Arachnid Build, ... or is it! (Highly Modified)

[Bill CNC]

why can't you just cut them in half, bevel, weld. then grind down and slide a coupler over, then weld it on?

I could, but my thinking is; If I don't get that dead on, ... their will be vibration that could either tear the rear right out or just be plain uncomfortable. The guy does shafts all day long, he is set up for this kind of stuff and has jigs to do just this.

Also, ... Everyone I know, knows that I like to barter services if at all possible. If not, then I can usually work out part cash and a partial trade of services.

For me, ... their is not enough hours in a day. I work full time 2 hours away from my house. So I have an 8 hour shift, 4 hour drive, and many other projects going on at the same time, plus I do side work out of my home shop. The family has come to understand that when I tinker, I am the nicest guy. If I cannot, ... I am usually grumpy. It's something that will never change I guess.

Something has to give, so Every now and then, ... it saves my sanity if I hand something off if I have no time for, or cannot do efficiently due to the lack of certain tools.

 

[Bill CNC]

Mikko,

Thanks for the kind words and welcome to the site.

I think I will extend it a little. I'm probably not going to start the center until last. My train of thought is if I complete the front and the rear which is still somewhat up in the air, the center section will fall in-line. I bought the front 9.750" shocks that the plans call for, ... but I too was thinking to go a little larger, perhaps 12.0", I need to assemble the front again and install the smaller shocks and get a good look at it before I fully decide. I am 225 pounds and 5'9 in height so I don't think extending it as far as you would, would be necessary, ... but a shocks swap might be!

 

[The_Machine]

The guy does shafts all day long, he is set up for this kind of stuff and has jigs to do just this.

LOL, like sex swings?

Just trying to save money. I've shortened and rewelded a halfshaft before with no noticeable wobble. I think theo has also.

 

[CKC & Dad]

I am kind of falling into the end of the middle of something here. But I wanted to ask why you guysa were spending so much time trying to work out the Ackerman and bump steer issues. I have spent a lot of time in the circle track world and I know guys who are local track champions that don't try to solve all of these issues to the extent you guys seem to be. The basic problems of Ackerman and bump steer are this- Ackerman as it relates to real world steering is really just measuring the difference in the angle of one tire to the other when you turn. In other words they have different turning radii. Bump steer really comes into play in that as your suspension travels it will turn the wheel, not the steering wheel, a little. I cannot see it affecting you very much on an off road cart.

 

[Bill CNC]

I am kind of falling into the end of the middle of something here. But I wanted to ask why you guysa were spending so much time trying to work out the Ackerman and bump steer issues. I have spent a lot of time in the circle track world and I know guys who are local track champions that don't try to solve all of these issues to the extent you guys seem to be. The basic problems of Ackerman and bump steer are this- Ackerman as it relates to real world steering is really just measuring the difference in the angle of one tire to the other when you turn. In other words they have different turning radii. Bump steer really comes into play in that as your suspension travels it will turn the wheel, not the steering wheel, a little. I cannot see it affecting you very much on an off road cart.

While I can only speak for myself, ... To be honest with you, ... I probably wouldn't have known about the Bumpsteer or the Ackerman effects if it bit me on the a$$.

I just wanted it to be fixed "IF" there was a potential problem and it has ill effects overall. What I do know is, ... I just make things, and I love doing it. I have been making things for many, many years. In fact, ... 98% of the the stuff I make, it's not mine, so when it is mine, I hold the same standards as if it were for a client of mine.

I get paid to make things and I enjoy the hell out of it. I'm also a sucker for a puzzle that is just begging to be solved and it seems the more confusion, ... the more I want to solve the problem. I was told that there would or could be a problem so that's all the excuse I need for that little light bulb in my head, ... and I spring into the problem solving mode. Why, ... I just don't know. ut:

I go to work and then I come home and do the exact same thing, ... make things, it's what I do best.

 

[dpaxson]

if eliminating bump steer is as simple as aligning the pivot points of the tie rods and the suspension pivots, why not just do it. i have to agree that ackerman isn't going to have much of an effect on loose surfaces like an offroad kart would be on. i would worry more about that on an on road kart

 

[theo]

You could be right CKC, but the race is usually short. I know when I go out it could be 3 - 4 hrs. and if the steering is off and or the suspension not designed correctly you will feel it.

 

[CKC & Dad]

These ackerman and bump steer issues are not necessarily problems, mistakes, or things which automatically need fixing. It helps to understand them because every time you improve one, you generally will change another. But you cannot and do not want theoretical symmetry ie perfection, in all of them, because that is not what makes good handling. The problem comes i in that you don't want perfect ackerman. You want your tires to have different turning angles, because they take turns at different radii. If you have perfectly symmetric steering then you will scrub one tire when you turn. So the closer you get it to symmetrical, the further you get from perfect. You can't really get rid of bump steer, AND ackerman, AND have neutral camber, caster, and toe. If I had to set it up I would give it Negative Camber, Neutral Caster, Try to control bump steer and let the Ackerman work itself out. Positive camber will cause it to push in turns, and I would think that you are going to want it to be loose. Just to clarify something-Bump steer cannot be felt in the steering. Bump steer is the action that causes the steering to turn without input from the steering. your wheel, not the steering wheel, turns some as it travels through the suspension arc, because of the changing geometry of the pitman arm, tie rod, and a-arms, (which it will) then that's the bump steer.

 

[theo]

CKC, how would you start out setting up suspension for off road? You learn something new every day.

