9398 - Lego Technic 4x4 Crawler

[Blakbird]

Remove differential is the worst thing you can do at my eyes. Before, all trial trucks used NO differentials but it was a mistake for me. Turning radious is just ridiculous without differentials and you can't maneuver your vehicle proporly.

Don't know if you have already participated in a trial competition and see the difference between trucks with differentials and without but it's astonishing how the differential allow a smooth drive!

So, yes, differentials hamper performances but with good suspensions, tires are still always in contact with the ground. You should also see that your obstacles are just enormous, (bigger than the diameter tire) which explain why it can climb your course !

Real off-road vehicles do traditionally have differentials. The problem with LEGO diffs is that they are completely open and therefore offer no resistance. A real diff is filled with viscous fluid that prevents it from turning until a certain differential torque is reached. This prevents the immediate wheel slip seen in the video but still allows turning. Not much we can do about this in LEGO.

[5150 Lego]

Still using diffs in an offroader INMHO is a bad idea. They may work in ideal situations, but real mud, dust, rocks and grass are not ideal. Closes thing to a perfect mix of maneuverbility and perforamnce I think is using 2 motors, one for each side of the truck's wheels like my Lynx used.

How did you compensate for when your model steers? Or do you use one motor to drive one side slower than the other? (like a tank)

I own a 4x4. I can tell you from experience running locked differentials full time is not the way to go. It makes it to difficult to maneuver around turns as well as certain obstacles. My vehicle has a selectable locking differential. I lock it when needed, and unlock it when you don't. other wire you'd never make it around the trail.

I know where speaking in terms of LEGO, but fully locking the diffs isn't the answer. Your idea seems intriguing though. Just curious how you turn your model.

Real off-road vehicles do traditionally have differentials. The problem with LEGO diffs is that they are completely open and therefore offer no resistance. A real diff is filled with viscous fluid that prevents it from turning until a certain differential torque is reached. This prevents the immediate wheel slip seen in the video but still allows turning. Not much we can do about this in LEGO.

What your describing is a limited slip differential. An open diff and a car will still do exactly what your describing the Lego diffs do. Since your correct that there's not much that can be done to fix this with LEGO, the best way to compensate if to have as much flex as possible and match the weight of the vehicle to the spring rate of the springs. Keep all 4 tires on the ground and you'll have the best chance of getting over the obstacle.

[raus]

In trial can even be used differentials, but crawler is impossible! crawler always obstacles in some or all tires were in the air. In the video Efferman was not as hard and the differential has interrupted the route.

[davidmull]

ok, on a slick ascending slope it works till 30°, then the rear axle motor goes into stall, because the frontaxle has no grip.

obstacles, my foot for example, against a single tire, are possible till 5cm height.

overall is grip the problem. with my ansmann tires is much more possible. the vid which was posted by anio shows good the possible performance.

Which video did anio put up? What's ur taughts or opinion on overall performance efferman?have u tryed dirt/or sand ?

[Sariel]

After playing with the Crawler for a while, I have to confess its performance disappoints. It's got a nice suspension and everything, but it lacks torque so desperately that it can get stuck on a thick carpet. LEGO advises you not to use it outdoors, probably because it would get stuck on grass. Also, differentials. Sorry, but anybody who claims differentials are OK for LEGO Truck Trial has not enough experience. Differentials kill in Truck Trial. Even when all your wheels are on the ground, it's enough for one of them to slip e.g. on sand - and you're done. In heavy-duty TrTr you don't need good turning radius - you need a drivetrain that stop only on walls.

Edited July 3, 2012 by Sariel

[JunkstyleGio]

I fitted the Unimog tyres on mine :D

Pictures please!

[rm8]

After playing with the Crawler for a while, I have to confess its performance disappoints. It's got a nice suspension and everything, but it lacks torque so desperately that it can get stuck on a thick carpet. LEGO advises you not to use it outdoors, probably because it would get stuck on grass. Also, differentials. Sorry, but anybody who claims differentials are OK for LEGO Truck Trial has not enough experience. Differentials kill in Truck Trial. Even when all your wheels are on the ground, it's enough for one of them to slip e.g. on sand - and you're done. In heavy-duty TrTr you don't need good turning radius - you need a drivetrain that stop only on walls.

Lacks of torque?! We have some reserve: what about using 8:24 at portal hubs ?

[davidmull]

After playing with the Crawler for a while, I have to confess its performance disappoints. It's got a nice suspension and everything, but it lacks torque so desperately that it can get stuck on a thick carpet. LEGO advises you not to use it outdoors, probably because it would get stuck on grass. Also, differentials. Sorry, but anybody who claims differentials are OK for LEGO Truck Trial has not enough experience. Differentials kill in Truck Trial. Even when all your wheels are on the ground, it's enough for one of them to slip e.g. on sand - and you're done. In heavy-duty TrTr you don't need good turning radius - you need a drivetrain that stop only on walls.

