Hell-raiser 72V Electric Racing Kart

[madprofessor]

..with good "wrap around" on both sprockets

2.2" between sprockets wouldn't be a lot on most fossil fuel setups, but it looks like it will indeed give you bite on enough teeth of that drive sprocket at 3.3:1 ratio. Glad to see you take that tooth-folding factor into consideration.

The center seems ta be bit further ahead of where I was hoping for

Were you wanting another rear-heavy wheelie machine?

 

[Functional Artist]

2.2" between sprockets wouldn't be a lot on most fossil fuel setups, but it looks like it will indeed give you bite on enough teeth of that drive sprocket at 3.3:1 ratio. Glad to see you take that tooth-folding factor into consideration.

Were you wanting another rear-heavy wheelie machine?

Thanks, looks like it should work

Nope, the exact opposite.

I was wanting the "X" (dimensional center) ta be (further back) under the batt pack (better weight distribution)
...but, it seems like I'd have ta move the rear axle back, quite a bit, to achieve that.

Like instead of a ~48" wb we would need a ~60wb
...& then, the overall kart, would probably be ~72" long

 

[Functional Artist]

Well, frame construction has come to a temporary halt
...'cause it's like 30* today & we got some snow. (it's been in the 50's, dry & sunny)

So, while we have a minute, lets discuss the propulsion system
...& I've come across some "problems" & potential "plan changes"

The plan, as noted in the first post, was to use a ME0709 brushed motor & a 72V 50 Lithium battery pack
...but, while luggin' this motor around (for fitment purposes) it seemed a bit "lighter" than it should
...so, I (double) checked the specs

ME0709
Product Description
The ME0709 (ME1908) is a Brush-type Permanent Magnet DC motor. Light weight, high efficiency design. Designed for 24-72 VDC battery operated equipment. Capable of 300 amps peak and 125 amps continuous. Totally open, fan cooled motor. Similar in performance to the Perm-motor 132 and the Lemco or Lynch LEM-200 motors.

Specifications
Power: 8 cont-- 19 pk hp
Voltage: 72 Volt rated
Speed: 3700 rpm @ 72v unloaded
Size: 8" OD, 6.5" long (w/o shaft)
Shaft: 7/8"x 1-3/4", 3/16" key
Weight: 36 lbs.

Then, I (double) checked the "actual specs" of "this" motor

Weight: ~30 lbs. (Hmmm)
Measured it: ~5 1/2" x ~8" (Hmmmmm)
Cleaned up the "markings" on the motor (WTF)


It's NOT a ME0709 (as the listing that I bought it from said)
...It's a ME0708 (which seems ta be quite a bit different)

Here are the specs
ME0708
Product Description
Brush-type Permanent Magnet DC motor.
- Light weight, high efficiency design.
- Designed for 24-48VDC battery operated equipment.
- 150 amps continuous at 48V (300 amps for 1 minute)
- Capable of 4.8 KW continuous and 15 KW for 1 minute.
- Totally open, fan cooled motor.
- Runs in either direction

Specifications
Power: 5 cont-- 15 pk hp
Voltage: 48 Volt rated
Speed: 3700 rpm @ 48V unloaded
Size: 8" OD, 5.5" long (w/o shaft), Shaft: 7/8"x 1-3/4", 3/16" key
Weight: 28 lbs.

* So, it looks like, this ME0708 motor will be lighter, than originally planned (- 6 lbs.)
...& having a lower voltage rating, we'll need a smaller & lighter 48V 50AH pack, to run it (- 25 lbs.)
...& another plus is they both seem to be rated for the same top speed of ~3,500 RPM's

** So, maybe things will still "work out"
...it's just a bit of a "jolt", ta find out that your NOT workin' with what you thought you were

 

[madprofessor]

...it's just a bit of a "jolt", ta find out that your NOT workin' with what you thought you were

I'll give that a 4X seconding on the motion. 4 ex(-wives), and I felt the same way every time.

 

[Functional Artist]

Well now, let's run some numbers, to see what this thing "could/should" do

This motor's top speed is rated @ ~3,700 RPM's (unloaded)
...but, we'll reduce that number a bit to ~3,400.00 (loaded)

The gear ratio we will be running @ is 3.3:1
...& we'll be running 13 x 6.50-6 slick tires (13" tall & ~40" circumference)

Ballpark Equation
MS/GR=ASxTC=IM/FT=FMxHR=FHxMM= MPH

Motor Speed/Gear Ratio=Axle Speed x Tire Circumference = Inches per Minute traveled/Foot(12) = Feet per Minute traveled x Hour(60) = Feet per Hour traveled x MPH Multiplier(.000189) = Miles Per Hour

So, that would be:
3,400 / 3.3 = 1,030.30
1,030.30 x 40 = 41,212
41,212 / 12 = 3,434.33
3,434.33 x 60 = 206,059.80
206,059.80 x .000189 = 38.95 MPH

Hey Denny, what do you think of those numbers?
&
Hey Mad Pro, I've been with my (1 & only) wife since 1999

 

[madprofessor]

(1 & only) wife since 1999

Egad, you guys have all had better success with the missus(es) than me. FA, that 23 years is more than all 4 of mine put together.
So, FA: 39 mph on paper, and kudos for being able to draw that up. Now please, add in the variable of driver weight, let's call it 200# in your case and not reflective of the supposed loaded top speed, and share what that real world practical number would be.

 

[Kartorbust]

I get gearing with gas engines fairly well, but I really just suck at figuring out gearing for electric motors. I don't recall a sticky to address this. Because I'm sure over the next decade, electric go karts, buggies, and mini bikes will be more and more common in the DiY community. I might be looking at one in the distant future to do myself.

