Compact Field Oriented Controller, ASI + Grin, limited run

[Mammalian04]

Hi Justin,

Is there any way that you could produce a few typical .XML files for common applications (e.g. Lightning Rods Small Block, New Cyclone 3000w kit, MXUS 3000, etc?)
I am not sure if this is technically feasible or if the variations in every motor will require individual settings.
I could gather up or coordinate sending you a few motors to test if you don't have local access.

Also, are there any plans for a high power Phaserunner for motors such as LightningRods BigBlock or maybe even Cromotor someday?

 

[r3volved]

I tried the Phaserunner on the LR small block and it hauled ass in sensorless mode. I just could not get sensored mode to work properly and in sensorless, could not rid the jerkiness in low speed.

I personally shelved it for now to use on a hub later. Note: I have not tried it with Justin's December software release.

 

[Mammalian04]

Thanks for the feedback r3volved. If Grin could provide a base setup .XML for us using the small block, that would help greatly.

 

[r3volved]

If someone had a working XML I would likely give it another go. Performance was on par with my lyen at 3kw and used less wh/km.

 

[tangentdave]

Attached is the xml file I'm using with a 3210, sensorless. I have no jerkiness issues or oscillations but am still tinkering with the starting torque.
View attachment BAC5000-29nov.xml

Mr Bill, it sounds like your PID loop is too tight, the controller may be using too large of an adjustment when attempting to maintain power output under varying loads. Two things to try:

1)Lower your 'Current Regulator Bandwidth' setting (Controller Debug->Control Loops & Tuning).
2)Try setting your 'Current Regulator Bandwidth'=0 radians and lowering the values for 'Current regulator Ki' and 'Current Regulator Kp' . Setting the regulator bandwidth to 0 causes the controller to use the Kp and Ki values you enter, otherwise the regulator bandwidth value is used in complex equations to automatically set the Kp and Ki values.

These Kp and Ki values are used in the PID to control overshoot and oscillations. If they're too high=oscillations, if they're too low=slow response. The speed regulator Kp and Ki work the same, but in speed mode, which we don't want, ignore them. I'm unsure of the exact effect of the PII Ki and PII Kp fields, still tinkering.


-dave

 

[mrbill]

Mr Bill, it sounds like your PID loop is too tight, the controller may be using too large of an adjustment when attempting to maintain power output under varying loads. Two things to try:

1)Lower your 'Current Regulator Bandwidth' setting (Controller Debug->Control Loops & Tuning).
2)Try setting your 'Current Regulator Bandwidth'=0 radians and lowering the values for 'Current regulator Ki' and 'Current Regulator Kp' . Setting the regulator bandwidth to 0 causes the controller to use the Kp and Ki values you enter, otherwise the regulator bandwidth value is used in complex equations to automatically set the Kp and Ki values.

These Kp and Ki values are used in the PID to control overshoot and oscillations. If they're too high=oscillations, if they're too low=slow response. The speed regulator Kp and Ki work the same, but in speed mode, which we don't want, ignore them. I'm unsure of the exact effect of the PII Ki and PII Kp fields, still tinkering.

Hi tangentdave:

Thanks for your help.

I tried your suggestions, both separately and in combination, but nothing damped out the oscillations adequately. I did notice that with lower Ki and Kp values the magnitude of oscillations was very slightly reduced, but the downside is that motor power decayed to zero too slowly when I commanded zero throttle.

I also tried adjusting PLL damping, Pll Kp, and Pll Ki, starting with changing each by a factor of 10, but no change made a discernible difference.

I think the problem is not the magnitude of the applied correction but its frequency, how often the controller applies a correction, given a changing load. There's definitely a resonance or excitation of about 3-4 Hz when the controller attempts to correct for changing drivetrain load, and this is about the same frequency as the fundamental resonance of my crank-drive bike's frame, about 1.5m in length from BB to rear hub.

Maybe ASI intended these controllers for use only with hub motors or fixed-gear single-speed motors and not for drivetrains with crank-drive, multiple gears and/or a "springy" load with a resonance frequency below 10 Hz.

For my build a PWM or voltage throttle may be the only solution. After looking through all the tabs in BACDoor version 1.5.4.0 I could find no setting that suggested this option. Perhaps a newer version of BACDoor will offer it.

 

[iser]

I tried to drive three-wheeler, but no matter how to set the parameters of BAC3K, it can't eliminate the crash of gear tooth.

