True 4WD with in-wheel motors

[Scotty]

As long as we're in the "anything goes" mode, why not in-wheel motors? Off the top of my head, I can envision some advantages:
* True 4WD with individual control of power/torque delivered
* Off-road traction maximisation based on weight distribution and slippage
* On-road traction maximisation from accelerometer input (acceleration/braking/cornering)
* Allow for braking of one individual wheel (is this only useful off-road?)
* On-road roll stability (the moose test -- the computer actively torques or brakes the correct wheel to reduce roll)
* Weight distribution much closer to the ground
* Elimination of the gearbox

A couple disadvantages I can see:
* Much more unsprung weight
* Left/right torque need to be precisely matched to avoid torque steer

I admit I am naive regarding the engineering and real-world application of wheel motors. I have no idea of the state of the art, or even if in-wheel motors would be good in an off-road vehicle. I'm sure there are volumes published about this, but I'd like to see what the reaction is here.

 

[LastDayScout]

As long as we're in the "anything goes" mode, why not in-wheel motors? Off the top of my head, I can envision some advantages:
* True 4WD with individual control of power/torque delivered
* Off-road traction maximisation based on weight distribution and slippage
* On-road traction maximisation from accelerometer input (acceleration/braking/cornering)
* Allow for braking of one individual wheel (is this only useful off-road?)
* On-road roll stability (the moose test -- the computer actively torques or brakes the correct wheel to reduce roll)
* Weight distribution much closer to the ground
* Elimination of the gearbox

A couple disadvantages I can see:
* Much more unsprung weight
* Left/right torque need to be precisely matched to avoid torque steer

I admit I am naive regarding the engineering and real-world application of wheel motors. I have no idea of the state of the art, or even if in-wheel motors would be good in an off-road vehicle. I'm sure there are volumes published about this, but I'd like to see what the reaction is here.

I think the Lordstown truck was supposed to have in wheel motors. Agreed it will probably add to unsprung weight. But, it offers some really great possibilities.

 

[IdahoJOAT]

I'm more of the school of KISS.

I think the motors in the pumpkins are what I'd like to see.

 

[speedrye]

I'm more of the school of KISS.

I think the motors in the pumpkins are what I'd like to see.

That should allow locking hubs as an easy option to disengage the wheels from the drivetrain for flat-towing, pushing, etc. All using readily available parts.

 

[IdahoJOAT]

That should allow locking hubs as an easy option to disengage the wheels from the drivetrain for flat-towing, pushing, etc. All using readily available parts.

Ayup, exactly.

While this is what I'd like to see, I think, I'm curious what the team is coming up with...

 

[absentEE]

As long as we're in the "anything goes" mode, why not in-wheel motors? Off the top of my head, I can envision some advantages:
* True 4WD with individual control of power/torque delivered
* Off-road traction maximisation based on weight distribution and slippage
* On-road traction maximisation from accelerometer input (acceleration/braking/cornering)
* Allow for braking of one individual wheel (is this only useful off-road?)
* On-road roll stability (the moose test -- the computer actively torques or brakes the correct wheel to reduce roll)
* Weight distribution much closer to the ground
* Elimination of the gearbox

* More usable space for spare tire, storage, etc.
* No CV joints/axles should improve durability, turning radius, and suspension designs (improved suspension travel and ground clearance).

A couple disadvantages I can see:
* Much more unsprung weight

Likely wouldn't be that far off the unsprung mass of a solid axle vehicle, also what really effects ride quality is the ratio of sprung mass to unsprung mass; so with a large battery and everything else being sprung mass shouldn't be much of an issue.

* Left/right torque need to be precisely matched to avoid torque steer

Haven't heard people mention torque steer being a problem in the Rivian R1T, which would be the vehicle out most analogous to what you are talking about in that it has four motors albeit they are inboard motors. That said people have complained about the Rivian not having lockers in regards to rock crawling because the wheels won't rotate in unison when there is slip, seems this could be solved by using switched reluctance motors instead. SRMs do have their negatives but I think the positives outweigh them, particularly for an off-road vehicle.

I admit I am naive regarding the engineering and real-world application of wheel motors. I have no idea of the state of the art, or even if in-wheel motors would be good in an off-road vehicle. I'm sure there are volumes published about this, but I'd like to see what the reaction is here.

SAE Aug 2021: Making the case for in-wheel motors

 

[skywalker]

I think the Lordstown truck was supposed to have in wheel motors. Agreed it will probably add to unsprung weight. But, it offers some really great possibilities.

The Endurance does have 4 in-wheel hub motors. From the reports I've gotten from those that have driven it off-road... You couldn't get it stuck. I would love to see Scout use 4 in-wheel hub motors. It's less parts, simpler, easily locked,/unlocked via software, etc. And you could blow up a hub motor or two and still make it back home. It is a lower center of gravity and allows for more weight to be put into batteries. I'd love to know what Scout thinks about this idea...

