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Old 04-02-2015, 08:36 AM   #1
mattadata
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Default Speed Calculator Help

I am trying to use the speed calculator at http://www.buggiesgonewild.com/speed-calculator.php
I need help with some of the inputs. What is the gear ratio?

I have a stock 36V PDS right now. I will be upgrading to Alltrax DCX500 soon.
What rpm should I use for stock? What rpm should I use with DCX500 controller?
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Old 04-02-2015, 02:41 PM   #2
cgtech
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Default Re: Speed Calculator Help

Stock ratio is 12.44:1.
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Old 04-02-2015, 04:19 PM   #3
sunking
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Default Re: Speed Calculator Help

I do not know what RPM the stock motor is, you will have to look it up, but a new controller is not going to change motor RPM as that is a function of the voltage which is not changing.
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Old 04-02-2015, 04:57 PM   #4
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Default Re: Speed Calculator Help

On a PDS cart you will see an increase in speed and torque.
With a stock motor I would I would set the power on a 500 amp controller at 80 percent...seems I read that 500 amps is a bit much.
Happy trails.
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Old 04-02-2015, 06:03 PM   #5
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Default Re: Speed Calculator Help

Quote:
Originally Posted by mattadata View Post
I am trying to use the speed calculator at http://www.buggiesgonewild.com/speed-calculator.php
I need help with some of the inputs. What is the gear ratio?

I have a stock 36V PDS right now. I will be upgrading to Alltrax DCX500 soon.
What rpm should I use for stock? What rpm should I use with DCX500 controller?
Speed is determined by actual tire height (Measured - not the mythical numbers stamped on the sidewall), the gear ratio of the differential and the motor RPM.

With stock height tires (18") and the standard gear ratio, the motor in a PDS is limited by the controller to about 4,400 RPM, or about 19MPH.

Put a DCX controller in it, which does not limit motor RPM, and the speed will be about 24 MPH (About 5,600 RPM) at 36V.

At 42V, the speed and torque increases by 16.7% to about 28MPH (6,500 RPM)

I only upped my pack voltage to 42V, so I don't know for sure what 48V would have done, but theoretically it would have been a 33% increase from 24 MPH, or 32 MPH (~7,500 RPM)

If the tires are taller than 18", the motor won't reach quite as high RPM for a given voltage due to the increased drag, but the cart speed may be higher.
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Old 04-02-2015, 06:11 PM   #6
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Default Re: Speed Calculator Help

Quote:
Originally Posted by sunking View Post
I do not know what RPM the stock motor is, you will have to look it up, but a new controller is not going to change motor RPM as that is a function of the voltage which is not changing.
I don't know about CC and other brand carts with SepEx drives, but the controller in a 36V EZGO PDS cart limited the max motor RPM, so when a controller that does not limit max motor RPM is installed, the speed does increase.

Of course, once that restriction is removed, getting more RPM (for the same drag) requires more voltage.
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Old 04-02-2015, 06:24 PM   #7
TerryH
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Default Re: Speed Calculator Help

You should get one of the speedometer apps for your smart phone. You can use that mph number and the gear ratio and figure backwards on the speed calculator to determine the rpm.
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Old 04-03-2015, 07:51 AM   #8
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Default Re: Speed Calculator Help

Thanks for all the info. I have been checking with my phone, and it is right on the money. With my stock setup and 17 inch tires, the calculator says 17.9 mph and my phone says 17.6 mph.

So with the new controller, if RPMs go up to 5600, then I should expect about 22.8 mph.

JohnnieB - I have seen a few post from you where you blew up your stock motor going downhill and letting of the accelerator? I am sure we don't have the same kind of hills here in north Texas.....but how can I avoid the same fate?
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Old 04-03-2015, 10:02 AM   #9
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Default Re: Speed Calculator Help

Quote:
Originally Posted by mattadata View Post
Thanks for all the info. I have been checking with my phone, and it is right on the money. With my stock setup and 17 inch tires, the calculator says 17.9 mph and my phone says 17.6 mph.

So with the new controller, if RPMs go up to 5600, then I should expect about 22.8 mph.

JohnnieB - I have seen a few post from you where you blew up your stock motor going downhill and letting of the accelerator? I am sure we don't have the same kind of hills here in north Texas.....but how can I avoid the same fate?
With tires about 17" tall, there is only about 75 RPM difference between 17.6 and 17.9 MPH, and the 0.3 MPH difference probable falls within the margin of error for either the GPS App and possibly the tire height measurement.

To determine my tire height, I drew a line down the center of a length of duct tape and used a level to find a vertical line that passed through the center of the axle and then placed the duct tape on the sidewall so the line on it was at the center bottom of the tire and overlapped onto the concrete sidewalk. Then I cut the tape, leaving part of it on the sidewall and the other part on the side walk. Then I drove the cart as far it could go between back porch steps and garage, and then back up until line on duct tape was at bottom of tire. Then I rolled cart by hand until the line on the tape was again extended through the center of the axle, place a blank piece of duct tape next to tire on sidewalk and drew a line on it that matched the vertical center line on the tire. Then I measured the distance between the two lines on the pieces of tape on the sidewalk. The two lines were 214.125" apart and the tires had rotated four times, so my driver side tire height is 17.039526". The passenger side is slightly taller (less weight on it?), but I just use 17" for my calculations.

GPS speed are reasonably accurate, but not exact since either of the adjacent points they measure elapsed time of travel between to calculate speed, can be off by about 10'.

--------------
I suspect your speed with a DCX will be closer to 24 MPH.

------------
You can avoid the same fate by not going downhill with your foot on the floor to see how fast your cart will go.

Actually, it was trying to slow down for the curve at the bottom of the hill that got me.


I was spinning a stock PDS motor over 8,000 RPM, but that isn't what caused it to fail. Definitely a contributing factor, but only one of several factors. Heat was another factor, the motor case temperature was well over 200°F before I started climbing the steeped backside of the hill I drove down at wide open throttle. Not sure what it got to, but I'm sure it climbed more after I topped the hill and the Turbo Kicked in. (When the PWM duty cycle is at 100% and the controller is not in current limiting, the field current is reduced, which increases the motor's max RPM for the voltage applied, but reduces the motor's efficiency and generates more heat.)

The motor failed when the regen braking kicked in. The faster a motor is spinning when it is transformed into a generator, the higher the voltage it generates, which in turn increases the amp flow back to the batteries. The higher the amp flow, the more heat is generated, and the stronger the magnetic fields. Either excessive heat melted something in the armature, or the magnetic forces, in conjunction with the existing centrifugal force caused by spinning at 8,000+ RPM pulled it apart, but it came apart and and grew until it came in contact with the field windings and the motor seized. Everything inside the motor was shorted together, so it took out the controller also.

Attached are pictures of what a PDS motor normally looks like and what mine did after I exploded the armature.
The armature was stuck so tight, I could drive it out with a sledgehammer.
Attached Images
File Type: jpg Stock PDS Motor -2.jpg (38.1 KB, 0 views)
File Type: jpg IMG_0059.jpg (472.4 KB, 0 views)
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Old 04-07-2015, 05:34 PM   #10
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Default Re: Speed Calculator Help

Is a GPS app smart enough to account for hills? Up and down run up miles, while not moving horizontally. Just curious.
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