 

[mrbill]

For all of my complaints about trying to run my ASI BAC2000 controller with its torque throttle through a drivetrain not tightly-coupled to the road, I discovered that this controller ably drives a Nine Continents M3006RC (as sold by Grin), a direct-drive hub motor.

I enjoyed a very pleasant outing today with this new configuration.

http://ridewithgps.com/trips/7687661

Some observations:

1) The hub motor emits a low hum at all times, even when not driven. The hum is loudest at about 12-13 mph (20 kph) when driven hard (e.g. 1000 watts), such as when climbing a hill. I recall that this motor also made its loudest noise with the Infineon controller under similar conditions, but then the noise was more of a buzz. I was a little disappointed that the operation is not completely silent, but the humming is not too annoying and is definitely softer than the buzz of the motor when driven by the Infineon.

2) I set engine braking to 100% and regen range from 0% to 100%, but the maximum regen power was no higher than 740 watts, and often maxed out at about 650 watts. "Nameplate" motor power was set to 1200 watts, so I'm not sure of what the percent refers. Has anyone managed to get more than 750 watts of regen power from their BAC2000 or Phaserunner?

That said, I find that regen has much less braking effectiveness than with the Infineon controller, even when commanding 100% regen. When descending at speed (e.g. 40 kph or higher) I can get several hundred watts of regen and barely notice the braking effect. But when descending a 12% grade on Metcalf Rd. today, I found myself using the friction brakes more than would have liked, the regen brake being insufficient to hold me to a safe speed.

This confirms my suspicion that the Infineon regeneration shunts much of the motor power for enhanced braking effect rather than sending the recovered power to the battery, and perhaps explains why my motor usually saw its hottest temperature when regenerating down a long hill.

I like that the BAC2000 can recapture significant energy without slowing me down too much. But sometimes I want lots of braking (with commensurate energy recapture), and even at 100% regen feels like lightly dragging the rear brake when moving faster than walking speed. I'd like to recapture more than 650 watts!

At walking speed or close to it, 100% regen changes character and feels more like a brake. The effect is so pronounced that if I come to a complete stop, the motor actually produces a mild reverse kick after reaching 0 speed. I recall Justin mentioning that at very low speeds the controller actually applies reverse power to produce a braking effect to 0 speed, so maybe this explains the different regen behavior at low speed.

3) But, this reverse kick is slightly annoying. Is there a minimum regen speed one can set in BACDoor that suppresses this behavior? And in any case I'm more interested in using regen to recapture energy and not as a brake with which I can bring the bike to a complete stop. I can use the friction brakes to finish the job of stopping the bike.

4) I'll need to run some more controlled tests to confirm, but I suspect the BAC2000 controller runs the motor more efficiently than the Infineon. Given my average speed of 19.3 mph (31 kph), the consumption rate of 10.6 wh/mi (6.6 wh/km) is remarkably low.

 

[justin_le]

But, I'm running a crank-drive motor that feeds through the bike chain, a rather long chain connecting two ends of a bike frame that has some "spring", and the rear wheel cluster, the shifts presenting a changing load. The torque is constantly varying on this drivetrain.

Every time I shift to a higher gear, the drivetrain presents the motor with an instantly greater torque. The controller apparently senses this and dials back the power, but overshoots, then reapplies power, overshooting, but not as much. ... Occasionally the torque feedback sets up an alarming resonance with my frame and does not settle down unless I interrupt it with the eBrake or by killing the power. I suspect the torque is going to zero momentarily as the controller tries to adapt to the changing load.

Hey Bill, this is an interesting observation that I can relate to firsthand as well. On our CycleStoker kits for long tail cargo bikes, the mid-motor similarly goes through a long chain drive to the wheel with a certain amount of flex in the mounting bracket, bike frame etc. and we also noticed a feedback resonance between the ASI controller trying to maintain constant motor torque and the loose coupling to the drive wheel. In that particular bike setup it was most pronounced when starting off at low speeds, more of a minor nuisance than a real problem but something that still stood out.
Then more recently on my dyno bench when I was trying to characterize some high torque hub motors. When I used a loose coupling (zip ties) rather than a rigid coupling between the test motor and the my dyno load motor (which has a feedback loop attempting to maintain constant RPM), at a certain torque level the system would go into a crazy oscillation which never happens with just a voltage mode controller. Once I linked the test motor to the dyno load motor with a rigid metal rod, then the dyno test went flawlessly with no issues.

So yes, if the inertial load to your motor is linked with some amount of flex or elasticity, then the field oriented controller trying to actively maintain a constant torque output may throw the system into an unstable feedback loop.