 

[Rustic_father]

I think HUB motors is not a good idea.

1 - HUB motors are un-sprung weight and therefore are more likely to get broken due to constant shock.

2 - Being exposed to the elements to include deep water (off-roading) will only increase the likeliness of a gasket failure or contamination erroding any of the other key components that supply the motor.

3 - HUB motors are less efficient for acceleration, and with capturing regeneration. With the Boxy un-aerodynamic shape that the vehicle already will have it is important to be as efficient as possible because battery space/capacity is limited.

4 - It isn't just slapping a HUB motor in a wheel and plugging in two wires. Motors this strong will need coolant. So The added complexity of a de-centralized and exposed coolant system will just add another place for a coolant leak to happen. Keep in mind typically the same coolant that supplies the motors will also cool the battery. So if you are off roading and rip out one of your coolant lines (because they are exposed) you will loose all of your coolant and you can't rely on the other 3.

If anyone is unsure of the capabilities of 4 central electric motors i suggest looking at how well rivian performs off road. There are tons of youtube videos of people doing amazing things with them.

 

[absentEE]

I think HUB motors is not a good idea.

1 - HUB motors are un-sprung weight and therefore are more likely to get broken due to constant shock.

2 - Being exposed to the elements to include deep water (off-roading) will only increase the likeliness of a gasket failure or contamination erroding any of the other key components that supply the motor.

4 - It isn't just slapping a HUB motor in a wheel and plugging in two wires. Motors this strong will need coolant. So The added complexity of a de-centralized and exposed coolant system will just add another place for a coolant leak to happen. Keep in mind typically the same coolant that supplies the motors will also cool the battery. So if you are off roading and rip out one of your coolant lines (because they are exposed) you will loose all of your coolant and you can't rely on the other 3.

No doubt one could design/implement an in-wheel motor or an e-beam for that matter that is susceptible to the above but hopefully the engineers at the companies working on these products (ZF, Magna, Linamar, Elaphe, Aptera, Lordstown and Lightyear etc) are doing their due diligence.

3 - HUB motors are less efficient for acceleration, and with capturing regeneration. With the Boxy un-aerodynamic shape that the vehicle already will have it is important to be as efficient as possible because battery space/capacity is limited.

In-wheel motors as a form factor are neither more or less efficient than inboard motors as it depends on motor type, design, implementation and application. That said, direct-drive IWMs have an inherent efficiency advantage due to not having to transfer power through a driveshaft and would work well for off-road focused vehicles as they are speed limited by their own AT/MT tires and benefit from low end torque.

If anyone is unsure of the capabilities of 4 central electric motors i suggest looking at how well rivian performs off road. There are tons of youtube videos of people doing amazing things with them.

Rivian made the correct decision putting the motors inboard because their goal as I gather was to create a sports/adventure truck. If that is Scout Motors’ goal also, then I would agree that neither IWMs nor e-beams belong in a sports car or truck.

 

[Rustic_father]

In-wheel motors as a form factor are neither more or less efficient than inboard motors as it depends on motor type, design, implementation and application. That said, direct-drive IWMs have an inherent efficiency advantage due to not having to transfer power through a driveshaft and would work well for off-road focused vehicles as they are speed limited by their own AT/MT tires and benefit from low end torque.

an in wheel motor has many sever limitations most of all size. In order for it to fit within a wheel the whole motor assembly might be at most the width of a tire which is likely at most 18 inches. Taking in to account the housing, and other components that have to go into the assembly that means the actual magnetic portions of the motor will be relatively very small compared to an inboard version. The more magnetic surface you have the more power the motor can output as well as the more power the motor can retrieve in regenerative braking.

Also considering the drive shafts are direct lines and to not have transfer cases or differentials or other power transfers the efficiency loss is minimal.

I used to really love the idea of hub motors to save a lot of space to really free up the design capabilities of a car but the more i research it seems there are more disadvantages than advantages. I do however think hub motors will likely make an appearance in the "smart car" or "City Compact" market where every Centemeter is needed and performance is less of an issue.

 

[absentEE]

an in wheel motor has many sever limitations most of all size. In order for it to fit within a wheel the whole motor assembly might be at most the width of a tire which is likely at most 18 inches. Taking in to account the housing, and other components that have to go into the assembly that means the actual magnetic portions of the motor will be relatively very small compared to an inboard version. The more magnetic surface you have the more power the motor can output as well as the more power the motor can retrieve in regenerative braking.

