Zerobricks

Wildcat 4x4 (With new planetary hubs)

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Posted (edited)

I wanted to test out the new planetay hubs in an actual MOC. To do so I took apart the Tiger and make a model that uses 4RC motor and 4 BuWizzes in order to get the maximum amount of juice out of the RC motors.

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42099 inspired me to give the model one one, but two pendular axles with independet suspension. A special longitudal swing arm balances the body between the both pendular axles.

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By having two different suspension systems in one vehicle, the truck can crawl over terrain smoothly without having to push springs and drive fast over rough terrain, absorbing bumps. Total suspensions flex angle is around 45 degrees:

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I tested different motor setups and confugurations and at the end I decided to use a 1:1 gear ratio from RC motor's slower output to the hub via 3x16 tooth gears. Each motor powers each wheels. You can see the stabilizer arm which holds the body up in red and is connected to each axle and can swing in the center:

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In order to share the power from front to rear axle when climbing uphill both axles are connected via differentials which also drive the fake V8 engine:

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For easy access to recharge BuWizzes the whole body can be removed by pulling out 2 axles and a single pin:

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Performance-vise the Wildcat's gear ratio is set somewhere between Tiger's low and high gear (5,4 from slow RC motor's slow output). There is enough to power to go up 45 degrees obstacles or a pile of blocks like this (Yes it drove over all of them and back down):

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The only limit to the performance is the thermal protection of the RC motors which can be triggered if you push the model hard. For example driving into a wall at full speed, spinning its wheels on rough ground will quickly overheat the motors.

Steering angle of the front wheels is around 30 degrees, allowing for very tight turn radious. If that is not enough the Wildcat can also skid steer. This is the turning radious when driving on a soft sand at full speed:

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I will post a video of the model when I return from my holidays alosg with detailed animated shots of the unique suspension. Meanwhile enjoy a few more photos of the obstacles successfully crawled over:

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Regarding the performance of the new hubs... They have their advanatges and drawbacks compared to portal hubs.

Advanatages I experienced:

  • High gear ratio.
  • Steering point is inside the wheel.
  • New CV joints allow for high suspensions and steering angles.
  • They are very robust - the model can do wheelies when reversing and accelerating at full speed.
  • Because they are sealed no debrees can enter and hinder performance as with portal hubs.

Disadvantages:

  • High internal friction compared to portal ones.
  • High friction and wear at the CV joints, especially in front where there is combination of high steering and suspension angle.
  • Vibrations caused by CV joints. They may be caused by a combination of U joints and CV joints, but none of my previous models had such high vibrations before, even at higher speeds.
  • The hubs are VERY difficult to implement in the model and require a lot of clever techniques.
  • Wheels are not as securely fixed as with portal hub + axle combination.
  • Lower ground clearance.
  • Both sides of the hubs have to be steered in order to keep backslash to a minimum.

At the moment I'm not too impressed by new hubs, maybe someone else can comment below with their expereinces?

IMO ideal hub would be a portal one with a deeper wheel rim combination and a higher gear ratio.

Edited by Zerobricks

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4
15 hours ago, Zerobricks said:

Advanatages I experienced:

  • High gear ratio.
  • Steering point is inside the wheel.
  • New CV joints allow for high suspensions and steering angles.
  • They are very robust - the model can do wheelies when reversing and accelerating at full speed.
  • Because they are sealed no debrees can enter and hinder performance as with portal hubs.

Disadvantages:

  • High internal friction compared to portal ones.
  • High friction and wear at the CV joints, especially in front where there is combination of high steering and suspension angle.
  • Vibrations caused by CV joints. They may be caused by a combination of U joints and CV joints, but none of my previous models had such high vibrations before, even at higher speeds.
  • The hubs are VERY difficult to implement in the model and require a lot of clever techniques.
  • Wheels are not as securely fixed as with portal hub + axle combination.
  • Lower ground clearance.
  • Both sides of the hubs have to be steered in order to keep backslash to a minimum.

For the fair play, I would compare them with Portal Hubs and well Normal/42000 Hubs separately, as they have many similarities and differences at the same time:

  Normal Hubs Planetary Hubs Portal Hubs
Gear Ratio Fixed 1:1 Fixed 1:5 (approx.) Depends on the gears used: 1:1 / 3:5 / 1:3
Steering point offset Inside the wheel Inside the wheel +3L offset
Suspension and steering angles Limited by CV joints Limited by new CV joints (similar to old ones) Limited by U-joints (smaller than CV angles)
Robust/Torque handling NO. CV joints are the weakest part and twist easily Amazing. The model can do wheelies when reversing and accelerating at full speed. Medium. Can handle a high torque but twist the axles between the wheel hub and gears
Sand/Dust/Grass protection Small. Some piecese may fall between hub parts Good. Sealed and more or less closed against the external environment NO. Some pieces may fall between hub parts and definitely will on opened gears.
Implementation in the model Good. There are a lot of examples in official models. Normal. Very similar to normal hubs but the ball joints are in-built. Hard. It really needs to plan the model before the portals applying.
Wheels fixation Good. 3-pin hubs + possibility to use an axle. Normal. Only 3-pin hubs. Good. 3-pin hubs + possibility to use an axle.
Ground clearance Normal. Normal. The same as for normal hubs Good. A much higher clearance

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Nice MOC. Reminds me of a heavily lifted Hummer?

It's really nice that we have more options for wheel hubs, they can be so good used in tatra.

P.s. Finally people have noticed that pendular suspension can be good*oh2*

 

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MOCs of this level are very rare. I mean, balancing the raw power of 4 RC motors is a very hard task. I had troubles with only 2 :laugh:

Also, using differentials to divide their power is very innovative and useful, this baby should climb anything

I am very pleased that you put the new hubs to good use, I was curious how they would hold out, in high torque situations.

So we only need the video now, hopefully soon :grin:

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Nice one ! Never tought of this configuration, I tought it was again a 4x4 without link betwin front and rear

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I'm sorry for the long delay, was travelling and had a busy couple of weeks...

But I will start the videoshoot of thes model in the weekend, so you can expect a video soon.

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Took the time to finish the LDD model today, which I will use to demonstrate the suspnsion system:

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I hope the weather clears up soon, so I can start the video shooting.

Edited by Zerobricks

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Here's an animation of the pendular suspension system created in LDD:

Suspension%20animation%204-3.gif

Edited by Zerobricks

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2 hours ago, Touc4nx said:

It's a nice design !
Can I ask you how you rendered that ?

 

I made 5 different models, each with a different suspension angle and copy pasted them into exact position to take the screenshots.

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I took the time to record the video today and it will be edited and posted very soon.

One thing I leaned is that the new hubs are not really waterproof and even small amount of debrees inside them cause noticable increase in friction.

I decided I will not use the new hubs in my hardcore offroaders anymore and will instead concentrate on the new defender's wheels and improved portal hubs.

Edited by Zerobricks

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Just now, Mechbuilds said:

Looks like the new hubs need some sort of grease or something inside..

They are already greased from the factory. But they are not water tight.

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On 9/11/2019 at 7:23 PM, Aerolight said:

what are the improved portal hubs - brickbuilt ones?

Yes, I'm working on these for a future project, but need a pair of the new defender hubs.

After a busy weekend, here is the finished video of the wildcat.

As you can see I really put it through it's pases and I think it held up quite well.

Funny story, after the shoot I took the model apart to clean it. While moving bricks from one bin to another a single 1x3 thin liftarm managed to end up in the nearby dishwasher, clogging the pump :wall: That was a good lesson to keep lego away from the kitchen sink :laugh:

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