[MOC] Trial Tractor 4x4 (Revenge of the Auto-lock Differential)

[JoKo]

Hello

I rebuilt 100% my trial truck to improve the design on two points: reliability for the gear train up to max torque and lowering the center of gravity.

The frame is 2 studs wider to separate gears from differentials, slightly better lateral stability also.

I relocated the battery box as low as possible with the two XL motors. there is a retained axle to push on the hub button. You can change the batteries directly from below and the differentials area are protected from below.

The self locking differentials works with the same principle as before with a substractor diff linked to the main diff and a miniaturized centrifugal device to lock the substractor when too much wheel slip.

By the way did someone give it a try? There was some people interested in this mechanism.

For more about the auto-lock system:

The mini centrifugal device:

[Jurss]

I like that prtection fram around cabin.

That fron shock absrober connection is not quite correct.

[2GodBDGlory]

Nice to see that differential lock in a more developed model!
I meant to try out that design, but kept forgetting. Seeing this model should be the push I need to get it built, though!

[2GodBDGlory]

I just built that lock, and I'm as impressed as ever! I did take the liberty of compacting the centrifugal mechanism a bit, and removing that 8T to 8T gear connection, though possibly at some cost of durability (I haven't had any failures yet, but my testing hasn't been too intense)

Now there's a part of me that thinks I need to make some super-maneuverable, 4WS crawler to use this lock design...
Perhaps after TC24 is done?

Edited February 2, 2023 by 2GodBDGlory

[JoKo]

55 minutes ago, 2GodBDGlory said:

I just built that lock, and I'm as impressed as ever! I did take the liberty of compacting the centrifugal mechanism a bit, and removing that 8T to 8T gear connection,

I don't get what 8t gears you are talking about? don't have any 8t gear in the model.

Nice to see it on someone else's desk overseas !

Bigger centrifugal devices are more consistent but this small butterfly gets the job done! And you'll have to find a way to ad steering somewhere. On this model the steering rack is just behind the bumper.

I would be pleased to have feedback!

Edited February 2, 2023 by JoKo

[2GodBDGlory]

44 minutes ago, JoKo said:

I don't get what 8t gears you are talking about? don't have any 8t gear in the model.

Nice to see it on someone else's desk overseas !

Bigger centrifugal devices are more consistent but this small butterfly gets the job done! And you'll have to find a way to ad steering somewhere. On this model the steering rack is just behind the bumper.

I would be pleased to have feedback!

Yeah, it'll definitely take some mods to put into a steered axle, but the theory should all be down!

Now that I look at this model, I see that you've got the mechanism integrated more nicely than in the mock-ups you had earlier, so you don't have those 8T gears anymore either. I was copying from this image that you shared in the other thread, so my modifications are relative to it:

[pow]

The topic haunted me until sleep tonight. I now felt somehow compelled to build my own version. Maybe the LBG gear sits a bit tight.

@JoKo thank you for that great concept! it has potential to be built relatively compactly. ~ no more motorized differential locks. *wohoo

Link to messy studio file: https://bricksafe.com/files/wop/studdstuff/AutoLockDifferentialByJoKo.io

[JoKo]

2 hours ago, pow said:

@JoKo thank you for that great concept! it has potential to be built relatively compactly. ~ no more motorized differential locks. *wohoo

You're welcome! Happy to see it receives attention!

Thanks for sharing your evolution!

The LBG gear seems perfectly OK but I would use a new diff with red gear on top (substractor) to increase the speed of the centrifugal device by higher gear ratio.

I don't think it can be as compact as a traditional or pneumatic lock but you don't need an extra servo or remote control channel. So I think it can be a competitive solution for some projects

Edited February 6, 2023 by JoKo

[Zerobricks]

A brilliant execution. Though I still think having seperate motor controls for left and right side wheel drive is an even better and more efficient solution.