 

[The_Machine]

You can't feel bump-steer? Depends on the circumstance. If you hit a bump hard with your left wheel and have not worked bump-steer out, it will twitch your entire vehicle off course. If you're hitting a speed bump with both wheels at once, you may not feel it, but your rubber will.

Ackermann in my opinion, is very important on off road vehicles built for navigating the tight loose corners you'll find on most atv tracks in the woods or desert, especially when you don't have reverse gear.

Bill, in late december I went to San Diego/Escondido and made quite a few trips around the area, even to see the Salton Sea. There was a nice ATV riding area out there just before Salton Sea. IF you haven't been there you should check it out when completing your project. it looked as to be ran by bearau of land management. (name?)

 

[CKC & Dad]

Excellent article on Ackerman Steering. Written for R/C cars, but very easy to understand.

Machine I am not saying you don't need ackerman steering. I am saying, you don't want to get rid of it. I haven't followed all of the posts on this thread, I tried to but I might have missed some. As for the Bump Steer. I understand what you are saying, and I'm not trying to argue, I'm just saying that by definition, you have no input or feel of bump steer, because it is the turning of the steering axle with no input from or change in the steering gear. You might want to minimize it or not, depends on the direction of the steer and how bad it is. You wouldn't want to get rid of it at the expense of screwing up the rest of your steering geometry.Either way, I wasn't trying to disagree with anyone really. I was just wondering why everyone was spending so much time on it, on a cart. If he takes all of the advice he's gotten, he should have a (mostly) good handling cart.

http://www.rc-truckncar-tuning.com/ackerman.html

 

[CKC & Dad]

CKC, how would you start out setting up suspension for off road? You learn something new every day.

I'm still thinking on that actually. Starting a suspension from scratch and using equal length a-arms is a new one on me, and opens up a lot of possibilities, I haven't had available to me. I know what I want my end results to be, Just thinking on how I would get them. I know That I would put in some ackerman, I know that I want negative camber to loosen up the rear-end. I don't know that I would be able to get the bump steer out as much as some would like and still get the other handling I want. I am not even sure that I would want equal length a-arms. But now that I shot my mouth off about it, I think I am going to to go figure out exactly what I would want and how I would get it there.

 

[mkuivama]

I haven't thought the bump-steer problem at all until now I read the whole thread.
SO, I bought years ago 11" rack and pinion. I have assumed that I can use this in my arachnid with no problems. Now I started to think what mods I have to make on suspension block to avoid bump-steer problems?

More width? With 11" steering rack the suspension block would be quite big and a-arms short? (if shortened to compensate block width). If I have undestand what I've read, rack's joints should be aligned with suspension pivots. According to that, my suspension block should be scretched from 5" to 8"
Or should I start looking 8" steering rack..... Any good ideas? I would use this rack if possible.. is it?

 

[Wobbly]

I haven't thought the bump-steer problem at all until now I read the whole thread.
SO, I bought years ago 11" rack and pinion. I have assumed that I can use this in my arachnid with no problems. Now I started to think what mods I have to make on suspension block to avoid bump-steer problems?

More width? With 11" steering rack the suspension block would be quite big and a-arms short? (if shortened to compensate block width). If I have undestand what I've read, rack's joints should be aligned with suspension pivots. According to that, my suspension block should be scretched from 5" to 8"
Or should I start looking 8" steering rack..... Any good ideas? I would use this rack if possible.. is it?

If you stick to the plans then you need an 8" rack. I didn't understand the principles of the front suspension set up until it was too late and made my suspension block too wide. If you decide to go with an 8" rack, I'll gladly buy the 11" rack from you as thats what I need to make mine work

 

[mkuivama]

I'll gladly buy the 11" rack from you as thats what I need to make mine work

I'll keep this on mind

What is width of your block and what made you to widen it?

 

[Wobbly]

I made my block 8 1/4" wide as this was the right size for the steering rack that I had bought to fit. One of the guys on here pointed out that it is much to wide to work, ie the steering rack joints don't align with the suspension pivots. I didn't understand the theory about this and things like bumpsteer until after I had welded my frame up. Have a look in my thread UK Arachnid build to see the problems with my rack.

 

[mkuivama]

Has anyone else done CAD modelling of the Arachnid? I started to modelling the front end just to make sure that everything is going to fit in there. I usually draw these things first with CAD before rush cutting some metal and after that noticing pieces won't fit each other (I have sure done these kind of mistakes a lot )
Before I can make the whole 3D model of the front end, I need to buy rest of the steering components. After that I can do some kinematic inspections on screen.

 

[Wobbly]

Nice drawing. I always thought the top brace for the shocks looks a little weak, I think a solid top piece would be better.

 

[Bill CNC]

Hi Guy's,

I have still been working out the rear end and I think I have it all worked out. I will be heading off to the junk yard to grab a couple of parts from a few 1985 Toyota Tercels.

Such as the short side halfshafts, front steering knuckles, rotors and the front brake system.

I am 95% sure I will be using the TT500 engine so Obviously I cannot use any stock drive chain or sprockets for a kart. Do you guys think the stock chain and sprockets will work for the kart?

The sprocket ratios are as follows;

TT 500, ... Front sprocket 15 tooth, Rear sprocket 50 tooth = 3.33

XT 500, ... Front sprocket 16 tooth, Rear sprocket 44 tooth = 2.75

Or, ... If you think it could be different, ... here is a chart to chose from;

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[redsox985]

I'd suggest gearing it lower than the original bike because your buggy will be heavier than the bike for which the motor was designed to haul around. This would eliminate the extra strain on the motor caused by gearing it equal to the original final drive ratio.