08-22-2015, 02:44 PM | #21 |
Getting Wild
Join Date: Aug 2015
Location: Conroe/Woodlands, TX
Posts: 133
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Jhnmflr, what voltage are you running? 36, 42 or 48?
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08-22-2015, 02:49 PM | #22 |
Gone Wild
Join Date: Jul 2012
Location: Sw Florida
Posts: 298
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Re: Xct500
48........ gotta do it!
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08-22-2015, 03:08 PM | #23 | |
Techno-Nerd
Join Date: Jun 2011
Location: West Virginia
Posts: 19,654
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Re: Xct500
Quote:
If your motor is spinning at 5140 RPM and the cart is moving at 28.45 MPH, the tire height is 23.15" if your are running stock gears (12.44:1) If the cart is going 28.45 MPH on 24.5" tire, the motor should be spinning at 4957 RPM. To go faster (more RPM), you need to up the pack voltage, which will give you more torque across the motor's entire RPM spectrum. --------- My tires are only 17.04" tall and I max out at about 6900 RPM at 42V and I get a whisper over 28 MPH on level ground. In a nutshell, my cart's acceleration and hill climbing ability is traction limited rather than torque limited. |
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08-22-2015, 03:11 PM | #24 |
Techno-Nerd
Join Date: Jun 2011
Location: West Virginia
Posts: 19,654
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Re: Xct500
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08-22-2015, 03:22 PM | #25 |
Gone Wild
Join Date: Jul 2012
Location: Sw Florida
Posts: 298
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Re: Xct500
The tire diameter was measured off of the cart with a string. So maybe the weight dropped it to 23.15. I am 48 volt and have the D&D 502.1 motor.
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08-23-2015, 08:24 AM | #26 |
Techno-Nerd
Join Date: Jun 2011
Location: West Virginia
Posts: 19,654
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Re: Xct500
The way I measured my tire height was to mark the installed tire's bottom-dead-center on a piece of duct tape using a level to get a true vertical through the axle and make a corresponding line on piece of duct tape on the pavement. Then I drove the cart about four tire revolutions, got off the cart and pushed the cart by hand until tire was at BDC again and made another corresponding mark on the sidewalk. Then I measured between the two marks and did the math to get the rolling diameter of the tire in actual operation under load.
The reason I only used four tire revolutions was because that is all the room I had on the sidewalk between the house and the garage. More revolutions would further reduce any errors caused by line thickness (I used a magic marker) and other measurement errors. According to the D&D website, their 170-502-0001 motor has about 33% less speed and 40% more torque than a stock PDS motor at 36V with a 300A controller. Ironically, going from 36V to 48V increases speed by about 33%, so the motor's speed loss and 48V battery pack's speed gain more or less offset each other. My spreadsheet says you ought to be getting 30.9 MPH with 23.15" tire or 32.7 MPH with 24.5" tires, but in real life, it will be less than that because tall tires take more torque to turn that stock height tires and the RPM vs Torque curve for most motors isn't perfectly linear. However, it may be possible to get closer to 30 MPH than 28.45. ----------------- On your data log, what is the minimum Field Amps and and maximum Motor RPM (Speed column) when traveling on level ground at 100% Throttle? |
08-23-2015, 01:38 PM | #27 |
Gone Wild
Join Date: Jul 2012
Location: Sw Florida
Posts: 298
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Re: Xct500
Toooo much math :). I will run in a moment to check the field amps and motor rpm and get back to you.
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08-23-2015, 02:11 PM | #28 |
Gone Wild
Join Date: Jul 2012
Location: Sw Florida
Posts: 298
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Re: Xct500
Okay Johnny. measured the center with the level and mark on tape. Went 8 revolutions and marked the same way. I measured 49'1". Soooooo, like I said, too much math.
Also just got back from a run and measured 5919 speed sensor and 192.9 motor current amps, field current amps 4.4 at full throttle, full speed. Did the same again and got, 4920 speed sensor, 159.4 motor current amps and field current amps were 4.2. I was driving and a neighbor kid was writing them down. Kinda of getting fun now! |
08-23-2015, 05:24 PM | #29 | |
Techno-Nerd
Join Date: Jun 2011
Location: West Virginia
Posts: 19,654
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Re: Xct500
Quote:
Your tires have a dynamic diameter (effective height while in operation) of 23.436" 2. With your motor at 5919 RPM, your cart speed was 33.2 MPH and at 4920 RPM it was 27.6 MPH. The numbers on the monitor screen jump around quite a bit, so it is pretty hard to look at two numbers at the same time and jot them down. It works better to have the computer save the data in a file and look at it later. In addition, you can see what voltage is being applied to the Armature at the time. The file format the data is saved in is .CSV (Comma Separated Values) and you can open it in Excel (or Quattro Pro like I use.). ---------- Your field is only being weakened to down in the 4.2A-4.4A range. Are you running in Turbo Mode? From what I can tell from the Field Amps values given, it looks like you might have some room for more Field weakening, which increases the RPM reached for the same voltage applied to the armature, but drops the motor's efficiency, so the more heat is generated and the motor gets hotter. |
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08-23-2015, 05:31 PM | #30 |
Happy Carting
Join Date: Dec 2007
Location: Southern California
Posts: 73,358
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Re: Xct500
In other words the way it is set up now is fairly safe for your new motor and still giving plenty of speed.
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