I see two possible solutions:
1) Dial back the controller's torque or current feedback parameters until these variations are so slow and gradual that the spurious drivetrain noise is damped out. Does BACDoor allow the user to do this, and if so, what are the parameters to adjust?

As you found, most of the feedback parameters for the controller are related to a much faster control loop for the phase current regulation, and don't have too much effect when there is an external lag/elasticity to the inertial load which is happening on a much longer time constant. I also didn't explore too deep into it since I was also thinking that:

2) Switch to PWM/voltage throttle mode

was going to be the easiest solution. However, the field that should work for this which is setting the "speed regulator mode" for "speed" mode instead of "torque" mode should have had this effect, but even with all the vehicle speed parameters set up correctly it's never worked as expected with the throttle behaving as a speed controller. Instead partial throttle always resulted in full RPM on the motor. If you set a vehicle maximum speed limit in the Peripheral Configuration -> Vehicle pane, then it does limit it to whatever speed is there, but it doesn't scale this speed with your throttle setting.

There is another setting that looked really promising, if you create a new parameter "Test Mode", you'll see that it describes Mode 2 as "open loop voltage mode"


which is exactly what we'd want, rather than the closed loop current mode, but when you set this to 2 then the throttle doesn't work at all.

Anyways I'll be in touch with the programmers at ASI soon to see if there isn't some way that we are missing in order to have the throttle signal command an effective voltage output to the motor, rather than commanding a closed loop current/torque output. Even if a torque throttle is ideal for like 90% of users, there are still a number of cases where the familiar voltage/PWM throttle can be more desirable.

 

[justin_le]

2) I set engine braking to 100% and regen range from 0% to 100%, but the maximum regen power was no higher than 740 watts, and often maxed out at about 650 watts. "Nameplate" motor power was set to 1200 watts, so I'm not sure of what the percent refers. Has anyone managed to get more than 750 watts of regen power from their BAC2000 or Phaserunner?

Hey Bill, in your sample XML file which you posted here even though you've set the regen phase current limit to 100% of your rated phase current (74 Amps), you've limited the battery regen current limit to 63% of your rated battery current.


Your rated battery current in this system is 1200 watts / 48 volts = 25 amps, and so 63% of this is 15.8 amps, which is exactly the 750 watts that you are getting with your 48V battery pack.

Set this to say 125% of instead of 63% and then you'll have up to 1500 watts into the battery during regen. Set this to 200% and you'll have up to 50 amps of regen current into the battery. This kind of stuff where we're trying to make our own phaserunner configuration software more intuitive to see and change than ASI's Bacdoor package.

At walking speed or close to it, 100% regen changes character and feels more like a brake.

That's because at low speeds, your regen is no longer being battery current limited because of the very low duty cycle in which the regen current flows back into the pack, so the regen phase current is able to reach the full 74A that you programmed as your max. If you weren't battery current limited, you'd have this same braking force at all speeds.

I like that the BAC2000 can recapture significant energy without slowing me down too much. But sometimes I want lots of braking (with commensurate energy recapture), and even at 100% regen feels like lightly dragging the rear brake when moving faster than walking speed. I'd like to recapture more than 650 watts!

The controller is doing exactly what you told it to do here, so once you tell it what you actually want by changing your battery regen current limit, I think you'll find your mechanical brakes starting to collect dust.

-Justin

 

[Cowardlyduck]

Seriously considering this controller as a neat little package for my Recumbent BikeE:

I currently have a little 4110 6 Fet tucked inside the space in the frame cut-out at the rear under the seat, here:

The 6 Fet fit's because it's width is just 35mm. For the PhaseRunner controller to work it would have to fit this same spot. It's not clear to me however if it's width is 34mm or 40mm from the dimentions on the ebikes.ca site:
http://www.ebikes.ca/shop/ebike-parts/controllers/c-phaserunner.html
Dimensions (L x W x H, mm) 99 x 40 x 34

Looking at the image, it would seem the width should be 34 not 40...am I just looking at it wrong?

Any help appreciated.

Cheers

 

[MrDude_1]

its 33 wide, but he calls it 34 incase the casting is a little wider.

You want to look at this:
Phase Runner Dimensional Diagram

oh his site, under additional information, are PDFs with all kinds of useful info.
http://www.ebikes.ca/shop/ebike-parts/controllers/c-phaserunner.html

 

[mrbill]

So yes, if the inertial load to your motor is linked with some amount of flex or elasticity, then the field oriented controller trying to actively maintain a constant torque output may throw the system into an unstable feedback loop.

