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Thread: Elmoto v2.0 Data sheet

              
   
   
  1. #11
    Moderator Nuts & Volts's Avatar
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    I noticed that your rolling resistance coefficient seems high. This data is tough to find. Also I can never tell if they are referring to one tire or two. In Build Your Own Electric Motorcycle By Carl Vogel i read that you should use .010-.012 as your Crr coefficient for motorcycle tires (I think this is both wheels?)

    I update if i find anything else
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  2. #12
    Moderator Nuts & Volts's Avatar
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    here is the acceleration sheet that i found somewhere online. Also I am working on my own EV sheet that calculates acceleration times. Ill post it when I refine it more.

    https://spreadsheets.google.com/ccc?...thkey=CNTc3egJ

    let me know if the link doesnt work
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  3. #13
    Seņor Member podolefsky's Avatar
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    Quote Originally Posted by Coninsan View Post
    If you can get aero to factor and show me how I would be gratefull
    Rigth now I'm working on implemening the features you suggested earlier, easy stuff compared to getting the top speed graph working.

    Anything else I should look into?
    This is super awesome...thanks for all the work!

    Off the top of my head, this algorithm might work:

    - KE = 0.5 m v^2 (KE = kinetic energy, m = kg, v = m/s)

    - delta_KE = KE_2 - KE_1, where KE_1 is KE at one speed, KE_2 is at the next speed (e.g., 1000 RPM and 1500 RPM), that's how much energy you need to add to get to the next speed

    - W_net = W_motor - W_required, where W_motor is the motor Watts, W_required is the required Watts at a given speed (both of these are in the spreadsheet already). The motor is already using W_required to maintain speed, W_net is how much power is left over for acceleration.

    - dt = delta_KE / W_net (dt = time required to get to the next speed, roughly)

    - t_total = sum(dt) (total time elapsed)

    This will be rough, more accurate with more RPM points, but not bad.
    Last edited by podolefsky; 01 March 2011 at 2217.
    - Noah Podolefsky -
    The GSX-E

  4. #14
    Moderator Nuts & Volts's Avatar
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    Good advice Noah. I went the Power route. I calculated the power losses (aero, rolling, incline, drivetrain) at 1 mph increments. I then calculated motor RPM using speed, gearing and wheel radius. Peak torque at each mph increment was manually added (need motor graph or motor constant). I used this to calculate the maximum power of the motor at each mph increment.

    Then I subtracted the power lost from the maximum motor power. This leaves you with the power left over for acceleration. So acc=Powera/(m*0.5*(v_i+v_f), basically power divided by mass and average velocity. This gives a good estimate of the maximum possible rate of acceleration at each mph increment. From acceleration and velocity you can use kinematics to calculate time and distance at each mph increment.

    Using 1 mph incrementation like I did is exactly like using rectangles to integrate the area under some curve.

    You'll also noted I left a place for tranmission losses this is for my own future experimentation. The whole process of this sheet is very manual, if anyone knows how to automatically find quarter mile time and things like that please enlighten me. I dont have enough excel expertise to do that. Also you can change the maximum speed on the sheet by deleting cells. You can also change the mph increments, smaller=better results, larger=less accurate results. All values labeled with yellow are values to be edited by the user.

    Question is I have - does rolling resistance remain constant over speed?? and what is a good rolling resistance to use per tire?? right now i use 0.011 as mentioned in an earlier post.

    Let me know if there is anything I could change and Coninsan feel free to implement this into your sheet however you would like.

    https://spreadsheets.google.com/ccc?...thkey=CMWRwowN
    Enjoy

    PS - power loss from aero = Force_drag*velocity = 0.5*air_density*v^3*frontal area*coefficient_of_drag
    Last edited by Nuts & Volts; 01 March 2011 at 2321.
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  5. #15
    Senior Member Coninsan's Avatar
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    Quote Originally Posted by Nuts & Volts View Post
    Question is I have - does rolling resistance remain constant over speed?? and what is a good rolling resistance to use per tire?? right now i use 0.011 as mentioned in an earlier post.
    Basic answer to your question: No, I found some figures last night about rollig resistances, comparing old fashion radial and cross ply tires, up to around 50-60 mph it remained constant but then rocketed up as aerodynamic forces inscreased. the force logging stopped at 0,03 which was at about 100 mph.
    You know what see for your self



    Basic info gathering around rolling resistances doesn't bother normal motorcycle riders, so information is scarce and far between. Of the top of my head I think that we can trust 0,01-0,012 to be accurate for modern tires based on the graph above, which factors older and more inefficiant tires.

