Some people have strong feelings about how things should be done, what is the proper way of building things, others don't care as long as it looks goods. Whatever is your point of view you guys got a lot of experience building things

I pretend to benefit from it

Steering, ackerman, return to center, camber.... there is a long list of terms every now and then get discussed here. Highly detailed super-cars trying to mimic their real counterparts to the last function are highly regarded, however performance is invariably disappointing. Weak PF and high weight are to blame.

So focusing in performance making things simpler and consequently lighter is the way to go. So the question is how simple?

I am trying to find some kind of consensus on where sits the line between functions hurting/improving performance/handling on a light fast medium model .

I'll try to make a short list and give you some constraints that may help you give an opinion.

Think of a 2 buggy motors model with a very light body work, some LiPo batteries powering them and a SBricks for receiver, so fast for Lego standards.

Differentials It is obvious what those are for, but given the low weight, is there a noticeable difference at high speed? Friction and complexity are worth it?

4 wheel drive. My guess is that for off road is worth it hands down, but what about fast road models? Do the use of differentials or lack thereof change your opinion on this?

Steering.Is there anything that you consider a must have no matter what for a fast road car even if it makes the model take a hit on the weight side? Servo or Medium?

Suspension Wishbones, struts, live axles, more concepts than I understand or remember....What is your suspension take on performance? Is it even necessary?

Gearbox Usually not worth the complexity nor the weight necessary to control it. Do you agree? Not? Explain please!

So that is it, what a fast car needs and what not and anything you may want to throw in.

In really, really fast cars, all of these play a significant role. When you're talking about fast LEGO cars, the only thing that really plays in is the differential.

Definitely, but I'd add suspensions which are useless only on a perfectly flat ground.

And the most important thing is for me the front wheel drive to make the model a bit playable, especially with 2 RC motors, because even with a one-RC lightweight model it is impossible to drive straight ahead with RWD...

To my mind 4WD are not necessary but, to have tested, the performances are a bit better, one RC-motor by axle makes the car turn (steer ?) better at high speed than two RC-motors on the front axle.

A gearbox will only make your drivetrain less efficient, you'll not have a better top speed because the RC motors don't have enough torque to accelerate more.

Edited October 16, 201410 yr by PG52

This was on a wet surface, when it was dry it was pretty easy to keep it under control, but I owe that to the proportional+return to center steering.

For me, you reach 'performance' level of building if the vehicle goes over 20km/h. Here's what I think is most important:

• Direct Drive - Even one pair of gears, especially perpendicular, will result in significant power losses. Having direct drive is the best option and requires a wide chassis, also necessary for high speeds.
  
• Differential - In the first video, I had 2 motors per rear wheel which acted as its own differential. The extra strain on the motors was minimal. Solid axle(no diff) will only work well if you don't use U-joints or CV joints as shown in the second video. This is because long driveshafts will twist or even break during high speed turns and jolts. Solid axle will also result in better control at high speeds but little oversteer, so no throwing the vehicle into the turn sideways
  
• Suspension - At speeds over 20km/h, regardless of terrain, suspension will be necessary. Without it, any bumps or simply the force of turning will put extra stress on the driveshafts and wheel hubs. Handling greatly benefits from suspension, and build according to terrain (stiff/low for roads and soft, high clearance for offroad). Also, if you can fit dampers into your suspension, it will absorb any bumps and go through turns beautifully.
  
• Suspension/Steering Geometry - I find the most important geometries you can incorporate in the strongest of systems are caster and ackerman. Anything to reduce bump-steer and stress on the shock absorbers will help. If you can incorporate camber, kingpin inclination etc without compromising strength, go for it!
  

​Gearboxes, unless you can shift them remotely and fluidly, as well as having no more than 2 speeds, are not worth it in vehicles capable of 20km/h+. 4WD...I don't know because I haven't tried it yet. If the system is mechanically linked, there will be significant power losses. If you have something like 2 motors in the rear and 2 in the front, just watch out for the suspension+drive, it has to steer smoothly and be able to survive stop-go motion. Personally, RWD is the easiest to build and most fun to drive, but if someone can build a FWD car with 4 buggy motors, that would be AWESOME, though understeer might be an issue

Edited October 16, 201410 yr by z3_2drive

This was on a wet surface, when it was dry it was pretty easy to keep it under control, but I owe that to the proportional+return to center steering.

