Lunar Rover (prototype)

[Functional Artist]

Made sure the "Goose Neck was centered & square
…then, marked the spot
...drilled a pilot hole
…then, used a hole saw (@ really low RPM's) to cut-out the top layer
…& then, on thru the second layer

* Hole saw teeth still looks "like new"

…& cut off the excess material

 

[Functional Artist]

A little bit of grindin' & shapin'
…some centerin' & levelin'
…& then, some weldin'

Then, I re-installed the axle & bearings
...just to be sure

* Thinkin' about addin' some bracin' to the "goose Neck" area
...but, so far, it only weighs ~7 lbs.

 

[itsid]

I think I would've liked that better with a mitered cut and no overlap
(that way you also wouldn't have partially covered the last hole)

'sid

 

[Functional Artist]

I think I would've liked that better with a mitered cut and no overlap
(that way you also wouldn't have partially covered the last hole)

'sid

I figured overlapin' 'em would make for a stronger joint @ that 3-way connection
...mainly cause their only 1/8" steel


I'm thinkin' the upper bar should transfer most of the forward thrust (applied by this axle anyways)
…but, there will still be "a lot" of "other" stress(es) applied to this junction

But, your probably right, a mitered cut woulda worked too

 

[Functional Artist]

It's been ~50* here lately
...business is kinda slow, 'cause of the holidays
…& the kids have been occupied with their "new" stuff

So, I've had some extra time to arrange my notes
…& make a "proper" drawing

 

[Functional Artist]

This vehicle is mainly designed around the Cock Pit

Requirements:
...easy to enter & exit (space suit's are kinda bulky)
…& roomy (technical term) the (astro-) driver has to be able to move freely

Here's what I have in mind

 

[Functional Artist]

Pin Stripe Pipe

Before we move on let me show ya a few tricks that I learned, about shaping & bendin pipe

I had ta make (2) of those "Cock Pit" frame rails
…& they need to be identical (or at least really close)

So, I started off with (2) pieces of (appropriate length) pipe.
…clamped 'em down (1 at a time) to a flat surface
...& added a "pin stripe"

* To do so, I drilled a 1/8" hole into a 3/4" conduit clamp
…& used it as a guide to make a nice-n-centered straight line on the pipe(s)

Then, clamped 'em down together (lined up nice-n-even)
…to measure & mark where the bend lines need to be
(used a square to make identical lines on both pipes, at the same time)

 

[Functional Artist]

After markin' the pipe's, accordin' to the plan, I got the bender out
…& bent 'em up

They look pretty darn close to me

 

[Functional Artist]

This next part is kinda hard to explain

Front of Cock Pit (top & bottom) ~8" apart
Bottom (rear) ~12" apart
Rear (mid) ~17" apart
Rear (top) ~12" apart

Maybe some pics will help

* I used some "spacer" boards (to help hold the front "pillars" evenly apart)
…then, after a lot of measurin' & double checkin', I used some conduit clamps (to "pin" the bottom rails down to a board)

 

[Functional Artist]

Tail 'er Hitch

Next, we gotta connect the (2) frame rails

A short piece of pipe will double as the lower, front, main frame "cross bar"
...& also a "thrust brace" for the rear of the battery box

A piece of 1/8" plate will double as the lower rear main frame "cross bar"
(with a couple of structural bends already in it)
…& a piece of 1/8" angle iron will establish the upper connection point for the Tail 'er Hitch.

* I usually try to avoid using angle iron
...but, this upper brace will encounter many dynamic stresses
(so, I figured a multi-dimensional piece was appropriate

* Maybe we can "thoughtfully" hide it.

** Looks kinda crooked in the pics
...but, I double checked, it's pretty square

 

[Functional Artist]

Attaching the Tail

The Tail 'er will pivot on a 1/2" "pin" goin' thru (2) brass bushings
…& mount in between the hitch brackets on the main frame

 

[itsid]

half inch Pin on a 13" lever?
with what? a 4" -6" height ??
If I interpret your drawing correctly, passenger weight is above and mostly behind the pin in question;
that seems sketchy

Any chance you can replace the brass bushings with slimline PTFE bushings and install a beefier pin (3/4" would be nice.. 5/8" may suffice... )

depending on the weight of your astronaut surrogate you should be aware of the torque involved..

essentially consider the passenger weight hanging on the axle
"swingarm" mounted by just the pin...
with say 220lbs of load that's ~240ft lbf
(plus whatever suspended weight the kart has)
spread over just the two bushings (spaced 4" or 6" apart means times three resp. two)
so we talk 480 to 720 ft lbf of lateral load on just a half inch through bolt, no?

Not sure, but a hefty bump in the road (like going down a curb or such) can already exceed the limits I guess...

