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Old 06-22-2015, 11:11 AM   #71
Gregorio
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Default Re: Converting CC (Ahem) to Lithium Power

Loaded tire diameter is much different than unloaded. Revolutions per mile (or whatever distance) is a much more accurate figure to use.
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Old 06-22-2015, 12:39 PM   #72
ronncat
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Default Re: Converting CC (Ahem) to Lithium Power

Quote:
Originally Posted by JohnnieB View Post
I measured how far the cart moves per tire revolution with me on the cart.

I put a piece of duct tape on the sidewall and the sidewalk, then used a level to draw a line on both that passed though the center of the axle to give me bottom dead center on the tire and a start point on the sidewalk.

I drove the cart while SWMBO counted the tire revolutions and let me know when the duct tape on the tire was at the bottom so I could stop. I pushed the cart about an inch manually until the line was bottom dead center again and then put another piece of duct tape on the sidewalk and made a mark on it that matched the mark on the sidewall. Then I measured between the two marks on the sidewalk and divided the distance by the number of tire revolutions (4) to get the circumference of the tire, which I divided by Pi (3.14159...) to get the effective diameter under load.

I could hardly believe the tire height was 1.3" shorter than what Carlisle listed on their website, but I get a whisper over 17" using a level and a yardstick, so the data posted on their website is even further off than the numbers stamped on the tires.

The max inflation pressure stamped on my tires is 22 PSI, but I run them 10% overinflated (25 PSI actually) for speed and range tests. For normal cruising, I run them at 18 PSI for a better ride.

----------
I was spinning my stock PDS motor a bit over 8,200 RPM when it exploded, but RPM alone didn't kill it. It was a combination of heat, intense regen braking and RPM that did it in.
I was also pondering the effective diameter of the tire under load. I was thinking that the portion below the axle is compressed from the weight of the vehicle. I have used your technique before when calibrating bicycle speedometers. I'll do the same for the cart when I have time
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Old 06-22-2015, 01:36 PM   #73
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Default Re: Converting CC (Ahem) to Lithium Power

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Originally Posted by ronncat View Post
I was also pondering the effective diameter of the tire under load. I was thinking that the portion below the axle is compressed from the weight of the vehicle. I have used your technique before when calibrating bicycle speedometers. I'll do the same for the cart when I have time
My original plan was to take the cart to a nearby parking lot and use a 100' tape measure (about 20 rotations had the tires be the 18.3" I thought they were), but end up using the sidewalk between my back porch and garage, so I only had room for 4 rotations. More revolutions of the tire will reduce the margin of error, but how accurate is accurate enough.

Using a automotive type DMM with a tachometer function, driven by the speed sensor on my SepEx motor, the correlation between the measured motor RPM and the calculated motor RPM using tire height I found, is consistent with the speed reported by the Garmin GPS I use for a speedometer, so it is close enough for my purposes.
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Old 06-22-2015, 01:45 PM   #74
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Default Re: Converting CC (Ahem) to Lithium Power

Make sure your tire is inflated to the PSI you plan to use because changing the inflation will change the effective circumference of the tire. This is a great method to calibrate things if you do it carefully.
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Old 06-23-2015, 07:50 AM   #75
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Default Re: Converting CC (Ahem) to Lithium Power

I got home last night and jumped right into the cart to try out my new torque curve.

Don't think I quite have a great understanding of programming the Alltrax SPM72500 yet, cause as soon as I stepped on the GO pedal, the thing shot forward like the proverbial "bat out of hell"

No wheelspin, but much quicker acceleration than the stock torque curve provided. As a matter of fact, too much…. The cart would get that herky jerky takeoff if I didn't mash the pedal to the floorboard. I think that on partial acceleration, my foot would bounce on and off the pedal giving that jerky takeoff.

So back to the toolkit. I changed the torque curve until it resembled the original S curve. Then I played around with the throttle rate, kicking it up towards 50%. This gave me a little more control off the line. It allowed me to creep along slowly at partial throttle (kind of important when using the cart for its intended purpose) and then accelerate VERY quickly to my ball (to insure that perfect lie)

Still have lots of experimenting to do. Would welcome any suggestions to how other SPM's have been programmed. Still need to fix the seat so it sits flush to the body. Then I'll calculate my tire diameter and go for a few high speed runs
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Old 06-23-2015, 09:28 AM   #76
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Default Re: Converting CC (Ahem) to Lithium Power

I don't know if it is adjustable in the SPM programming, but take a look at the Throttle Linearization curve.

What I ran into on my XCT is that the default curve was generating a throttle position signal the was greater than the physical position of the pedal during the first half of pedal travel. (Attachment-1)

I adjusted it so the throttle position signal increases very gradually and the first half of pedal travel only invokes a 30% throttle signal. (Attachment-2)

I've still got a lot of tweaking to do with the Speed, Torque and Linearity curves, but I think I'm getting closer to what I want.

I don't actually do what is considered off-road, so I call it cross-country, but it is bumpy and my foot bounces on the pedal, so the cart was jerky because it only took a small movement on the top end of the pedal travel to produced a lot of acceleration. Now I can drive around my property at about 6 MPH without the need of a HANS device.
Attached Images
File Type: png throttle curves 6-1.2.png (38.5 KB, 0 views)
File Type: jpg Throttle Linearization - JBB.jpg (164.2 KB, 0 views)
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Old 06-28-2015, 12:19 PM   #77
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Default Re: Converting CC (Ahem) to Lithium Power

Just got back from my first test round of golf. Loaded the cart up with myself and a buddy and took the short blast up the road to the clubhouse. Hit 37.2 mph on the way up Then played a quick round of golf. Quite a few jackrabbit starts would throw my buddy right back into his seat. A lot of going back and forth to his ball meant I travelled a lot longer distance than I do during my normal round. Anyhow, at the end of the round, I still had 57% SOC which means that I used roughly 43% of the pack. If I drive a little more conservatively and play as a single, two rounds will be easy to get and possibly be able to squeeze out three.

So compared to my 84 volt cart with AC motor and regeneration, this cart uses a few more amps. It is not quite as quick off the line, nor as controllable, and the max speed is roughly 80% of the AC cart.

However, for a little more than one third of the cost for controller and motor for the DC version vs the AC, it's quite a bargain Just as much fun on the course and still guaranteed to always have that perfect lie
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Old 12-08-2015, 05:57 PM   #78
MC1
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Default Re: Converting CC (Ahem) to Lithium Power

Sent a PM to Ronncat to get some info on where he purchased all his stuff. Appears he does not visit thus website much.

He notes Elcon out of Sacramento, but i cannot seem to find the correct department.

Anyone know where he purchased the main components
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