I'm frankly surprised that ASI hadn't considered that some drivetrains might not be compatible with a tight-loop torque/current throttle and didn't offer a PWM/voltage throttle mode. This makes the controller sub-optimal to unusable in mid-drives.

Anyways I'll be in touch with the programmers at ASI soon to see if there isn't some way that we are missing in order to have the throttle signal command an effective voltage output to the motor, rather than commanding a closed loop current/torque output. Even if a torque throttle is ideal for like 90% of users, there are still a number of cases where the familiar voltage/PWM throttle can be more desirable.

Good. I was planning to buy a second controller at some point, but I'll wait until I can first confirm that a PWM/voltage throttle is supported.

I tried to drive three-wheeler, but no matter how to set the parameters of BAC3K, it can't eliminate the crash of gear tooth.

This gear "crashing" might be the torque/current throttle control loop setting up a resonance in a drivetrain with some backlash.

 

[MrDude_1]

So yes, if the inertial load to your motor is linked with some amount of flex or elasticity, then the field oriented controller trying to actively maintain a constant torque output may throw the system into an unstable feedback loop.

I'm frankly surprised that ASI hadn't considered that some drivetrains might not be compatible with a tight-loop torque/current throttle and didn't offer a PWM/voltage throttle mode. This makes the controller sub-optimal to unusable in mid-drives.

Anyways I'll be in touch with the programmers at ASI soon to see if there isn't some way that we are missing in order to have the throttle signal command an effective voltage output to the motor, rather than commanding a closed loop current/torque output. Even if a torque throttle is ideal for like 90% of users, there are still a number of cases where the familiar voltage/PWM throttle can be more desirable.

Good. I was planning to buy a second controller at some point, but I'll wait until I can first confirm that a PWM/voltage throttle is supported.

I tried to drive three-wheeler, but no matter how to set the parameters of BAC3K, it can't eliminate the crash of gear tooth.

This gear "crashing" might be the torque/current throttle control loop setting up a resonance in a drivetrain with some backlash.

for the record, the chain drive in my scooter had a TON of backlash and I could tune it out.
the #1 thing to do was to set the regen to "off"..... that way the motor only pulled it forward, it never tried to regen off the chain. (my chain tensioner wouldnt allow it.)

 

[mrbill]

Hey Bill, in your sample XML file which you posted here even though you've set the regen phase current limit to 100% of your rated phase current (74 Amps), you've limited the battery regen current limit to 63% of your rated battery current.

Your rated battery current in this system is 1200 watts / 48 volts = 25 amps, and so 63% of this is 15.8 amps, which is exactly the 750 watts that you are getting with your 48V battery pack.

Set this to say 125% of instead of 63% and then you'll have up to 1500 watts into the battery during regen. Set this to 200% and you'll have up to 50 amps of regen current into the battery. This kind of stuff where we're trying to make our own phaserunner configuration software more intuitive to see and change than ASI's Bacdoor package.

At walking speed or close to it, 100% regen changes character and feels more like a brake.

That's because at low speeds, your regen is no longer being battery current limited because of the very low duty cycle in which the regen current flows back into the pack, so the regen phase current is able to reach the full 74A that you programmed as your max. If you weren't battery current limited, you'd have this same braking force at all speeds.

The controller is doing exactly what you told it to do here, so once you tell it what you actually want by changing your battery regen current limit, I think you'll find your mechanical brakes starting to collect dust.

-Justin

Ah, ok. Thanks for the pointing this out.

To be fair, though, I didn't set this to 63.3545%; BACDoor set it by default.

This bike's battery uses 12p Samsung INR-18650-29e cells. Samsung gives a standard charging current for this cell of 1.375 Amps/cell, which in 12p is 16.5 Amps, just about the same as what I get using the BACDoor default. Samsung further cites a maximum charge current of 2.75 Amps/cell, which would be 33 Amps total, or about twice the default. BMS allows up to 40 Amps in or out. That's probably enough to get a decent braking effect without stressing the batteries unduly.

Occasionally I run a 9p battery in parallel for extra range, so I suppose then I could set it for up to 57 Amps, if I remember to reprogram the controller when adding the supplementary battery.

Any thoughts on whether allowing these or higher regen currents will reduce battery life noticeably?

Also, is there a way to tune out that little reverse kick I get after stopping using 100% regen?

 

[robbie]

Also, is there a way to tune out that little reverse kick I get after stopping using 100% regen?

Hey Mr. Bill,

You can set a "regen brake speed" which will cut the regen braking off when below this speed.

