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Hi, do you guys like this?

640x360.jpg

4x4 "drone" car with

- "Adaptive Caster Angle" by virtue of shocks on roof. 5 - ~10 degrees

- 6 L-motor drive, two front, three rear

- three buwizz, option for fourth

- independent suspension 

- Carbon fibre axles where needed

- wheel hubs copied from didumos.

- 28 tooth gear driving 28 tooth "new" differential

- 1:1.66 gear ratio, roughly 15 KM/H

Album

Edited by CharlesD
added information

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Hello. It's quite a short description for such a large model, but I took a look at some of your pictures and *.io file...

The model is heavily reinforced, but, somehow, uses weak u-joints. Considering you have 3 buwizz and 6 L-motors, it's highly recommended to replace those u-joints to cv-joints (if you ask any suggestion, ofc). Or, at least, to reinforce them this way:

400x213.JPG

Also I have some questions about the front suspension's geometry. The model has double wishbone suspension with equal length arms. This leads to some restrictions:

1) The steering arm has to be the same length as wishbone (8 studs in this case).

2)  The steering arm has to be parallel to the wishbones both horizontally and vertically.

This blue line defines a steering arm in terms of geometry. As you see, it's not parallel to the wishbones. Also, your steering arm has different lengths at the same time. From the top view it's the one lever with 7+ studs length.

4.JPG

From the rear view it's the other lever, now parallel to the wishbones and it has length of 8 studs.

5.JPG

These issues happen because of this (axes of rotation don't cross):

2.JPG

Also, the kingpin axis is strictly vertical, so the scrub radius is pretty big and it causes a stress for servo to turn the wheels left-right. In addition, there are no auto-centering of steering and other benefits of the non-zero kpi-angle.

6.JPG

Besides that it'd lovely to see a video to watch it in action)

Edited by romashkaman

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Looks really agressive. More details would be nice. I'd also suggest you use the new, stronger CV joints which came in 42099. They do get worn out a bit, but have yet to break any, even when propelling a 4+ kg heavy car to over 35 km/h.

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Thanks for the feedback.

I use CADA metal U joints, they work excellent (except for intallation)

I reckoned that the steering link starts at this point;

1.jpeg

Also the angle is needed to clear other components and achieve the required ackermann angle.

Does the KPI angle need to be slanted relative to vertical? to create a Toe angle?

19 minutes ago, Zerobricks said:

Looks really agressive. More details would be nice. I'd also suggest you use the new, stronger CV joints which came in 42099. They do get worn out a bit, but have yet to break any, even when propelling a 4+ kg heavy car to over 35 km/h.

Thanks, i updated the information.

I used didumos wheel hubs because the standard wheel hubs have a lot of play in them, combined with the metal U joints they perform quite well.

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Looks brutal indeed. :wink: Would be nice to see in action, that says more than a hundred words.

On the subject of steering geometry, I did not see any problem, in fact it was a clever solution on ackerman geometry, but I had the benefit of the doubt as I'm geting rusty. Looked it up and it's almost identical setup as the Greyhound had, made by @Didumos69. Now as much as I remember, when it comes to geometry, he knows his way around that subject, so I respectfully disagree with @romashkaman. (apart from the position of the kingpin, but that is on the choice of the built hubs)

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13 minutes ago, Attika said:

Looks brutal indeed. :wink: Would be nice to see in action, that says more than a hundred words.

On the subject of steering geometry, I did not see any problem, in fact it was a clever solution on ackerman geometry, but I had the benefit of the doubt as I'm geting rusty. Looked it up and it's almost identical setup as the Greyhound had, made by @Didumos69. Now as much as I remember, when it comes to geometry, he knows his way around that subject, so I respectfully disagree with @romashkaman. (apart from the position of the kingpin, but that is on the choice of the built hubs)

Thanks, i wanted to make a video for a while but the weather got in the way.

I honestly copied the greyhound's geometry, the steering links also have the same dimensions, only the pivot inside the model is further outwards to clear the drive axles.

 

 

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12 hours ago, Attika said:

I respectfully disagree with @romashkaman. (

I also don't see issues with suspension, steering geometry (yes, steering will be harder because of kingpin position). Everything should work.

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17 hours ago, CharlesD said:

- wheel hubs copied from didumos.

Looks amazing! I bet like Greyhound, it'll do those 15 km/h whatever terrain happens to be in the way.

You can make those excellent hubs from @Didumos69 just a little stronger as follows.

