DrWrench's Dragula

[DrWrench]

Started life as a bruised, battered wreck of an old Carter "Hot bodies" kart.

I swapped out the abused 5Hp tecumseh and ancient belt centrifugal for a 346 Predator I found for $150 - brand new - and a 40 series comet clone torque converter. Switched the stock 10T final drive sprocket to a 17T.

The speed and torque were where I wanted them. But with the added momentum the suspension, or complete lack-there-of, became a problem.

I welded up some spring loaded spindles, and cocked the wheels out just a hair so they'd dig in on turns. And while I was working over the front end I toed the wheels in a degree or two. (1/8th or 1/16th of an inch closer measure on front than back) Also dropped the ambient pressure in the rear wheels from 15lbs to about 8lbs.

Had steering issues at 1/2 throttle and up because of how light the front is, and how much weight sits on the live axle. So I welded up a bumper. Gives my front workings a bit of crash insurance, and the handling improved noticeably.
Also raised the steering wheel about 7" to comfortably accommodate a 250lb 6ft adult.

Stats:
35Mph, kicks up fountains of dirt and grass from a standstill, and will do donuts till the sun goes down. Let off for a second, crack the steering wheel, and stomp the throttle at full speed, and it kicks into a smooth arc.

I like to leave governors intact. I'm superstitious about removing the longevity devices the factory thought were necessary... but! If I reach back and pull the linkage, I can reach about 43-44Mph. And that's with little 6" tires.

What's next? Probably a rear-end rework. 1" axle to replace the 3/4 one. I have some 22x11 knobby tires laying around and a whole 1" rear-end [sprocket, brake, and 4on4 hubs]. I work as a service tech on industrial doors and dock equipment for Overhead Door, so I have access to shafts and sprockets of just about any kind. But I'm pretty happy with it as it is now.

Time to move onto another project! I'll leave this one in running condition so I have something to have fun on while I build the next little monster.

 

[OzFab]

I can't tell from your pic whether the tierods cross over or not but, lookong at the spindles, it appears the steering arms point in, giving you reverse ackermann; this could be why the handling is a bit non existent

 

[DrWrench]

Ackermann? As in the wheel running the inside of a turn runs a smaller radius than the wheel on the outside? I think I've got that down.

 

[Doc Sprocket]

You've got the concept, but I'm not sure about your geometry. Can we see the same pic with the wheels straight?

 

[DrWrench]

Yes, of course Doc. Picture.
I'm fairly certain (not accounting for the doubt Fabro has inspired) that I have this functioning correctly. When taking a turn the wheel on the inside seems to be at a much sharper angle than the one on the outside.
However I'd be glad to learn anything you have to offer.

 

[Doc Sprocket]

Odd. Normally, to achieve proper Ackermann geometry with forward-facing arms, those arms would face outward, not in. Might be just the camera, but it looks like you have a ton of toe out. (I DID see your notes above).

 

[DrWrench]

I catch the effect to. I think it has to do with the slant of the wheels. They're leaned in pretty aggressively on the vertical axis.

 

[Doc Sprocket]

I can't see camber factoring in. But... Who knows?

 

[OzFab]

Ok, this is doin' my head in... By the angle of the wheels, it looks the part but, with that geometry, it's not possible...

Can I ask you to take 3 pics from directly above the front end, one with the steering straight, one turned full right & one turned full left. That should settle things

 

[DrWrench]

It's dark out now. But I'll try to get them tomorrow after work. If there's an issue I need to fix it.

 

[itsid]

For now I'd say you have a toe out.
Enough that the wheelcenterlines would cross at the rear axle.
Basically AntiAckermann

And since the left wheel would like to steer left, the right wheel to steer right,
It will wobble if the toe angles are not 100% identical of course.

So after taking the pics, measure your tie rods and the distance Kingpin - steering shaft base (not pitman arm) on both sides.

'sid

 

[Doc Sprocket]

Ok, this is doin' my head in... By the angle of the wheels, it looks the part but, with that geometry, it's not possible...

You and me both, my friend!

 

[DrWrench]

Can I ask you to take 3 pics from directly above the front end, one with the steering straight, one turned full right & one turned full left. That should settle things.

Well... time to eat a heaping plate of crow.
In the process of taking the pictures while standing over the steering column the toe out became apparent, after I was sure I'd corrected it. I went ahead and readjusted it.
And... and the counter productive angle of the wheels is also obvious.

So without lingering on my oversight, what's the simplest route to remedy this poor bit of engineering?


Images Attached per request.

 

[souperman000]

Have a read of this steering thread - http://www.diygokarts.com/vb/showthread.php?t=11760

Basically, you need to cut and reweld your spindle arms in the proper position. The instructions are in the thread, I can't explain them coherently atm

Note: With forward facing arms, proper Ackermann will mean the spindle arms are angled towards the tire. Clearance issues may or may not result.

 

[itsid]

Doc had the exact same problem with his restomod here
Fast Forward links:
Anti-Ackermann and his solution

Or, maybe you can just swap the spindles right to left and vice versa (having the steering arm backwards as on most modern karts);
it may fit under the pan, I can't tell, but that wouldn't require welding

'sid

 

[landuse]

Dang!! turning your kart at speed with your wheels at that angle is going to make you flip over forwards. You don't really want your wheels to turn nearly 90 degrees

 

[OzFab]

Or, maybe you can just swap the spindles right to left and vice versa (having the steering arm backwards as on most modern karts);

You know, that would probably be the simplest solution...

 

[DrWrench]

I apologize for the long silence. Work was time consuming this week. Stumble in after dark, try to stay awake long enough to shower, go sleep for 5 hours. Rinse, repeat, Ect.

Found a little time here and there over the weekend to turn the spindles around. I'm not sure what I've gained.

While the angles, even though not entirely correct, are for the most part on the axis outlined by Doc's method.

But I'm not blown away by the results. I may revert it after considering the return on investment. It handled better before. And for a mysterious reason that I think Doc was onto before, the "problem" persists when the kart has a rider.

The camber bit me in the end. Because of the slant of the wheels, when the spindles slide up the kingpins the spindle arms raise the tie rods, thus leveling them out and forcing the steering arm out further than it was adjusted.

So, without a rider, the Ackermann appears to function. When ridden, and the spindles under load, all I receive is an extremely obtuse turn radius and very awkward pedal operation [tie rod placement].

Pictures.

In summary:

I'll leave the new column arm in place, but revert the setup.

May cut the front crossbar, and re-weld the spindles to a new one. Would go with a much slighter camber and perhaps a ten-degree low-end-forward castor to absorb impacts more effectively.

Any other input is welcome.
But I didn't intend this kart to be a project. I considered it done. I joined because I wanted help on something else. But now I'm not certain. I'm doubting my skills and now my intellectual resources...

 

[souperman000]

Any other input is welcome.
But I didn't intend this kart to be a project. I considered it done. I joined because I wanted help on something else. But now I'm not certain. I'm doubting my skills and now my intellectual resources...

Some things are never done..

I think everyone goes through those phases of "Wow I really suck at this" and "I'm just messing everything up" (I know I do on almost a regular basis...) but just take a break and come back to it.

You can do it!

 

[DrWrench]

Update. See attached.