Tag Archives: steering

Still thinking about improvements

Yep, mind still churning about the Sprint-T. This time I’m thinking about how to mount the steering box.

There are two orientations the box can take and still turn the front tires in the correct direction as commanded by the steering wheel: the kit orientation was pitman arm pointed forward controlling a steering arm pointed back, or the OE orientation of the pitman arm pointed back controlling steering arms pointed forward. The problem I’m trying to solve is making room for the engine and radiator and also sneaking the steering shaft from the steering wheel to the box around the radiator without hanging out in the breeze.

Aero is not critical but it is important for freeway fuel economy. I mean there is going to be a lot of junk hanging in the breeze simply because T-Bucket, but that’s still not an impediment to decent but not fantastic aero. For examples of decent aero and exposed wheels see https://www.google.com/search?rlz=1C1CHBF_enUS809US809&sxsrf=ALeKk02olFWp4zhsrQs1tNKIuVFdAMTU0A:1602022917053&source=univ&tbm=isch&q=images+lakester+racers&sa=X&ved=2ahUKEwiP3JG3gKHsAhUEKawKHdSNBDoQjJkEegQIChAB&biw=1517&bih=694 “lakester racers” that are required to have exposed wheels. The old belly tank racers are a good example of that.

Anyway, I have been thinking about it and there is a 1½” gap under the radiator because it sits on top of the frame that would be good to sneak the steering shaft through without hanging out in the breeze. The closest to a problem would be clearance for the U-joints to turn that close to the bellypan. And something to block the air from going under the radiator, but that would be a great place to mount the bearing that guides the steering shaft under the radiator. I really need to find out how big are those U-joints that connect to the steering shaft. I may need to make a relief bump in the pan for the U-joints to swing, but if I need one it wouldn’t be very big.

The other problem is properly bracing the top of the box to prevent it from rotating in reaction to the forces from the pitman arm hanging off the bottom of the box. Side to side is easy, just weld the mount to the top of the frame rail. Boom, you’re done! The other is a bit more tricky, because there has to be something to brace against to do the top part of the mount. On the kit the mount welds to the side of the frame rail, so the twisting moment from the force through the pitman arm is close to zero and is resisted easily by the sheer mass of the frame rail and the extremely short arm the force has to act through. It’s basically all sideways against the rail for the kit mount. Now there is another frame rail to run a brace from on the same side of the frame, plus its mirror on the other side of the frame for slightly better angle on the force. Which brings us to the actual point of the post, the reason why I mentioned the OE orientation of the steering box: I’m thinking of attaching the steering box mount to the front bulkhead with the drag link under the steering shaft and ahead of the axle.

If I move the box in front of the axle, then I could brace the top of the box against the front bulkhead at whatever place is convenient to mount the brace. The bottom of the mounting bracket still mounts to the frame extension that also acts as the mount for the panhard rod. As a point of fact, that was the original reason for the frame extension in the first place, someplace to mount the frame end of the panhard rod so the panhard rod could be the same length and parallel to the drag link for no bump steer. And now it looks like I only need to make a slight adjustment to the front of this extension to mount the steering box, because there are braces from the bulkhead in two directions to locate the front and triangulate it in two dimensions, and the vertical one can be used as the actual place to weld the mount.

So these are the pros and cons of moving the steering box in front of the axle:
Pros: simplifies the top mount of the box, lighter, gets the drag link completely away from interfering with any suspension links.
Cons: puts weight in front of the axle, increases to moment resisting changes in direction, susceptible to damage when hitting curbs while parking.

And that last one is only mentioned because it is a slight possibility, not because it’s likely to happen, and a curved skid plate in front of the box will prevent even the slight possibility from coming true. Or it might not even be a possibility because of how high the box has to be mounted for the drag link to be level, especially if I don’t drop the drag link at the steering arm on the spindle. I think mounting the drag link to the top of the pitman arm and the bottom of the steering arm will give enough offset to prevent binding. This will raise the bottom of the box to about 9-9½:” above ground with the street tires. Considering the frame is about 6″ above ground with the street tires that would be a very tall and vertical curb to hit the steering box. It would have to be a really tall and narrow parking bumper that didn’t block either front tire, a freak of parking bumpers.

And I still haven’t gotten this editor down pat, because I have no idea how to insert text to a link and not leave the URL all over the page, so I’m going to quit fighting it and publish the post.

Still thinking, but more specifically

Relax, I’m thinking about the steering on the Sprint-T, not doomsday devices. Besides doomsday devices are a one and done thing, and unlike most mad scientists (we actually prefer the term aggravated engineers, thank’ewverra’much) I actually thought ahead and know if I blow up the world I lose my place to sleep at night, lacking a means of space travel. Besides have you checked the price of plutonium lately? No, thanks, I’m out of the doomsday device business.

So, back to the main topic, I’m pricing the specialty metal to make the steering arm that makes the steering quicker, and it’s super expensive for what I need. I mean in absolute terms it’s not much, it’s just I have to buy 4 linear feet of stock to make a part that will be just over 6″ long finished. And that 4 feet of stock costs $33, so most of the stock is wasted unless I find something else that needs to be that strong.

