Ultralight Rev-Tri-Go-Kart build

[vlad]

Bought Bridgeston go-kart tires, 5x5, slightly used. Made a mockup to see if it's a viable project:

Rear bearings in lightweight plastic housing:

80/20 aluminum extrusions, 15 series for the longtitudal part of the frame. 96 oz when cut to size. Which is 38" long. That'll be almoust all the length of the kart:

Go-kart racing seat, smallest size:

1" aluminum rear axle (24 oz) and aluminum hub:

DWT 5x5" aluminum wheels, 10.8 lbs for 3:

---------- Post added at 10:23 AM ---------- Previous post was at 10:13 AM ----------

The fun/scary part.

I did some small carbon fiber projects before, but nothing of this size, and no experience with vacuum infusion technology.

Vacuum infusion is the process where you put your part in a bag and let vacuum suck the resin into it. Or wetting the parts by hand, but using vacuum to create pressure and extracting the excess of resin.

Had to buy a lot of stuff for it. On the left is 1/2" balsa core, to make a strong sandwich. I know, not your usual go-kart construction and vocabulary

Did some experiments to find out how many layers of CF I need and how strong the sandwich will be:

The panel came out extremely light

And extremely strong. Here in the picture I have 1/2" carbon-balsa sandwich, on suspended at 18", and loaded with 40 lbs of weights. The wood block in front is not under it, it's in front to see the deformation. Which is around 1/16"

So it'll def work for what I have in mind. So I went ahead and did the full size chassis.
Laying out the chassis:

Little sauna made out of ladder, tarp and construction lights, to speed up the cure:

 

[vlad]

Carbon fiber cured. It is pretty beautiful

Not exactly perfect on the bottom, but only the ants will see these imperfections

A few (very itchy) hours later:

Weight of the whole thing? Under 5 lbs! It came out even lighter than I expected. The panel, suspened at corners, can hold my 200 lbs easily without visible deformation.

---------- Post added at 10:50 AM ---------- Previous post was at 10:37 AM ----------

Mock up of the concept. Looks pretty cool already, as in that commercial where parked car gets ticket for looking to fast:

Lots of hardware to mate it with aluminum t-slots, cut to 38"

Done. The total weight of hybrid chassis on this pic is 15.8 lbs:

I also bought a 250w/24v scooter motor and matching pulley and a belt. Motor weights under 3 lbs, I think. Mock up of mounting schema:

At that point I run out of enthusiasm, time and money, and that's where project paused for over a year, till this summer. Hope you'd agree, it's far from 50% ready.

 

[landuse]

I like the vacuum idea. Is the motor strong enough?

 

[vlad]

The gear ratio on motor and shaft is now 11:90. The whole thing with driver is <110lbs. According to my calculations it should and does take it to 12mph with no problem and pretty good (but not neck-snapping) acceleration. Because I have to make an effort to keep up with it on mountain bike. For 4 and 6 year old it's more than adequate. But I'll upgrade once kids master this. 400w motor should be easy upgrade and double the power

 

[vlad]

When I picked up the project this summer, I started with motor mount.

I gave some thoughts on materials to use. I have only simple tools, and no access to router,cnc or laser cutting. So after researching some, It looked like Derlin Acetal is the stuff I need. Light, strong, stiff, easy to drill, cut and shape. I ordered a sheet of 1/2" acetal at mcmasters. It worked just as I hoped - easy to cut with Mitre saw, yet very strong.

Making motor mount didn't take long at all. The idea here is to be able to mount motor on a t-slot, and move it along the t-slot to adjust tension and for different belt sizes when changing gear ratios. This 250w motor is pretty small so it's really easy to work with, but if I decide to upgrade to 400W later - the same mount should accommodate.

Then I took the motor control unit from the Spyder (thing in my avatar) and installed it "under the seat", i.e. where the seat will be. The controller has a connector for master kill switch, so I added master kill switch. Which will become a secret on/off under the seat when the seat is installed. The idea is to prevent non-authorized kids from jumping in and running away in the thing they can't control. Lesson learned from Spyder

Then I bolted the motor in. Adjustment along the t-slot worked beautifully. First big step towards running car

 

[vlad]

I thought for a looong time about how to mount go-kart seat to a flat floor. It's awkward idea from any angle. I thought about using the usual go-kart style supports and mounting them to longtitudal t-slots. But it would complicate thing, and won't look pretty. In the end I decided to mount it from the bottom only via fiber-glass (same material as seat) brackets.

