Planning/Imminent build of 4x4 kart

[bread]

ok so I know two projects at once = twice the fun

still, won't be starting this until mid june

the plan:
1 use the 5hp tecumseh off a snowblower (4th pic)
2 full time 4x4 with single DS running the length of the kart
3 engine mounted transversely, using either torque converter or centrifugal clutch
4 double wishbone independent suspension at each wheel
5 use of snowblower/auger worm gear box for each axle (IK that the gears will shear under the load so they will be swapped)(3rd pic)
6 a lot of sus. travel (shootin for 20ish" shocks)
7 geared LOW (this machine is not intended to be a fast offroader in any way, more trials, etc)

the immediate issues:
1 coupling the main DS to the snowblower gearboxes input (shaft adapter, etc)
2 coupling u joints to snowblower gearbox outputs and to hubs
3 the u-joints (not a common item at this "scale") still, have found a couple suppliers, another u joint issue is that with parallelogram suspensions, the axle decreases in length significantly when the suspension flexes, meaning the joints will have to be splined or in some other way expandable/collapse-able
4 there is going to have to be bearings all over this thing to hold the DS + axles in place
5 engine lacking power

other project plan info:
Frame material: 1”ODx.065”DOM,
Frame rectangular dimensions: 78"x 17"
Suspension Arms: 1”ODx.120” DOM
Suspension type: equal-length double wishbones, parallelogram style
Steering mechanism: with the shafts, etc being the way, a bell crank steering will be used, putting the tie rods above the drive-train components (if this doesnt have enough steering torque, a rack and pinion will replace it)
Tire size: 13"
Approximate cost: $2500

looking for insight regarding "immediate issues" as well as any other observations for the kart



so I will attach a couple pics of the rough design, sorry still using sketchup, note the shocks are not yet in the design nor are the axles/DS

and a still "rough" parts list

this gearbox is a 1:10, great for trailing

5hp, 1" bore crank stepped down to 7/8"at end (this engine has no air cleaner, but electric start!)

finally incomplete parts list

 

[ezcome-ezgo]

Where are you sourcing the u-joints?

 

[bread]

Where are you sourcing the u-joints?

wup, I guess you can't click on links in an image

these look like these would work as joints, but the axle needs to be able to change length as the sus. flexes, meaning machining spines, etc would be necessary

https://www.surpluscenter.com/Brands/G-G-Mfg/1-KEYED-12-HP-UNIVERSAL-JOINT-1-2730.axd

these would probably work because they are expandable , but more expensive

https://curtisuniversal.com/products/assemblies/

 

[ezcome-ezgo]

If your a-arms are parallel to each other, and the drive shafts are parallel to the a-arms, u-joints placed with the center of their axis on the same plane as the axis of the a-arms will make expansion/contraction of the drive shaft unnecessary, won't it? Or am I wrong?

 

[bread]

If your a-arms are parallel to each other, and the drive shafts are parallel to the a-arms, u-joints placed with the center of their axis on the same plane as the axis of the a-arms will make expansion/contraction of the drive shaft unnecessary, won't it? Or am I wrong?

that is correct, after I investigated using sketchup, if the u joints are placed on the same axis as the parallel arms, the axle length remains the same

however, creating hubs that have the u joint on the same understood "line" of axis would be difficult, also it would be very tight to mount the inner bearings of the axle on the frame rails if the u joint is to be kept on its understood "line" with the axis of the sus. arms

now I'm not saying it would be impossible to have fixed length axles, but the location of the u joints in relation to those of the suspension tabs would have to be very precise, so at this point I remain undecided on which kind u joints to buy...

first, joints on same axis as arms

length is same

now with the joints outward 1"

a lengthening of 3/8"

 

[ezcome-ezgo]

I agree wholeheartedly that great precision would be required for a fixed length shaft. How do you intend to hang the a-arms on the frame?

 

[bread]

I agree wholeheartedly that great precision would be required for a fixed length shaft. How do you intend to hang the a-arms on the frame?

mounting tabs will be welded to the frame rails, suspension arms will have bushings on frame side and on hub sides, rod ends for adjustments

sorry the design has not caught up to my thoughts yet

 

[ezcome-ezgo]

I have thought about this with a KISS mindset for a while. The pic below illustrates what is in my head. Looking from left to right, frame to hub. Green is the drive shaft, blue bearings, a-arm pivots are red. I imagine using rod ends for pivots.

 

[bread]

that is what is now in my head, see the irregular/not linear shape the hub must be?

although that setup is far from impossible, if expandable shafts are similar in price, they may well be the easier route

 

[lurch9]

What is this things intended use? Terrain type? 4 wheel drive with 13" tires and tons of uptravel. Geared LOW?
Curious setup that I can't see a logical use for.

