Maximum Overdrive

[Chavannigans]

This is another “So hear me out” post by yours truly.



Low Speed Overdrive would be a game changer in some situations and would make more sense than a Front Dig.



We had quite a few scale RC rock crawlers in storage and I recently got them all back out now that the kids are getting old enough to play with them. So this weekend I tore them all down and started getting them running again.





Most of them have the same differential ratios which is awesome for trail running, but one of our SCX24 Jeep Rubicons has a set of brass axles with an overdrive gear in the front differential. It is incredibly capable when you are climbing obstacles, but it doesn’t like full speeds for long periods of time.

An overdriven drivetrain has mismatched differential gears with a numerically higher ratio in the front. So basically your front tires always turn faster than your rear tires which has its own pros and cons.

Typically 10%-20% overdrive is acceptable for trails and higher speeds while 24%-30% are used in competition rock crawlers. Having a front overdrive can also make turning with your lockers engaged much easier on you as well as your vehicle.



Am I comparing Scouts to remote controls cars? Yeah I guess I am. But many people have given their lives so I can say stupid things on the Internet, where nobody knows I’m really a dog.



Woof (I digress)



A big benefit of the Scouts having a divorced drivetrain is you can drive each axle separately.



But when you have both lockers engaged in low speed situations, specifically inclines, it would be awesome if the front motor could be manually sped up to a faster rate than the rear. And while I expect this to already be a feature managed by the Traction Control system regardless if the lockers were engaged, I would love being able to adjust it myself within a reasonable range.



Maybe around 10%, give or take with a few levels of adjustment.



Obviously not an ideal feature for higher speeds with any meaningful traction for any period of time, but in some specific low-traction scenarios it may be really useful. Snow, loose rock, wet rock shelf’s. Etc.



It could disengage in speeds above 5mph and when the vehicle is on level or down-sloped terrain to prevent drivetrain stresses and undesirable steering behavior.



Having the ability to pull yourself over an obstacle is a lot safer than having to “bump it” and jab the throttle as often. Slow controlled crawling is the way to go and puts a lot less stress on your body as well as your off-roading Connection Machine.



But it would also be beneficial when you are making sharp turns in low traction situations like switchbacks covered in loose rock, snow, or soil.

That’s because the front motor would be pulling you forward in the direction you want to go, and the rear axles would push at a slower rate to make long vehicles feel even shorter offroad as it drags the rear tires to pivot around obstacles or hazards.



It could be a feature already enabled in specific offroad modes like Rock Crawl Mode or Snow/Mud Mode to varying degrees already and this could all just be a fever dream.



I’m going to go do human things now. Good night.

 

[SpaceEVDriver]

I love the “hear me out” posts where we talk about these kinds of fantastic ideas for EVs.

Both of my EVs can and do command different torques out of the front and read motors depending on all the inputs, including traction control. This can, effectively, cause different speeds at the tires. So, it’s clearly not impossible to do this. The challenge is in how to safely and without much cost enable control over it for a driver.

There’s no reason low speed control of the front and rear can’t be done in the way you’re describing other than time, cost, thoroughness, and safety. Enabling a user-controlled setting like this opens up a lot of liability.

One of the things I hope Scout does differently from Rivian is make their internal computer system a lot more accessible to the DIYer. Scout talks about right to repair, and that should include software.

We can adjust a lot of parameters in the Fords. I’ve enabled experimental features that Ford wasn’t ready to release to the public. Some of those I’ve turned off again because they really weren’t ready. I hope Scout enables whatever CAN bus they use to be somewhat (securely) accessible to DIYers so things like this can be played with. At that point, it must be user-beware, though.

 

[Chavannigans]

I love the “hear me out” posts where we talk about these kinds of fantastic ideas for EVs.

Both of my EVs can and do command different torques out of the front and read motors depending on all the inputs, including traction control. This can, effectively, cause different speeds at the tires. So, it’s clearly not impossible to do this. The challenge is in how to safely and without much cost enable control over it for a driver.

There’s no reason low speed control of the front and rear can’t be done in the way you’re describing other than time, cost, thoroughness, and safety. Enabling a user-controlled setting like this opens up a lot of liability.

