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Go-Krawler Flatfender - Articulating 4x4 Go-Kart

Joined
Nov 28, 2020
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3093
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Sacramento, CA
Alright I figured I might as well make a thread for this thing because I think it's pretty sweet. This is one of those ideas that's been rolling around in my head for years, but my nieces and nephews are getting close to the right age for driving things around so it's time to make it happen.

So what is it? It's just a pint-sized crawler. Essentially has one links front and rear, crossover steering, transverse leaf springs, a HF predator motor with centrifugal clutch (CVT could be added at some point), and a gearbox with reverse. Completely made from aluminum sheet metal (except the cage and drivetrain stuff). The design still needs refinement before it goes out to laser, but everything is there and in its final position.

-22" tires
-Hoping for ~250lbs (or less, but haven't started adding things up yet)
-About 6ft long, 4ft wide
-Pedal box has over a foot of adjustability in it. Designed for kids, but by some miracle it looks like an adult up to around 6ft can squeeze into it with the pedals fully pushed out to the grill.
-Also building a remote control box that can be dropped in in minutes converting it to an RC car, then removed just as easily when kids want to drive

If it performs like I hope, and holds up, I've genuinely thought about manufacturing them in kit or preassembled form. But I'm not thinking about that too heavily until I have confidence this will work the way I want it to, there's a decent amount of outside the box stuff going on. But this is a build thread for this #1 for my family, I'll bump this thread as things come together!

Kid Flatfender - Assembly - 24.jpg



Kid Flatfender - Assembly - 22.jpg


Kid Flatfender - Assembly - 23.jpg
 
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I think it's pretty sweet.
I think so too!
one links front and rear, crossover steering, transverse leaf springs
What axles?? Details :flipoff2:
a HF predator motor with centrifugal clutch (CVT could be added at some point), and a gearbox with reverse.
I suggest go CVT right from the start. Centrifugal clutch will be glowing orange in no time. Unless you’ll gear it deep, so the clutch will stay engaged most of the time. Very low top speed and engine running against governed rpm a ton, imho are undesired.
-Hoping for ~250lbs (or less, but haven't started adding things up yet)
A riding lawn mower weigh about that much. A good, realistic goal I’d think.
-Also building a remote control box that can be dropped in in minutes converting it to an RC car, then removed just as easily when kids want to drive
I love this.
I'll bump this thread as things come together!
Please do :smokin:
 
I think so too!

What axles?? Details :flipoff2:

I suggest go CVT right from the start. Centrifugal clutch will be glowing orange in no time. Unless you’ll gear it deep, so the clutch will stay engaged most of the time. Very low top speed and engine running against governed rpm a ton, imho are undesired.

A riding lawn mower weigh about that much. A good, realistic goal I’d think.

I love this.

Please do :smokin:


The axles are custom using some oil filled industrial worm drives, and 1.25" tubing as axle shafts. That's one of the points that I won't be confident in until I try them out, so we'll see.

The CVT vs centrifugal is definitely an interesting one. I settled on the centrifugal with heavy reduction (10-15mph top speed) for this specific one because this will be the kids first gas powered anything, so speed isn't as critical and the reduction takes a lot of stress off the clutch. Especially because I want this thing to actually be capable of slow technical crawling, so burning belts would also be a concern even with the CVT. In the ideal world I'd have a multi speed transmission, but trying to accommodate that pushes this thing even more over the top than it already is lol.

As far as weight goes I'm trying to be pretty conscious about every decision, I want one person to be able to heave it onto a trailer or rack of some kind for easy transportation. I would be damn happy if I landed anywhere in that 250 range, and would be ecstatic if it came in under that. But who knows, it could go the other way.

I think the RC thing is a huge perk to just make this thing as versatile as possible. Kids can drive it, adults can drive it, and anyone can RC car it. So if the kids get bored it doesn't just sit there taking up space, it can be enjoyed by everyone
 
The CVT vs centrifugal is definitely an interesting one. I settled on the centrifugal with heavy reduction (10-15mph top speed) for this specific one because this will be the kids first gas powered anything, so speed isn't as critical and the reduction takes a lot of stress off the clutch. Especially because I want this thing to actually be capable of slow technical crawling, so burning belts would also be a concern even with the CVT. In the ideal world I'd have a multi speed transmission, but trying to accommodate that pushes this thing even more over the top than it already is lol.
I used centrifugal clutch and CVT on my mini bikes.