It took quite a few days. From metal sheet I bent a simple mold for the brackets. Vacuum infused two brackets out of fiberglass. Cut the top of the brackets to accomodate for the seat shape (wasn't easy task with totally 3D shape of the seat. Then attached brackets to the seat with 5 layers of fiberglass on each side of the bracket.

The end result came out extremely strong and still pretty light. The whole seat ready to be bolted to the floor is 3 lbs. Painted it black to match the color scheme and hide the fiberglass details/defects. Added some reflective tape in the back and will add more later.

Now I can take it off pretty fast to get access to the control unit under the seat.

 

[landuse]

Nice

 

[Desertduler]

I use Delrin quite a bit for things,it is lighter than aluminium and it is better suited in some instances,easy to machine and drill etc.

 

[vlad]

Yes, delrin acetal is great. I tested a piece and it's indestructible, yet light and machinable. The miracle of the modern science! I also used it in the front suspension / steering mechanism, which I'll come to soon

 

[Desertduler]

Yes, delrin acetal is great. I tested a piece and it's indestructible, yet light and machinable. The miracle of the modern science! I also used it in the front suspension / steering mechanism, which I'll come to soon

Cool, I will be interested in your Delrin components.

 

[vlad]

Components may be too big of a word, but my whole front, I call it "suspension" is based on Delrin acetal.

Out of 5/8" bolt and two shaft collars, my friend welded a spindle for me. The only other welded thing will be a steering arm. Since I couldn't calculate the spindle arm angle at the moment, I asked to do 90deg.

I then cut two pieces for each wheel, out of 1/2" delrin acetal sheet. One to mount wheel on a t-slot, with 10deg caster. I'll call it upright:

And one to bolt on to a spindle arm to achieve correct Ackerman geometry, and provide adjusting for steering feel:

I used two hi-strength rod ends and a threaded rod to mount the spindle. Adding some shims/washers under the lower one will provide negative camber, if I find it necessary later. The wheel axis is above the rod ends mounting points to keep whole component low profile. It took some creative thinking to come up with this low profile and lightweight spindle design. Hope it'll work on the track.

I used one 7/16 bolt and two 5/16 bolts to attach acetal uprights to the t-slots.

When using 1/2 plywood to prototype - the upright was very flexible. I was worried it won't work at all. But with acetal in place - no visible flex.

The spindle arm acetal bolt-on provides perfect Ackerman geometry with two mounting points for steering rod (there's one to the right of where it's attached now). The top right bolt is a stop for the wheel to not turn beyond designed angle

During that time, on July 26, 2015, I did some tests. Since there were no steering wheel or anything like that, I just connected spindle arms with solid rod, and attached some ingenious plane-derived steering stick based on 2x4, plank, screw, and some wire. Unforeseen side effect was that you have to tilt stick to the left to go to the right. To my surprise, kids didn't complain and got used to it pretty fast. I also used gravity as a cheap propellant.

Here's my 4 y.o son bravely yells "Close the garage door" meaning to prevent him from running into the cars there. I didn't pay attention, busy with holding my phone steady. So he steers perfectly in between the cars (there are no brakes too!). Kimi in the making.
https://www.youtube.com/watch?v=UhuM0wxMVOg

The rolling chassis passed the inspection. It looked like it'll work, when steering wheel is added.
https://www.youtube.com/watch?v=IXvYsfWveok

 

[KartFab]

No matter what, thanks for sharing. Its a really cool kart!

 

[vlad]

Next I started on steering support. that was in August 2015. As can be see on my ebay purchase summary for on/off switch:

I made a simple mold out of sheet metal:

In that I vacuum infused a carbon fiber part with some wooden structural inserts. The back of it isn't perfect, but decent enough:

The front is nice! The whole part is 6.75 oz / 191g:

Next I made a control panel with voltmeter and battery on/off switch. The switch controls both voltmeter and battery on two separate circuits.

Bit the bullet and bought 24v 10ah LiFePo4 battery. Just 5 lbs and 329 bucks + 50 bucks for smart charger for it. Ouch! But it is small. Very small. Nothing like those huge lead boxes you see on old electric karts. I can mount it just anywhere.

Put it all together. Now it starts to look like something!

The battery will be in the best place for it - center of the car. Between steering support and /under the seat

The whole structure is under 6 lbs. Good.