One of the things I hope Scout does differently from Rivian is make their internal computer system a lot more accessible to the DIYer. Scout talks about right to repair, and that should include software.

We can adjust a lot of parameters in the Fords. I’ve enabled experimental features that Ford wasn’t ready to release to the public. Some of those I’ve turned off again because they really weren’t ready. I hope Scout enables whatever CAN bus they use to be somewhat (securely) accessible to DIYers so things like this can be played with. At that point, it must be user-beware, though.

Omg yes. If we get anything remotely close to Forscan, I will be beside myself! I don’t think any other car manufacturer does it better and the level of granular adjustments is very impressive.

I am still very unfamiliar with EVs, but on ICE vehicles traction control is usually disabled completely when both lockers are engaged because they manage torque by applying brakes to the slipping wheel. When the tires all turn at the same speed there really isn’t a way for them to manage wheel slip.

But having the ability to turn both axles at the same speeds, and adjust torque bias to the front in specific conditions could set it apart from the entire industry.

I don’t think there is a single vehicle out there that can do this because it would only be possible with an EV drivetrain since they are completely divorced and ICE vehicles are linked by a transfer case.

 

[SpaceEVDriver]

Omg yes. If we get anything remotely close to Forscan, I will be beside myself! I don’t think any other car manufacturer does it better and the level of granular adjustments is very impressive.

I am still very unfamiliar with EVs, but on ICE vehicles traction control is usually disabled completely when both lockers are engaged because they manage torque by applying brakes to the slipping wheel. When the tires all turn at the same speed there really isn’t a way for them to manage wheel slip.

But having the ability to turn both axles at the same speeds, and adjust torque bias to the front in specific conditions could set it apart from the entire industry.

I don’t think there is a single vehicle out there that can do this because it would only be possible with an EV drivetrain since they are completely divorced and ICE vehicles are linked by a transfer case.

We're getting a ton of rain. I might go play in the clay a couple miles from the house with my obd2 reader to see what the truck does with the front vs rear motors in different modes and situations. I know it can command different torques and different wheel speeds, including different directions. But I haven't experimented a lot with recording those at low speeds.

 

[dreamweaver]

We're getting a ton of rain. I might go play in the clay a couple miles from the house with my obd2 reader to see what the truck does with the front vs rear motors in different modes and situations. I know it can command different torques and different wheel speeds, including different directions. But I haven't experimented a lot with recording those at low speeds.

Sounds like a good experiment, and a bit of fun. Happy mudding.

 

[Chavannigans]

We're getting a ton of rain. I might go play in the clay a couple miles from the house with my obd2 reader to see what the truck does with the front vs rear motors in different modes and situations. I know it can command different torques and different wheel speeds, including different directions. But I haven't experimented a lot with recording those at low speeds.

“Babe why is the truck completely covered in mud?”

“I did it for science.”



That would be really interesting if you can make the time to do it.

 

[SpaceEVDriver]

“Babe why is the truck completely covered in mud?”

“I did it for science.”



That would be really interesting if you can make the time to do it.

Oh, she knows me.

She works 9 longer days instead of 10 8-hour days. I asked if today was her flex day. It’s not, so she doesn’t get to go with me, but said it sounded like fun.

I do need to get stricter with myself about washing the mud off before parking in the workshop...

 

[BeerParty]

<snip>

Am I comparing Scouts to remote controls cars? Yeah I guess I am. But many people have given their lives so I can say stupid things on the Internet, where nobody knows I’m really a dog.

Woof (I digress)

<snip>

I’m going to go do human things now. Good night.

Good doggy, have a treat.

 

[BeerParty]

A big benefit of the Scouts having a divorced drivetrain is you can drive each axle separately.

But when you have both lockers engaged in low speed situations, specifically inclines, it would be awesome if the front motor could be manually sped up to a faster rate than the rear. And while I expect this to already be a feature managed by the Traction Control system regardless if the lockers were engaged, I would love being able to adjust it myself within a reasonable range.

Maybe around 10%, give or take with a few levels of adjustment.

If I understand what you are talking about, you shouldn't be talking about speed, but rather torque. If you were to drive the axles at different speeds the faster axle would cause the tires to spin or the slower axle would cause the tires to drag. I don't think you want either of those in an off-roading environment.