Again mixed reviews , others say its great I'm confused :( looks like great torque in the videos.

[Sariel]

Lacks of torque?! We have some reserve: what about using 8:24 at portal hubs ?

That makes things slightly better - the default gear reduction is minimal, to be honest - but it's nowhere near the performance the XL motor provides. I'm just finishing the video that shows Crawler struggling in many situations where XL-powered trial truck manages. I expected better from a set that comes with "Extreme Off-road Performance" on the box. IMHO a car that can't climb its own 8 cm thick box is hardly extreme.

Again mixed reviews , others say its great I'm confused :( looks like great torque in the videos.

If you wait for my video, you will see it stopping dead when a single wheel meets my fist resting on the floor.

Then again, I may be expecting too much from it, because I'm used to watching top-notch Truck Trial vehicles. The 9398 comes with a great suspension and some clever building techniques that many people will enjoy. I'm just disappointed with the motors that stop fairly easily.

Look at it this way: Crawler weights nearly 1.6 kg and has two motors, each with some 150% of Medium motor's torque. But the motors are not connected and there are situations where their torque doesn't really sum up. For example when climbing uphill, most of the weight rests on the rear axle while the front one doesn't help much because it loses grip. So you get 1+ kg on a single axle with small gear reduction to be handled by a motor not-so-much stronger than the Medium motor.

Edited July 3, 2012 by Sariel

[DLuders]

If one looks at the last third of

below, one can see that it's quite capable of running over INDOOR obstacles. If one runs it OUTDOORS (against the recommendations of The Lego Group), maybe one expects too much from the model. However, it seems that it can be customized. Perhaps folks were expecting the performance of Marceloraus/ Raus Lego Technic Rock Crawlers (with their custom, oversized tires to handle steep rock surfaces), like in the

. Perhaps the key is to get LARGER WHEELS and TIRES to meet your expectations....

Edited July 4, 2012 by DLuders

[Sariel]

It's a great video, but what's the single tallest not-sloped obstacle there? 2cm, 3 maybe? That's less than half of the Crawler's wheel diameter. Also, all obstacles shown there seem to provide excellent grip, there's no opportunity for differentials to show their worst.

Edited July 3, 2012 by Sariel

[rm8]

using speed remote control for steering

Edited July 3, 2012 by rm8

[DLuders]

I'm wondering whether everyone used the same voltage of batteries in the 9398 driving tests (shown in the recent videos). If one used six RECHARGEABLE AA batteries, the available voltage is only 6 x 1.2V = 7.2 Volts. A set of six new Alkaline batteries produces 9V initially -- that's 25% more Voltage. The comparisons of the 9398's performance needs to be an "Apples to Apples" one done with the same kind of battery.

If the Power Functions L-Motor has ~50% more torque than the PF M-motor, one could extrapolate the information that Philo did on his "LEGO® 9V Technic Motors compared characteristics" webpage. The "Mechanical Power" of a PF M-Motor is substantially less at 7.2V than at 9V. One could "bump up" the curves ~50% to get an idea of the PF L-Motor's "Mechanical Power".

Edited July 4, 2012 by DLuders

[raus]

I always work with 9 volts. The yield is much better. For comparison, the video follows the same crawler but with original tires.

[DLuders]

@ Raus: I'm noticing that when your Lego Technic Rock Crawler "approaches" the rock, it does so at a slight angle. The two front wheels don't simultaneously contact the rock slope at the same time. It seems that efferman's "approach" to his obstacles was not done in this manner; both the front and rear wheels have trouble "grabbing" the rock because one tire is not ANGLED to the rock face. Perhaps he used Rechargeable AA batteries (7.2V) instead of new Alkalines (9V):

Edited July 4, 2012 by DLuders

[efferman]

i have used eneloop accus out of the box. so it is possible that they are not completely full

[grohl]

In my opinion the Crawler performs more than well. Yes, the differentials do not help much its climbing abilities, but I can understand the reason why they are present in the axles.

People that say that steering radius is not important in Truck Trial have probably never seen Czech races. Unless you have 45° on the front axle, your chances of winning are getting very low.

[GuiliuG]

After playing with the Crawler for a while, I have to confess its performance disappoints. It's got a nice suspension and everything, but it lacks torque so desperately that it can get stuck on a thick carpet. LEGO advises you not to use it outdoors, probably because it would get stuck on grass. Also, differentials. Sorry, but anybody who claims differentials are OK for LEGO Truck Trial has not enough experience. Differentials kill in Truck Trial. Even when all your wheels are on the ground, it's enough for one of them to slip e.g. on sand - and you're done. In heavy-duty TrTr you don't need good turning radius - you need a drivetrain that stop only on walls.

