Parameter P1 is used for speed alignment
Below, you’ll read how I managed to align the actual speed with the speed shown in the S-LCD3 display, using parameter P1. I also managed to get the setup to taper off power as intended. I live in Europe, so I chose max 25 km/h on my ebike.
First, I got it wrong, by choosing a wrong approach to aligning it. Then I got both the approach and speed alignment right. And finally, I tested the max speed setting. The sections below follow this approach. I hope you get your speed alignment and taper off right too.
Table of content
- How to get it wrong
- How to get it right
- Testing the max speed setting
- Summing up
When this motor is used in combination with s-lcd3-diplay there are a few things to understand. First, the LCD display will show your speed based on the wheel size that you register in it. And only that. However, as with cars from the ‘good old days’, it is not accurate. When driving with an actual speed of 23 km/h, the display shows +28 km/h (too high).
My setup is:
- a Q100 motor 328 RPM, in a size 20” wheel
- a S06S Torque simulation sine wave controller
- S-LCD3 display
- 36v 14,5 ah Li-ion battery
How to get it wrong
On online forums I found a few threads discussing Q100 parameter P and C. These threads will tell you that parameter P1 is a value between 0 and 255. That’s correct.
You’ll also read that it should be calculated by timing the number of magnets in the motor with the reduction gear ratio. That is not correct. But it is a starting point, and therefore you should use it, when beginning the installation.
However, I started out by doing what the internet forum threads suggested:
- Magnets in the motor: 16
- Reduction gear ratio: 8,2
- Internet forum P1 suggestion: 16*8,2 = 131
I changed the parameter P1 value from 223 (original value) to 131. I live in Europe, so therefore I want the motor to stop/taper off at 25 km/h, and I typed that in as max speed.
Having typed in max speed = 25 km/h and wheel size = 20, my motor tapered off at 23 km/h (actual speed), measured of GPS-speed-tracker on my smart phone, while the LCD showed a speed of 27 (wrong speed).
When I increased the P1 to 141, the motor would stop/taper off at exactly 25 km/h (correct speed) and the display would show +28 km/h (wrong speed). To begin with, this difference puzzled me.
It turns out, that the system operates with three speeds.
- Actual speed you ride with
- Max speed registration, when the system should taper off power
- The speed displayed in the S-LCD-Diplay
P1 is used to align the actual speed with the max speed setting of 25 km/h, and not the speed that is displayed in the LCD-display when riding. When trying to get it right, I used a GPS-speed-tracker on my smart-phone to measure actual speed. Whenever I lowered P1 the motor stopped/tapered off at lower speeds, and when I increased P1 the motor stopped/tapered off at higher speeds.
However, even when I found the correct parameter P1 setting, and I got the motor to stop/taper off at exactly 25/h the LCD-display would still show +28 km/h. I tried and tried and tried to get the display to match the wheel speed, by changing parameter P1, but with no luck. The only thing that was affected was the speed at which power was tapered off.
This means that the display doesn’t use P1 for calculating speed. The display is not at all affected by P1. The display only used the registered wheel size and number of rotations to display a speed.
Thus, the actual speed of the wheel and LCD-display speed are two separate things. And therefore, you need to setup the system in reverse order. First, get the display speed more-or-less-accurate. Second, align the actual speed registration of the wheel. This is explained in the next section.
How to get it right
First you need to register whatever wheel size in the display, that lets the display show your actual riding speed as correct as possible. In my setup, I need to register 18” wheels on the display, even though my bike has 20” wheels with balloon tires.
I checked my riding speed on LCD-display speed against a GPS-speed-tracker on my smart-phone. With this setting, the display shows just 1 km too high. Previously it was way off (very high).
Now that I have registered smaller wheels, the display speed is correct (read: correct enough for purpose). And the setup now needs to have the calculation of stop/taper off re-adjusted, because the setup now “thinks” it is riding slower than it actually is.
It “thinks” that the actual speed is lower, because I “artificially” made the wheels smaller, by registering smaller wheel, than what is actually on the bike. And since I didn’t adjust parameter P1, (which the setup uses to calculate the actual speed of the wheels), the system gets the actual speed of the wheels wrong.
At this point, the “stop/taper off” didn’t occur until I rode 28 km/h, even though I set the max speed to 25 km/h. I needed to align the “stop/taper off”-speed with the actual speed of the wheels. And that re-adjustment/correction is exactly what parameter P1 is used for.
With a 18” wheel-registration, and a max speed registration of 25 km/h, I now needed to re-adjust parameter P1 all the way down to the value of 122, in order to get the motor to stop/taper off at exactly 25 km/h. At this point, the actual speed matches the speed shown on the display (plus/minus the infamous 1 km/h).
Testing the max speed setting
After having finalized this basic speed alignment, I tried to increase the max speed setting/taper off to 35 km/h. However, the setup is not capable of reaching speeds of 35 km/h with a 36v battery. Instead it tapers off at around 30-31 km/h. It can’t go any higher with just 36v.
This limit is affected by the actual voltage of the battery. Mine is a 36V battery, with a max of 42V and a minimum of 28V. So, fully charged at 42V the setup is noticeably faster (31-32 km/h) and already half way through the battery it struggles to reach 29 km/h.
To my understanding, the motor builds up a “back-draft-voltage” as it spins up in speed. Thiefaster it spins/speed, the higher the “back-draft-voltage”. In order to increase speed, your battery has to have a higher actual voltage than the “back-draft-voltage” in order to accelerate.
To go faster with this motor, you should choose a 48V battery. This will give you an additional 12v/33% power to “spin up” the motor/speed. I have chosen to go “street legal in Europe”, so 36v is enough for me. To my understanding, the legal speed limit in the US is 32 km/h (20 M/h), so you should probably chose 48V batteries there, when using a similar setup (small 20” wheels and 328 RPM Q100 motor). Be aware, that larger wheel sizes and different RPM may not need 48 volt to go faster than 30 km/h (18 m/h)
To get the speed of your system aligned correctly you should do the following:
- First, pick whatever wheel size that lets your display show your actual speed correct. Use a GPS-tracker to check when the display matches you actual speed.
- Then, adjust you max speed setting (the speed at which the system should taper off power) to 25 km/h before continuing with adjusting the parameter P1. While performing this speed alignment, the taper off setting needs to be way lower than the actual max speed of the system. Otherwise you can’t be certain, that you get it right.
- Now, hop on your bike and go for a ride. Use a GPS-tracker to check if the motor tapers off correctly at 25 km/h. Most likely, it doesn’t. If the motor tapers off at 23 km/h, then increase the parameter P1 setting a bit. If the motor tapers off at 28 km/h, then lower the parameter P1 setting a bit. Small adjustments have significant effect. I suggest to start out by changing the parameter by 10. If that takes you from e.g. 23 km/h to 26 km/h, then go down 3 and recheck. Small adjustments are easier to work with.
…Enjoy your bike…
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