Car accelerates harder from a roll than a stop. (HPEVS)

is there a way to "prime" the rotor flux before launch? maybe try a brake torque launch?

steveob said:

is there a way to "prime" the rotor flux before launch?

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I suppose I could. I understand the reason for a lack of torque from a dead stop. The weird part is that it doesn't have the same current at equivalent speeds higher up.

Say I have my car in 1st gear with a 45 mph top speed.

My amps (acceleration) during a 20 mph punch is fantastic, near peak controller output.

When doing max acceleration from a stop, the amps are nowhere near as high at the same speed.

It should have gotten over the initial lack of torque due to a weak initial field by that speed. Right?

can you clarify if you mean battery amps or motor amps? battery amps is always going to be lower at the start.

It is possible, even likely, the controller is waiting for a "good" speed signal before dumping lots of amps too, or other slew variable.

but doing a brake torque launch might prove informative (w/out wheels spinning, just loading the motor at 0 rpm).

I don't know how you tweak these controllers, but I would have a look at the parameters on the top of page 31 here (i.e. full Accel Rate LS), and make sure you consistently apply the throttle during testing (and note the values, as well as the rotor time constant).


http://www.thunderstruck-ev.com/Manuals/1234_36_38 Manual Rev Feb 09.pdf

steveob said:

can you clarify if you mean battery amps or motor amps? battery amps is always going to be lower at the start.

It is possible, even likely, the controller is waiting for a "good" speed signal before dumping lots of amps too, or other slew variable.

but doing a brake torque launch might prove informative (w/out wheels spinning, just loading the motor at 0 rpm).

Click to expand...

Battery amps. Either way, the battery amps never match between the two scenarios.

steveob said:

I don't know how you tweak these controllers, but I would have a look at the parameters on the top of page 31 here (i.e. full Accel Rate LS), and make sure you consistently apply the throttle during testing (and note the values, as well as the rotor time constant).


http://www.thunderstruck-ev.com/Manuals/1234_36_38 Manual Rev Feb 09.pdf

Click to expand...

That wouldn't apply to the situation because it is in "torque mode". Torque mode basically sets throttle response to correspond to amps (torque). In speed mode, throttle response would correspond to a specific motor speed, which would not behave like a normal car.

It *should* affect how quickly it responds to the throttle, they have one for low speed and one for high speed. and low speed has a low throttle and a high throttle version. I assume you want the "punch it" version. So that it can take up to 30 seconds to get up to full torque(motor current) limited by the firmware setting, or as little as 0.1 second, regardless how hard you are pressing on the throttle.

if you get a look at the parameters and Full Accel Rate HS and Full Accel Rate LS and they are vastly different, that might explain most of the difference as well. And you can apparently set the threshold between LS and HS.

I'm just guessing though, you will need to sort out a programmer and have a look.

apparently you can rent a 1313 programmer for $40/mo, no idea if it will work for you, just sayin.
https://www.ebay.com/sch/i.html?_fr...0.Xcurtis+1313.TRS0&_nkw=curtis+1313&_sacat=0
though you should also inquire with whomever you got the motor from as well as to how to proceed.

steveob said:

I don't know how you tweak these controllers, but I would have a look at the parameters on the top of page 31 here (i.e. full Accel Rate LS), and make sure you consistently apply the throttle during testing (and note the values, as well as the rotor time constant).


http://www.thunderstruck-ev.com/Manuals/1234_36_38 Manual Rev Feb 09.pdf

Click to expand...

Actually use the accel rate setting as seen at top of page 35 when in torque control. There's no LS or HS with that one.

major

I see the distinction now, thanks!.

A bit of creep torque might help too, but could be problematic.

steveob said:

I see the distinction now, thanks!.

A bit of creep torque might help too, but could be problematic.

Click to expand...

I thought about that. Not sure it'd help with harder launch. I have creep in my factory EV (Think City). I really like driving with it. After years in conversions and racers without creep I was unsure about the feature when I got the Think 6 years ago. But quickly grew to like the feature. Really nice for parking and inching forwards, or backwards.

major

major said:

Actually use the accel rate setting as seen at top of page 35 when in torque control. There's no LS or HS with that one.

major

Click to expand...

Yeah, my Accel Rate is definitely already set at 0.1 seconds, it's at max current, and 8000 rpm limit. I'm not sure what else I can play with at this point. I have a hacked programmer, so I could mess around with other settings if people have ideas.

It's not bad by any means; I can certainly live with how it is, but I figured I'd ask if I could get some improvement for free with some tweaking.

I'd try adding some creep torque, so you have to push the brake pedal to keep it from moving ahead, like in a car with automatic transmission. Just a guess, but it might keep the motor excited.

or see if it will brake torque as-is, though there are settings that could prevent that.

Hi there,

I had the same set-up in my motorbike, AC-20 with Curtis controller at 103 V. I also felt the acceleration was less strong from dead stop than at speed.

I then changed for AC-30, and the acceleration from dead stop is much better, then becoming less than AC-20 at above 80 km/h for my gear ratio (7:1)

I attach my .cpf file that i exported from my Curtis, you should be able to open it with your Curtis software, just don't upload it to your controller as-is though, but you can compare the parameters

details of my build here: zvexx.com