Drift chassis question

[1963maniac]

4 hours ago, Gray Gear said:

@1963maniac Why would you use a locked up differential instead of just using a gear? What advantage does it have, surely using a normal gear is much stronger?

 

7 hours ago, 1963maniac said:

Sam Wystrach uses this differential set up in his Crawler.  https://rebrickable.com/mocs/MOC-51296/wystrach_sam/rc-crawler-4x4x4/#comments

With this you can still drive an axle with a differential while it doesn't work as a differential. It has 2 half 2L beams with a 2L axle inside it.

 

 When using a 5X7 frame, you will not have room for a 20t driver gear and a 28t gear (differential being 28t).

[Mechbuilds]

When you look at "Gears of doctor"'s drift Skyline. 
I kinda like the 4 buggy motor setup for 4wd drift. 

I don't have 4 buggy motors though.. I only have 2. I wonder if it's possible to make a setup that has 2 buggy motors + 1 servo and buwizz for power. 
I'll probably put one buggy per axle. 

Biggest issue will be the front axle. Figuring out how to get room for the buggy motor in the middle to power both tyres and then have enough room for a servo. 
Suspension will probably be impossible to add in this size and scale if i want a drifter to be nearly the same size but i think 2 stud narrower than the skyline. 
And even if the suspension is possible, it needs to be very minimal and extremely stiff.. So basically if the moc is shown as a display piece, you get very minimal suspension flex to barely call it a suspension and it won't interfere with drifting. 


EDIT:



Ahh ofc.. 

Edited November 22, 2020 by Mechbuilds

[Gray Gear]

Can you explain why would you want to go AWD for a LEGO drift car? IRL the best drift cars are FR's and AWD was developed to improve grip in rally in the first place. Its a lot harder to break the traktion of 4 tires than 2... 

 

Btw that "Drift Skyline GT-R" is a really weird naming choice. The GT-R's Attesa AWD system was developed keep the car from loosing tracktion... 

Edited November 22, 2020 by Gray Gear

[Mechbuilds]

Rear wheel drive will just spin around a circle doing donuts.. Drifting is not doing donuts.. It's going a long curve sideways. 
AWD is better so you can actually maintain some controlability and actually handle the car drift.. Most if not all RC drift cars are also AWD.. 

I think the issue on this is that people keep thinking about real cars in real life. 
I know it's hard to understand but for RC cars, they behave completely differently when drifting compared to real life cars. 

If you want to break traction easily, you setup the gearing so rear wheels are spinning faster than the front wheels. 
That way your car will move like a front wheel drive so it steers and moves the car while the rear end is just spinning and sliding about. 


@Attika already made a thread with the drift wagon explaining why AWD is better than RWD with video evidence. 


EDIT:
@Gray Gear You are correct that it's a lot harder to break traction of 4 wheels than 2.. But who said that you are breaking traction of 4 wheels? The front wheels will never lose traction. The front wheels will steer and move the car while the rear is drifting. 

Edited November 22, 2020 by Mechbuilds

[Gray Gear]

@Mechbuilds using these different speeds, got it. But why would you tape the front wheels if they are not supposed to lose traction? 

Cant wait to see this thing in action 

[Mechbuilds]

28 minutes ago, Gray Gear said:

@Mechbuilds using these different speeds, got it. But why would you tape the front wheels if they are not supposed to lose traction? 

Cant wait to see this thing in action 

You can do it so it skids with all 4's or you can make it so the front wheels are not taped. Both have their benefits and issues. 
You can for example, create front wheels that are only half taped and add camber. That way when you drift in a corner, you maintain grip on the inner side and have no grip on the outer side. 
That way you get grip in the turn which will make the turns sharper.. Or you can tape it the other way so the outer wheel has grip and inner wheel doesn't. That way you get loose grip on the inside which will make the turns less sharp. 

[Gray Gear]

23 minutes ago, Mechbuilds said:

You can do it so it skids with all 4's or you can make it so the front wheels are not taped. Both have their benefits and issues. 
You can for example, create front wheels that are only half taped and add camber. That way when you drift in a corner, you maintain grip on the inner side and have no grip on the outer side. 
That way you get grip in the turn which will make the turns sharper.. Or you can tape it the other way so the outer wheel has grip and inner wheel doesn't. That way you get loose grip on the inside which will make the turns less sharp. 

