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Old 08-22-2015, 02:44 PM   #21
Fastest1
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Jhnmflr, what voltage are you running? 36, 42 or 48?
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Old 08-22-2015, 02:49 PM   #22
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Default Re: Xct500

48........ gotta do it!
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Old 08-22-2015, 03:08 PM   #23
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Default Re: Xct500

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Originally Posted by jhnmflr View Post
okay so been real busy but got a chance to play today. My tire diameter off of cart is 24.5". I unplugged cart and it sat for about 20 minutes. I forgot to check voltage. My top speed with a helper neighbor was 29.06. The average I came up with after a few full speed runs was 28.45. At 28.45 the motor speed was 5140. I can live with that. I can say also that my tires are A/T with a 20 psi max and they are set @ 28 psi. Gotta say very pleased........ what ya got Johhny? Would be nice to pull a little more rpm and hit 30mph. Any thoughts? Chime in Scotty! Oh and why does the controller temp have to be in Celsius, I'm old school need F.
You MPH vs RPM vs Tire Diameter don't add up right.
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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Old 08-22-2015, 03:11 PM   #24
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Default Re: Xct500

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48........ gotta do it!
Are you are already running 48V?

What motor?
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Old 08-22-2015, 03:22 PM   #25
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Default 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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Old 08-23-2015, 08:24 AM   #26
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Default 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?
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Old 08-23-2015, 01:38 PM   #27
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Default 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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Old 08-23-2015, 02:11 PM   #28
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Default 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!
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Old 08-23-2015, 05:24 PM   #29
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Default Re: Xct500

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Originally Posted by jhnmflr View Post
1. 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.
2. 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!
1. I put together a spreadsheet that does the math.

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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Old 08-23-2015, 05:31 PM   #30
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Default 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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