[MOC] Quattrack | Dominating extreme angled hills with ease + video

[896gerard]

Already two years ago, I got inspired at defeating steep hills with the LiteJeep. That could already beat 50 degrees, but because of its high riding height (good for offroading) and relatively heavy PF L motors, I reckoned there would be more irons to put into the hill-climbing fire. Very important things for hillclimbing are sufficient grip, huge power and a low weight. Weight ultimately gives more grip, but it also causes the vehicle to flip earlier when it is located above the center of gravity. With these factors into the equation, I decided to create a vehicle with loads of grip, so with 4 rubber tracks, and with articulated steering to make a sturdy connection between right and left possible, which is essential for climbing: when any vehicle is climbing, the suspension does unexpected things, so a stiff frame and suspension setup are required. Lightweight design requires a low complexity too, so that is why articulated steering is chosen. Having a front and rear part to let the vehicle adjust  its shape to the terrain is an option I used several times in my rubber-tracked vehicles. This is the first vehicle in which I used the maximum footprint instead of the triangular form, again for maximum grip. Please note that, when you choose for the sturdyness and simplicity of articulated steering ánd want to let it adjust to the terrain, the middle joint becomes very complex as it contains joints in two axes! There is always a place where pain comes back. The Law of Conservation of Pain holds here.. In this case, all the trouble was in the difficult joint, which took about 5 hours alone. Then for the power: initially an XL motor was used in the front, but having a driveshaft through the already complex dual joint proved to be impossible. 

And then the idea came. Why not generate the power at the place where it is needed? Why not, if there are two separate parts, have some powerplant in both front and rear? But then there was a problem: I have a very large project in which all my three L motors are used. This pushed me in the direction of using M-motors, which proved out to be a very good forced choice. Combined with the lightness of the overall model, they proved to have ample torque left with a 3:1 gear ratio, having enough torque to keep the four tracks spinning all time when grip was lost. This is amazing, and you can see why Lego has put two M motors in their latest Tracked Racer. But the limits of that thing are way lower than the Quattrack's limit.  

 

Using two PF medium motors for drive and one for steering, this one of my very few (and maybe the last) Lego Technic MOC with only 2006 components. The Sbrick will throw all range headaches away and have much less delay than the stone-age PF IR remote it is replacing. Why did I use such standard power functions components? The new PF servo is slow and quirky, a medium motor allows for much more smoothness in steering. Moreover, if you are driving at steep slopes like this, it asks all your concentration to keep it on the move. If you cannot feel where the remote control knobs are (The intrinsic problem of the Sbrick) the vehicle will fall of before you've compensated. So the old system proved to be the best system in this situation. 

The articulated joint actually contains 3 joints, to have a suspension force on it in both directions: up and down. That is why there are rubber bands and one shock absorber. By the way, also the steering joint is included. Now, because the front and rear part of the Quattrack are relatively conventional (no steering nor differentials), all the pain of good and accurate steering is shifted to the design of this central joint. I dare to state that the success of this vehicle relies for a big part on this 2D joint. In the video, the operation is explained. 

 

On this photo, it looks as if the ground clearance is half a stud. This is not the case; in fact, it is over 1 stud. The underside is very smooth, which helps the low superstructure to glide over obstacles. 

Because of the weight saving, I designed it to have very clean looks. Styling means more weight. However, I managed to squeeze in some little details like fake cabin flashing lights, front lights, rear lights, cabin seats and a steering wheel. The reason why I did this, is that I wanted it to be a possible real-life vehicle as well, not just a scientific experiment. Adding weight is bad for climbing ability, so I tested the Quattrack also with the cabin removed and say what !!? The climbing angle was the same. This front look shows all that. The Quattrack contains everything, but nothing more. 

You do not need a zillion pieces of Lego to break records. Only 556 grams of it is sufficient in some cases.

 

The video is the proof of all my theories...

[media]

I have not put all text and photo's on Eurobricks. More is to be found on Brickshelf and MocPages. If you like my video's, you might want to take a look on my YouTube channel. 

Edited December 23, 2016 by 896gerard

[Sariel]

I like it, but it looks like ground clearance between the tracks is nearly non-existent. Maybe you could fix it?

[Beck]

I have always had an interest in lego climbers and out of all that I have seen so far, this is by far the most impressive design. However, the placement of the battery box is questionable. Would it have been better to place it in the front? I believe this would further prevent the machine from flipping back. Although you could simply test this by driving it backwards.

