Ebike System Simulator

Using the Ebike simulator to estimate the performance of your ebike.

Contents

Intro

We are often asked about how our kits perform, how fast or powerful a kit might be, and how they compare to others. The challenge is there are several crucial variables affecting any given system. Luckily, there exists a pretty accurate simulator which helps predict the performance, and it's totally customizable. Grin Technologies has, throughout its history, conducted extensive dyno testing of various ebike motors, and from those tests, developed a very reliable "Ebike Simulator" to predict results. The problem is,

  • Most builders do not know how to use the simulator appropriately,
  • Often times a particular motor will not be listed on the simulator, leading to
  • Having to guess which motor is closest to the motor the builder intends to use.

Realizing this, Kinaye donated four different windings of the "3000W" (45mm) MXUS motors for Grin Tech to dyno test and list on their simulator. Regarding the MXUS motors, Justin LeElmore (Grin's Owner and chief engineer) had this to say:

"The measured peak efficiency of the 4T motor at both 36V and 48V was right around 90%, and the no-load losses were about 2-3 times lower than say the similar sized Crystalyte Crown motor. So really quite an impressive electrical performance spec, and the same lamination material in a normal 25-30mm wide motor would have one of the lowest cogging drags of any direct drive hub out there."

When specifying a system for a custom turn-key Ebike project, we use this simulator to ensure the parameters meet the customer's stated performance goals. Familiarizing yourself on how the simulator works will help you to use it in the same way. In addition, the benefits include understanding how all the various components and their "ratings" affect the performance of the system as a whole. We suggest investing some quality time playing with different configurations. The tool is fun and addictive, though we feel in a good and useful way.

Here is the link for the Ebike Simulator

Setting the Parameters

In this section we shall discuss the numerous settings required for proper simulator configuration.

  1. Motor Specification
  2. Battery
  3. Controller
  4. Throttle/Speed
  5. Vehicle Parameters
  6. Aerodynamic Profile
  7. Load
  8. Grade
  9. Chart Options

1. Motor Specification

The MXUS motors we sent to Grin are listed in the Simulator's first Parameter as:

  • "MXUS 4503" (45mm Magnet, 3T "3-Turn" Winding)
  • "MXUS 4504" (45mm Magnet, 4T "4-Turn" Winding)
  • "MXUS 4505" (45mm Magnet, 5T "5-Turn" Winding)
  • "MXUS 4506" (45mm Magnet, 6T "6-Turn" Winding)

To get to these options:

  1. First select "SHOW ALL", and then
  2. Select the first parameter again; the four MXUS motors are in the last half of the drop-down list.

At the time of this writing, be aware that we only stock the 3T and 4T windings in a 142mm wide version, and the 5T and 6T windings in a 170mm (Fat Bike) version. Thus, depending on the bike frame, your selection should be limited to a couple different windings. However, for special ordered motors, we can order ANY winding in either configuration; it's just that it would take several months to order, produce and ship.

Once a particular motor is selected, enter or select the rest of the input parameters as accurately as possible.

2. Battery

The second Parameter is the battery. There is a list of various batteries, although we find that it's actually preferable to manually enter the voltage, Resistance, and Amp-Hour capacity of the battery. To do this:

  1. Select "custom battery" at the bottom of the list; a red box will appear on the screen with three variables to complete.
  2. Type in the Nominal battery voltage of the battery that is intended for purchase. Examples are 36V, 48V, 52V, 60V, 72V, etc. The Nominal voltage is the "average" voltage of a battery.
  3. In the middle box, the app asks for the battery resistance (in Ohms). For 18650-based packs, this should be approximately 0.2 Ohms. For Lithium Polymer (LiPo) Batteries, we would change this value to about 0.05 Ohms: Lower resistance settings will result in less voltage sag of the battery pack under high current loads.
  4. For the third box, type in the total capacity in Amp-Hours of the pack. This is based on the seller's specifications, usually noted as "XX" Amp-Hours. If only Watt-Hours are listed, we calculate Amp-Hours by dividing the watt-Hours by the nominal voltage.
  5. Click "Continue" to lock in these battery settings.