It allows you to put the X hole of the wheel nearer the drive axle (less play) and have the wheel ride pin in pin hole instead of axle in pin hole (less play).

800x1023.jpg

800x824.jpg

That's a whole lot of drive motors. I wonder if you get much advantage after the 4th? Since the 5th and 6th require adding the weight of the motors, and an extra buwizz.

Is there space on board for buggy motors?

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I've broken a couple of servos on Greyhound, so your model also definitely has the possibility of doing same.

Considering PF servos are 80€ now, that's no joke... how about converting to a PU large motor for steering, and powering the whole show with a couple of Buwizz3? You get more accurate steering from a cheaper motor, and higher voltage all round. The PF outputs kick out more amps than a bw2 can, so I reckon two would be enough in that case.

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Wow thanks, i will try those hubs.

I was trying to create something like the greyhound but faster which led to to motors needing to be internal and adding differentials, which led to the standard differentials not being strong enough which led to  using the new differential and having to do a lot of upgearing because you can only drive the new differential with a 12 tooth gear in a normal 5x7 frame. Which then led to me using a 28 tooth gear to drive the differential which made everything wider and heavier. So to then to get the required thrust/weight ratio i had to add motors.

My logic also being that the greyhound was about 1.4 kg with a gear ratio of 1:1, so to get a gear ratio of 1:1.66 with the same weight i have to add 50% more torque to get the same performance.

I am not really into buggy motors, it kinda feels like cheating. Plus i have a bunch of L- and XL- motors laying around.

2 hours ago, amorti said:

I've broken a couple of servos on Greyhound, so your model also definitely has the possibility of doing same.

Considering PF servos are 80€ now, that's no joke... how about converting to a PU large motor for steering, and powering the whole show with a couple of Buwizz3? You get more accurate steering from a cheaper motor, and higher voltage all round. The PF outputs kick out more amps than a bw2 can, so I reckon two would be enough in that case.

Thanks, I tried a PU L motor as servo but it made really weird noises and did not want to cooperate fully with my buwizz 3.0, i can try again tough, maybe they did an update in the meantime.

Weirdly enouh when using the buwizz template for the 42099 it did work allright.
 

I have two buwizz 2.0 and one 3.0, the 2.0 are powering the rear L motors and the 3.0 powers the two front motors, that actually works quite well.

Edited by CharlesD

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On 12/14/2021 at 7:40 PM, Attika said:

when it comes to geometry

I mean, we have a little more play (unintended rotation) in extreme position (for example, it's a left turn for the left wheel) than we want (but, ofc, it's not easy to avoid in every possible case):

1.gif

I tried to change some things, also added KPI-angle and made wishbones with unequal lenghts (this is just a mockup, many things could be improved, but you'l get the idea):

2.gif

Here are some pics if animations don't show all stuff well enough: bricksafe

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1 hour ago, romashkaman said:

I mean, we have a little more play than we want

:classic:  Yes we do. Surely less than in a bad design, and just slightly more than the theoritically best possible. Don't let the perfect be the enemy of the good.

2 hours ago, romashkaman said:

 

2.gif

On this specimen the suspension travel is limited if the steering is in that extreme position if I'm not mistaken, the link slips under the frame and two will collide . I do understand it is a "mockup", but I find that being a very convenient excuse after such a harsh criticism in your first reply on the topic. :wink:  

 

2 hours ago, CharlesD said:

I made a video to show how it performs;

Steering only? You really want us to beg to see it running around in your kitchen? :sweet: 

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It took a while, but here it is;

Video

A bit disappointing, the car goes fast for a moment and then it just stops, after a minute it goes again. I am affraid the battery life of my buwizz 2.0's has depleted to much.

I did manage to use a PU servo, but that has a tendency to not react in time, hence the crash.

I removed two motors and supporting structure, managed to delete 350 grams for a total weight of 2KG, same result.

Contrary to before the buwizz 2.0's lights do not go to red when driving anymore.

Do you guys reckon the weight is too high?

 

Edited by CharlesD
update

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Thanks for the video. It certainly sounds like the buwizzes are overloaded. For a start I'd experiment by changing gear ratios to make it slower. In case it solves the problem, there is your answer. 2 kg is quite a weight for the current gear ratios.

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Thanks, i reckon that is the problem.

I dabbled with an automatic gearbox in the past but could not get to work with high weight and torque. I might gvie that another try.