Thats very cool and intresting, maybe I'll do a small scale drift car too sometime in the future. I'd have to find a usable RC solution tho, Buwizz and 2x LEGO buggy motor is out of my budget tbh 

[Mechbuilds]

I'm still trying to figure out if i should make Axle connection for tyre and use U joints for big steering lock. Or should i use those black wheel hubs for stud connection to tyre and a more robust chassis. But with CV joint i will loose a fair bit of steering angle. 
But then again if i'm going 4wd, will it matter if i loose all that steering angle? 


Also suspension or no suspension? Tough call.. Space is fairly limited. Dodge charger wheels are pretty wide and when steering, they really need lots of room. 

[Gray Gear]

55 minutes ago, Mechbuilds said:

Also suspension or no suspension? Tough call.. Space is fairly limited. Dodge charger wheels are pretty wide and when steering, they really need lots of room. 

If there really is no space for suspension just slam the car on its nuts and call it a day 

You could first make a test chassis without suspension and fix some weight on top to simulate the weight of the body. Once wou are happy with the drifts you can still try to put some suspension in the final model.

[Mechbuilds]

Oh well i have the 2 buggy motors in place and i'm starting to build a chassis around it.. Next issue is creating the front axle and steering. 
After i get the front axle done, the rear axle will be easy.. Still haven't decided what scale to make it or what car to make. 

I started to think about scale. I wonder if i build a working independent suspension, will the car be so large that the two buggy motors won't have enough power to drive it? 
Ofc taped wheels will help it drift but i wonder how big can i build before it's weight will be an issue? 
Considering i want to build bodywork on it instead of just using an axle frame. 

Edited November 23, 2020 by Mechbuilds

[FoxOne]

So I've been inspired by Gears of Doctor / RM8's drifting performance, too )).

 

As a result, I've built a simple testbed for a drift car concept. It's capable of decent performance on a hardwood floor, doing both donuts and controllable power slides. It's powered by 2 * PU XL motors, plus 1 * PU L for steering, and uses a standard Control+ hub. I skipped suspension, Ackermann and castor, for the sake of simplicity and building speed. There's ain't no bodywork as well, since it's a testbed. U-joints for the steered axle, 4WD drive, forward open diff, rear is welded.

 

The following is a sort of a long read -- please kindly let me know if it's considered the offtopic.

------------

I've done some tests while experimenting with it, happy to share / discuss. Goes without saying it applies to Lego plastic cars, and not everything can be projected to real life scenarios.

My findings are:

 

Most important factors for drift performance are Power, Steering geometry and Wheels traction

 

Out of these three, Traction affects performance the most (in Lego case, of course). Given wheels are slippery enough you can brake traction with almost any reasonable power / geometry, but doing controllable stunts requires fiddling with different types of wheels.

I ended up with plastic rims from 42099's wheels on the rear axle, and some strange orange plastic wheels form 10 years old Mars Rover (Mars Invasion, Creator series, smth like that). I've also tried regular rubbery wheels w and  w/o taping them, but this (plastic ones) particular configuration has proved the best.

 

Talking of Power, it's a combination of 3 factors: model weight, power plant power and it's distribution between axles.

-- it's easier to brake traction with lightweight model

-- trying to get something overpowered enough with standard motors / power (i.e. w/o BuWizz and buggy motors) isn't simple, to say the least

-- regarding drive type, tried and true configuration is 4WD with welded rear diff

 

I've compared different configurations myself:

-- RWD, welded rear diff -- easy to break traction, but it's only donuts and sharp uncontrollable U-turns; weak acceleration

-- 4WD, welded rear diff -- donuts and U-turns are still possible, but not so sharp; nice controllable power slides; healthy acceleration rate

-- 4WD; both diffs welded -- doesn't turn at all

-- 4WD or RWD; both diffs open -- very hard to break traction

 

Geometry boils down to wheel base and max steering angle:

-- it was a lot easier to drift with the short wheel base, but it's harder to control the skid

-- larger max steering angle has a strong impact on breaking traction

 

And 2 more finding re geometry:

-- rate of steer is of importance, too -- the faster, the better

-- I've tried to drift even with articulated steering -- in short, it's next to impossible

 

No effect / haven't tried yet:

-- weight distribution between forward and rear: I moved the hub along the longitudal axis, but effect was negligible; maybe wheel base was too short to notice the difference

-- there's a recipe to drive rear axle with higher RPMs than forward; kinda tried that, using bigger wheels at the rear, to no avail

-- I was limited with the choice of wheels, but small wheels (with appropriate transmission adjusting) should be better, due to faster acceleration

 

Sort of serendipity:

If a rear side of your forward wheel touches the chassis and stops at the extreme steering angle, it promotes very sharp and clean donut: braked wheel becomes the pivot, while the forward differential moves all the torque to the opposite wheel, promoting the spin even further

 

Bonus track:

First prototype was built on EV3 platform, with 2 EV3 large motors for driving. Oh man..those beasts do pack a punch, but ain't have no RPMs, was a quest to gear it up enough; that and sheer weight / size of EV3 made it ineffective, though I made it drift a little with taped wheels

 

[Mechbuilds]

@FoxOne Interesting input. 

