, rear 4 wheels steeropposite the same direction as front wheels.
As always I used few of non-Technic parts. Big roof tile was used for saving weight, curve slope parts were better choice for filling the gap. LBG axles sticking out the roof are visible indicator for steering mode. They are mechanically connected to switching mechanism. In the video you can see how they work.
Instructions of white version will be available. (Building it in red is possible by using red parts instead of white.) It will take more than weeks because building process was complicated. So please wait.
Original Topic: http://www.eurobricks.com/forum/index.php?showtopic=137034
Since TLG released 76023, I had been waiting for affordable Technic set which includes so-called Tumbler Tires. So I jumped at 42050 Drag Racer. I also bought some extra tires separately, then revived old project which had failed three years ago.
Avtoros Shaman 8x8
Weight: 2550g
- 4x L motor for 8 wheel drive
- 2x Servo motor for 8 wheel steering
- M motor for switching steering mode (AWS and crab)
- M motor for winch
- 3x LED for front and rear lights
- 2x SBrick powered by 2x 8878 rechargeable battery box
- Independent suspension for all wheels
- Working steering wheel
- Openable hood, doors and roof hatch
Back in 2013
As you may know, real Shaman is Massive Russian ATV which can go through almost any kind of terrain. It has three steering modes and can scale 45-degree incline. On top of that it is amphibious. Seeing pictures and videos, I instantly fell in love with it.
When I started the project, I was too ambitious to realize all features above. Sadly I could not build even steering mechanism while keeping all wheel drive and independent suspension. So I changed the project to building another 8x8 vehicle. It ended up as my Tatra 813 Trial Truck, but that is another story.
Focus on characteristic features
Two months ago, I suddenly came up with an idea that enables both normal AWS and crab steering. In the case of four-wheeler, you can do it by switching rotation of second Servo motor for rear axle. But in eight-wheeler like Shaman, you should change turning radius of second and third axle.
In normal mode, the steering angle of inner two axles is smaller than outer axles.
But in crab mode, all axles should be steered at the same angle.
This is the basis of steering idea. I used the way of fixing/moving pivot of steering linkage.
A: There are two 7L steering racks connected to 7L beams. Front rack is connected in the middle of beam, rear is one stud backwards. Both ends of beams are connected to steering arms of each axle.
B: In normal mode, rear rack is fixed by 12T bevel gear. So the fixed pivot of 7L beam is its 5th pin hole. Which makes front end of beam moves twice as rear end does. That means the steering angle of 1st axle is twice as 2nd axle.
C: In switching crab mode, 12T bevel gear moves one stud forward and fix front rack. Fixed pivot is 4th pin hole of beam. Which makes both ends of beams move equally. That means the steering angle of 1st axle is the same as 2nd axle.
And there is one more twist.
D: I put main steering rack (moved by pinion gear) on one stud forward of 7L beam's front-end (which means 9L beam’s front-end). Seeing from the pivot point, this rack is connected to farther than the point of front steering arms connected. So front steering arms always move slightly shorter than main rack does. When Servo fully turns 90 degrees, pinion gear moves the rack in one stud sideways. Steering arms move less than one stud. This was necessary for keeping CV joint (connected to steering hub) rotate smoothly even when fully steered.
Challenge and compromise
First of all, this MOC is NOT amphibious. It is too heavy to float. And because of driving motors of low position, chassis is not waterproof at all. So it is not recommended driving it through even shallow water pool. My aim was to achieve decent crawling capability. But I had to lower the bar because there was no room left for portal/planetary hub reduction. Without them, heavy load from 81mm tires directly goes to 12T half bevel gears.
First attempt was using two XL motors geared 25:9. I put each motor for left/right side of axle. The result was unsatisfied. Even when climbing over small obstacles, bevel gears often slipped and got damaged.
So I replaced them with four L motors geared 3:1. Each one drives a pair of half axles. Thanks to their good speed and smaller torque, new drivetrain proved to be more reliable. Although bevel gears were still slipping a bit, I accepted overall performance.
The picture above shows two L motors for driving right side of axles. The power functions switch for changing rotation of rear Servo motor is synchronized with moving steering pivot mechanism. In crab mode, rear 4 wheels steer
As always I used few of non-Technic parts. Big roof tile was used for saving weight, curve slope parts were better choice for filling the gap. LBG axles sticking out the roof are visible indicator for steering mode. They are mechanically connected to switching mechanism. In the video you can see how they work.
Instructions of white version will be available. (Building it in red is possible by using red parts instead of white.) It will take more than weeks because building process was complicated. So please wait.
Original Topic: http://www.eurobricks.com/forum/index.php?showtopic=137034
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