-Robbie

 

[mrbill]

I tried to drive three-wheeler, but no matter how to set the parameters of BAC3K, it can't eliminate the crash of gear tooth.

This gear "crashing" might be the torque/current throttle control loop setting up a resonance in a drivetrain with some backlash.

for the record, the chain drive in my scooter had a TON of backlash and I could tune it out.
the #1 thing to do was to set the regen to "off"..... that way the motor only pulled it forward, it never tried to regen off the chain. (my chain tensioner wouldnt allow it.)

Perhaps iser can followup with a more detailed description of the problem. If the objective is to tune out backlash, then, yes, you wouldn't want to use regen at all, esp. if there are slack-side pulleys and/or tensioners. But, I was thinking that iser's problem was related to the resonance Justin and I have observed in drivetrains that are "springy". This would include mid-drives that run motor power through a bike's shift-able rear cluster, or a chain-drive on all but the stiffest of bicycle frames.

 

[iser]

for the record, the chain drive in my scooter had a TON of backlash and I could tune it out.
the #1 thing to do was to set the regen to "off"..... that way the motor only pulled it forward, it never tried to regen off the chain. (my chain tensioner wouldnt allow it.)

I almost disable all function of controller but reverse function to clarify this issue.
Whenever give a big or full throttle signal to controller, whether static or spin status, the clash will happen.

 

[mrbill]

Also, is there a way to tune out that little reverse kick I get after stopping using 100% regen?

Hey Mr. Bill,

You can set a "regen brake speed" which will cut the regen braking off when below this speed.

-Robbie

Hi Robbie,

Thanks for the suggestion. I actually did experiment with this, setting it for yesterday's ride to 1 km/hr, but I still got a kick.

I discovered another parameter, "Negative braking torque ramp" (with a default setting of 250ms). I set this to its minimum, 1 ms. When testing on the stand with the rear wheel spinning freely, I was able to eliminate the reverse kick when the "Regen brake speed" was set higher than 8 km/hr. After testing on the road I can confirm that I get no reverse kick upon stopping when "Regen brake speed" is set to 0 km/hr. I suspect this is because the inertia of the whole bike is in play instead of just the rear wheel. They key is to reduce "Negative braking torque ramp".

 

[iser]

Perhaps iser can followup with a more detailed description of the problem. If the objective is to tune out backlash, then, yes, you wouldn't want to use regen at all, esp. if there are slack-side pulleys and/or tensioners. But, I was thinking that iser's problem was related to the resonance Justin and I have observed in drivetrains that are "springy". This would include mid-drives that run motor power through a bike's shift-able rear cluster, or a chain-drive on all but the stiffest of bicycle frames.

I tried my BAC3K controller on both hubmotor and mid-motor.
For hubmotor the most common issue is resonance in low speed range(5~20Km/h). In order to solve this question i bought 3 different brand or specification hubmotor(Pole pair 23/24/28) to find the best mute effect under big or full throttle torque condition in low speed range, although i set small Current Regulator bandwidth(150~300) and small PLL bandwidth, the test result is not ideal. While if you pursue small Current Regulator bandwidth(C-Kp<0.1) and PLL bandwidth too much, it will leads to over current protection when heavy load changed suddenly.

So i try to look at this issue in another way, maybe ASI wish user to use their controller to drive mid-motor but hubmotor; While when i try it on my friend's mid-motor tricycle, the crash issue puzzle me.

 

[iser]

Hi Justin,
Does it works if enable bit 0(Set bit 0 as 1) for mid-motor?
I tried it and then the mid-motor can't spin, if disable it(Set bit 0 as 0) the mid-motor will spin normally.
For hubmotor, this function works.

tks.

 

[mrbill]

Perhaps iser can followup with a more detailed description of the problem. If the objective is to tune out backlash, then, yes, you wouldn't want to use regen at all, esp. if there are slack-side pulleys and/or tensioners. But, I was thinking that iser's problem was related to the resonance Justin and I have observed in drivetrains that are "springy". This would include mid-drives that run motor power through a bike's shift-able rear cluster, or a chain-drive on all but the stiffest of bicycle frames.

I tried my BAC3K controller on both hubmotor and mid-motor.
For hubmotor the most common issue is resonance in low speed range(5~20Km/h). In order to solve this question i bought 3 different brand or specification hubmotor(Pole pair 23/24/28) to find the best mute effect under big or full throttle torque condition in low speed range, although i set small Current Regulator bandwidth(150~300) and small PLL bandwidth, the test result is not ideal. While if you pursue small Current Regulator bandwidth(C-Kp<0.1) and PLL bandwidth too much, it will leads to over current protection when heavy load changed suddenly.

