Off Road Dreaming

[Deleted member 3316]

From what I understand the motor casings are the same with or without casts. Those steering knuckles are the main reason you can't put larger tyres on.

Withthe lift kit the limiting factor will be CV joint angle on the driveshafys and how much wear you think is acceptable.

Yes, that’s why custom knuckles would be needed. An integrated portal axle would give about 150mm of lift, the bigger tyres would give a further 100-150mm then the body lift another 50-100mm. Air suspension can then give about 200mm of functional height range.

Starting with a nominal 150mm of ground clearance, the above mods would give at minimum 500mm of clearance, all keeping those shafys in the same orientation.

Another Question to the crowd. Would there be any issues running the motors backwards? Would a simple switch of polarity cause mechanical issues for the gearbox?

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[HaulingAss]

Given that the CT requires the larger casting machine in order to actually make a production version, how long do you think it will take before we start seeing testing on actual vehicles? I know there is SOME testing that can be done but there are limits and I'm interested to see some of the more extreme testing... rock crawling type of stuff.

A healthy amount of testing has probably already been done without the aluminum subframe castings. It's not a tricky engineering job to fab up some steel subframes with similar characteristics to the aluminum castings for testing vehicle dynamics. They can put load sensors in place to measure the amount of load transfered through these assemblies. The extra weight of the steel fabrications would be inconsequential for most testing purposes.

All that said, Tesla, more than any other manufacturer, makes good use of 3D load analysis software such that they largely know the results of the testing before they physically test it. Good software is only as good as the engineers putting it to work.

 

[SwampNut]

Another Question to the crowd. Would there be any issues running the motors backwards? Would a simple switch of polarity cause mechanical issues for the gearbox?

Well the front motor is AC. You’d have to program the controllers to do it, and I’m thinking that seems unlikely.

 

[Ogre]

A healthy amount of testing has probably already been done without the aluminum subframe castings. It's not a tricky engineering job to fab up some steel subframes with similar characteristics to the aluminum castings for testing vehicle dynamics. They can put load sensors in place to measure the amount of load transfered through these assemblies. The extra weight of the steel fabrications would be inconsequential for most testing purposes.

All that said, Tesla, more than any other manufacturer, makes good use of 3D load analysis software such that they largely know the results of the testing before they physically test it. Good software is only as good as the engineers putting it to work.

Tesla has access to very large scale CNC equipment which could machine a block of solid aluminum with nearly identical performance of the gigacasting.

Seems to me it’s more likely the later prototypes were the product of that sort of production rather than a steel subframe. I strongly suspect they’ve done a lot of testing on a truck which is extremely similar to the final design.

 

[Ogre]

Well the front motor is AC. You’d have to program the controllers to do it, and I’m thinking that seems unlikely.

I’m a bit confused here. How do current model Tesla’s reverse? I’m pretty sure they run the motors in reverse, is there some other mechanism at play I haven’t heard of? (I’m feeling lazy or I’d look this up, but I’m pretty sure they just reverse the motors)

 

[SwampNut]

I’m a bit confused here. How do current model Tesla’s reverse? I’m pretty sure they run the motors in reverse, is there some other mechanism at play I haven’t heard of? (I’m feeling lazy or I’d look this up, but I’m pretty sure they just reverse the motors)

They do, but they don’t simply reverse polarity. Maybe it’s semantics, but reversing isn’t that simple. I’m saying the motor controller has to be told to reverse, and the question was phrased as if you could just switch wires. Trying to be clear about the complexity.

 

[SwampNut]

Actually, wait, if the AC motor is three phase, you could reverse two phases to reverse the motor. There’s no polarity, but the phases determine direction. Not in a single phase motor though.

 

[JBee]

Yes, that’s why custom knuckles would be needed. An integrated portal axle would give about 150mm of lift, the bigger tyres would give a further 100-150mm then the body lift another 50-100mm. Air suspension can then give about 200mm of functional height range.

Starting with a nominal 150mm of ground clearance, the above mods would give at minimum 500mm of clearance, all keeping those shafys in the same orientation.

Another Question to the crowd. Would there be any issues running the motors backwards? Would a simple switch of polarity cause mechanical issues for the gearbox?

Well technically, and I do this practically all the time with brushless UAV PM motors, you just have to swap two of the three phase cables around to run them backwards. The same should be true for the AC motor, which I believe is in the back not the front?

The thing that might upset it is if the motor has a rotary encoder or a rpm sensor that can detect direction. That would also need to be swapped/reconfigured. The wheel ABS sensors should be fine as rhey spin the same way. Mechanically, I don't think it should affect the CV, gears or bearing much, if at all.