 

[bread]

What is this things intended use? Terrain type? 4 wheel drive with 13" tires and tons of uptravel. Geared LOW?
Curious setup that I can't see a logical use for.

a sensible observation, most independent buggies are fast

first, the objective here is to use the 5hp tecumseh, so I could have just built a normal go kart (rwd, not much sus. travel, etc) but I want to build a kart that brings the most trail/offroad performance out of the small engine, this to me, implies loads of travel, low gears, but the tires have to be small so the engine doesn't work as hard. basically I'm compensating tire size for suspension travel, furthermore independent suspensions are relatively light when compared to solid axles/link suspension. but also understand when I say "trail performance" i'm not talking about moab or anywhere near what jeep/other proven offroaders can do. So to get as much as I can from the little motor, 4x4 is a must, the sus. travel is neccesary, small tires for less stress on hubs, suspension components and engine, and low gears (max speed: 17-18mph).

take this 4x4 baja sae rig, small, light, underpowered. imagine it with no roll cage, irs, and snowblower worm gears

 

[lurch9]

Ok. Makes sense now. I would go up in tire size and gear it lower. Even if you nail the suspension geometry and this thing flexes like a boneless lady of the night on muscle relaxers, you will be severely limited by the tire size choice. 13" is tiny. I would at least try to go with something like the 16x8-7 trail wolf's from bmi. A little more clearance and aggressive tread. Once 13s are mounted and bolted to a hub you're looking at maybe 4" of clearance at the lowest point of your suspension arms.

 

[bread]

Ok. Makes sense now. I would go up in tire size and gear it lower. Even if you nail the suspension geometry and this thing flexes like a boneless lady of the night on muscle relaxers, you will be severely limited by the tire size choice. 13" is tiny. I would at least try to go with something like the 16x8-7 trail wolf's from bmi. A little more clearance and aggressive tread. Once 13s are mounted and bolted to a hub you're looking at maybe 4" of clearance at the lowest point of your suspension arms.

your right, I've read too many places that tire size means everything, gap filling, etc

I'll probably go with the 16x8s, thanks

 

[chancer]

Figure out how to go with 20"s. I am thinking with 13 or 16s the fully independent suspension is almost no good If a tire cant climb a 6 or 8 inch Rock.

But what do I know! LOL

 

[lurch9]

Figure out how to go with 20"s. I am thinking with 13 or 16s the fully independent suspension is almost no good If a tire cant climb a 6 or 8 inch Rock.

But what do I know! LOL

Totally agree. Go with the biggest knobbys possible. Also go with a narrower rim than your tire really needs. That way you can run lower air pressure without fear of popping or rolling a bead. Lower air pressure and the tire can deform and gain more traction on the trail.

 

[Denny]

Those snowblower auger drive gearboxes will never hold up. That's why augers are mounted with sheer pins to them.

Denny

 

[bread]

Totally agree. Go with the biggest knobbys possible. Also go with a narrower rim than your tire really needs. That way you can run lower air pressure without fear of popping or rolling a bead. Lower air pressure and the tire can deform and gain more traction on the trail.

i think what I'm going to end up doing is using like a 20ish in tire, but pretty narrow, like 5-6 in because this way I can sneak a bigger tire, but the stress on the motor is less because there is a smaller surface area touching the ground. I think the trick to this project is reducing strain on the little engine, 4x4 creates plenty in the first place, adding big, wide tires (even if geared properly) would load the engine immensely

---------- Post added at 09:42 PM ---------- Previous post was at 09:37 PM ----------

Those snowblower auger drive gearboxes will never hold up. That's why augers are mounted with sheer pins to them.

Denny

the gearbox itself? or the gears inside it?
could the gears be replaced with stronger ones, or would the effort in doing so be equal to just putting diffs in the kart?
Diffs, IMO are too heavy for this application... if one gearbox can take the load of a 5hp tecumseh, couldn't two take it more easily under the same power? or am I wrong? are there other forces that create stress on the gears?

wow lot of question marks, but I was worried these gearboxes would be an issue

 

[SkidooTNT]

Those diffs are designe to work under constant load. The sheer pin is designed to snap when a sudden large load is encountered. All components of a diff like that are not designed for the loads that you would be putting on it.

I've seen a few set ups with a short jack shaft that is gear driven which turns the axels. Someone posted a picture of one under "from scratch build". It's where I started asking questions about my project.

Not sure what your budget is but if you have the money for axels you should probably consider getting a snowmobile engine. I'm going to use a 340 for my project ( 2 wheel drive live axel ). Any sled engine will have 10X the power and not weigh that much more.

 

[chancer]

Just rereading your original posts. and your Drawings look LOOOONG
Wheelbase. I get this is still design phase. But Rock crawler right?
Shorter wheelbase less chance of getting high centered.
Just a thought because you asked

 

[Poboy kartman]

Eminence front...it's a put on!