CVT is the way to go for your purpose. Centrifugal clutch is not suitable for applications where there’ll be a lot of throttle modulating.

I was at my friend’s place and he test drove his project car (70’s? Muscle car) and it stalled and will not restart. It was down the road and it’s a steep hill, no less than 8-10% grade. I used my mini bike to tow it back up to his shop and to my surprise it did. (Yes I had my body well over handlebars to keep front end down).

I reckons you’re planning on to use Predator 212cc which will use a CVT based off Comet’s TAV-30. They have 2.7:1 in low range (when subjected to low throttle and/or high load).

 
The ebay torque converters are the way to go. The model depends on what size predator your running. (If your planning a 212, I'd look into a 223 wildcat) the torque converter has lower gears up into a overdrive. All the "shift points", engagement rpm and even if you want to limit it getting into overdrive can all be adjusted to get you what you want
 
Hmmm good notes, thanks guys. Yeah I was thinking the 212, or something at least the same/similar form factor. Are there different length belts available if I can't put the reverse gearbox in the same orientation as they're set up for? The reverse gearbox I got is the common import one that actually already has the shaft layout for the cvt/torque converter so it's definitely doable, as long as I can make it all happy with the way things are packaged

I'm not dead set on the centrifugal, but I didn't realize that centrifugals were held in such low regard these days. The little briggs powered cart I had as a kid is my only experience, but it was centrifugal and pretty bulletproof and fun, so I figured I could get away with it for a decent while with low gearing
 
May be able to find a cheap sled that has a small air cooled engine, cvt, and maybe even a disc brake that would work for you. Reverse may be tough to find. Just a thought.
 
May be able to find a cheap sled that has a small air cooled engine, cvt, and maybe even a disc brake that would work for you. Reverse may be tough to find. Just a thought.

Something like that could definitely work, and someone could prob retrofit if they want a little more umph haha. As of now I'm thinking the predator 212 is the way to fly in part due to the bang for the buck, and because it's a nice universal platform that anyone can get their hands on (just in case I make more of these things)

Great call on the Wildcat 223 Angelo, I've been looking at the various different engine options in that form factor, and that one looks to have great bang for the buck, especially with the electric start.

Are all of the torque converters considered equal? This one looks to be Comet based like you mentioned Trail, just a generic example that I've looked at a couple times

https://www.amazon.com/Torque-Converter-Clutch-Predator-Replacement/dp/B07S3TX4C5

And then I see most belts are around 27" long with a ~22cm center-center installed distance between pulleys. It would be sweet to use the engine and gearbox in their current layout, but it's probably the best decision to rearrange everything to use common parts. Is there any easy way to get a brake drum on the gearbox output shaft with the torque converter installed? With this swap I might be losing by drum brake config, so I'll need to figure that out as well

https://www.amazon.com/Adorish-Drive-Replacement-203589-203589A/dp/B08FH3TLMC
 
It definitely seems like the best bang for your buck, and it's not that much more then a 212 predator.
A comet brand one is the best. All the cheap ones are probably the same, and pretty much as good for way less. Just upgrade to a comet brand belt.
 
It definitely seems like the best bang for your buck, and it's not that much more then a 212 predator.
A comet brand one is the best. All the cheap ones are probably the same, and pretty much as good for way less. Just upgrade to a comet brand belt.

Yeah totally worth the added cost especially for the convenience of already having the electric start. Cheaper and easier than adding the electric start to a predator. Great note on the belt too, I'll make sure to go name brand there even if I go with an import torque converter

Just buy a rotted out Samurai, rip the body off, and teach the kids to drive a stick 🤣

Good luck with the build, this will be fun to follow.
Haha right. I'm sure they will be driving full sized rigs before too long anyways :cool2:

Don’t think you will do it for 250 lbs.

I haven't added all of the weights together to have an exact estimate but I do have a few, and it doesn't seem impossible yet. It may be a stretch, but time will tell. The wheel/tire combos I got are 18.5lbs a piece, so 74lbs total there. The engines are around 37lbs, and the reverse gearbox around 12lbs. So that's 123lbs, which leaves another 127lbs for the chassis and axles.
 