The continuous power of four L1500 in-wheel motors is 308 kW and peak of 440 kW, the Rivian large pack battery for instance has a peak charge rate of around 220 kW currently and the hummer ev's peak is around 350 kW.

Also considering the drive shafts are direct lines and to not have transfer cases or differentials or other power transfers the efficiency loss is minimal.

If I recall correctly it's a loss of around %2 but varies with the angle, every mile you can get helps if you're looking at having to walk the rest of the way.

I used to really love the idea of hub motors to save a lot of space to really free up the design capabilities of a car but the more i research it seems there are more disadvantages than advantages. I do however think hub motors will likely make an appearance in the "smart car" or "City Compact" market where every Centemeter is needed and performance is less of an issue.

more space for more batteries or a spare tire. Also have to say a "smart car" with a peak of 590hp (like that of four L1500s) sounds pretty scary, I'm not judging but it's definitely not for the faint of heart.

 

[Rustic_father]

The continuous power of four L1500 in-wheel motors is 308 kW and peak of 440 kW, the Rivian large pack battery for instance has a peak charge rate of around 220 kW currently and the hummer ev's peak is around 350 kW.

The link you showed says each motor has a peak of 110kW. Combing them won't simply add up, but even if they did the rivian's total kW output is 623kW and is much higher. Also charge rate is not the same as discharge rate. Discharge produces less heat than charging does and for safety as well as logevity of the pack charging speeds are limited, they don't disclose the discharge

One thing that i still maintain is a huge drawback of hub motors is the fact that their compact size likely sacrifices cooling solutions. In an SUV application where heavy loads or even something in tow will likely generate a lot of heat, and without a proper cooling solution the motor will lose lots of power. Perhaps it does have a cooling solution and it is simply not displayed on that picture.

If I recall correctly it's a loss of around %2 but varies with the angle, every mile you can get helps if you're looking at having to walk the rest of the way.

1% is very small. even over 300 miles that 3 miles. and considering charging rates are so fast at DC fast chargers it really boils down to sitting at the charger for 15minutes as opposed to 15 minutes and 5 seconds.

more space for more batteries or a spare tire. Also have to say a "smart car" with a peak of 590hp (like that of four L1500s) sounds pretty scary, I'm not judging but it's definitely not for the faint of heart.

my idea behind a smart car would be to use 2wd and use 2 weak motors for city driving...especially considering most cities are flat power/range/performance isn't crucial. and since those are so compact already it is best to move as much as possible away from the cabin.....but either way we arn't here to talk about that we are here to talk about the scout

 

[absentEE]

The link you showed says each motor has a peak of 110kW. Combing them won't simply add up, but even if they did the rivian's total kW output is 623kW and is much higher. Also charge rate is not the same as discharge rate. Discharge produces less heat than charging does and for safety as well as logevity of the pack charging speeds are limited, they don't disclose the discharge

Let’s start with the motor. Both types of AC motor commonly used in EVs – the asynchronous induction and the permanent-magnet synchronous – work equally well as a generator or a motor, so this shouldn’t be a limiting factor when it comes to regen braking force. The inverter can also work equally well in either operating mode. Of course, regen braking becomes less effective as motor RPM approaches zero, just as the rate of acceleration declines once motor RPM exceeds a certain value, but aside from these limits – and the other laws of physics, road conditions, etc. – the motor and inverter won’t intrinsically limit regen braking.

The battery is the part of the EV drivetrain most likely to be the limiting factor for regen braking. The Li-ion cell types most commonly used in EVs are capable of at least a 2C continuous discharge rate, but only a 0.8C to 1C charge rate. This suggests that the rate of charging has to be limited to no more than 40-50% of discharging, at least on a continuous basis. Of course, Li-ion batteries can tolerate much higher discharge rates for short periods of time; this is implied by the ratio of the motor/inverter power rating to the battery capacity (e.g. a Nissan Leaf with a 24 kWh battery and an 80 kW motor/inverter rating subjects its battery to a maximum discharge rate of 3.33C). However, an excessive discharge rate mainly results in a higher cell temperature, whereas charging at too high a rate can cause the lithium ions to plate out as metal onto the cathode, which results in a permanent loss of capacity, or can even cause catastrophic failure of the cell.

The Rivian’s motors (or the L1500s) would be limited by the battery's ability to accept charge.

One thing that i still maintain is a huge drawback of hub motors is the fact that their compact size likely sacrifices cooling solutions. In an SUV application where heavy loads or even something in tow will likely generate a lot of heat, and without a proper cooling solution the motor will lose lots of power. Perhaps it does have a cooling solution and it is simply not displayed on that picture.

We’ll see what the engineers come up with, for sure some implementations will be better than others.

1% is very small. even over 300 miles that 3 miles. and considering charging rates are so fast at DC fast chargers it really boils down to sitting at the charger for 15minutes as opposed to 15 minutes and 5 seconds.

