Regenerative Braking while Flat Towing

[KevinRS]

I have no interest in flat towing my self but it's looking like the summary is this.

Slate has only stated that they would look into flat towing.
If they did add it, it would likely be by disengaging the tires from the motor unit in some way, as other methods are more complicated and expensive.

Regenerative braking while towing is complicated, for it to work, the truck's systems would have to be operative, running cooling pumps and similar.

A deceleration sensor to activate it would be problematic because what happens when you start to climb a grade? A system using a sensor like that would start braking, making it even harder to climb the hill. It would have to be connected at least to the brake light wiring coming from the RV.

So, the truck has to basically be "running" to safely use regenerative braking, and needs to detect braking signal from the RV and have software to apply braking at some level when the RV is braking, as well as keep the motor in a "coasting" state otherwise.

It's sounding like engineering and testing all that would get expensive, and out of the scope of what Slate is trying to do. Maybe at some point in the future a vehicle would have flat tow regen braking, but it doesn't sound like it's happening soon. What can be hoped for but not counted on is a method to just disengage the wheels from the drive, otherwise you are looking at either a full trailer, or put the rear wheels on a dolly tow.

 

[bloo]

A few AC motor control engineers on this site.

 

[Imhotep]

A few AC motor control engineers on this site.

That’s not a discipline I’m familiar with, but I’m just a simple aerospace engineer.

 

[cadblu]

Slate has only stated that they would look into flat towing.

Correct, Slate's patent reply to chats and texts is, "great idea, we'll look into it." The same kind of response and smile you get when you provide feedback to your HR rep at your job.

My take is don't expect brake regen during flat towing, or just plain flat towing anytime soon. I hope someone will prove me wrong.

 

[KevinRS]

Correct, Slate's patent reply to chats and texts is, "great idea, we'll look into it." The same kind of response and smile you get when you provide feedback to your HR rep at your job.

My take is don't expect brake regen during flat towing, or just plain flat towing anytime soon. I hope someone will prove me wrong.

You are probably right. Flat towing would require new parts, and regen is complicated.

 

[paulrobsj]

Can one of you smart people explain how my Lexus NX450H+ starts out with the rear wheels being driven by the electric motor, then they disengage if traction is not needed. Can the same technology be used on the Slate truck to make it towable?
I am in the same camp as a lot of other people here. The attraction is a cheap towable EV. If it can’t be flat towed, I will not convert my reservation to a purchase. Regen while going down hill would be a nice feature, but its not a deal breaker.

 

[BigB]

I know Munro helped in the engineering but this is what triggered my thought process

 

[BigB]

I accidentally created two posts but hopefully this gets to the engineers because this is a big game changer in my opinion and I will actually come to Indiana and spend the entire summer building these things with you guys for real I am not one to BS

The Slate "DeepDrive" Protocol is a revised technical plan to transform the Slate into the ultimate affordable, flat-towable, high-performance machine.
By replacing the stock JJE motor with DeepDrive's patented Dual Rotor technology, we address the critical engineering conflict between Permanent Magnet (PM) efficiency and Flat Towing safety.
The Core Upgrade: DeepDrive Central Motor (CD450)
We will not use the in-wheel hub motors for this specific application. Instead, we will utilize DeepDrive's Central Drive (CD450) unit.
* Why? The Slate uses a DeDion rear solid axle suspension. Retrofitting in-wheel motors would require a complete suspension redesign (converting to Independent Rear Suspension), blowing the budget and violating the "$20,000 affordable" constraint.
* The Fix: The CD450 drops directly into the space occupied by the current 150kW JJE motor, mounting to the chassis and driving the wheels via half-shafts, preserving the Slate's rugged, low-cost suspension architecture.
Phase 1: The "Tow-Safe" Drivetrain
* The Problem: DeepDrive motors are Permanent Magnet (PM) machines. If you flat tow them, the magnets spin, generating electricity (Back EMF). This will fry the inverter or cause the battery to overheat if towed behind an RV for hours.
* The Solution: The "Dog Box" Decoupler.
* We will install a simple, cable-actuated mechanical dog clutch between the DeepDrive motor output and the rear differential.
* Operation: Before towing, the user pulls a lever (located in the frunk or near the hitch). This physically disconnects the motor from the wheels.
* Result: The rear wheels spin freely. The motor remains stationary. Zero drag, zero Back EMF, 100% safe flat towing at any speed, with no odometer accumulation.
Phase 2: Performance & Efficiency Stats
By swapping to the Dual Rotor Radial Flux technology, we achieve immediate gains over the stock Slate specs:
| Feature | Stock Slate (JJE Motor) | Slate "DeepDrive" Edition |
|---|---|---|
| Power | 150 kW (201 hp) | 230+ kW (308+ hp) |
| Torque | ~350 Nm | 2,400+ Nm (Dual Rotor Advantage) |
| Efficiency | ~92% | 97.6% (DeepDrive Peak) |
| Range | 240 miles (Extended) | ~288 miles (+20% from motor efficiency) |
| 0-60 Time | 6.2 seconds | < 4.5 seconds |
Phase 3: Regenerative Braking System
The DeepDrive unit allows for Variable High-Authority Regen:
* One-Pedal Drive: The dual-rotor design provides massive braking torque (up to 1,000 Nm of negative torque).
* Brake Life: We can program the regen to handle 95% of all braking events, meaning the physical drum/disc brakes on the Slate basically never wear out—a huge maintenance saving for college students.
* Tow Charging (Emergency Only): If the user needs to charge the Slate while towing (and accepts the drag on the RV), they can leave the Dog Clutch engaged. The DeepDrive motor will act as a generator, recharging the Slate's battery using the RV's pulling power. Note: We recommend this only for short durations to avoid overheating.
Phase 4: Economics & Affordability
* Cost Reduction: DeepDrive motors use 50% less magnet material and 80% less iron than standard motors. This lowers the Bill of Materials (BOM) significantly.
* Student Budget: By removing the gearbox (Direct Drive) and simplifying the cooling system (DeepDrive is highly thermally efficient), we offset the cost of the custom Dog Clutch.
* Export Potential: The simplicity of the "Slateboard" chassis combined with a motor that requires almost no maintenance (no transmission fluid, no gear wear) makes it perfect for developing markets.
Summary of Operations
* Source the Slate "Glider" (chassis without motor).
* Mount the DeepDrive CD450 to the rear subframe.
* Install the Mechanical Dog Clutch on the output shaft.
* Flash the inverter with a custom "RV Mode" map (disables parking brake automatically when clutch is disengaged).
* Deliver a sub-$25k vehicle that can outrun a Mustang, tow a jet ski, and be towed behind a Class C RV across the country.
Efficiency Made in Germany: DeepDrive's GENIUS motor
I selected this video because it provides a clear, visual explanation of the specific "Dual Rotor" technology and efficiency advantages of the DeepDrive motor that make this revised Slate plan feasible.

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[KevinRS]

This forum is not owned or run by Slate. There is little chance that stuff posted here gets to engineers. Maybe a few people on the marketing side are looking at what socials and forums are saying, but they aren't going to pass everything along to the busy engineers. They are highly unlikely to make large design changes at this point anyway. Maybe in a few years they could do something like that, but they would have to see a market in the hundreds of thousands over several years for it to make sense.