I like it, but it looks like ground clearance between the tracks is nearly non-existent. Maybe you could fix it?

 

I believe increasing the ground clearance would raise the center of gravity, which would be detrimental to the function of the vehicle. 

Edited December 22, 2016 by Beck

[896gerard]

Just now, Sariel said:

I like it, but it looks like ground clearance between the tracks is nearly non-existent. Maybe you could fix it?

It proved to be very difficult to make the actual joint higher (I have considered this problem off course), as the complete chassis structure would have had to be lifted a bit for that. And then the shock absorber would be much higher and so on. I would have ended up with a vehicle that can leave very steep hills more easily, but the main focus was climbing. And for climbing, the lower center of gravity is essential. It's all about priorities. 

Just now, Beck said:

I have always had an interest in lego climbers and out of all that I have seen so far, this is by far the most impressive design. However, the placement of the battery box is questionable. Would it have been better to place it in the front? I believe this would further prevent the machine from flipping back. Although you could simply test this by driving it backwards.

The front is already very packed, there is no space left. Futhermore, it is way more important to have the main weight (yes, in such a lightweight model even the lipo battery box is 'heavy'..) on the axle line, to have it low. Having the battery box in the front would cause the front to be very long and out of proportions. And think about the weight on the rear tracks. Some weight needs to press them down, otherwise there's no mechanical grip. The main point of this MOC is the continuous fight between grip and gravity, remember? ;)

[Beck]

Maybe custom treads using the 1x2 rubber parts would be even grippier than the standard lego tread. 

[Leonardo da Bricki]

That is an impressive demonstration of climbing ability!  I understand the need to sacrifice ground clearance, IMO its totally worth it here.

[896gerard]

8 hours ago, Beck said:

Maybe custom treads using the 1x2 rubber parts would be even grippier than the standard lego tread. 

I'm not really sure about that, as the ridges and edges on it are smaller than for the standard Lego tread. It will be better on smooth surfaces, but on rocky surfaces (that I simulated), the standard tread will be better. Another problem of these custom treads is that they take more volume (thus are heavier) and need a least some torque to rotate, which is an energy loss. So these 1x2 parts do not allow for a lightweight, light powered design. 

[wissamms]

Very nice design, and great thinking about the different issues! Bravo

[syclone]

Fantastic work, I like that you used m-motors!  

[BusterHaus]

This was very fun to watch. The performance is quite astonishing,and it looks very cute. 

[braker23]

I am truly amazed by it's performance, I love its straight-to-the-point design, great work :)

[Kristof]

Wow, that really outperforms any expectations I have had. Clearly, this is also thanks to many design sacrifices (ground clearance, nimimum weight...) but still I think it is very much worth it. I'd only be cautious driving this outside since the motors have nearly direct contact with the ground, meaning the moisture can easily get into them.

[896gerard]

8 minutes ago, krisandkris12 said:

Wow, that really outperforms any expectations I have had. Clearly, this is also thanks to many design sacrifices (ground clearance, nimimum weight...) but still I think it is very much worth it. I'd only be cautious driving this outside since the motors have nearly direct contact with the ground, meaning the moisture can easily get into them.

It was only 15 minutes outside. From my electronic engineering background, I think that all electric motors should be able to handle moist air. The Lego electric motors are more protected (have plastic around them) than the starter motor in your car, and still it starts every morning. 

[Kristof]

Oh yes, of course it probably won't be an issue, especially since you are aware of it. Moist air is one thing and possibly wet grass is other :) But I didn't want to be this Mr. Cautious really, I'd probably dare to drive it outside too if I knew it wasnt partucularly wet :) As long as there is no chance for water leaking into and developing shortage or some corrosion in long term, it really shouldnt be an issue.

That being said, I still consider lego PF (and in fact Lego in general) to be indoor thing :D Everytime I see some off road action, besides awe I also feel a bit... inpropper :)

[896gerard]

2 hours ago, krisandkris12 said:

Oh yes, of course it probably won't be an issue, especially since you are aware of it. Moist air is one thing and possibly wet grass is other :) But I didn't want to be this Mr. Cautious really, I'd probably dare to drive it outside too if I knew it wasnt partucularly wet :) As long as there is no chance for water leaking into and developing shortage or some corrosion in long term, it really shouldnt be an issue.