Two percent can be the difference between getting to a fast charger or not, also two percent more gained from regen when not battery limited. In F-150 extended range battery terms two percent is $719 worth of batteries. No its not massive but worth it when combined with all the other benefits (for non-sports cars/trucks).

my idea behind a smart car would be to use 2wd and use 2 weak motors for city driving...especially considering most cities are flat power/range/performance isn't crucial. and since those are so compact already it is best to move as much as possible away from the cabin.....but either way we arn't here to talk about that we are here to talk about the scout

590hp seems like plenty but I guess it depends on what people are looking for from the Scout brand.

 

[Harris005]

Enjoyed reading both of your guys insight on these topics. I happened to come across this today https://www.tiktok.com/t/ZTRVah3mo/ and thought...I wonder what @absentEE and @Rustic_father take would be ?

For the offroad Scout enthusiasts it seems like it might be worth looking into.

 

[Rustic_father]

Enjoyed reading both of your guys insight on these topics. I happened to come across this today https://www.tiktok.com/t/ZTRVah3mo/ and thought...I wonder what @absentEE and @Rustic_father take would be ?

For the offroad Scout enthusiasts it seems like it might be worth looking into.

I have seen those types of energy capture devices. There are some of those being used to capture energy from waves in the ocean.

While I think it would be a great idea to get as much energy back whenever possible I think that the benifits would be less than putting a solar panel on the roof. 90% of driving will likely be done on smooth roads.

Perhaps it would be best used while driving in NYC going through all the pot holes.

I love finding new sources for energy this surely something fun to consider if it does not add much weight or doesn’t take up much space compared vs traditional suspension components

 

[speedrye]

I have seen those types of energy capture devices. There are some of those being used to capture energy from waves in the ocean.

While I think it would be a great idea to get as much energy back whenever possible I think that the benifits would be less than putting a solar panel on the roof. 90% of driving will likely be done on smooth roads.

Perhaps it would be best used while driving in NYC going through all the pot holes.

I love finding new sources for energy this surely something fun to consider if it does not add much weight or doesn’t take up much space compared vs traditional suspension components

My first thought was the suspension seats in the 70-series Land Cruiser. Put the driver's weight to work for you!

 

[absentEE]

Enjoyed reading both of your guys insight on these topics. I happened to come across this today https://www.tiktok.com/t/ZTRVah3mo/ and thought...I wonder what @absentEE and @Rustic_father take would be ?

For the offroad Scout enthusiasts it seems like it might be worth looking into.

Saw BMW is working on something similar, will definitely be interesting to see how it performs when/if brought to market.

Two percent can be the difference between getting to a fast charger or not, also two percent more gained from regen when not battery limited. In F-150 extended range battery terms two percent is $719 worth of batteries. No its not massive but worth it when combined with all the other benefits (for non-sports cars/trucks).

It’s worth noting the two percent efficiency loss on an inboard motor versus a direct drive in-wheel motor is when both motors are otherwise identical. If on the other hand the inboard motor also has a single speed transmission as most EVs with inboard motors do, then obviously there would be additional efficiency losses versus a direct drive in-wheel motor. That said, the issue with not having a single speed transmission/reduction gear is that some motors don't operate very efficiently at lower rpms. So gearing though not ideal, can sometimes be the more efficient option even with in-wheel motors. But this is all hypothetical and in the end all that matters is execution, as there are so many variables.

Also as not to be trolled in the future, when I suggest in-wheel motors won’t work well for sports cars/trucks; I’m speaking of currently available ones due to weight and limited angular velocity. If newer motor/material tech (axial flux motors, carbon fiber usage, etc.) can overcome these barriers then by all means.

05/22/23:

In-wheel motors as a form factor are neither more or less efficient than inboard motors as it depends on motor type, design, implementation and application. That said, direct-drive IWMs have an inherent efficiency advantage due to not having to transfer power through a driveshaft and would work well for off-road focused vehicles as they are speed limited by their own AT/MT tires and benefit from low end torque.

Having looked more into this, wheel motors too would likely require a reduction gear to rock-crawl or for 100% grade stuff.

 

[Harris005]

fb://photo/6003281649751347?set=a.857234577689439&sfnsn=mo&mibextid=6aamW6

 

[Rustic_father]

fb://photo/6003281649751347?set=a.857234577689439&sfnsn=mo&mibextid=6aamW6

link doesn't work

 

[Harris005]

link doesn't work

See if this one works.

Rivian Patents Bolt-On Low-Range Crawler Gearbox for Off-Road EVs

Rivian has been patenting a lot more technology than usual, and now its been granted what could be the first low-range gearbox for EVs.

www.thedrive.com