I personally agree that AWD + welded rear diff is the best option to go if you want to get controllable drifts instead of just making donuts all the time. 

I haven't even considered using the chassis of the moc to brake the front wheel when turning. 
I'm very interested in seeing your test bed. I'll PM you on my project if you could help me with it. 
I'll post progress on my drifter build in my projects thread. 

If i figure out anything cool to add on making drift cars from lego, i'll add info here. 

[FoxOne]

Happy to share, will follow your project!

 

One more thing in favor of AWD: Without proper castor, it's a challenge to drive accelerating RWD car in a straight line. No such problem in AWD mode, and acceleration rate is better.

 

Another crazy setup would be FWD with a handbrake. Not sure if it's practical with standard motors, too much weight (extra motor to power handbrake).

Edited November 24, 2020 by FoxOne

[2GodBDGlory]

21 hours ago, FoxOne said:

If a rear side of your forward wheel touches the chassis and stops at the extreme steering angle, it promotes very sharp and clean donut: braked wheel becomes the pivot, while the forward differential moves all the torque to the opposite wheel, promoting the spin even further

 

 

I've probably done that plenty of times on drift-focused vehicles--except it was always by accident!

[Mechbuilds]

I've been looking at supercar builds with 17 studs between wheel hubs. 

If i were to build a car of that scale. Would RWD be enough? If i had two buggy motors powering the rear wheels with welded diff. But having the front axle with a larger turning radius.. 
Not only at that scale i'd get a working suspension but also a cool big supercar. 

But would it drift is the question. AWD is impossible with wheel hubs because CV joints have very limited turning radius.

[Mechbuilds]

Made a 4wd drift chassis. Very light. The servo placement is kinda awkward. it would protrude trough the windshield. 
As for power, it has plenty enough power.. Almost too much power. Drifting is kinda impossible because the tail will just whip aggressively. So basically turning will result into a donut. 

For the servo placement, can't really flip it upside down because it would interfere with the drive shaft. 
Can't really mount it in front of the front axle because then placing the buwizz would be harder. 

I think my chassis needs more weight in the rear to stop it from tailwhipping. 


One solution would be to mount the servo to the rear and have a very long axle for steering.. Which is probably the only way.. 
Currently my chassis is 35 studs long and 13 studs between tires. 

Definitely a good start to work from. 




EDIT:

Notes:
For RWD drifter, make sure that the tail is light and have lots of weight on the front axle. 
For AWD drifter, make sure that the tail is heavier than the front. 

Edited November 25, 2020 by Mechbuilds

[Gray Gear]

@Mechbuilds Would there be enough space to mount te servo in front of the Front axle somehow? I you could try to move the Buggy Motors back further for more weight in the rear

Edited November 25, 2020 by Gray Gear

[Mechbuilds]

15 hours ago, Gray Gear said:

@Mechbuilds Would there be enough space to mount te servo in front of the Front axle somehow? I you could try to move the Buggy Motors back further for more weight in the rear

Building the servo on the front would create many issues.. Nose being very long.. Wire not long enough.. Awkward buwizz placement.. 

I wonder if i can make RWD work if the moc is much larger. Talking about 1:10 scale.  
I've built @Charbel Volcano RS front axle with slight modifications to accept servo. 

The steering isn't too bad. It isn't drift steer by any means but it's good enough. 
But now i have suspension.

I think i really want a model car that can drift. To make it work is extremely difficult because motor placement and buwizz placement and trying to have a fake engine in the mix is almost impossible with interior.. 
Probably if i scrap the fake engine, it could be done. 

To make it drift however..  I might do a 2 RC motor solid real axle instead of independent suspension rear axle. 
The tyres are 68.8 x 36 chinese copy tyres. Why? Because the chinese copy rubber is very stiff and hard. So it provides less grip. Which is better for drifting. 
Lego tyre rubber is very soft and grippy. 


Does anybody know the largest drift lego car ever built? 
I'm sure lego motors have their limitations but how big can we build before weight becomes an issue? 

Edited November 26, 2020 by Mechbuilds

[Mechbuilds]

Finally the front axle is done. Complete with the next features:

-Ackermann steering. 
-Positive caster. 
-Output for steeringwheel. 
-Suspension




This is a good start.