That being said, I still consider lego PF (and in fact Lego in general) to be indoor thing :D Everytime I see some off road action, besides awe I also feel a bit... inpropper :)

You are right. It felt unlogical to me too when I went outside for the first time. But I think, if any Lego Technic MOC has to survive in severe conditions, it has to be this one. 

I have not posted this image to Eurobricks yet, but as you can see the Quattrack can be equipped with a cargo bay. I can invent myself a battery heating system for in the cargo bay, in which case it can survive snowstorms, as electric motors do their work in extreme colds, as long as they don't freeze. The tracks then provide grip to let it rescue itself ;)

Edited December 23, 2016 by 896gerard

[technic_addict]

Very impressive climbing ability!  Did you modify the battery?  I am surprised the M motors kept going.

Would be interesting to see how the XL motor would do.

[896gerard]

Just now, technic_addict said:

Very impressive climbing ability!  Did you modify the battery?  I am surprised the M motors kept going.

Would be interesting to see how the XL motor would do.

No, I don't modify Lego batteries. Please note that this battery only puts out 7,2 to 8 Volts, so you could say that (, compared to all Power Function Technic sets), this MOC was even underpowered...

The problem is that the Lego Technic group does not use the full potential of their M motors in their models. This oversizing of power is done because most builders (children etc) are generally bad builders and have way more friction in their transmissions than us. This habit of TLG makes us believe that M-motors are weak. I'm swimming against that tide, and you can see which great engineering can be achieved with that ;)

Adding an XL motor in the front would make the center of gravity higher, as the XL motor is higher. Then there is the difficulty of having the drive axle through that complex joint. And why do it? When you have a look at the video, you see that always the available torque is more than enough: always it looses grip rather than stalling. The only reason why you would want bigger motors is to make it faster. But let's not forget that the main goal was: climbing the steepest hill. Having a bigger motor would increase weight, which decreases the climbing angle. Having said that, even the M-motors supply already a very reasonable speed (the video is not speeded up), so I think my choice for M-motors was one of my best 2016 choices. 

[technic_addict]

20 minutes ago, 896gerard said:

No, I don't modify Lego batteries. Please note that this battery only puts out 7,2 to 8 Volts, so you could say that (, compared to all Power Function Technic sets), this MOC was even underpowered...

The problem is that the Lego Technic group does not use the full potential of their M motors in their models. This oversizing of power is done because most builders (children etc) are generally bad builders and have way more friction in their transmissions than us. This habit of TLG makes us believe that M-motors are weak. I'm swimming against that tide, and you can see which great engineering can be achieved with that ;)

Adding an XL motor in the front would make the center of gravity higher, as the XL motor is higher. Then there is the difficulty of having the drive axle through that complex joint. And why do it? When you have a look at the video, you see that always the available torque is more than enough: always it looses grip rather than stalling. The only reason why you would want bigger motors is to make it faster. But let's not forget that the main goal was: climbing the steepest hill. Having a bigger motor would increase weight, which decreases the climbing angle. Having said that, even the M-motors supply already a very reasonable speed (the video is not speeded up), so I think my choice for M-motors was one of my best 2016 choices. 

You have made a very light and capable machine and it clearly shows the M motors are enough for your design.  My comment for using XL motors was intended if the build was scaled up a bit.  You can maintain a low COG with a larger built machine.  XL motors actually rotate slower than M motors so I was not thinking to speed it up.  Another poster has done some work with tracks and found excellent methods for grip.

 

[Mantarri]

Wow, now this thing is awesome, and it looks nice too, good great job!

[896gerard]

6 hours ago, technic_addict said:

build was scaled up a bit.  You can maintain a low COG with a larger built machine.  XL motors actually rotate slower than M motors so I was not thinking to speed it up.  Another poster has done some work with tracks and found excellent methods for grip.

 

Good thinking! Off course, I was considering using the large tracks but.. the rubber parts added onto plastic tracks did not convince me (expensive, relatively low grip). Can you put a link of that poster here? 

Please note that I've cracked 60 degrees on a bathing towel. I'm not sure that plastic tracks with rubber mounts on it will grip onto that quite smooth surface. 

[mocbuild101]

WOW! it looks like it could climb up a wall if you let it , such an amazing amount of traction! and you even made it look great too!