Muckmudd's 2018 Build off "Astro Rat" [2018 Build-Off Entry]

He is assuming high gear. Number of input turns to one output turn. Plus engine to trans pulley size, and trans to axle sprocket size. He plugs that in and presto bingo, top speed

Thanks guys, I will go check it out. Biggas you are using a peerless 700 right? this is a foote and i'm not sure if the gearing would be the same. I don't have numbers for the size of the pulleys at the moment because that's what i'm trying to figure out before I go buy them.

I can come up with some pulley sizes for you to hit 40 mph.  That's not a problem.  Here's some important top speed talking points

1)  You hit your top speed in your highest gear.  I need to know how many times the trans input shaft turns for one revolution of the output shaft.  ?:1

2)  I need a rear tire size.  Tire circumference makes a big difference in distance traveled in relation to one rotation of the rear axle.  I can't wave the top speed magic wand without that

3) You need to come up with what you're roughly planning for axle sprocket size.  One main thing to be concerned about here is ground clearance.  If you take you tire radius minus the radius of your rear axle sprocket you'll get ground clearance at the rear axle.  Wouldn't want to design a rig where you're dragging your chain and sprocket on the ground all the time.

4)  I'm not going anywhere so if you're design changes or you come across some pulleys you would like to use I'll gladly re-work the top speed calculation for you.

Thanks a lot Carl you're the best man. I will get some more measurements but I already said that the sprocket on the axle is a 44 tooth. I will put her in 3rd gear and find how many revolutions of the input it takes to spin the output shaft.

Ok so,
I'm using the stock lt130 tires that have an 85" circumference.
2 turns of the input shaft equals 1 turn of the output shaft.

Are you really running 27" tall tires?  That seems big.

With a 6" on the motor and a 4" on the trans you'll hit 38 mph at 4000 rpm

sorry 57.5" circumference. I don't know where that other number came outta in the back of my head lol. maybe I rounded it off and switched the numbers around....

The foote internal 3rd gear ratio is the same as the 700.

ok thanks I figured.

Okay with a 9" on the motor and a 4" on the trans you'll hit 30 mph at 4000 rpm.



That 7 tooth to 44 tooth spocket is a pretty big reduction in the rear end.  I'd consider running a smaller axle sprocket, but maybe the 7" pulley will fit just fine in your application.

On one mower I ran an 8 tooth to a 44 tooth on a mudding mower and it went about 24 mph with 22 inch diameter tires . then I swapped in a 15 tooth on the trans and it ran around 48 mph. Pretty sketchy when tour on a lifted mower setup lol

Thanks carl. how else could I get more speed? I think that 9 and 4" pulleys is like the max size I could go with.

Like Biggas said, if you want to get more speed you need to go with bigger tires or change out the sprockets. You really need to have your front end dialed in really well for high-speed handling too.

yeah I'm not looking forward to the front end. It's gonna be a lot of work and i'm not to sure how to do it. If I put a bigger sprocket on the trans it would go faster right? or I could find a smaller one for the rear. Anyways, the sprockets are easy enough to change later for more speed if I want.

Hmmmm. I wonder how you can swap sprockets on the foote. On the 700 I just cut the brake rotor down to fit inside the bore of a hubless 15 tooth w sprocket and welded it up and it swapped right on the splines. The speed increase was insane.

@muckmudd Check out as many go-kart front end build videos as you can. Try and learn from other peoples mistakes. There's a lot of good information on simple go-kart front ends out there. Don't forget there's guys here are willing to help.

yeah the thing is most go karts have the engine on the back, I don't and I need to avoid it obviously. I was thinking I could do it with the steering shaft over the engine and some geometry off the front like Mike'sBigBlock did on one of his mowers. It looks little complicated though but IDK how else to do it. Instead of getting a bigger sprocket for the foote I could get a smaller sprocket for the axle with less teeth.

Yeah that's what I would too to speed it up and you would gain some ground clearance too.

You have a good point there about how do you run the steering shaft.

I think a beefed up version kinda like a craftsman would work well in almost any machine. Where you have one tie rod connecting your two spindles. A steering arm on one of those spindles that connects to a drag link that goes to a pitman arm on a steering box. That's a really common setup on commercial trucks too. The drag link goes on one side or the other on the bottom of the frame so it's pretty easy to get around the motor. AllisKidD21 has a setup like this too. It's does take some time and head scratching to figure out all the details and get it working right.

Yeah, steering and drivetrain are my least favourite things to work on. Build looks good man!

I will have to see what most people do with race mowers and get some ideas.

There's probably a thread or two on here you could check out muck. There's a steering section in the technical forum and there should be a thread on proper steering angles like caster, camber, toe, king-pin inclination, etc. That should give you some good ideas.

Thanks Allis I will definitely go check them out.

No problemo! Hopefully that helps you out.

https://www.atltf.com/t1550-using-motorcycle-handle-bars-need-quick-ratio-steering
I found this topic. Not really what I was looking for but there is some good pictures that show the steering setup. Would this be ok? I would think it's easier than making a over the engine thing like mikesbigblock. What about the craftsman steering box thing. It's not really a box but it always seems to skip. Would it be ok to re utilize it if I made something like this?

So I done a bit more research today. As I don't like geometry that much, I will do it last and try to do it simple.
I watched a few more videos.
I like this concept:
https://www.youtube.com/watch?v=4a-sVgJUWfE&t=254s
As opposed to this concept:
https://www.youtube.com/watch?v=z9gXmPUogak
Because it just looks easier. Obviously I do not take credit for these videos.
for the shaft that comes down in the first example ( the steering shaft) does it just go straight through the frame and ride on a flange bearing or something. It's hard to tell.

I'm thinking
0* toe
0* camber
10* positive caster?
What do you guys think?