For me, you reach 'performance' level of building if the vehicle goes over 20km/h. Here's what I think is most important:

• Direct Drive - Even one pair of gears, especially perpendicular, will result in significant power losses. Having direct drive is the best option and requires a wide chassis, also necessary for high speeds.
  
• Differential - In the first video, I had 2 motors per rear wheel which acted as its own differential. The extra strain on the motors was minimal. Solid axle(no diff) will only work well if you don't use U-joints or CV joints as shown in the second video. This is because long driveshafts will twist or even break during high speed turns and jolts. Solid axle will also result in better control at high speeds but little oversteer, so no throwing the vehicle into the turn sideways
  
• Suspension - At speeds over 20km/h, regardless of terrain, suspension will be necessary. Without it, any bumps or simply the force of turning will put extra stress on the driveshafts and wheel hubs. Handling greatly benefits from suspension, and build according to terrain (stiff/low for roads and soft, high clearance for offroad). Also, if you can fit dampers into your suspension, it will absorb any bumps and go through turns beautifully.
  
• Suspension/Steering Geometry - I find the most important geometries you can incorporate in the strongest of systems are caster and ackerman. Anything to reduce bump-steer and stress on the shock absorbers will help. If you can incorporate camber, kingpin inclination etc without compromising strength, go for it!
  

​Gearboxes, unless you can shift them remotely and fluidly, as well as having no more than 2 speeds, are not worth it in vehicles capable of 20km/h+. 4WD...I don't know because I haven't tried it yet. If the system is mechanically linked, there will be significant power losses. If you have something like 2 motors in the rear and 2 in the front, just watch out for the suspension+drive, it has to steer smoothly and be able to survive stop-go motion. Personally, RWD is the easiest to build and most fun to drive, but if someone can build a FWD car with 4 buggy motors, that would be AWESOME, though understeer might be an issue

How do you make such powerful cars?

How do you make such powerful cars?

He's a proper Lego Expert,he knows what he is doing....

4 buggy motors are powerful with any batteries, but I use custom ones along with a 3rd party RC system. Much better than IR (range/current) and less bulky than using the official Lego RC system. I shoot for low weight and no gears, just the strong red U-joints for driveshafts, and try to build chassis' that don't bend. Other examples of excellent performance MOCs would be clarkdef's work or 2LegoOrNot2Lego's

The power that a pair of buggy motors can deliver with an S-brick and an unrestricted power supply is going to change the way people build. I tend more towards the performance side of the spectrum. Each feature or mechanism must pass the winnowing process. I have built multi speed transmissions and air lockers into my models and those capabilities have not made it into subsequent iterations.

Right now I am working on a 2x buggy motor crawler that use some non lego parts and some of Efferman's Shapeways parts. Building at these power levels changes the whole paradigm. 9398 has less than 10 watts of power depending on battery. My new creation has over 70 watts of power. Finding weak links is a constant revision process. If a feature doesn't improve the performance, then it is hard to justify.

v/r

Andy

The power that a pair of buggy motors can deliver with an S-brick and an unrestricted power supply is going to change the way people build. I tend more towards the performance side of the spectrum. Each feature or mechanism must pass the winnowing process. I have built multi speed transmissions and air lockers into my models and those capabilities have not made it into subsequent iterations.

Right now I am working on a 2x buggy motor crawler that use some non lego parts and some of Efferman's Shapeways parts. Building at these power levels changes the whole paradigm. 9398 has less than 10 watts of power depending on battery. My new creation has over 70 watts of power. Finding weak links is a constant revision process. If a feature doesn't improve the performance, then it is hard to justify.

v/r

Andy

Now this was said to me so now I'm telling it to you... First off batteries are not measured simply in terms of watts. Batteries are also measured in hours so in order to measure the expected power you got rate it in terms of Watts Hours. See now your seeing it, Building at these power levels changes the whole paradigm, especially when you working with POWER puller tires and 18V motors. But just ignore this, that is way beyond the level of building your at...

Edited October 18, 201410 yr by Boxerlego

For me small and simple to play, big and complex just to show it.