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Now you deleted 2 motors, maybe you could move the two remaining buwizz units into the motors' spots (IDK exactly if there's space), allowing you to reduce the width of the vehicle by deleting the side pods. This would improve ground clearance, and further reduce weight.

What's the story with the "adaptive caster"? Does it basically mean there's an additional pivot in the chassis? It strikes me as extra complication (weight) and a weak/flex point.

Are you open to non-Lego motors? I ask since you already use carbon axles and CaDA u-joints. These CaDA motors bring almost double the speed for similar torque to Lego motors. They are too hungry to let you run a buwizz2 on Ludicrous, but then you won't need to. https://www.custombricks.de/motors-cables-sbrick/cada-power-functions-l-motor.html

Edited by amorti

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Thanks, i am going to start over, this is too much weight and size.

The whole steering assembly/front suspension is hinged and connected with the ducati shocks to the top.

See for yourself; Design

I actually have four of those, but they are in a different project at the moment.

There they work quite well with one connected to each buwizz 2.0 and two connected to the 3.0, but it only has a weight of about 1.3 KG

Edited by CharlesD
update

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On 12/16/2021 at 1:20 AM, Attika said:

the link slips under the frame and two will collide

This frame is there just as holder for the steering rack (and it's not even a rack cause it's indeed a mockup). It can be rearrenged in million ways, I was targeting to reduce a slack in the steering knuckle. Also it's strange you consider my criticism as harsh - I said nothing about visual design or things like this (it's a matter of taste), I talked only about effectiveness of the build (with arguments). Purpose for that - original author asked all EB-members if we like this model. It's a big budget model with big potential - it'l be a pity to not get max of it)

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I could net let go of it so i ordered some CADA pro L motors and did a redesign of the drive unit.

1280x720.jpg

Managed to shave off about 300 Grams

1280x720.jpg

 

1280x720.jpg

In order to fit the motors lengthwise i had to resort to some "chinese prototype" perpendicular liftarms of the 5 and 7 studs variety.

Also redesigned the steering actuator to use sliding axles in stead of liftarms.

I will post the results once the motors have arrived.

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I have 7 pcs of the Cada Pro L (the squarish boxy one) with 4 of it on this. 4 identical motors connected to 10A ESC. Stall current for these motors is 2.5A as per the manufacturer claimed, therefore 10A ESC is good enough for 4 of these motors based on the stall current. The inner core motor is of lower turn number than the Lego PF L, thus it has higher speed but lower torque at lower rev range, therefore, without reduction, it's not the ideal motor especially when the vehicle has higher mass.

The motors gets relatively hot for the thermistor within due to higher current, the motor will trip before the limit of the ESC.

Even with 4 units of these motors, when accelerating, the motors are working hard, which means the current draw is high and eventually gets hot and trip the thermistor.

For heavy vehicle, I'd stick to motor with higher turn number (preferable Lego stock L motor).

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Buwizz 2 specs state max 4A per channel, so if i connect one motor to it, would that not be more than enough?

Buwizz 3 specs state max 2A per channel, that might not be enough.

Also, since these l motors draw twice the power of a lego L motor, does that mean they also make twice the amount of torque? theoretically that should suffice. And if not i can alwyas down gear them, should still be faster.

I am going to try anyway, the lego l motors just can not hack it.

 

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Buwizz 2.0 specified 4A per channel, but I don't think 4A per channel for 4 channels concurrently. 4A per channel, very likely one channel at a time, they did not indicate this on the specification. There is reason why it can't run more than 1 buggy motor concurrently at ludicrous mode. Buggy motor stall current is only 3.2A according to Philo

Buwizz to me, it's only a 2S lipo bettery (7.4V) to motor drivers thru voltage boost, that's is all I see plus it's not the most cost effective solution for RC. The only positive side I see using buwizz is, ease of integration, and more Lego-ish.

With higher ratio of reduction, those motors will draw lower current than direct drive, thus, I don't see any problem. Direct drive with these motors are not recommended. The inner motor, as suggested, is of a lower turn number, meaning it's a high speed high power motor, the efficiency at low speed is very poor especially when the vehicle is heavy, adding resistance to the motor to run at lower torque range (low speed). If you're to have direct drive, it's more sensible to use motor with higher turn number, which translates to low speed high torque motor, in another word, stock Lego motor.

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Well buwizz is what i have, and buwizz is what i shall use.

I appreciate the advice, will post my findings.

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