Radio Control Off Road Kart

[shyflyguy]

The light bulb finally came on and I saw what you've been trying to say, although it took seeing the arc that the trailing arm will be travelling on. You're right all the angles of the triangle would change, meaning that the guide rod would bind in the bushing.

 

[shyflyguy]

Questions for the experts

Previous debates now closed:
Suspension, Rear-trailing arm, front-modified MacPherson strut,
--planned shocks not useful, building my own
Frame, 1.5" 14ga square tube, $1.15 & 1.6lb/ft


I'm a first time builder, so am behind a huge learning curve here. I've read just about everything I can find looking for answers to these topics, but the answers seem to be more opinion, rather vague, or simply no information available that seems to apply to my use. So please, let's hear your expert input. Thank you for any and all info you can provide.

1)
6.5hp, 30 series TAV2, 12T-45T, 14.5" rear wheels
Complete kart weight 250lbs max (rc, so no rider)
Low gear ratio with converter 10.05
High with converter 3.375
Am I geared too high?
Would going to a 10T-45T make enough difference?
These would be 12.06 low and 4.06 high.

2)
Steering via standard pitman arm attached to a car power window motor. Off road fun kart with suspension designed for 0 castor, 0 camber, intend to use tie rods to obtain a few (<10°) of toe uni for better tracking. I couldn't find anything useful for off road karts on this.

 

[chancer]

I prefer to steer with my right foot if you know what I mean. This means once the kart is turning the direction I want the actual steering wheel may be full lock in the opposite direction. I guess I could have just said "Drifting". Anyway...
How fast can you steer lock to lock with the power window motor? Specially since I think you said you want this kart to do like 40mph.

 

[shyflyguy]

Day Whatever

Ok so I can't keep track of days when I'm being called in on overtime, switching between days and nights, and the friggin' clock jumps forward an hour in the middle of it all.

For the past week I have done more algebra, trigonometry, and physics that I ever did in any 3 week period of high school or college! I've worked the spring load problem over and over countless times trying to figure out just how stiff or soft of a spring that I need to use. I've come to several conclusions. A) Rotational inertial energy of go kart tires isn't worth doing the math for, B) Such simple problems are worthy of laughter over in the Physics Forums, C) Once I sat down and thought about each part of the force equation working I actually got pretty close, D) I didn't search Google hard enough and just this afternoon found a nice little calculator that did all of this work for me. That stupid little calculator took about 15 seconds to figure out what I had worked on for more than 20 hours. Now there is some satisfaction that my calculations are within 5% of the calculator, which also doesn't factor in rotational inertia.

The front and rear will require different spring strength, but this shouldn't be a problem as long as I can keep the size and spring travel relatively the same. In an effort to keep the center of gravity lower, I reexamined a rear end design I had previously dismissed. Upon closer examination the design might work for me, although I still have concerns about ground clearance and actual rear suspension movement with it. I'll be watching lots of YouTube videos over the next week and am planning to build a mock up to see how well it works with such a lightweight kart.

I've found a good simple medium for building a wood mock up, which just happens to be on sale at Lowe's this month. It's a 2x2, which treated is really 1.5x1.5 the perfect easy to work with sub for 1.5x1.5 steel square tube. They come in 8ft sections and are a whopping $0.89 ea (item 472838). I could spring a couple bucks a piece more for fir/spruce furring strips, but why pay 3x the price for something that is just a little stronger if I'm not planning on actually weight loading the thing anyway? I'm hoping to get to playing with the mock ups this week for both rear end designs. Of course that is also dependent upon other activities which seem to have filled my upcoming weekend.

While there's not been much posted help coming up in this thread, I've had some great help from members in chat/email messages. So while I'm physically not doing much with the kart at the minute, it's because I'm trying to design as many questions and WTF moments out of the build as I can. I promise pictures of mock ups when I get around to them. Thanks for all the help, and please keep the ideas coming!

 

[shyflyguy]

So I started a mockup with wood today and I'm glad that I did. I had planned a lateral support just above the hinge joint that coincides with the jackshaft of the torque converter. Obviously from the pictures that won't work because it would run right through the engine carb and muffler. I'm liking the idea of the shorter trailing frame and the shorter drive chain that comes with it. The design I had in mind for the ladder frame will have to be reworked though.

I also ended up spending about 3 hours cleaning up around the shop and making more room to work.

 

[Young One With A Manco]

Look very closely at the computer... DIY KART CHAT! I see me
Nice mock up anyway Luke!

 

[Poboy kartman]

Look very closely at the computer... DIY KART CHAT! I see me
Nice mock up anyway Luke!

That's not DIY Kart Chat.....That's gokart room on Chatzy....not affiliated with DIY....

 

[shyflyguy]

So after some more thinking (I've already been accused several times of overthinking this kart), here's a few more changes as a result of the mock up. The rear hinge joint will be completely different, meaning that the trailing arm frame will now be in line with the ladder frame. Instead of doing a side by side with two pieces of the same pipe, I'll be welding some thick flat steel to an A type frame on top of the ladder. The flat steel will create a C type point where the square tube it's welded to being the center. The long top of the A frame will extend past the vertical support to allow me a place to mount shock/spring assembly to. This will also be cross braced near the upper end since it will clear the engine.

I haven't yet decided if I need to weld a bushing or round pipe for a bolt to slide through on the trailing arm frame. I'm pretty sure that just drilling holes in the square tube of the trailing arm frame is not sturdy enough. Although since the shock/spring assembly will be using eye bolts drilled through the frame, I'm almost certain I need to mount these on the vertical support for the cross brace on the back of the trailing arm frame, and not through the frame between the axle and hinge point as shown in the picture. I've also done away with the A frame on top of the trailing arm frame, as I think a second attached vertical support should support any torque load the cross brace can take by hitting bumps on one side and not the other. This may not even be required, but it certainly assisted in stiffening the mock up frame.

I'm still debating about bolt size for this and the front suspension joints. I'm pretty sure that grade 5 or 8 will be used, and 5/8" seems to be about the right size. After all it is good enough for a kingpin. I've been told to use 3/4" but I'm certain that is absolute overkill. Has anyone ever bent a 5/8" kingpin?

 

[shyflyguy]

 

[MadManAndrew]

Same exact project I started out aiming for. I think you'll find that this project ends up costing you MUCH more than you anticipated. Also, plan on using a wiper motor for the brake actuator too.