Hmmm. I'm sorry, but I think that I have some Truck Trial experience, after building three of them which where performing well enough. Two of them were built without differentials and my last used them. From what I have seen, the last using differentials was the most responding, and the most playable.With a litte experience, you can pass almost the same obstacles as you will pass without differentials You probably don't see the point to use differentals because truck trial in Poland is in outdoor and turning in a small space is not the point. But we have not the same philosophy in france ( or in any case the guy which participate at the fana'briques competition has the samephilosophy as I have I think). The course showed in Anio's video is small and a good turning radious IS needed when you know that each time you drive in reverse you lost point. I hope you will see soon some videos of this competition to see that differentials were a most ( for me, naturally). Our trial truck are light and manoeuvrable where Poland's one are more heavy, more slow and it's probably for this reason we don't have the same trial truck conception.

Yes blakbird, there are in real life multiple technics to block totaly or partially a differential but in lego, most of these technic or not possible. I simply say that I prefer put differentials in a truck trial rather than not use them, because the first solution has more advantages in my opinion.

Edited July 4, 2012 by GuiliuG

[Zerobricks]

How did you compensate for when your model steers? Or do you use one motor to drive one side slower than the other? (like a tank)

I own a 4x4. I can tell you from experience running locked differentials full time is not the way to go. It makes it to difficult to maneuver around turns as well as certain obstacles. My vehicle has a selectable locking differential. I lock it when needed, and unlock it when you don't. other wire you'd never make it around the trail.

I know where speaking in terms of LEGO, but fully locking the diffs isn't the answer. Your idea seems intriguing though. Just curious how you turn your model.

What your describing is a limited slip differential. An open diff and a car will still do exactly what your describing the Lego diffs do. Since your correct that there's not much that can be done to fix this with LEGO, the best way to compensate if to have as much flex as possible and match the weight of the vehicle to the spring rate of the springs. Keep all 4 tires on the ground and you'll have the best chance of getting over the obstacle.

A video might explain:

[Sariel]

You probably don't see the point to use differentals because truck trial in Poland is in outdoor and turning in a small space is not the point. But we have not the same philosophy in france ( or in any case the guy which participate at the fana'briques competition has the samephilosophy as I have I think). The course showed in Anio's video is small and a good turning radious IS needed when you know that each time you drive in reverse you lost point. I hope you will see soon some videos of this competition to see that differentials were a most ( for me, naturally). Our trial truck are light and manoeuvrable where Poland's one are more heavy, more slow and it's probably for this reason we don't have the same trial truck conception

Good point. We model our races after real Truck Trial races held for example in Czech Republic, where you have to go through the gates, but you are free to drive as you like between the gates. Example:

That inevitably makes torque more important than handling. We simply try to be accurate not only with vehicles, but also with courses. But leaving the torque aside, the Crawler handles very, very well and has an excellent, very stable suspension - as Anio's video shows.

Edited July 4, 2012 by Sariel

[Jetro]

Pictures please!

Here you go, first with the grey rims:

And then with the black ones:

Front view just for the fun of it:

[DLuders]

Thanks, Jetro, for showing the Unimog tires on the 9398! Here is a side-by-side comparison of the 9398's original Lego tires (picture by efferman), the larger-diameter (but smooth) Lego Unimog tires (picture by Jetro), the 3rd-party RC tires (picture by efferman), and the Lego "Power Puller" wheels/tires (picture by Blakbird):

Edited July 4, 2012 by DLuders

[Jetro]

It's a great video, but what's the single tallest not-sloped obstacle there? 2cm, 3 maybe? That's less than half of the Crawler's wheel diameter. Also, all obstacles shown there seem to provide excellent grip, there's no opportunity for differentials to show their worst.

The highest solid obstacle I had handy was a 8,5cm thick dictionary and the crawler had no problem with it. As a matter of fact, it would have done something taller but for the bar at the front which reduces the attack angle. Driving backwards, the only reason it didn't scale the wall full on was lack of power (I used the rechargeable Li-Ion battery) and the fact that the wheels slipped on the floor.

[DLuders]

The Lego Group has posted the 9398 4x4 Crawler PDF Building Instrructions on this Technic.Lego.com webpage -- both the "A-Model" (4 booklets) AND the alternate "B-Model" (2 booklets)!

Edited July 4, 2012 by DLuders

[Zerobricks]

Looking at these it seems you could get a higher steering lock on each axle if you would move the whole steering rack half a stud closer to the wheels...