Polaris

[Functional Artist]

I ran outta weldin' wire
...so, I rode my ElMoto up ta HF & got some more.

When changing the wire I also change out the "wire cleaning pad"

See how much sh!t it wipes off of the wire?

New "cleaning pad" ready for installation (it's just a folded-up piece of shop rag/paper towel stuff in an Alligator clip)

Cleaning pad installed on the wire

As you can see, the wire just runs thru the cleaning pad, before entering the welder
...& most any contaminates get wiped off & collected in the pad

 

[Functional Artist]

When building structural stuff, there is the strength of the material (itself)
...& there is strength in/of the design (itself)
The best designs try to incorporate both concepts, as much as possible.

I designed the main frame to be made from strong but, kinda heavy water pipe (~1 lb. per ft)
...& the main cross members too
...but, for most of the braces, I'ma gonna try & use some smaller/lighter material (1/4" rod)

Front axle supports

Profile

Frontal view

Another frontal view

* I didn't do any kinda math
...but, this 1/4" rod is pretty strong
...& probably ~75% less material, than the 1/2" Schedule 40 water pipe that the rest of the frame is made outta.\
...so, they are less bulk & hopefully less weight too

Testing will tell us for sure

** It's kinda difficult ta see the aerodynamics, that I've incorporated into the front
...but, they are there

 

[BaconBitRacing]

Good work keep going!

 

[Functional Artist]

Good work keep going!

Thanks!

We had a big storm coming so, I had ta remove the chassis from the workbench/jig
...& bring 'er inside for the night.

It seemed pretty light so, I set 'er on the scale, just ta see

Wow! still a little less than 40 lbs.

 

[Functional Artist]

Rollbar mock up

Rollbar welded on

* The rollbar braces connect within 4" of top, to meet specs

Close up of welded area

 

[Functional Artist]

Figurin' the gear ratio for a 20" bicycle wheel

I measured how far a 20 bicycle wheel travels, by marking the tire & workbench

...& then rolling it until the mark (on the tire) went all of the way around, until it got to the bottom again

According to this, a 20" bicycle tire travels about 59 1/4"
...but for easier math let's say 60"

Theoretical specs
MY-1020 48V 1,000W motor has a max RPM (under load) of ~3,000's
It'll have a 10 tooth drive sprocket (for #35 chain) on the motor
...& maybe a 60 tooth driven sprocket, on the rear wheel

So, using the:

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

If the motor does 3,000 RPM's
...& were running (for this example) 6:1 gear ratio
...& the bicycle tires have a ~60" cir.

Then, the math would look like:
3,000/6 = 500 (axle speed)
500 x 60 = 30,000 (inches per min traveled)
30,000/12 = 2,500 (feet per min traveled)
2,500 x 60 = 150,000 (feet per hour traveled)
150,000 x .000189 = 28.35 MPH

Hmmm, 23MPH isn't super fast
...but, a good starting point

A 60 tooth #35 chain sprocket is ~7.3"
...& so, a ~7.3" sprocket, on a ~20 wheel, is still a less than 50% sprocket to wheel ratio

IIRC on most go karts, the sprocket to wheel ratio is more like 75% (like a 7" - 8" sprocket on a ~12" wheel)

 

[Functional Artist]

I ordered these BMX 6 spoke wheels (1 rear wheel with freewheel & 2 front wheels)
https://www.ebay.com/itm/195397518210
...(2) of these rotors
https://www.ebay.com/itm/175716099348?var=475102205451
...(2) of these calipers (180mm)
https://www.ebay.com/itm/275959525534

Once everything gets here, I gotta try-n-figure out how ta get them to "play nice" together

Like figuring how to get the rotors securely attached to the front rims
...& fabricating a couple of caliper mounts, for the front spindles that I haven't made yet

According to the rule book,

9 BRAKES and AXLES
1. At least two wheels must have brakes.
2. Brakes must be fitted to two wheels of the same axle. Either both front wheels or both rear wheels depending on vehicle construction.
3. The two brakes must have separate actuation cables. If both brakes are to be actuated by a single hand or foot lever then both cables should be attached to the lever.
4. Regenerative braking is permitted in addition to conventional brakes.
5. The vehicle must not roll if pushed while brakes are applied. The vehicle must also be able to demonstrate a straight stop from a speed of 25 MPH in less than 40 feet.
6. Axles supported at both ends must have a diameter of at least 3/8"(10mm).
7. Axles supported only on one end must have a diameter at least ½"(12mm)
8. Safety wire or cotter pins must be used to secure cantilevered wheel axle nuts. Nylon lock nuts and double nuts alone are not acceptable
Also, gotta figure out how to mount a 60T (or maybe a 72T) sprocket to the freewheel, on the rear wheel