    Let me know if there is anything I could change and Coninsan feel free to implement this into your sheet however you would like.

    https://spreadsheets.google.com/ccc?...thkey=CMWRwowN
    Enjoy

    PS - power loss from aero = Force_drag*velocity = 0.5*air_density*v^3*frontal area*coefficient_of_drag
    Thanks I might knick your Chain loss and Aero loss fomulas and implement them into my calculations.
    And actually, I think i have a way to work in a 1/4 mile time into my sheet, since I already have calculations implemented that work around the cicufrance of the rear tire. From there its not a long way to a 1/4 mile time.

    Talking about accuracy, my sheet is based of 500 increments in RPM, which is unaccurate for the longer run, but plotting between the points is done by excels advanced algoritms, so the general plot should be accurate. Plus, specific speeds are calculated seperately for accurate results
    "I reject your reality and substitute my own." Adam Savage

  6. #16
    Moderator Nuts & Volts's Avatar
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    Proll = mass*gravity*(R0 + R1*V + R2*V^2 + R3*V^3)*V

    This is a power loss equation i found for calculating rolling resistance losses. All the R's are coefficients, but the site does not direct me to a good source for finding the coefficients. So maybe this could work to more closely model rolling resistance at speed??

    Maybe ill just try to find a equation that closely models your graph and use the coefficinets from that??

    here is the source of the equation http://downloads.openchannelsoftware...ocs/index.html
    Whats under my tank may shock you!!! R6 Build, Blog/, [/URL] OSU Current webpage

  7. #17
    Senior Member Coninsan's Avatar
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    Quote Originally Posted by Nuts & Volts View Post
    Proll = mass*gravity*(R0 + R1*V + R2*V^2 + R3*V^3)*V

    This is a power loss equation i found for calculating rolling resistance losses. All the R's are coefficients, but the site does not direct me to a good source for finding the coefficients. So maybe this could work to more closely model rolling resistance at speed??

    Maybe ill just try to find a equation that closely models your graph and use the coefficinets from that??

    here is the source of the equation http://downloads.openchannelsoftware...ocs/index.html
    I believe that something like that has already been integrated from the calculations that Lennon rodgers did in his sheet. The trick is to get the rollig resistance to factor not as a constant but a variable as a product of speed.

    But you know what?

    Here comes version 2.1 of the Elmoto sheet.
    Check the intial post for info on it, I'll update the intial post with new download link and specifications.
    "I reject your reality and substitute my own." Adam Savage

  8. #18
    Moderator Nuts & Volts's Avatar
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    Quote Originally Posted by Coninsan View Post
    I believe that something like that has already been integrated from the calculations that Lennon rodgers did in his sheet. The trick is to get the rollig resistance to factor not as a constant but a variable as a product of speed.

    But you know what?

    Here comes version 2.1 of the Elmoto sheet.
    Check the intial post for info on it, I'll update the intial post with new download link and specifications.
    Yea in my sheet I could factor it as a product of speed (ill have to look how lennon does it), but it may be harder with your sheet. Ill take a look at 2.1 and let you know how it goes!

    Edit: Lennons sheet treats rolling resistance as constant and he uses 0.02 for the rolling resitance coefficient for reference. So at really high speeds it seems that rolling resistance will increase, but maybe the lift effect on the bike chould help negate this addition.
    I think i will continue to treat RR as constant, but overestimate it some to take this into effect.
    Last edited by Nuts & Volts; 02 March 2011 at 1048.
    Whats under my tank may shock you!!! R6 Build, Blog/, [/URL] OSU Current webpage

  9. #19
    Senior Member Coninsan's Avatar
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    Quote Originally Posted by Nuts & Volts View Post
    Yea in my sheet I could factor it as a product of speed (ill have to look how lennon does it), but it may be harder with your sheet. Ill take a look at 2.1 and let you know how it goes!
    It should be available now.

    But how does one remove attachments?
    "I reject your reality and substitute my own." Adam Savage

  10. #20
    Not to be taken seriously DaveAK's Avatar
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    Good work! A couple of questions though. Here's the spec sheet for my motor: http://www.thunderstruck-ev.com/Manuals/D&DSepEx72.pdf I can't figure out the torque numbers to put in at a given RPM. It seems backwards to me. (The spec sheet, not your spreadsheet.)

    Also, is gravity different in Denmark, or are you just so far ahead of the game you thought we might like to use our bikes on Mars?

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