TFL Says Cybertruck Won't Offroad (Well)...and I Respond (Newest Video)

[ldjessee]

I have high centered on rock a short wheel base 4WD (with locking hubs) vehicle.
There is always going to be some terrain that will defeat the particular geometry of any off-road vehicle. (That is why one of the first things someone will tell you to get is a winch for your rig).

A longer wheel base (ie, a rectangle as opposed to a square) will drive better on the road.
Even if I lived somewhere where most of my driving was on dirt or gravel roads, still would want a longer wheel base with shorter overhangs than a shorter wheel base with longer overhangs.

Here is something I have been thinking about... Now that people have gotten used to the steering wheel not being mechanically connected to anything that makes the front wheels turn (steer by wire), when will people become ok with the two front wheels not being mechanically connected?

Also, what about rear-steer on a vehicle that can drive itself? Seems like something that could be included on such a 'long' vehicle to allow for better maneuverability in tighter spaces.

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[cybertrucktruckguy]

I have high centered on rock a short wheel base 4WD (with locking hubs) vehicle.
There is always going to be some terrain that will defeat the particular geometry of any off-road vehicle. (That is why one of the first things someone will tell you to get is a winch for your rig).

A longer wheel base (ie, a rectangle as opposed to a square) will drive better on the road.
Even if I lived somewhere where most of my driving was on dirt or gravel roads, still would want a longer wheel base with shorter overhangs than a shorter wheel base with longer overhangs.

Here is something I have been thinking about... Now that people have gotten used to the steering wheel not being mechanically connected to anything that makes the front wheels turn (steer by wire), when will people become ok with the two front wheels not being mechanically connected?

Also, what about rear-steer on a vehicle that can drive itself? Seems like something that could be included on such a 'long' vehicle to allow for better maneuverability in tighter spaces.

 

[ldjessee]

I already watched that video.
Scrubbing tires on asphalt/cement is not ideal.

The problem that seemed to happen with other vehicles having rear steering was complexity of control. Some very customized off-road rigs have rear wheel steer, but with the computing and ability to self drive, I think software could be developed that would allow the truck's computer to control the rear steering.

 

[ajdelange]

The Rivian has eight degrees of freedom in its torque vectoring capability: 4 brakes and 4 motors. The Tesla Trimotor will have 7: 4 brakes and 3 motors. Thus the Rivian will always have more flexibility in what it can do in this regard than the TriMotor (if marginally) . Torque vectoring can be used to great advantage in stabilization of the vehicle especially where there are frictional differences at the four wheels and it is in those situations where torque vectoring will be used. Tank turns are a fantastic showcase for the 8 DOF Rivian has but these machines are not graders, lawn mowers, front loaders or tanks. They are transportation vehicles. So tank turning is mostly a marketing tool. Scaringe goes on at great length about how it is to be used only in appropriate (low mu) situations where the environment will not be damaged by the ruts etc and has announced that slip will be sensed and the feature disabled where mu is high.( roads, driveways, parking lots...) Thus people who fancy that they will be able to pull into their garages and not have to back out because they can tank turn in place are going to be disappointed and given the number of posts from people who seem to think that they will be able to do this that's going to be a fair number of people.

I wonder if Rivian will actually offer it as its frequent use is going to destroy tires and put tremendous lateral loads on other drive train components. To protect themselves from lots of warranty problems they will either have to offer a different warranty to people who buy this feature or limit the use to very limited situations (sand?). I doubt Tesla will touch it at all. But who knows?

 

[TyPope]

The Rivian has eight degrees of freedom in its torque vectoring capability: 4 brakes and 4 motors. The Tesla Trimotor will have 7: 4 brakes and 3 motors. Thus the Rivian will always have more flexibility in what it can do in this regard than the TriMotor (if marginally) . Torque vectoring can be used to great advantage in stabilization of the vehicle especially where there are frictional differences at the four wheels and it is in those situations where torque vectoring will be used. Tank turns are a fantastic showcase for the 8 DOF Rivian has but these machines are not graders, lawn mowers, front loaders or tanks. They are transportation vehicles. So tank turning is mostly a marketing tool. Scaringe goes on at great length about how it is to be used only in appropriate (low mu) situations where the environment will not be damaged by the ruts etc and has announced that slip will be sensed and the feature disabled where mu is high.( roads, driveways, parking lots...) Thus people who fancy that they will be able to pull into their garages and not have to back out because they can tank turn in place are going to be disappointed and given the number of posts from people who seem to think that they will be able to do this that's going to be a fair number of people.

I wonder if Rivian will actually offer it as its frequent use is going to destroy tires and put tremendous lateral loads on other drive train components. To protect themselves from lots of warranty problems they will either have to offer a different warranty to people who buy this feature or limit the use to very limited situations (sand?). I doubt Tesla will touch it at all. But who knows?