3. Controller

The third Parameter is related to the controller, and primarily how much current output the controller is able to produce. We recommend selecting the "custom controller" option on this field as well:

  1. In the first box, enter the current limit of the controller (our kits range from 30A up to 65A).
  2. In the second box, optionally change the resistance of the controller: The default value is 0.03 Ohms resistance. If using an 18FET controller with 10AWG battery and phase wires, set the value to 0.02 Ohms. Otherwise leave it set to the default; lower resistance will result is higher system efficiency.

4. Throttle/Speed

The fourth Parameter is the throttle slider. If we want to know the maximum speed, leave this at 100%. If we want to simulate the efficiency of the system at a specific speed (say at 20 MPH), move the slider bar or change the throttle percentage lower and click simulate (assuming all other parameters have already been adjusted) until the result displays the desired speed.

5. Vehicle Parameters

The fifth Parameter is to set the bike tire size; the Outside Diameter. Since tire size will affect overall speed as well as perceived thrust, it is important that this be entered as accurately as possible. Common sizes are:

  1. 26" (Typical Mountain Bike tire Outside Diameter)
  2. 29" (Typical Fat Bike tire Outside Diameter)
  3. 24.5" (Outside Diameter of a 19 x 2.75 Moped tire)
  4. 22" (Outside Diameter of a 17 x 2.00 Moped Tire)

Note: To determine the outside diameter of a moped or motorcycle tire, take the rim diameter and add 2 times the tire size. Example: 19x2.75 = 19" + 2.75" + 2.75" = 24.5". Reason: We add twice the tire size, since the tire height is added to both the top AND bottom of the wheel.

If the tire size is one of the top options, select it. Otherwise choose "custom wheel size" and type the outside diameter in manually.

6. Aerodynamic Profile

The sixth Parameter is related the aerodynamic profile of the vehicle. At higher speeds, the aerodynamics of the bike play a LARGE factor in the top speed and efficiency of the drive system. This is perhaps the most difficult parameter to estimate. For a worst-case scenarios where there is no intention of doing any aerodynamic improvements to the bike or the rider's apparel, we suggest using the "Mountain Bike" option: This will show the lowest maximum speed and highest consumption value.

For an idea of how improving aerodynamics will improve top speed and efficiency, try changing to "Race Bike (tuck)" and then to "Semi-recumbent" and then "Full recumbent", each of which progressively lowers the assumed aerodynamic drag of the system, plus shows higher speeds and better economy. We think you will soon begin to appreciate the value of better aerodynamics on your bike and apparel.

7. Load

The seventh Parameter is the total load of the system. For a quick estimate we recommend selecting the 150 kg (330 lbs.) option. If we have a good idea of the load, then enter it in the "Custom Weight" option. The Load should include ALL of the following:

  1. Rider's Weight
  2. Bike Weight, including motor and battery (most high-performance ebikes weight between 70 and 100 lbs.)
  3. Cargo Weight (Rear racks, panniers, add-ons, trailers, etc.)

Weight will not have a significant effect in efficiency (and range) on flat terrain with few starts and stops, although on hills or in stop and go traffic, it will definitely have a measurable effect.

8. Grade

The eighth Parameter is Grade. If we want to know if the system can climb a hill without overheating, we need to determine the grade of the hill, and enter it into the simulator. To determine the grade of a hill we recommend visiting the site http://veloroutes.org/hillgradecalculator/ and locate the hill to simulate. Also it should be noted that grade and angle are not the same thing. A grade of "100%" is a 45 degree slope, or equal units of rise and run. A grade of 10% is pretty steep, and would be an "Angle" of about 6 degrees. The steepest hills in San Francisco are up to 40% grade, however the simulator only goes up to 20% grade. Grades steeper than 20% are pretty difficult and generally only mid-drive motors with very tall gearing (or 2WD systems) will be able to climb these.