Also look into the juggernaut or torkzilla drivers. I think they are more a benefit for high rpms but they might help with torque also
 
Alright a small bump for this thread. I've got the R-N-D gearbox, the CVT ("Torque Converter"), wheels and tires, steering box, primary bearings, ujoints, worm drives, steering wheel, and some of the steering components. I still need to finish adding all of the bolt interfaces to the CAD, then I'll get that made and assembled, and the build can really start!
 
Bump. I now have the Wildcat engine on hand, along with a CVT. You guys are bad (good) influences :flipoff2:. I haven't circled back to the cad to give it a final round of improvements before having pieces cut, but most of the other pieces are on hand at this point. I'll snap some pics in the next few days of the parts pile for fun
 
Also look into the juggernaut or torkzilla drivers. I think they are more a benefit for high rpms but they might help with torque also
I have juggernauts on both of my small block bikes. Way better up top and smoother everywhere than even a resprung/reweighted primary.

Speaking of which he'll benefit eventually from changing the secondary spring too. I've sprung mine as heavy as comet sells springs and with the juggernaut feeding it there is a definitive shift from 1st to 2nd for damned sure.
 
I like all of the ideas you've been putting out there from this, the jeep in a box deal and all that.... But would you build them already!? :homer::flipoff2:
 
I like all of the ideas you've been putting out there from this, the jeep in a box deal and all that.... But would you build them already!? :homer::flipoff2:

Haha this thing is on the round 'tuit list, so it gets attention here and there. I'm ready for it to start coming together though, so I'm going to attempt to get the cad finalized soon. Then if I played my cards right, I should just be able to bolt most of it together...as if anything ever works out like that haha :laughing:
 
Yeah pretty much lol. The more work I've done designing and manufacturing for production, the more I've appreciated intentionally looser tolerances to make sure everything works even with fluctuating manufacturing tolerances. Now that being said I'm sure I'll still have mistakes, but that's how it goes lol.

Not a ton of actual progress, but a couple things. First, the model is now reworked to have a CVT, while still keeping the reversible gearbox and drum brake. I was concerned that the CVT was going to mess up my ability to keep the drum brake up here out of the elements, but looks like it's going to work. Also kinda gives you an idea of what's going on with the transverse leaf setup


Kid Flatfender - Assembly - 26.JPG


And the parts pile. Just about all of the big ticket items are accounted for at this point. I appreciate the engine recommendations, and twisting my arm into getting the CVT :flipoff2:. I know it'll be better because of it.

Parts Pile - 1.jpg


The key is going to get relocated to somewhere within reach of the driver, and the transmission will have a convenient shifter as well

Parts Pile - 2.jpg
 
Well, like any kids buggy I have overcomplicated the hell out of this thing and burn way more time than necessary :laughing:. Redrawn basically the whole thing a couple more times, rearranged the engine and transmission combo again as well. But thankfully, it's damn near ready for manufacturing now. I have the cage hidden just for better pics

Kid Flatfender - Assembly - 29.JPG


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I've seen those things, I thought they were pretty cool. But being just 2wd with a non articulating rear swingarm, not nearly capable enough haha. So I had the bright idea to reinvent the wheel. We'll see how much I regret it depending on if this thing actually works like I hope. I have a little reservation about the spring setup, but theoretically....guess we'll find out
 
yeah those things are junk for sure they use a honda 70 clone engine if im not mistaken.

I'm sure yours will end up absolutely killer like everything else you do
 
Looks sweet so far. Keep it coming. Transverse leaf setup is a cool idea!

I'm pretty pumped to be experimenting with the leaf setup TBH. A little timid, but it's the simplest and most compact way to package everything the suspension needs, at least as far as I could come up with.

I put 4" trailer lights in the front and rear today, along with 1.25" ambers up front so it has some running lights for style points. Also added a battery tray up front, it's really light on front weight (including passenger) so I'm trying to put as much up there as I can

Kid Flatfender - Assembly - 35.JPG


Kid Flatfender - Assembly - 36.JPG



Kid Flatfender - Assembly - 37.JPG
 
The ujoints for this thing can definitely hang with 1480’s :lmao:

I started crunching numbers over the weekend, all of the sheetmetal combined comes in at 117lbs. I haven’t done all of the accessories yet, but that list is at about 150lbs so far. So we’re at 267lbs so far, I honestly think there’s a small chance it comes in under 300. I’m pretty confident it’ll be below 350 though

IMG_9618.jpeg
 
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