I'm assuming you're asking this because the change in direction from the portal axle gears? There's an Aussie company that does them for cruisers, but they use two auxiliary gear cogs in their portals meaning there is no motor direction change. They are just as compact as a normal portal but have twice the torque handling because of the two cog transfer. They not cheap though, I think they were around $4-5k each last time I checked a while ago.

The portals are also normally put on live rigid axles not independent suspension. As you say you'll need custom wheel knuckles all around to get the scrub point/angles right and mount the portals too, as well as give you more clearance for larger wheels.

Overall I think it shouldn't be to complicated to so, but I think 500mm of clearance is a little to much, and I'd leave the mod with whatever you get out of the portal hubs and tyre size change which should leave you with around 350-400mm of clearance which is plenty for that wheelbase and limited suspension travel it has.

The biggest encumbrance I see it having is wheel travel and articulation from the suspension. You'd at least have to switch out the shocks to account for the extra unsprung mass but adding independant "smart" air suspension would be best. As you know clearance is only half the problem, it's the ability to put equal pressure on each wheel to get traction down that keeps you moving. So using actively controlled airbags will make the most of the little articulation you have.

I don't know if Tesla uses custom diffs or gets them from a supplier but another way to give you a traction boost is either a LSD or a locker on the rear, and if you wanted to go all out a locker on the front too. I wouldn't put an LSD up front for normal on road driving purposes, seeing you need a licensed car to get down most of the beaches here. The traction control using brakes is better than nothing, but won't bring much joy in comparison simply because of the lag and the inability to modulate constant torque before you even run into articulation based traction problems. In this case even with one wheel in the air you at least have three wheel drive, which is 50% better than 2 wheel drive.

Would be interesting to see how it performs if someone ever does it.

Otherwise grab yourself a Vanderhal Brawley, for about the same price the MY mod will cost, but for a whole new vehicle with even better offroad specs.

 

[rr6013]

grab yourself a Vanderhal Brawley

Vanderhaul will survive if that is able to be licensed
The SXS Blazer knock-off(below)

 

[JBee]

Note the gearbox assembly on the Brawley has the driveshafts coming out of the middle housing (with the black oil filter) and has the disc brakes mounted inboard on the otherside of the motors. This is by far a better combination for an off-road vehicle, in that it reduces unsprung wheel mass, keeps the brakes out of the dirt and grind for best performance without excessive wear and affords the longest possible driveshafts to the wheels which result in reduced CV wear and lighter components throughout.

Depending on the weight and numbers brought into a country there is some room for some road registrations. If you add a mower attachment point you can also license it as a agriculture machine.

Actually reminds me of a life sized versoin of these eRevo's I use to race with my boys:

 

[Ogre]

Cybertruck is likely capable of far more than I am comfortable with off road. I just want to have a little fun, not break the bank.

 

[HaulingAss]

If I had money to burn I would totally take a CT4 on these trails! But since I don't, I will stick to modest off-road trails where the biggest risk to my precious machine is running out of power in the wilderness.

Where I off-road most often, it's possible to run out of gas but not out of battery power. You heard me right.

All the good off-road ventures lead out of the river valley up into the mountains. If I am dumb enough to run out I would just regen back down. In my Model 3 I can generally add 17-20 miles in a 12-mile return trip, more than enough to take me back down the valley highway to various charge locations. However, the Model 3 can only go on roads without high drainage swales, storm damage and landslides on the road. Most of the highest and best routes require a high clearance 4x4 vehicle.

In my F-150 I would be stuck because it would be foolhardy to try to descend without the engine powering the brakes and (especially) the steering. In most cases, I don't think it's even physically possible due to the steepness of the grade and need to turn the steering from lock to lock to traverse washouts and sections of road that have fallen away. These can take many years to get repaired, if ever. But, even the roads I've managed to navigate on my Model 3, the steepness ensures exceptional regen, even as I'm dodging larger rocks, drainage swales and other hazards that could cause bottoming without careful choice of lines.

There are no canyons around here that are below the highways and county roads, all the four wheeling is up, up, and away! Still, I've found the Model 3 to be super-efficient when crawling these rugged roads at 2-15 mph. There is essentially no drag from air resistance, so it all comes down to the delta between drive efficiency and 100% efficient and regen efficiency and 100% efficient along with whatever is used for auxiliary purposes like the stereo, lights and climate control. I've found the draw of those things to be really minimal when I have up to 75kWh to work with. Even if I start the venture with only 50 kWh, that is a lot of power! The Cybertruck will have much more. When you climb a big mountain trail you are left with a bunch of potential energy represented by the weight of your vehicle and the elevation it's sitting at. As you descend, it's surprising how quickly it can charge your battery! This also works on paved roads, but they are rarely steep enough to get a lot due to wind drag consuming most of the potential energy. Four-wheeling the speeds are slower and the grades are often steeper so the regen potential increases more than you might guess.