Watts are the unit of measurement for power. The amp hour rating on a battery tells you how long it can deliver a certain load. A 1,000 hp car with a 20 gallon tank makes the same power as a 1,000hp car with a 5 gallon tank, but they do differ in how long they can deliver that 1,000 hp.

Yes, batteries are measured in more than just how much current they can supply, but that is the relevant metric when determining whether the battery is a choke point in the power system.

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The distinction between simplicity for playing and complexity for demo is quite relevant. I don't show my projects and tend to play with test them. Hopefully; I'll be attending an RC crawler event this year. I'll probably be the only truck made out of Lego.

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One of the things that I have found is that it I not how much power goes through the drivetrain but how abruptly that power is applied. The shock loads are much higher than any of the sustained loads.

v/r

Andy

And the most important thing is for me the front wheel drive to make the model a bit playable, especially with 2 RC motors, because even with a one-RC lightweight model it is impossible to drive straight ahead with RWD...

That's why you need proper suspension geometry. Caster for example and kingpin inclination. Both very important if you want to drive straight.

Edited October 19, 201410 yr by nicjasno

That's why you need proper suspension geometry. Caster for example and kingpin inclination. Both very important if you want to drive straight.

Is that achievable without cutting parts etc. though?

Depends what you want...

If you want a simple fun light and efficient model, than you can just stick an RC model, some simple suspension and have a go with it. If you want a good looking model, that usally means its gonna also be heavy because LOOKS=BRICKS=WEIGHT. The more weight you have the more efficient and tougher everything has to be in order to support it. Suddenly you need diffs in order to steer better, complex suspension to compensate for weight transfers, gearbox in order to get the most of the drive motors which in big scale are usually underpowered, etc... It all depends at what you want...

I tried both extremes:

For example the trophy truck is as simple and light as possible

While the Tatra 8x8 was quite mechanically detailed and complex

Which one is better? Both in their own ways, the trophy truck is almost indestructable and always ready for action, while the tatra was more impressive, mighty and technically correct.

If you are gonna race the models, than KISS (Keep It Simple Stupid).

If you are gonna exhibit models, which are not really too mobile, than stick all the diffs gearboxes, ackermann's mcpherons, gearboxes, limited slip diffs, anti roll bar suspensions, caster, camber, toe, panhrod's and whatever else you might think of inside.

Thats my 2 cents

Edited October 19, 201410 yr by Zblj

You gotta have one small torquey motor doing as much as it can do.

Look at the 42009, and I think that can be modded so the motor can also drive the wheels.

I try to use as few parts as I can however still keep it rigid so that it does not break.

my problem used to be that I was doing this the

wrong way, cramming everything into one unit and forgetting that theres differentials, shafts and gears far away that need connecting. so now I space it out properly but still use as little parts as possible.

Bodywork adds a fair bit of weight, I'm fine not having bodywork as I like to see the internals but I'm sure most people would rather have bodywork on their models.

I try to make my models have good handling however since it can be impossible or very hard to do, having poor handling is ok.

Edited October 19, 201410 yr by SNIPE

Is that achievable without cutting parts etc. though?

Yep.

Watts are the unit of measurement for power. The amp hour rating on a battery tells you how long it can deliver a certain load. A 1,000 hp car with a 20 gallon tank makes the same power as a 1,000hp car with a 5 gallon tank, but they do differ in how long they can deliver that 1,000 hp.

Yes, batteries are measured in more than just how much current they can supply, but that is the relevant metric when determining whether the battery is a choke point in the power system.

----------

The distinction between simplicity for playing and complexity for demo is quite relevant. I don't show my projects and tend to play with test them. Hopefully; I'll be attending an RC crawler event this year. I'll probably be the only truck made out of Lego.

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One of the things that I have found is that it I not how much power goes through the drivetrain but how abruptly that power is applied. The shock loads are much higher than any of the sustained loads.

v/r

Andy

But that is still a misuse of Watts when describing about the battery discharge curves and characteristics. In a ideal situation where the battery is expected to deliver 70Watts of power in one hour then sure that is what you would go by but if your consuming 10 Watts per hour out of the 70Wh battery then you will have a maximum run time of 7 hours before the battery discharge curve hits its knee (or the choke point in power) and then you enter that region of sharp discharge where your degrading the performance/life of the battery. Simply saying that your new creation has over 70 watts of power doesn't really show how powerful it is or how the power is distributed over time.