Wait a second. Even my 13 year old F350 has an electronically lockable rear differential which is quite close to being able to control which wheel gets power. You are assuming that just because Tesla has a single motor back there that they can't control which wheel gets the power and that seems a little unbelievable. The ability to torque vector the rear wheels should be very simple to add if not already there. But, like you, I believe there is VERY limited use of the tank turn.... maybe turning around on a narrow dirt trail but that's about it.

 

[ajdelange]

No, no. Tesla doesn't have a single motor back there. They have 2. Hence 4 DOF at the rear and 3 in the front. I'm obviously talking about the TriMotor here. Even the single motor version has 3 DOF (brakes and 1 motor) and the AWD 6 (for brakes and two motors).

 

[TyPope]

No, no. Tesla doesn't have a single motor back there. They have 2. Hence 4 DOF at the rear and 3 in the front. I'm obviously talking about the TriMotor here. Even the single motor version has 3 DOF (brakes and 1 motor) and the AWD 6 (for brakes and two motors).

Oh. I thought they'd put two up front and one in the rear. There isn't as much grip back there as in the front so I figured (incorrectly, apparently) that Tesla would put two motors up front and one in the rear. Either way, torque vectoring can be electrically controlled allowing for individual wheel control which gives the CT the same 8 that the Rivian has. (just with fewer motors)

 

[ajdelange]

Why do you say there is more grip at the front? This is true when a vehicle is decelerating (it's the reason the front brakes are heftier than the rear ones) but in an acceleration situation, especially where there is tongue weight from a trailer, the opposite is true. I don't know that there will be two in the back and one in the front but I am assuming that will be the case as the TriMotor is what it is, as far as I can tell, so it can tow. To get a large trailer moving you need lots of traction and you want to put the motors where you can get it, in the rear. In towing sway is a big concern. You've got this great mass hanging off the back of the truck and anything that pushes it to the side, such as a wind gust or the blast from a passing semi, pushes that mass to one side or the other putting a big torque about the rear wheels of the truck trying to point its nose towards the other side. The reason for 5th wheels, goosenecks and pivot point projection hitches is to minimize that torque by getting the pivot point (or effective pivot point) forward thus minimizing the arm. But with two motors in the back supplying different amounts of thrust you can neutralize the torque about the centerpoint of the rear wheels even if the pivot point is rearward. So I think it's going to be two induction motors in the back for the torque needed to start a large trailer moving and the vectoring to improve lateral stability and one switched reluctance up front for range but that is all speculation on my part. I am not privy to any more information than any of have.

Each motor provides a DOF. Thus if you have fewer motors you have fewer DOF. And in addition to that we could say a motor provides twice as many DOF as a brake as it can provide torque in either direction relative to the rotation of the wheel whereas a brake can only provide it in the direction opposite to the direction of rotation.

 

[Sirfun]

Why do you say there is more grip at the front? This is true when a vehicle is decelerating (it's the reason the front brakes are heftier than the rear ones) but in an acceleration situation, especially where there is tongue weight from a trailer, the opposite is true. I don't know that there will be two in the back and one in the front but I am assuming that will be the case as the TriMotor is what it is, as far as I can tell, so it can tow. To get a large trailer moving you need lots of traction and you want to put the motors where you can get it, in the rear. In towing sway is a big concern. You've got this great mass hanging off the back of the truck and anything that pushes it to the side, such as a wind gust or the blast from a passing semi, pushes that mass to one side or the other putting a big torque about the rear wheels of the truck trying to point its nose towards the other side. The reason for 5th wheels, goosenecks and pivot point projection hitches is to minimize that torque by getting the pivot point (or effective pivot point) forward thus minimizing the arm. But with two motors in the back supplying different amounts of thrust you can neutralize the torque about the centerpoint of the rear wheels even if the pivot point is rearward. So I think it's going to be two induction motors in the back for the torque needed to start a large trailer moving and the vectoring to improve lateral stability and one switched reluctance up front for range but that is all speculation on my part. I am not privy to any more information than any of have.

Each motor provides a DOF. Thus is you have fewer motors you have fewer DOF. And in addition to that we could say a motor provides twice as many DOF as a brake as it can provide torque in either direction relative to the rotation of the wheel whereas a brake can only provide it in the direction opposite to the direction of rotation.

Imagine trying to pull a heavy boat up a wet boat ramp with front wheel drive. No Bueno!

 

[ajdelange]

I don't immagine it. I do it. Twice every fall as there is NO traction on the vehicle's rear wheels whatsoever. This being the case there is no torque around the horizontal axis from rear wheel thrust and weight is not transferred to the rear wheels. The front wheels's weight is only reduced by the tongue weight as as long as I'm going easy on the gas (I'm not backing my X into that lake) I can develop enough thrust to pull them out.