I make the distinction because while ICE vehicles have to use "tricks" to distribute torque (like applying the breaks to force torque to a non-spinning wheel) when their diffs are unlocked, EVs can do this directly. Most already do. When AWD EVs are at highway speed, they will usually de-power one axle to make them more efficient. What you are asking for is all software, not hardware. So, I think it is very reasonable to ask for this.

BTW - thinking about this a bit more, there is no reason to restrict the torque bias setting to slow speeds. A torque bias to the front would just make the Scout's feel like a front wheel drive vehicle. I am sure there is someone out there that would prefer that.

 

[SpaceEVDriver]

If I understand what you are talking about, you shouldn't be talking about speed, but rather torque. If you were to drive the axles at different speeds the faster axle would cause the tires to spin or the slower axle would cause the tires to drag. I don't think you want either of those in an off-roading environment.

I make the distinction because while ICE vehicles have to use "tricks" to distribute torque (like applying the breaks to force torque to a non-spinning wheel) when their diffs are unlocked, EVs can do this directly. Most already do. When AWD EVs are at highway speed, they will usually de-power one axle to make them more efficient. What you are asking for is all software, not hardware. So, I think it is very reasonable to ask for this.

BTW - thinking about this a bit more, there is no reason to restrict the torque bias setting to slow speeds. A torque bias to the front would just make the Scout's feel like a front wheel drive vehicle. I am sure there is someone out there that would prefer that.

When attempting to take a very, very sharp turn at very low speeds, one might sometimes want the tires to turn at different speeds. Locking the rear tire on the inside of the turn allows that tire to become the pivot point, greatly reducing the turning radius of the vehicle. If that rear tire can turn in the opposite direction, it would allow the turning radius to—effectively—become shorter than the wheelbase of the vehicle. There are times when offroading that that would be great, especially for a long wheelbase vehicle.

 

[J Alynn]

Sounds like a good experiment, and a bit of fun. Happy mudding.

Post pics

 

[SpaceEVDriver]

I did the run. I thought I had captured a full drone video of one run of the loop, but… It doesn’t seem to have been saved.

The rain was soaked into the ground by the time I got to the trail, so it was more of a damp, sandy run rather than a mud run.

Note: The Lightning doesn’t pretend to be an off-road optimized truck. The “Off-road mode” is much more of a gravel/dirt road with some mud or loose sand mode, not a mode meant to compete with a Tacoma or a Jeep.

Legend:
HV EV Battery Power kW = what it says
PriMor rpm = Primary (rear) motor speed (RPM)
PriMoTqC N*m = Primary motor commanded torque (Newton-Meters)
SecMoR rpm = Secondary (front) motor speed (RPM)
SecMoTqC N*m = Secondary motor commanded torque (Newton-Meters)
Vehicle acceleration m/s^2 = What it says.


First image: Drive on our gravel road to the pavement, then a quick, rolling start full-throttle acceleration, then on to the trailhead. This is in Normal mode, 1PD, but no diff lock. The front and rear motors are being commanded to have the same torque and have the same RPM, as one would expect for normal mode.

Second image: First run of the small loop.
Setting: Normal, One pedal drive, no diff lock, TRAC on.
Of note: Already, you can see that the torques and speeds are different. They’re similar, but there’s clearly some slipping. The ABS engaged a couple of times while climbing the loose, sandy slopes.
Also note that the scales on the y-axis are different for the primary vs secondary motor graphs.
Where the speeds, power, torques all drop to zero in about the middle of the graph is where I stopped the vehicle at the top of the hill after turning around. Just wanted some clear reference points in the graphs.

Next run: Off-road mode, diff locked, no one pedal drive, TRAC off.
I sat at the start a bit longer getting things configured the way I wanted them.
But then you can see, again, that the primary and secondary motor scales are different, though the plots look similar.
Note that you can identify where the front wheel slipped by noting where the commanded torque dropped near the center of the graph and where the RPM shot up suddenly but just for the secondary motor.

Next run: Sport mode, diff locked, one pedal drive on, TRAC on.