Below the Grade slider is the "Simulate" button. Click this once all the parameters have been properly set.

One more thing: Below the "Simulate" button is an option to open a second "System B" to compare to "System A". We don't recommend using this since the simulation comparisons are not really very accurate as it forces system B to match the speed of system A which may be greater or less than a full load. It's actually better to run two different simulations to a common speed (using the throttle slider to adjust the target speed of each system), and then compare the resulting data between the two systems at a common speed.

9. Chart Options

Adjusts the units of measurement to what is familiar to you for display on the graphs.

X Axis units can be set to specify kilometers per hour or miles per hour. Select your preference.

"Blue Curve" can show torque in "Newton-meters" or the thrust in "lbs. thrust." We recommend choosing lbs. thrust, since this is what a rider "feels" as acceleration: It's like someone pushing on your bike with XX lbs. of force. Lbs. thrust is dependent on the motor winding (Kt of the motor), the total current output of the controller, and the tire size.

"Black Curve" is related to the loading of the motor. We recommend leaving this set to "Load Line". The point at which the load line and the motor power (Red Curve) cross will signify the speed of the system per the other design parameters. If the dashed vertical line on the chart (Speed) is NOT at this intersection, the results assume we're either climbing a hill (Dashed line on the left of the intersection) or descending a hill (dashed line on the right of the intersection).

Observations

Lines and Curves

Pay close attention to the Motor Power Curve (Red Line) and the Black Curve (Load Line). Typically the Motor power curve will rise up in an arc, and then abruptly fall off on a straight line down to "0" The highest point (Apex) of the motor power curve is when the motor is demanding the full current output of the controller (and where it is least efficient).

If the Load line intersects to the right of the apex of the motor power curve, then the controller is powerful enough for the system. If the load line intersect the motor power curve to the left of the apex of the motor power curve, then the controller is too small, and we should look for a more powerful (higher current) controller.

Generated Data in the boxes below the graph

  • Motor torque - noted in Blue. The displayed value is the torque output at the speed and conditions indicated by the graph.
  • Motor Power - noted in Red. The displayed value is the motor's power output. Note that it is lower than the battery power. This is because no System is 100% efficient.
  • Load - the power required to perform the work indicated by the graph. Generally this should be very close to the value "Motor Power".
  • Efficiency (Green curve on graph) - how effective the system is at converting battery power into motor power. Values lower than 80% are generally bad and values greater than 85% are good. The best motors in use today approach 93% peak efficiency. MXUS motors will peak around 90% efficiency. Our goal is to get the dashed vertical line as close as possible to the apex of the efficiency curve. (See "How do I improve the efficiency of my system?")

What happens to the excess power? It gets converted into heat, inside the motor. Heat is bad. It's wasted energy, and does really bad things to your motor if not kept in check.

  • Motor Amps - the phase current being fed from the controller to the motor. Waste heat is directly related to the amount of phase current being fed to the motor, and the "Overheat In" time is directly related to the Motor Amps. More Amps = More heat.
  • Battery Power - the power being drawn from the battery (Battery amps x Battery volts).
  • Battery Amps - the current being drawn from the battery. Be sure that the battery is able to "continuously" support the current shown here. If not, the battery will die a horrible, quick death. Also - the battery should also be able to support the "Maximum" Current for which the controller is rated.
  • Battery volts - how much the battery voltage will "drop" or "sag" based on the battery current noted in the box above it. "Voltage Sag" is dependent on the resistance of the battery, which we entered in the battery (Parameter 2), where smaller value (Ohms resistance) will result in less voltage sag.
  • Acceleration - how much the bike is changing speed in feet or meters per second per second. Usually this value will be low, unless we move the dashed speed line with the mouse left or right to indicate climbing (Left) or descending (right) a hill.
  • Consumption - how many Watt-hours of energy will be used per mile. Generally speaking, the faster we go, the higher the consumption and the less range we will have. Speed reduces range; get that through your noggin: If we want to have greater range, go slower. If we want to have high speed AND longer range, get a bigger battery.