 

[Functional Artist]

I was thinkin', running @ 48V instead of 72V is "safer" to work with
...& brings us out of the "High Voltage" designation (almost anything 60VDC & above is considered high voltage)

But, there are also a couple of "minuses" to running a ME0708 @ 48V
...instead of the bigger ME0709 @ 72V

1.) the torque constant of the 0708 is 0.13 nM (per) Amp
...whereas the torque constant of the bigger 0709 is 0.20 nM (per Amp)

2.) the 0708 is 4,800W & running @ 48V it should draw ~100A (4,800W / 48V = 100A)
...whereas the bigger 0709 is 8,000 W & running @ 72V it should draw ~111A (8,000W / 72V = 111A)

* So, the ME0708 is ~1/2 the size (wattage-wise) compared to the ME0709
...but, draws about the same amps


Also, I did a little research
...& put together a quick comparison chart (for you'all)

Category---- Predator 212-- ME0708-- ME0709
Horse Pwr (cont.)- 5.1HP-- 5HP-- 8HP
Horse Pwr (max.)- 6.5HP-- 15HP-- 19HP
Torque (cont.)- 11.3nM ---- 16nM-- 25nM
Torque (max.)- 12.4 nM ---- 39nM-- 60nM
Weight (lbs.)- 34 lbs.----- 30 lbs.-- 39 lbs.

 

[madprofessor]

Horse Pwr (max.)- 6.5HP-- 15HP-- 19HP

Torque (max.)- 12.4 nM ---- 39nM-- 60nM

Those figures right there tell me I'm correct to have the 48vdc setup in my ebay watchlist for if/when I build an electric..............
1800W 48V Brushless Motor Controller Throttle Pedal Wire Harness Electric gokart 882511121951 | eBay

 

[Functional Artist]

Those figures right there tell me I'm correct to have the 48vdc setup in my ebay watchlist for if/when I build an electric..............
1800W 48V Brushless Motor Controller Throttle Pedal Wire Harness Electric gokart 882511121951 | eBay

The comparison chart didn't "line up" all nice-n-pretty like I typed it
...so, to clarify those figures "Horse Pwr (max.)- 6.5HP-- 15HP-- 19HP" & "Torque (max.)- 12.4 nM ---- 39nM-- 60nM" mean that:

...a Predator (gas engine) has a max HP rating of 6.5 & a max torque rating of 12.4nM (~9.1 ft lbs.)
...a ME0708 (electric motor) has a max HP rating of 15HP & a max torque rating of 39nM
...& a ME0709 (electric motor) has a max HP rating of 19HP & a max torque rating of 60nM

Also, Watt to Horse Power conversion is "roughly" 745W = 1 HP

So, a 1,800W motor has (Horse pwr (max) ~2.4HP & Torque (max) ~10nM)
...& with the weight of an average kart & driver, a 2 1/5 HP with ~7.5nM, just can't (isn't powerful enough) to move it very fast

* I've tried a 48V 1,800W motor on several karts El Dingo II, E-lemon-aid & Damien
...& it moved all of them, well, just not "super fast"

Here are some video's of them (in action)
ElDindo II

E-lemon-aid

Damien

 

[Functional Artist]

My $32.95 ea. "solid gold" gray steel rims showed up today
...but, Um...their (2) different shades of gray
(the rear's don't match the fronts)

On the bright side, the stuff got here in (4) days, not bad

I got a kool "racing style" seat too (red of course, for our Hell-raiser)

 

[Kartorbust]

Could've done the Mopar Hellraisin purple.

 

[madprofessor]

Mopar Hellraisin purple.

Thought they only went with the Plum Crazy Purple.

kool "racing style" seat

Nice bright red color, about the same as my backside would look after riding in it. I'd have gone with a nice bright red seat cushion over whatever color of miserably hard fiberglass shell would be underneath it. 6'3", with weight in the 150's right now, no natural cushioning being carried around with me. Mostly just bony lumps in the midst of my "goneass" (to quote an ex-sister-in-law). That lumpy bumpy bony ridge down the center of my back feels the same way about it.

 

[Denny]

So, it’s gong to be kinda slow then?

 

[Functional Artist]

So, it’s gong to be kinda slow then?

We'll seeeeeeeeeee

I noticed a couple of bumps on my battery pack
...so, I had 'em checked out
...& one of 'em tested positive (+)
...I think it might be terminal

 

[Functional Artist]

Re-calculating_
...recalculating_

Ok, so the 48VDC 50AH Lithium battery pack is now (2) 24VDC 50AH Lithium packs
...& now, instead of being mounted behind the driver, Ima thinkin' that their now, gonna be mounted onto the nacelles


Then, worked on widening the main frame, a bit (ta help support them load(s) better)

 

[madprofessor]

What the heck, go for broke. Mount the 24's behind the rear axle, along with the red buttbruiser, and make it raise hell with wheelies.

 

[Denny]

Can you wire them in series? It would give you your 48 volts then.

 

[Functional Artist]

Can you wire them in series? It would give you your 48 volts then.

Yea, sure

So, Ima gotsa the "main frame" trimmed, notched, cleaned, layed out, butted up, squared & then strapped 'er down, in the "jig"

Most every piece of pipe has pieces of wood abutting them to help 'em maintain their "proper" position
...then, I "pinned" 'em down, with a couple of "cross boards" (to help ensure there's no movement during welding)

Here's another angle/view

 

[madprofessor]

I'm a big fan of making jigs like that for fitment and welding, for a number of reasons including warpage caused by heat. Wondering about that base though, looks like a hollow-core interior passage door. Don't know about other folks, but I could probably mess up the correct welding of that frame in such a way that either the hollow-core itself would warp up or the screws in it would pull out of the thin veneer, meaning the frame would be warped too.