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Old 10-27-2014, 12:21 PM   #11
paintdude96
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Default Re: RPM

now I have another question is im looking at a 6:1 hp motor with a 6:1 gear . well if I was to add all this on my cart and it lifted with 6hp motor and 6:1 gear and 36v with the 500amp controller with I burn anything up
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Old 10-27-2014, 12:49 PM   #12
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Default Re: RPM

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Originally Posted by Sir Nuke View Post
well somehow, here on this site, I got a copy of it in EXCEL......and I was pretty sure it came from you, lol if he had given us that specific info.....I would have just "plugged and chugged" the numbers for him.
I saved it in an EXCEL format to post it.

BTW: I'm working on a new version.

It appears that speed gain and torque loss are not exact opposites when you increase tire height.

Looks like going from 18" tall tires to 23" tire ups the speed by 28%, but only reduces the torque where rubber meets road by 22%.

Speed is straightforward. Increase the height by xx% and the circumference increases by xx%, so the distance traveled per tire revolution increases by xx%, so with the tire spinning at the same RPM, the speed increases by xx%.

Torque is more complicated. Torque originates at the motor and is multiplied by the final drive ratio and tire height is part of the final drive ratio, so changing it changes the final drive ratio.

I've been beating my head against a brick wall for a bit, but the fog is starting to clear some.

IIRC: There is a line on the spreadsheet I posted that says % change.
The % change under the Tire Height and Tire Circumference columns is the Speed Change and the under the MPH columns it is the Torque Change, so it is a labeling issue.
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Old 10-27-2014, 01:17 PM   #13
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Default Re: RPM

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Originally Posted by paintdude96 View Post
now I have another question is im looking at a 6:1 hp motor with a 6:1 gear . well if I was to add all this on my cart and it lifted with 6hp motor and 6:1 gear and 36v with the 500amp controller with I burn anything up
Possibly the High Current cables and F/R switch.

Mathematically, if the cart goes 18 MPH with 20" tires and 12.44:1 gears @ 36V, it should go 37.3 MPH with 20" tires and 6:1 gears @36V, but I'm not sure a 6HP motor will still be able to turn at 3,673 RPM @ 36V since the torque multiplication of the final drive ratio has been more than halved. (Going from 12.44: to 6:1 is a 52% reduction in torque)

It depends if the 6HP motor is wound for torque, or wound for speed, or would for something between those two extremes.

Overall, with 20" tires and 6:1 gears, you are losing nearly 60% of the stock torque. so you may end up with a cart that you can get speeding tickets with, but will have to be pushed to get moving.

-------------
BTW: There are Two-Speed series motors available as well as Two-Speed differentials.
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Old 10-27-2014, 01:57 PM   #14
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Default Re: RPM

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Originally Posted by scottyb View Post
Can you post a current calibration certificate for that yardstick?
No, I'm afraid I haven't kept the certificates on my NIST traceable stuff current since I retired in 2009.

But it was only used confirm what the calculations based on measuring the distance traveled told me and even though the 25' tape measure I used wasn't NIST traceable either, I did use four tire revolutions to minimize any errors.
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Old 10-27-2014, 01:58 PM   #15
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Default Re: RPM

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Originally Posted by JohnnieB View Post
No, I'm afraid I haven't kept the certificates on my NIST traceable stuff current since I retired in 2009.

But it was only used confirm what the calculations based on measuring the distance traveled told me and even though the 25' tape measure I used wasn't NIST traceable either, I did use four tire revolutions to minimize any errors.
How many times did you repeat the test for averaging results AND what was the ambient air temperature
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Old 10-27-2014, 02:06 PM   #16
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Default Re: RPM

so 36v 6hp motor and 500amp controller and 6:1 gear would run 37is and slow taken off
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Old 10-27-2014, 02:28 PM   #17
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Default Re: RPM

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Originally Posted by paintdude96 View Post
so 36v 6hp motor and 500amp controller and 6:1 gear would run 37is and slow taken off
About 37 MPH is what it figures out to mathematically, but a 6HP motor running at 36V is very likely to run out of torque before it reaches the same RPM as it was turning with 12.44:1 gears.

Saying it is a 6HP motor is sorta like saying it is chartreuse motor. IE: Without the RPM associated with the HP rating it really doesn't mean much.
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Old 10-27-2014, 02:36 PM   #18
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Default Re: RPM

ok the motor is ge motor hp:6.1 , rpm:5330, volts:36, amp:157, wound:series
MOD:5bc48jb3084 Ser NO:kbba283p011 ...........
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Old 10-27-2014, 03:52 PM   #19
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Default Re: RPM

scottyb- You must be selling tin hats again and do they come with CU stickers?
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Old 10-27-2014, 04:27 PM   #20
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Default Re: RPM

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Originally Posted by paintdude96 View Post
ok the motor is ge motor hp:6.1 , rpm:5330, volts:36, amp:157, wound:series
MOD:5bc48jb3084 Ser NO:kbba283p011 ...........
HP is Torque times RPM divided by 5252, so you multiply HP times 5252 and divide by RPM to find Torque.

6.1 * 5252 = 32,037.2
and 32,037.2 / 5252 = 6.01
So that motor only has about 6 ft/lb of torque at 5330 RPM and 5330 RPM works out to 53 MPH, which I seriously doubt will ever happen at 36V with 20" tire and 6:1 gears.

Advertised Motor HP is typically given at the peak HP point on the Torque - RPM curve, so that sounds like a speed motor while you need a high torque motor to turn those tall tires, through those high speed gears.

There are more than one way to skin a cat, and some cats simply cannot be skinned.

What is you speed goal?
What else do you want the cart to do, other than just go fast?
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