FYI, to calculate the watt-hour capacity of a battery, multiply the nominal voltage by the amp-hours of capacity. Example 72V-20Ah = 72X20 = 1440 Watt-Hours, or 1.44 Kilowatt-hours of capacity. If we are consuming "50 Wh/mile" with this battery, we will have a range of 1440/50 = 28.8 miles.

Quick quiz: Which battery has more total energy (Watt-Hours)? 36V -15Ah or 60V-10Ah

  • Range - how far the bike will go assuming the battery stated out fully charged and we ran it all the way to "empty." Range is dependent on consumption and the watt-hours of capacity of the battery. See explanation above.
  • Overheat in - how quickly the motor temperature will reach the critically damaging temperature above 120 degrees Celsius. Note that it's entirely possible to run the motor at the power level simulated for less than this amount of time: For Instance, if we want to know if the motor can handle a very long ride at a given power level, we want this value to be "never" (as in "Never overheat"). However, if we are drag racing the bike in a 1/4-mile drag strip that will last for less than 30 seconds, it's possible we can crank up the controller's current to the point where the motor will overheat in "60 seconds" and still likely be OK. This is how we are able to attain speeds of 66 MPH with a modest "3000W" rated motor: It is akin to boiling a frog in a pot of water. The frog can handle mild temperatures indefinitely, and increasing temperatures for a little while, but eventually the water will get so hot, that it kills the frog. The hotter the water, the shorter the time it takes to kill the frog. Clear as mud?

Refining your system design Q & A

How do I improve the efficiency of my system?

  • Improve the aerodynamic drag of the bike & rider
  • Decrease the load by lowering the weight and/or speed
  • Choose a smaller diameter tire
  • Choose a higher efficiency motor design
  • Lower the battery voltage (Which lowers the speed of the system)
  • Choose a motor with more "Turns" (Lower Kv, higher Kt, which also lowers the speed)

How do I increase the speed of the system?

  • Improve the Aerodynamic Profile of the bike & rider
  • Increase the voltage of the battery
  • Increase the tire diameter
  • Choose a motor with fewer "Turns" (Higher Kv)
  • Increase the current output of the controller
  • Reduce the resistance of the battery and controller (This raises the effective voltage slightly)

Can I improve the efficiency of a system AND increase the speed?

The only way to do so is to improve the Aerodynamic profile of the system. This is how human-powered velomobiles can achieve such high speed.

My Speed seems low. Are you sure the simulator is correct?

If we are using the nominal battery voltage, the speed will be based on the 50% state of charge voltage of the battery. If we want to know the speed on a fully charged battery, then we have to calculate 100% charge voltage. Using the formula 1S = 4.2V,

  • 36V (10S) Lithium Battery = 42.0V Fully Charged
  • 48V (13S) Lithium Battery = 54.6V Fully Charged
  • 52V (14S) Lithium Battery = 58.8V Fully Charged
  • 60V (16S) Lithium Battery = 67.2V Fully Charged
  • 72V (20S) Lithium Battery = 84.0V Fully Charged

Additionally, some controllers have an "overdrive" feature where the controller can make the motor spin faster than normal: Sine Wave controllers call this feature "FOC" (Field oriented Control), and our Xie Chang Controllers can be programmed to output up to 120% (20% overdrive). This effectively raises the voltage the motor sees by 20%. We can adjust for this by increasing the fully charged battery voltage by 20% to get a more accurate results for actual top speed. Note, however that range will not be as accurate by doing so.

Summary

Characterizing the performance of an electric bike system is challenging, yet this process can made much easier and fun even by using this well-developed tool from Grin Technologies. We've walked through the parameters used for configuration of the simulator, identified and discussed the merits and pitfalls, and touched upon the visual and physical effects. We've provided Kinaye Product Data to help enhance the user experience and make the most of what the simulator can provide: A measure of performance relative to other like configurations. In our opinion, this is the best public free-to-use ebike system simulator, and hope you mine it as we do frequently.