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My thoughts is that performance and functionality are intertwine. Functionality certainly is key when it comes to certain things like gears, suspension, and steering. Differentials are certainly worth having if you want good performance in turning and weaving. To get the best results from the differential you'll need to shim it to avoid it from grinding the gears together from sudden shock loads. Listen to AndyCW above, he is spot on when it comes to this. To quote from him "Its not how much power goes through the drivetrain but how abruptly that power is applied." Doing small stuff like this will improve both functionality and performance. Servo for steering is much worth it even tho there are some miner technical problems, it still beats the M motor steering setup in a heartbeat. Suspension is very important and necessary towards performance and distributing weight forces. Functionality wise suspension always has the notion that it is there to give the driver a comfortable ride experience. Now gearbox are interesting and can certainly add a lot more function in the model. However gearboxes are just to intricate and bulky to get real good performance with it in a model like you would with the standard gearing of buggy motors.

Edited October 19, 201410 yr by Boxerlego

Is that achievable without cutting parts etc. though?

It definitely is.

Yes, but at which scale ? I use the 8421 wheels and I ordinary use a little variable camber angle, no caster angle (because of too much friction with the McPherson suspension so I use a double wishbone system), and a pseudo-kingpin inclination (the steering respects the kingpin inclination but the suspension only works following a vertical axle).

It's quite difficult to respect all the criteria well with 8421 wheels and FWD. Some solutions exist to have the caster angle, which helps driving straight ahead, with a correct geometry and ground clearance. But none have still satisfied me.

Edited October 20, 201410 yr by PG52

My Mustang has lots of suspension features in a 19-wide setup:

Mustang Suspension by VKTechnic, on Flickr

My current project also has a 15-wide McPherson setup:

Rally WIP 1 by VKTechnic, on Flickr

8421 wheels are pretty useful for realistic suspensions. I don't know much about driven front axles, but it should be doable if e.g. the steering motor is moved elsewhere.

8421 wheels are pretty useful for realistic suspensions. I don't know much about driven front axles, but it should be doable if e.g. the steering motor is moved elsewhere.

I agree, the 62.4x20 tires are the smallest that allow for really complex suspension geometry. They also have the advantage (to my eyes at least) of having more realistic proportions than most Lego tires - the height to width ratio is very close to those of many real-world tires. Most Lego tires are far too wide.

8421 wheels are pretty useful for realistic suspensions. I don't know much about driven front axles, but it should be doable if e.g. the steering motor is moved elsewhere.

Steering motor looks good. Your picture certainly shows what a servo driver could be like if one existed where any motor can be a steering motor. The disadvantage behind the return to center spring is that it forces the steering motor to work harder and that could wind up effecting the RPM/speed duration on drive motors especially if your planing on using the V2 receiver...

After researching some more reliable suspensions for the front axle I started working on my own design, which is a mix of inspiration from various builders. My goal was to have caster, unequal length arms, and as little bump steer as possible while still being very strong. At the moment I am trying to find a good way to place a large gear and a servo to match the rack placement.

The design is reinforced so there's little to no bend and it will stay together at high speed:

I got the bump-steer down to a few millimeters at most, and I think that's as good as it'll get with the plan I have in mind.

If you move the steering rack to the level of the lower suspension arms, it'll be basically 0. And you will have more space for everything aswell and the servo sitting much lower in the frame.

The problem is that you have the 6l steering link close to the much shorter suspension arm, causing big differences in the radiuses they describe when moving.

Another problem is that it is angled in the oposite direction, causing further problems.

If you mimic the angle of the lower suspension 6l link and move the whole thing to its level, the bump steer will be gone and the steering will also be lighter and more precise.

Edited November 2, 201410 yr by nicjasno

I noted from your videos that the steering arm must be closest to the arm that is the same length, but this was a quick solution that was very strong. How do you suggest moving it down (on the hub) in a manner that will keep the strength? I'll be fiddling around with it for a while until it's perfect so thanks for the input :)

Edited November 2, 201410 yr by z3_2drive