 

[Functional Artist]

Thinkin' about designin' & makin' a couple of spindles ta mount the front wheels

We have (2) options:
Spindles, like on go karts
...or forks, like on bicycles

IMO dual forks would be a bit more complicated
...& look kinda dorky on a kart (just my opinion)
...so, I'm goin' with spindles
Didin' some research, according to the rulebook:

9 BRAKES and AXLES

6. Axles supported at both ends must have a diameter of at least 3/8"(10mm)
7. Axles supported only on one end must have a diameter at least ½"(12mm)

So, #9.6 says if using forks (axle supported on both ends) the minimum axle size permitted is ~3/8"
...& #9.7 says, if using spindles (axle only supported on one end) the minimum axle size is ~1/2"

* Now we have a new question, how to install a 1/2" axle (& bearings) in a bicycle wheel


Also, I'm gonna incorporate some King Pin Inclination to this one (probably ~8* - 10* of inclination)
...so, the King Pin or "hinge" that the wheel pivots on, is angled toward the center of the "contact patch", of the tire

This should help relieve some of the lateral stress off of the axle/center of the front wheels, in turns
...by directing some of that force, downwards into the contact patch

Maybe something like this

A closer view

 

[Functional Artist]

Almost forgot, the rule book has lots of info, about steering geometry

Page 18, shows some of the various steering concepts

Page 19, explains & illustrates
Camber & King Pin Inclination

Castor

Toe in & Toe out

Ackermann Angle

 

[Functional Artist]

This is kinda what I'ma thinkin'

 

[Functional Artist]

Why did you name it Polaris?
...after the Slingshot?

Nope!

I wasa jammin' to some old Megadeth (Rust in Peace) while thinkin' about & designing this chassis
...& the perfect racing "talkin' trash" phrase "popped in my ear"

"Tremble you weaklings
...cower in fear

I am your ruler
...land
...sea
...& air"

For reference (& your entertainment) enjoy

 

[Functional Artist]

Since I have ta make custom spindles, I wasa thinkin' about usin' some scooter axles & bearings that I gotsa layin' around

The scooters axle bearings, seem ta fit inside of some scraps of pipe, I have left from when I made the brush guard for my mini-Jeep

Maybe something like this

 

[Functional Artist]

I tac welded the Boss Tubes on to the ends of the spindle supports (or nacelles)
...at ~10* Negative Camber

...& ~10* Positive Castor

After measuring, I put a straight edge, across from boss tube to boss tube, just to be sure that they were nice-n-aligned

* Notice the nacelles are made up of (4) triangles
...on (4) different planes

 

[Functional Artist]

Waitin' on parts
...so, I played with some CAD (Cardboard Aided Design) body panels

Looks kinda aerodynamic

Even up underneath
The center section will be covered by the required, Belly Pan

 

[Functional Artist]

I received my bicycle wheels today
...& gotta see if I can upgrade the axle & bearings from a 3/8" axle up to a 1/2" axle

Here are the stock bearings (with axle removed)

Measurement

Looks like the bearing "race" maybe removable

Another view

Better measurement

I think, if that "race" is removed, cartridge bearings can be installed & used

What do you think, Hack?

 

[Master Hack]

Maybe....
Get an accurate measurement of the OD needed. Calipers please...

 

[Functional Artist]

Maybe....
Get an accurate measurement of the OD needed. Calipers please...

Um...put your glasses on, I'm clearly using a measurin' stick
JK...JK

Just pop them cups (bearing races) out?
...& then, measure?

 

[Master Hack]

Just pop them cups (bearing races) out?
...& then, measure?

Yup

 

[Functional Artist]

OK did it
Bearing race removed

Got out my fancy digital caliper
...& of course, the battery is dead

Plan B (this one ain't dead)

Measured the inside of the rim

This pic seems a bit clearer

It looks like it's a little bit bigger than 1 1/8"
...or ~29mm

I measured the outside of the bearing race too
...& it seems like it's closer to 30mm (maybe for a snug fit inside of a 29mm opening?)

I measured a 1/2" bolt, that I'll be using for an axle, with the bearings
...& it looks ta be 1/2" &/or 13mm

So, I'ma thinkin' I'ma needin' 30mm OD x 13mm ID bearings

Does this sound right?
...& do they make such a thing?

 

[Master Hack]

Probably not. But there are options.
Little bigger than 1.125? sure would be nice to know EXACTLY how much. 1.130? .140?
There are metric bearings and there are inch. Maybe we hit a metric number, maybe we hit an inch number?
Are you stuck on a 1/2 bolt?

get a battery for the digital calipers