Munro Live: Beta Factory Hoist Review of Slate Battery, Motor, Suspension, Underbody, Frunk, Body, Electrical System, Software, Safety & More

[Dorbiman]

Also, the engineer made kid of a big deal about the motor being mounted to the “frame” rather than the axle. (Less unsprung weight.) Are some EVs built the other way around?

Yes, sometimes the motor is built into the differential. It's known as an e-axle

 

[AZFox]

In the video, I noticed drive axles going to both rear wheels. This makes it a bit more capable in low-traction situations. Is this typical of modern RWD vehicles? In “traditional” pickups, when you’re in RWD, only one of the two is the drive wheel.

Both wheels are driven. This 22M-view video explains how that works, and why the Center Section of a traditional live axle is called a "differential":

 

[AZFox]

Assuming Slates will be one wheel peel machines with that EV torque. A locking differential option would be nice.

Combine an open differential with ABS brake capability and you get Traction Control.

It works by applying brakes to the spinning wheel, thereby sending power to the wheel on the other side.

 

[PACMAN]

Both wheels are driven. This 22M-view video explains how that works, and why the Center Section of a traditional live axle is called a "differential":

That’s a super cool old video! Thanks!

 

[Luxrage]

AXLE.
Forum spelling NAZI on duty.

I blame Beverly Hills Cop and Twisted Metal 2 for burning Axel into my head at an early age!

 

[Driven5]

Despite the 'one wheel drive' jokes, an open diff applies the same torque to the tire that grips as is being reacted (pushing forward) by the ground on the tire that slips. What people notice most is that the excess torque beyond that just goes into the slipping tire. Thankfully the Slate is not a 60's muscle car, with terrible weight distribution and a live axle. Greater percentage of weight on the rear axle means better grip, and drivetrain torque through typical live axles try to further unweight the passenger rear tire. See the photo on the previous page, and notice which side the one wheel peel is on.

Slate should have good weight distribution, and being RWD acceleration further transfers weight to the drive tires. Like an independent suspension, the DeDion will also equally weight both tires in a straight line. It'll also react the same left and right turns. The only real shortcomings will be in high performance driving at the limit, when trying to apply significant power while the inboard tire is also significantly unloaded, and unevenly slippery surfaces.

The auto industry has found that for all but the most extreme use cases, the 'eLSD' (electronic LImited Slip Differential) is more than adequate for these two. It simply uses the previously noted characteristic to it's advantage, by using the brake on the slipping tire to artificially react more torque, thus driving more torque to the side with grip. A true limited slip or locking differential would certainly be welcomed by racers and off-roaders... But neither of those are even close to the target market here to be worth the cost.

 

[AZFox]

Despite the 'one wheel drive' jokes, an open diff applies the same torque to the tire that grips as is being reacted (pushing forward) by the ground on the tire that slips. What people notice most is that the excess torque beyond that just goes into the slipping tire. Thankfully the Slate is not a 60's muscle car, with terrible weight distribution and a live axle. Greater percentage of weight on the rear axle means better grip, and drivetrain torque through typical live axles try to further unweight the passenger rear tire. See the photo on the previous page, and notice which side the one wheel peel is on.

I think it works this way:

In a front-engine / RWD vehicle, when power is applied there's a twisting force created between the engine/transmission assembly and the differential/live-axle assembly.

Twisting Force Writ Large:

On a surface that has equal traction on both sides, the One Wheel Peel happens because the twisting force presses downward on the left rear wheel and lifts upward on right one.

In the Slate, however, the motor and its one-speed transmission will be bolted directly to the the differential. Twisting problem solved! There's nothing to twist.

 

[Driven5]

Exactly. That's why the old Hotchkiss (live axle on leafs) setups pretty much always tend to one-wheel-peel with decent power applied to open diff. Getting into 3 and 4 link setups with more advanced geometries can also mitigate this though.

Bolting the differential to the chassis in front engine RWD with IRS (or DeDion) will resolve that twisting within the chassis, or within the block/case on transverse (common FWD and EV type) drivetrains, and actually spin both tires with an open diff as long as there is sufficiently equal grip... Or if both tires are sufficiently close to the limit of their grip when cornering. I had an open diff Miata that could still be easily drifted.