If you want to "supercharge" your regen potential when in the mountains, simply load the bed with, for example, 15 100 lb. rocks. Or shovel the bed full of snow heavy spring snow. This could be useful if running low on range and still having another pass to climb before getting back to civilization. Just make sure to remove the ballast after you make the descent and before you have to make the ascent. The amount of extra regen the extra weight provides is substantial, even compared to the amount of work to get it into the bed or trunk. That's because you are only lifting the weight a few feet compared to the regen opportunity provided by, for example, a 2000–4000-foot descent. This is an option that is simply not possible with a gas or diesel rig which unfortunately consume a surprising amount of fuel, even when descending and even when travelling at very slow speeds.

 

[HaulingAss]

Tesla has access to very large scale CNC equipment which could machine a block of solid aluminum with nearly identical performance of the gigacasting.

Seems to me it’s more likely the later prototypes were the product of that sort of production rather than a steel subframe. I strongly suspect they’ve done a lot of testing on a truck which is extremely similar to the final design.

My point was simply that it wouldn't even need to be aluminum for most testing purposes, steel can be fabricated with properties so similiar to aluminum, it wouldn't even matter. Thanks to expertise with materials engineering - it's all in the way the materials are used. Maybe aluminum would be cheaper, but even that's not a given considering the size of these subframes.

Eventually, they will need to test the actual giga-castings but since they will probably be slightly more robust than the test assemblies, they might not need to make any adjustments.

 

[Deleted member 3316]

Note the gearbox assembly on the Brawley has the driveshafts coming out of the middle housing (with the black oil filter) and has the disc brakes mounted inboard on the otherside of the motors.

It would be great if Tesla took up this configuration. In board brakes seem like such a good idea for an electric drive train. A simple blocking park brake at the wheel would mitigate the risk of a catastrophic drive shaft failures at all four wheels.
Gives more room for 4 wheel steering and possibly reduced part count if the same components can be used front and rear.

37” tyres on 16” rims would be awesome….

 

[JBee]

Where I off-road most often, it's possible to run out of gas but not out of battery power. You heard me right.

All the good off-road ventures lead out of the river valley up into the mountains. If I am dumb enough to run out I would just regen back down. In my Model 3 I can generally add 17-20 miles in a 12-mile return trip, more than enough to take me back down the valley highway to various charge locations. However, the Model 3 can only go on roads without high drainage swales, storm damage and landslides on the road. Most of the highest and best routes require a high clearance 4x4 vehicle.

In my F-150 I would be stuck because it would be foolhardy to try to descend without the engine powering the brakes and (especially) the steering. In most cases, I don't think it's even physically possible due to the steepness of the grade and need to turn the steering from lock to lock to traverse washouts and sections of road that have fallen away. These can take many years to get repaired, if ever. But, even the roads I've managed to navigate on my Model 3, the steepness ensures exceptional regen, even as I'm dodging larger rocks, drainage swales and other hazards that could cause bottoming without careful choice of lines.

There are no canyons around here that are below the highways and county roads, all the four wheeling is up, up, and away! Still, I've found the Model 3 to be super-efficient when crawling these rugged roads at 2-15 mph. There is essentially no drag from air resistance, so it all comes down to the delta between drive efficiency and 100% efficient and regen efficiency and 100% efficient along with whatever is used for auxiliary purposes like the stereo, lights and climate control. I've found the draw of those things to be really minimal when I have up to 75kWh to work with. Even if I start the venture with only 50 kWh, that is a lot of power! The Cybertruck will have much more. When you climb a big mountain trail you are left with a bunch of potential energy represented by the weight of your vehicle and the elevation it's sitting at. As you descend, it's surprising how quickly it can charge your battery! This also works on paved roads, but they are rarely steep enough to get a lot due to wind drag consuming most of the potential energy. Four-wheeling the speeds are slower and the grades are often steeper so the regen potential increases more than you might guess.

If you want to "supercharge" your regen potential when in the mountains, simply load the bed with, for example, 15 100 lb. rocks. Or shovel the bed full of snow heavy spring snow. This could be useful if running low on range and still having another pass to climb before getting back to civilization. Just make sure to remove the ballast after you make the descent and before you have to make the ascent. The amount of extra regen the extra weight provides is substantial, even compared to the amount of work to get it into the bed or trunk. That's because you are only lifting the weight a few feet compared to the regen opportunity provided by, for example, a 2000–4000-foot descent. This is an option that is simply not possible with a gas or diesel rig which unfortunately consume a surprising amount of fuel, even when descending and even when travelling at very slow speeds.

So what you really want is a self loading shovel to load dirt into the bed at the top of the hill, and then tip it out down the bottom.

So use that "crazy" underslung storage idea I drew up a while ago as a "scraper".
Just deploy blade over soft ground to collect dirt and then use air pressure to drop it out the back again:

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