[JoKo]

6 hours ago, Zerobricks said:

A brilliant execution. Though I still think having seperate motor controls for left and right side wheel drive is an even better and more efficient solution.

It seems hard to control 4 motors independently plus servo for steering without another Bluetooth hub.

For pure performance I can believe it's more efficient and could be fun to drive but honestly I find this crude and nothing much interesting to put together. So I'll leave it to Tesla until I create something heavy enough to need them.

I think efficiency is also about not using more electronics than needed but smart way to use it. And for me the pleasure of Technic is finding creative solutions not taking brute force to power a RC model

Edited February 6, 2023 by JoKo

[pow]

On 2/6/2023 at 4:54 PM, Zerobricks said:

A brilliant execution. Though I still think having seperate motor controls for left and right side wheel drive is an even better and more efficient solution.

it depends on the size of your build. building larger scale (cars) i would tend to use one motor per wheel. But in smaller builds this differential is pretty smart. because it packs a lot of functionality into a very small form factor.

Best wishes

[2GodBDGlory]

I was planning out a new MOC in my head, and was hoping to use this diff lock in it, but I think I ran into a snag.

I was hoping to include a two-speed gearbox in the MOC, but because the diff lock is based on one specific activation speed, this would essentially mean that if I wanted the lock to function normally in low gear, it would become extremely sensitive in high gear, and likely lock up when turning corners normally, because of the ~3x difference in wheel speed between gears. I suppose this could also be a problem with a single-speed vehicle off-roading at a time where the motors are under enough load that they have slowed down enough to avoid diff locking, though this seems less likely.

Does anyone have any ideas for how we could work around this quirk? I've thought about adding some mechanism coupled to gear selection, that could potentially just turn off the lock in high gear, allowing for smooth operation at speed and normal locking function when going slowly, but that adds some regrettable complexity.

[JoKo]

On 2/24/2023 at 7:06 PM, 2GodBDGlory said:

I was hoping to include a two-speed gearbox in the MOC, but because the diff lock is based on one specific activation speed, this would essentially mean that if I wanted the lock to function normally in low gear, it would become extremely sensitive in high gear, and likely lock up when turning corners normally, because of the ~3x difference in wheel speed between gears. I suppose this could also be a problem with a single-speed vehicle off-roading at a time where the motors are under enough load that they have slowed down enough to avoid diff locking, though this seems less likely.

Does anyone have any ideas for how we could work around this quirk? I've thought about adding some mechanism coupled to gear selection, that could potentially just turn off the lock in high gear, allowing for smooth operation at speed and normal locking function when going slowly, but that adds some regrettable complexity.

Hi!

Nice to have evolution on this concept!

You d'like a two speed gearbox with 3x speed difference between high and low gear?

That would indeed be out of the system's capability but I think it's a little extreme without intermediate gear.

With a closer gears 2-speed gearbox I think you can find the right ratio to drive the centrifugal device. If you have 4 wheels steering with high steering angle you will maybe need to slow down in tights curves. Not so far from actual off road driving.

By my experience when the motors are under enough load to slow down, a loss of grip leads to wheel spin and motor speeds up, locking the system.

And if you struggle to fine tune the minimal size centrifugal device, try with a bigger one. They have more options possibles and can have the sensitivity tuned with different shapes and locking obstacles.

 

[2GodBDGlory]

2 hours ago, JoKo said:

Hi!

Nice to have evolution on this concept!

You d'like a two speed gearbox with 3x speed difference between high and low gear?

That would indeed be out of the system's capability but I think it's a little extreme without intermediate gear.

With a closer gears 2-speed gearbox I think you can find the right ratio to drive the centrifugal device. If you have 4 wheels steering with high steering angle you will maybe need to slow down in tights curves. Not so far from actual off road driving

 

Yeah, I am going for something with at least that 3x difference, because I want to have a fairly dramatic speed difference between the two, with a low crawling gear, and a fairly fast cruising gear. You're right, I think I could make a tighter-ratio gearbox work, but I'm trying to avoid that compromise!