Final run: Sport mode, no one-pedal drive, no diff lock, no TRAC

 

[Chavannigans]

If I understand what you are talking about, you shouldn't be talking about speed, but rather torque. If you were to drive the axles at different speeds the faster axle would cause the tires to spin or the slower axle would cause the tires to drag. I don't think you want either of those in an off-roading environment.

I make the distinction because while ICE vehicles have to use "tricks" to distribute torque (like applying the breaks to force torque to a non-spinning wheel) when their diffs are unlocked, EVs can do this directly. Most already do. When AWD EVs are at highway speed, they will usually de-power one axle to make them more efficient. What you are asking for is all software, not hardware. So, I think it is very reasonable to ask for this.

BTW - thinking about this a bit more, there is no reason to restrict the torque bias setting to slow speeds. A torque bias to the front would just make the Scout's feel like a front wheel drive vehicle. I am sure there is someone out there that would prefer that.

No, I actually mean speed, not torque.

The front wheels spin 10%-20% more times than the rear tires would.

What you described is the intended effect.

Your front tires would pull you at a faster rate than the rear is pushing you. This gives you a tighter turning radius and also helps pull you up over obstacles as opposed to being pushed up by the rear tires.

This would give you superior offroad performance in any type of hill climb situation. Not make it worse.

 

[SpaceEVDriver]

No, I actually mean speed, not torque.

The front wheels spin 10%-20% more times than the rear tires would.

What you described is the intended effect.

Your front tires would pull you at a faster rate than the rear is pushing you. This gives you a tighter turning radius and also helps pull you up over obstacles as opposed to being pushed up by the rear tires.

This would give you superior offroad performance in any type of hill climb situation. Not make it worse.

If nothing else, you could accomplish this by dropping the front tires from 35s to 32s. Carry two 32” spares and when you get to the trail swap them in for your normal 35s.

 

[J Alynn]

I did the run. I thought I had captured a full drone video of one run of the loop, but… It doesn’t seem to have been saved.

The rain was soaked into the ground by the time I got to the trail, so it was more of a damp, sandy run rather than a mud run.

Note: The Lightning doesn’t pretend to be an off-road optimized truck. The “Off-road mode” is much more of a gravel/dirt road with some mud or loose sand mode, not a mode meant to compete with a Tacoma or a Jeep.

Legend:
HV EV Battery Power kW = what it says
PriMor rpm = Primary (rear) motor speed (RPM)
PriMoTqC N*m = Primary motor commanded torque (Newton-Meters)
SecMoR rpm = Secondary (front) motor speed (RPM)
SecMoTqC N*m = Secondary motor commanded torque (Newton-Meters)
Vehicle acceleration m/s^2 = What it says.


First image: Drive on our gravel road to the pavement, then a quick, rolling start full-throttle acceleration, then on to the trailhead. This is in Normal mode, 1PD, but no diff lock. The front and rear motors are being commanded to have the same torque and have the same RPM, as one would expect for normal mode.


View attachment 8314



Second image: First run of the small loop.
Setting: Normal, One pedal drive, no diff lock, TRAC on.
Of note: Already, you can see that the torques and speeds are different. They’re similar, but there’s clearly some slipping. The ABS engaged a couple of times while climbing the loose, sandy slopes.
Also note that the scales on the y-axis are different for the primary vs secondary motor graphs.
Where the speeds, power, torques all drop to zero in about the middle of the graph is where I stopped the vehicle at the top of the hill after turning around. Just wanted some clear reference points in the graphs.

View attachment 8315


Next run: Off-road mode, diff locked, no one pedal drive, TRAC off.
I sat at the start a bit longer getting things configured the way I wanted them.
But then you can see, again, that the primary and secondary motor scales are different, though the plots look similar.
Note that you can identify where the front wheel slipped by noting where the commanded torque dropped near the center of the graph and where the RPM shot up suddenly but just for the secondary motor.


View attachment 8316


Next run: Sport mode, diff locked, one pedal drive on, TRAC on.


View attachment 8317

Final run: Sport mode, no one-pedal drive, no diff lock, no TRAC


View attachment 8318

At least the heartbeat kept going and didn’t flatline based on your images . When you are up to it can you man-plain it to me and others who are literate in the graphing above?

 

[JAngley]

If I remember correctly the Red Toyota (Red Lobster) in this video had mutiple speed transfer cases for front and rear. Always thought that was badass. This sounds similar!