 

[TyPope]

Why do you say there is more grip at the front? This is true when a vehicle is decelerating (it's the reason the front brakes are heftier than the rear ones) but in an acceleration situation, especially where there is tongue weight from a trailer, the opposite is true. I don't know that there will be two in the back and one in the front but I am assuming that will be the case as the TriMotor is what it is, as far as I can tell, so it can tow. To get a large trailer moving you need lots of traction and you want to put the motors where you can get it, in the rear. In towing sway is a big concern. You've got this great mass hanging off the back of the truck and anything that pushes it to the side, such as a wind gust or the blast from a passing semi, pushes that mass to one side or the other putting a big torque about the rear wheels of the truck trying to point its nose towards the other side. The reason for 5th wheels, goosenecks and pivot point projection hitches is to minimize that torque by getting the pivot point (or effective pivot point) forward thus minimizing the arm. But with two motors in the back supplying different amounts of thrust you can neutralize the torque about the centerpoint of the rear wheels even if the pivot point is rearward. So I think it's going to be two induction motors in the back for the torque needed to start a large trailer moving and the vectoring to improve lateral stability and one switched reluctance up front for range but that is all speculation on my part. I am not privy to any more information than any of have.

Each motor provides a DOF. Thus is you have fewer motors you have fewer DOF. And in addition to that we could say a motor provides twice as many DOF as a brake as it can provide torque in either direction relative to the rotation of the wheel whereas a brake can only provide it in the direction opposite to the direction of rotation.

Typical pickup trucks are so light in the rear that if you were to try to use the rear end for regen, you'd end up dragging the tires every time you tried to stop. On acceleration, a truck will not hesitate to spin those light back wheels while the front which has most of the weight just sits there. I suppose that will be different as the CT will have better weight distribution. It does make sense to pull the trailer with motors closer to the trailer's weight rather than require spreading the force through the whole body to the front tires as they try to pull it along. The trailer sway is easily mitigated in my wife's car with the ABS system though that leads you to a false sense of security. My wife met a guard rail once when a trailer suddenly started fishtailing on an icy road... Thanks, Wyoming weather. It did a lot of damage but she and the kids were fine. I watched it all happen in my side mirror... "Hey, the side of the trailer is pretty dirty. Hey, I shouldn't be seeing the side of the trailer." Crash! Car parts everywhere. It took me 1/4 mile or more to finally stop and that was with full brakes (I was hauling the 38' camper, she was hauling an 18' cargo trailer with all our 'immediate' household items. I would later go back and get my 30' enclosed car hauler with the rest of our stuff). It made for a horrible end to our move from Ohio to Utah but could have been worse. I digress.

When it comes down to it, I'm hoping that in about 3 weeks, we hear that the 500 mile range will be while towing some kind of trailer and that actual range will be much higher than originally stated due to some battery change that Tesla will make in the next year. Oh, AND, the CT will get one bonus motor for every tier of order. (Tri becomes quad, dual becomes tri, etc.) Can't have the competition too close!

 

[ajdelange]

Yes, the story will be very different with the CT. Weight distribution on the current crop is pretty even between front and rear.

ABS does provide a measure of torque vectoring and can, thus, mitigate sway, With the CT that torque vectoring will be much more sophisticated - probably by an order of magnitude.

 

[ldjessee]

Yes, the story will be very different with the CT. Weight distribution on the current crop is pretty even between front and rear.

ABS does provide a measure of torque vectoring and can, thus, mitigate sway, With the CT that torque vectoring will be much more sophisticated - probably by an order of magnitude.

Yes, the even weight distribution should be nice.

The annoying thing for me is I know it is 'wasting' energy by braking one side.. but probably not as much as carrying around an extra motor or two when I do not really need a motor for each wheel.

 

[ajdelange]

For this very reason torque vectoring will be done with the motors to the extent possible. That is one of the major reasons for having multiple motors the other being increased efficiency (use the inductions when necessary and go to the switched reluctance when you can).

 

[Camper Van Someren]

Brake based torque vectoring also wears your brakes down in situations when you want to split torque 60/40 or 80/20. Then you have the brake squeezing enough to slow the wheel but not enough to lock it, causing lots of heat and brake wear and “wasted” energy.

My car uses brake-based torque vectoring on the front axle and clutch-based vectoring at the rear (twinster system) and the rear is much better in every way. I have fried my front brakes driving on the racetrack because they are always either distributing torque or slowing the car. The rear can send 70% of the engine power to either rear wheel which makes it very agile, and would also be great for off-road situations.

I really hope Tesla develops a similar system for situations where they have a single motor powering an axle (front of the tri-motor, both axles on the dual etc)