'sid

 

[Functional Artist]

half inch Pin on a 13" lever?
with what? a 4" -6" height ??
If I interpret your drawing correctly, passenger weight is above and mostly behind the pin in question;
that seems sketchy

Any chance you can replace the brass bushings with slimline PTFE bushings and install a beefier pin (3/4" would be nice.. 5/8" may suffice... )

depending on the weight of your astronaut surrogate you should be aware of the torque involved..

essentially consider the passenger weight hanging on the axle
"swingarm" mounted by just the pin...
with say 220lbs of load that's ~240ft lbf
(plus whatever suspended weight the kart has)
spread over just the two bushings (spaced 4" or 6" apart means times three resp. two)
so we talk 480 to 720 ft lbf of lateral load on just a half inch through bolt, no?

Not sure, but a hefty bump in the road (like going down a curb or such) can already exceed the limits I guess...

'sid

Very good observation, my friend

I was (& still am) kinda concerned about this articulating joint as well
...but, I figured the weaker area would be where the upper Tail 'er Hitch mounts/attaches to the frame.

So, I kinda "boxed" 'em with some 1/8" steel "stress plates"

I'm gonna have ta think a bit, on the "pin"
...maybe we can "beef" 'er up

* The (astro) driver seat will be mounted to the lower frame rails
(just ahead of the pivot point) mainly to help keep the COG (center of gravity) low.

Does that affect the equation (any)?

 

[Functional Artist]

I did a quick (~1 min.) video to show the Tail Waggin"

https://www.youtube.com/watch?v=kWX9G_fezcQ

 

[itsid]

* The (astro) driver seat will be mounted to the lower frame rails
(just ahead of the pivot point) mainly to help keep the COG (center of gravity) low.

Does that affect the equation (any)?

not positively at least..
the kart is always suspended by the wheels,
so all weight between the axles means stress on the pivot bolt.

In fact the closer the mass is to the axles, the better,
the closer to the pivot the worse.
worst spot would be dead center between the axles.. maybe somewhat towards the hitch.

I mean sure, you can unload the hitch a bit by packing batteries and such behind the rear wheel .., but who would want that?

Let's hope for the best for now...
you might need to swap the pivot tube to a larger size in worst case..
and frankly.. swapping a tube, widening two drill holes...
I can't see how that would be a problem for you

'sid

 

[Functional Artist]

Pivot Pin Upgrade

Thank you sir I've taken your advise & upgraded the pivot pin to a 3/4" grade 8 bolt

* The "action" of the pivot seems even smoother now

 

[JTSpeedDemon]

Investing in Grade 8 hardware really does save headaches down the road. I can happily say that from experience!

 

[Functional Artist]

Here's about how it'll look with the seat in place

 

[Functional Artist]

The Nose Section

Next in line, (just ahead of the Cock Pit) would be the battery box,

The batteries will be
...oriented sideways
...lined up in a row
…& slung way down low

And finally, the front axle which is to be located just ahead of the battery box
…with some "foot pads/floor boards" on each side of the battery box & sprocket area

* There will be a protective "cage" around this sprocket & rotating shaft.

 

[Functional Artist]

Concept re-evaluation

not positively at least..
the kart is always suspended by the wheels,
so all weight between the axles means stress on the pivot bolt.

In fact the closer the mass is to the axles, the better,
the closer to the pivot the worse.
worst spot would be dead center between the axles.. maybe somewhat towards the hitch.

I mean sure, you can unload the hitch a bit by packing batteries and such behind the rear wheel .., but who would want that?

Let's hope for the best for now...
you might need to swap the pivot tube to a larger size in worst case..
and frankly.. swapping a tube, widening two drill holes...
I can't see how that would be a problem for you

'sid

This still concerned me

So, I've done a complete concept re-evaluation
…& some more research too

It seems that most articulating vehicles are set up with the "tractor" or power unit "balanced" over (1) axle
…& the "pay load" or bed/bucket pretty much over the other one

But, that's NOT how "most" go karts are designed
…& NOT quite what I have in mind

The largest mass (heaviest thing) supported between the axles on an electric kart is the driver (usually ~150-200 lbs.)
...then, the battery pack (~40 lbs.)
…then, the motors (~10 lbs. ea.)
…& then the frame (but, its weight is kinda spread out)
(the weight of the axles, wheels & tires are "actually" supported by the ground)

So, we can "balance" the weight of the motors mostly over the axles
…& move the batteries around a bit
...but, that driver????????????
...it seems like it's best to keep 'em low & mostly in the middle

* I kinda like the concept in the (6th) pic
...but, I don't think our (astro) drivers legs will bend like that

Well, after extensive evaluation, (I've thought this thru 100's of different ways)
I think I've got it Overcompensation
...maybe we'll upgrade to a 3/4" x 36" pivot pin, on that ~13" lever

How does that effect the equation?