 

[SpaceEVDriver]

At least the heartbeat kept going and didn’t flatline based on your images . When you are up to it can you man-plain it to me and others who are literate in the graphing above?

Sure thing.

Apologies to anyone with color vision issues. My app doesn’t let me change the colors of the plots. I know red/green is terrible for visualization and I’d like to find a better color scheme, but I haven’t been able to tell CarScanner to do it better. I will try to fix it sometime later this evening and if I do, I’ll update the graphs.


This first one was meant to give a baseline of how the two different motors behave in normal driving mode.
Everything before the spike is on a 2-ish mile gravel road. No need for any kind of 4x4 behavior. I leave the truck in normal mode with one pedal drive on.

It takes very little power to get the truck moving and keep it moving on the gravel road at 20 mph. There are a couple of turns, so that’s where you see the little jumps in the HV EV Battery Power graph. It’s difficult to make it out on this graph because of the spike, but the peak draw on the gravel road was about 42 kW. The average was something more like 5-10 kW. For a 20 mile/hour speed, that translates to 20 mph / 5 kW = 4 miles/kWh to 20/10 = 2 miles/kWh. That’s pretty typical for me on gravel roads: 3 miles/kWh is my expectation when I’m on forest service roads, etc.

Okay, now we get to the turn onto the highway. That’s at about 11:01:15 or so on the x-axis. There’s a short stop at 0 kW as I checked for traffic, and then I pulled onto the Rt. 66. There was traffic coming up behind me, so I didn’t stop on the highway. I was going about 30 kph (19 mph) when I punched it. This drew about 475 kW of power and gave me an acceleration of about 6.5 m/s^2 (about 0.66 Gs), sending my speed up to 110 kph (68 mph) in about 2.5 seconds. Then I let off the accelerator and regen took over and fed energy back to the battery. Shortly after, I turned off the highway onto another dirt road. The graph ends there.
Note the 475 kW of power from the battery translates to about 637 HP, but that’s at the battery. There are some losses as well as some multipliers to get to the brake HP most people think of when they think of HP.

Comparing the Primary and Secondary motors:
Commanded torque is just how much torque has the computer told the motors to put out.
Let’s compare the torque from the primary and secondary motors:
They’re nearly identical in shape and in magnitude. Mostly where they differ is when the vehicle is turning. I overlaid the graphs here so you can see just how close to the same they really are. The max torque commanded was about 650 N-m, to each motor. That’s about 1300 N-m total (about 960 ft-lbs), but again, that’s at the electric side of the motor. There’s a step-down gear in the motor, and you have to multiply by that ratio, then you have to do the multiplication by the tire radius, etc.

Okay, moving on to comparing the motor speeds:
These match very closely as well. Why does the rear motor turn ever-so-slightly more slowly at times? I think it’s to do with when I’m slowing down slightly. I believe there’s a slight bias toward higher regen on the front tires than on the rear. But I’m not 100% certain of that.

I’ll look at one of the mild off-road runs in another post.

 

[SpaceEVDriver]

For this post, I’ll talk about Off-road mode.
A reminder: Off-road mode turns off one-pedal drive, disables TRAC, and engages the rear locking differential.

I’m trying a different color scheme, but I still can’t change the line colors. For those with color vision issues, I again make my apologies. The primary motor torque in this plot stands significantly above the secondary motor torque whenever there’s a separation between the lines except in very few cases.

Torque:
This plot shows that in Off-road mode, the front and rear motors are commanded to have different torques depending on what’s going on. In this example, most of the time the torque is higher for the rear motor than for the front motor. When the torque is less than 0 N-m, it’s regenerating power. And you can see there, most of the time both motors are contributing about equally to that regen.

When climbing the hill, the rear is commanded to push more than the front is commanded to pull. This is a pretty standard profile for most 4x4 / AWD vehicles. A common split is (something like) 60% rear, 40% front. Different transfer cases are designed differently for different purposes.

Motor speed looks different. The plots are much closer together and in only a few instances are they wildly different. This is what you would expect for most vehicles, and is what @Chavannigans is talking about having access to change. There are a couple of times the front tires slipped and you can see those clearly where the secondary motor speed spikes while the primary motor speed does not.