So i try to look at this issue in another way, maybe ASI wish user to use their controller to drive mid-motor but hubmotor; While when i try it on my friend's mid-motor tricycle, the crash issue puzzle me.

Hi iser:

The issue that Justin and I discovered on some of our builds is that the torque/current throttle control feedback loop sets up a resonance in sympathy with the "springiness" of our drivetrains. This resonance appears when changing the load on the drivetrain as a "hesitation" of applied power or repeated "slamming" in the drivetrain that may or may not damp out. Stiffening the motor mounting may be sufficient for Justin's test rig, but on my bike the frame itself is like a long leaf spring that bends about the y-axis (vertical). Short of building a new wider space-frame for my bike that is stiffer about the y-axis, there is no practical structural change I can make. (Btw, I can see my bike's frame visibly deflect outward to the left as a high load is introduced to the drive chain.) I tried adjusting all of the BACDoor control parameters you mention above by two orders of magnitude or more but was unable to tune out this resonance.

A direct-drive hub motor can't get any more closely coupled to the road and is least likely of any drivetrain to suffer the problem I described above. Your problem may have some other cause.

Did you go through the motor auto-tune process for each of the motors you tried?
Do you have any backlash or "springiness" in your drivetrain between the motor and the road?
Are you using direct-drive or geared hub motors?

 

[mrbill]

Here is a question I posed earlier that seems to have gotten lost:

5) Can Grin or others give any advice/guidance with the setting of parameters under "Advanced Motor" (field weakening), such as when to use, how much, and the trade-offs?
Thanks.

I played a little with the field, "Maximum Field Weakening current", adjusting it from 0 to 30 % and leaving the other parameters at the defaults (0 for all but Field weakening speed 6, 7, and 8) and observing the unloaded spinning wheel's behavior while on the stand. Increasing this appears to give a higher top RPM. The behavior is similar to that of the >100% throttle settings on the Lyen (Infineon-style) controllers.

Has anyone played around with this feature?

Thanks.

 

[iser]

Did you go through the motor auto-tune process for each of the motors you tried?

Yes, i run this program 2 or 3 times to get a stable parameters.

Do you have any backlash or "springiness" in your drivetrain between the motor and the road?

No, only resonance i can feel in low speed range.

Are you using direct-drive or geared hub motors?

All my hubmotor is D-D hubmotor.

 

[justin_le]

But, I was thinking that iser's problem was related to the resonance Justin and I have observed in drivetrains that are "springy". This would include mid-drives that run motor power through a bike's shift-able rear cluster, or a chain-drive on all but the stiffest of bicycle frames.

Just to be clear, the field oriented controllers work perfectly well with any normal mid-drive bike system like a BBS0X, ecospeed, cyclone kit etc. on a regular diamond frame bike. That's all well within the realm of stiff enough to not see any of this behavior, and it would only be a small fringe if ebike drives that have enough elasticity from the motor to the wheel where you get this instability.
It's easy to understand why a torque control controller has that problem. It would be like towing a trailer that's linked to a truck with a bungee cord, and having as the only feedback for how hard to step on the gas being a force sensor on the trailer hitch, with a goal of keeping that force constant while you drive over different terrain and bumps etc..

Here is a question I posed earlier that seems to have gotten lost:
mrbill wrote:
5) Can Grin or others give any advice/guidance with the setting of parameters under "Advanced Motor" (field weakening), such as when to use, how much, and the trade-offs?
Thanks.

The field weakening was discussed in quite some depth earlier in this thread, see https://endless-sphere.com/forums/viewtopic.php?p=984725#p984725 and related posts on that page.

Ideally you would never use field weakening, choose your motor winding and battery voltage so that you are happy with your top-end RPM. But if you are constrained to a setup that isn't as fast as you want it to be and can't afford either a faster motor or a higher voltage battery, then you can use automatic field weakening to get a higher top speed from the motor. The more field weakening current you use, the higher your top speed, and the more your efficiency at those speeds plummets since a large portion of your phase current is simply countering the PM fields rather than producing torque.

I'm not sure that there is much more to say than that. Look at your CA to see how a given amount of field weakening current increases your motor RPM and look at your full throttle no-load current draw to see how much extra power is being wasted to allow these higher speeds, and make the trade-off which suits what you want. The graphs that I included in the post linked above show the general relationship quite well.