For sake of space above my rear axle, I'm actually going to be mounting the diff lock in the chassis and then running individual shafts down to each wheel. Because of this, it'll actually be very close to the gearbox, so I don't think it'll be too hard to disable the diff lock in high gear.

2 hours ago, JoKo said:

By my experience when the motors are under enough load to slow down, a loss of grip leads to wheel spin and motor speeds up, locking the system.

Yeah, I'd agree, there's not going to be many times when the wheels are spinning, but at the same time creating enough friction to slow the motors down that much. It's probably nothing to worry about!

[JoKo]

50 minutes ago, 2GodBDGlory said:

Yeah, I am going for something with at least that 3x difference, because I want to have a fairly dramatic speed difference between the two, with a low crawling gear, and a fairly fast cruising gear. You're right, I think I could make a tighter-ratio gearbox work, but I'm trying to avoid that compromise!

For sake of space above my rear axle, I'm actually going to be mounting the diff lock in the chassis and then running individual shafts down to each wheel. Because of this, it'll actually be very close to the gearbox, so I don't think it'll be too hard to disable the diff lock in high gear.

 

Interresting idea mounting it close to the gearbox. you could event have a gearbox for the diff lock, it's not that more than disabling the lock

By the way are you going 2WD or 4WD?

[2GodBDGlory]

4 hours ago, JoKo said:

Interresting idea mounting it close to the gearbox. you could event have a gearbox for the diff lock, it's not that more than disabling the lock

By the way are you going 2WD or 4WD?

Yeah, I could probably control a manual lock pretty easily from the gearbox, but I want to try this out, and I guess I don't care that I'm trying to make it work in a compact model where it's maybe not ideal!

It'll be 4WD.

[Sentinel]

What about an automatic transmission?

[2GodBDGlory]

11 hours ago, Sentinel said:

What about an automatic transmission?

It could be done, but it would probably run into the same issue if it had a wide ratio spread, and because the complexity of actually getting an automatic to work right is so high, and because the complexity of the diff lock isn't insignificant, stacking the two together would add too much friction and be too unreliable to be an ideal combination. It'd be very cool if someone could pull it off, though!

[Daniel-99]

On 3/3/2023 at 5:54 PM, 2GodBDGlory said:

It could be done, but it would probably run into the same issue if it had a wide ratio spread, and because the complexity of actually getting an automatic to work right is so high, and because the complexity of the diff lock isn't insignificant, stacking the two together would add too much friction and be too unreliable to be an ideal combination. It'd be very cool if someone could pull it off, though!

I was thinking about automatic transmission for quite a while. Here are my thoughts:

1. If you want to build a playable and durable RC Lego car, then you should avoid unnecessarily gears, giving as much power from motor to wheels as possible
2. If you want to build a "realisitc" prototype, then it should have an "automat": a robot, that shift gears depending on the velocity and torque of wheels, detected by special sensors... Mechanical automatic transmission is not that realistic nowadays 

[2GodBDGlory]

40 minutes ago, Daniel-99 said:

I was thinking about automatic transmission for quite a while. Here are my thoughts:

1. If you want to build a playable and durable RC Lego car, then you should avoid unnecessarily gears, giving as much power from motor to wheels as possible
2. If you want to build a "realisitc" prototype, then it should have an "automat": a robot, that shift gears depending on the velocity and torque of wheels, detected by special sensors... Mechanical automatic transmission is not that realistic nowadays 

Those are both very true observations!

I'd agree that no gearbox and minimum gears is definitely the best option for peak performance, though sometimes a two-speed can be enjoyable for a multi purpose machine.

I've built autos before, both mechanical and electrical, and I'd agree that electrical is much more practical, at least for gearboxes with 3+ gears. 2-speed planetary automatics can be somewhat practical, though, when made using a planetary hub.