The biggest instance of a non-slip deviation is just before 11:20:10 (the time when the truck was put in park). You can see the plots diverge, again with the front motor speed higher than the rear motor speed. But without the spike that is characteristic of slippage you might usually think of when climbing a hill. This occurred while I was turning the vehicle around on the trail. Because the rear differential was locked, the inside rear tire controlled the rear motor speed. That tire dragged because of the locked differential, and the rear motor had a lower RPM.

So why is torque different when the speeds are the same? Because the computer can detect wheel slippage >1000 times per second and can modulate the commanded torque in an attempt to keep the wheel speeds the same. Sometimes it fails and the tire slips, usually because there’s literally no traction to be had. Those two spikes in the graph are when one of the front tires stopped touching the ground entirely. Remember that the front axle is an open differential, which means that whichever tire has the least traction spins more than the other. And because there’s no traction control engaged, the only thing to stop those tires from spinning is the ABS or my manual braking. I didn’t brake, but ABS did apply and that’s why the spike was very short. You’ll also notice that the commanded torques did drop for the front motor when the wheel spun.

 

[Chavannigans]

For this post, I’ll talk about Off-road mode.
A reminder: Off-road mode turns off one-pedal drive, disables TRAC, and engages the rear locking differential.

I’m trying a different color scheme, but I still can’t change the line colors. For those with color vision issues, I again make my apologies. The primary motor torque in this plot stands significantly above the secondary motor torque whenever there’s a separation between the lines except in very few cases.

Torque:
This plot shows that in Off-road mode, the front and rear motors are commanded to have different torques depending on what’s going on. In this example, most of the time the torque is higher for the rear motor than for the front motor. When the torque is less than 0 N-m, it’s regenerating power. And you can see there, most of the time both motors are contributing about equally to that regen.

When climbing the hill, the rear is commanded to push more than the front is commanded to pull. This is a pretty standard profile for most 4x4 / AWD vehicles. A common split is (something like) 60% rear, 40% front. Different transfer cases are designed differently for different purposes.

View attachment 8331


Motor speed looks different. The plots are much closer together and in only a few instances are they wildly different. This is what you would expect for most vehicles, and is what @Chavannigans is talking about having access to change. There are a couple of times the front tires slipped and you can see those clearly where the secondary motor speed spikes while the primary motor speed does not.

The biggest instance of a non-slip deviation is just before 11:20:10 (the time when the truck was put in park). You can see the plots diverge, again with the front motor speed higher than the rear motor speed. But without the spike that is characteristic of slippage you might usually think of when climbing a hill. This occurred while I was turning the vehicle around on the trail. Because the rear differential was locked, the inside rear tire controlled the rear motor speed. That tire dragged because of the locked differential, and the rear motor had a lower RPM.


View attachment 8332


So why is torque different when the speeds are the same? Because the computer can detect wheel slippage >1000 times per second and can modulate the commanded torque in an attempt to keep the wheel speeds the same. Sometimes it fails and the tire slips, usually because there’s literally no traction to be had. Those two spikes in the graph are when one of the front tires stopped touching the ground entirely. Remember that the front axle is an open differential, which means that whichever tire has the least traction spins more than the other. And because there’s no traction control engaged, the only thing to stop those tires from spinning is the ABS or my manual braking. I didn’t brake, but ABS did apply and that’s why the spike was very short. You’ll also notice that the commanded torques did drop for the front motor when the wheel spun.

I sincerely mean it when I say, you are an absolute legend for what you do in this community.

Thank you so much for taking the time to compile all of this data for us and sharing your findings.

I’m blown away.

 

[SpaceEVDriver]

Okay, one more. Sport mode, no differential lock, no one-pedal drive, no traction control.

Torque: Again, the rear motor stands above the front motor for most of the drive (more torque was commanded to the rear motor).
The shapes are similar, but the values are different. This mode sends more torque to the rear motor—about 30% more than in off-road mode, from my understanding.

Motor speed: Here, it was the rear tires that spun. The front tires were providing more of the traction pulling the truck up the hill, but only in minor instances. That rear tire spin is because of the extra torque being sent to the rear tires and no traction control reducing slip. This is not the mode you want to be climbing hills in.