Cutting the stock to the length I need for the steering arm, henceforth to be named “the part” in this doc, I need to cut about 8″ to make the part. The part needs to have an arm that is 33/16” from the spindle axis to center of the hole for the drag link, but there is the attachment hole to the spindle on the other side of the axis from the drag link hole to also account for, plus the gussets needed to prevent flex in the part because the load will be off-axis no matter how I bolt up the drag link to the part. And dropping the drag link down to clear the suspension links will make the leverage off-axis greater causing more flex in the system. Therefore the part needs to be made from heavy stock, and gusseted, to keep the flex as low as possible.

I don’t think there will be any detectable flex in normal driving, but autocross and SCCA Solo Racing are not “normal” and put the steering under about as high a stress as you can get without going off-pavement or banging curbs. And now that I think of it there is a slight possibility of banging an actual concrete vertical-faced curb doing that, so I guess that means another gusset. The plan is now to have a gusset on either side of the bolts holding the part to the spindle, because curbs. Anyway, this stock is right at the limits of my welding equipment and cutting tools, so if I need to use heavier stock to make this part I will have to farm the part out to a professional with better equipment.

Just a passing note, I made the suggestion on Twitter that if @realDonaldTrump refuses to vacate the White House as he claims he will, then he should be treated like he says protestors against police brutality should be treated, but obviously in fewer characters because: Twitter. I’m now locked out of reading Twitter until I apologize by taking the tweet down, which obviously I will do as soon as Agent Orange apologizes for saying the same thing about protestors or when pigs fly. I don’t care, either one is equally likely. I don’t really need Twitter, it was just something to kill time with.

And with that act of defiance I’ma put this thing to bed.

It’s finally here!

And by “It” I mean the steering box that has been on backorder since early June because of the Stupid Virus. I’m changing the name because the existence of COVID19 seems to make people stupid, besides what it did to my employer and the GOP. Anywho, this is a picture of it below.
Steering box, remotes and bumpersticker for scale

I’m keeping it in the plastic bag for the nonce, having learned my lesson about surface corrosion from the spindles I bought a few years ago. I may be slow, but I’m not stupid. And FYI that thing is HEAVY! no, it’s HEAVY! That tiny chunk of metal has to be over 15 pounds (6.8 Kg) which brings up the question of why they still use iron in the main casting? Probably because steel or iron is cheaper than aluminum, but then the question is why it isn’t an option since this is a repop for a part that has been out of production for five decades, the Vega stopping its run in 1977, and presumably GM stopping production of replacement parts shortly after.

And it turns out that it was fortunate I bought the Pitman arm for the 5/8” heim joint, because this was shipped with the arm for the Ford taper tie rod end. There is something I can use the extra Pitman arm for, by placing the two arms side by side with the ends reversed I can get an fairly accurate center-to-center distance to use in making the steering arm to mount on the spindle. I mentioned this in a post a while back, this post to be precise, that I can use the steering arm to change effective steering ratio without adding any weight. In the post I was thinking that since I was using the steering arm at the spindle instead of a steering quickener the difference between the arm and the quickener box was the amount of weight I was saving, but in reality the arm at the spindle has to be there regardless of what I do at the box, so I save the entire weight of the steering quickener when I go with the shortened steering arm on the spindle, plus the weight loss of using a shorter arm instead of the one normally used. I think what I was thinking about was there’s no need to use a steering arm at the spindle because there is an extended bolt to attach the drag link on the arms I already have, except that unless I move the steering box further behind the axle the drag link will hit the tie rod, and I don’t have that problem with the steering arm for the drag link mounted to the lower holes of the spindle and the steering arms for the tie rod mounted to the upper holes of the spindles, especially if I use the extended bolt on the drag link arm to drop the drag link even further from the suspension links.

Now I just need to figure out the load path from the steering box mount that was in the kit with the box, to the rest of the frame. For the application the kit was made for the box mount welds directly to the frame rail of a ’23-34 Ford. This is going to be a bit more complicated as the frame rails are either over a foot above the box or several inches below it, and beyond just holding the box in a certain place in space relative to the frame and axle there are significant forces that will be applied to the mount, off axis forces at that. That means either the mount will be very heavy and apply torsion to the frame tube, or the mount will have to be braced from the other side of the frame. Since there’s nothing in the way of the mount going to the other side of the frame I’m going with that unless and until something else has to be put in the space between the radiator and the front axle. The radiator will be mounted slightly to the right to make the nose symmetrical and keep everything under cover, but since the tie rod and the pitman arm are both going to have to extend beyond the side of the nose it’s actually a moot point. The steering will come out of the left side of the nose because it has to, the Pitman arm will swing to the left further than the confines of the nose at full lock anyway, even the reduced amount of lock with the shorter steering arm at the spindle. The fun part now is how do I adjust the internal stops in the box to prevent the steering linkage from getting damaged by over travel caused by the steering box? Without internal stops the drag link could be overcentered and the car be unable to return to center when the steering wheel is turned the other way. Or I could use a stop on the axle that hits something on the spindle to prevent turning far enough to the right get to that point. Turning to the left the drag link hits the back of the spindle before getting to the over center point, I could use a stop on the axle that stops the spindle at the same point of rotation in the opposite direction. Hitting those stops would generate substantial forces on the steering mount, getting back to the original topic of internal stops in the steering box and the steering box mount. There is also the point that at full lock the tires will be almost perpendicular to the axis of the car. This would be useful for moving the front of the car sideways when not running, but I don’t see any practical application for this much steering angle.

And here we see yet another example of how I think, wandering here there and everywhere as I solve a problem. I’m not sure which part of my mental problems this typifies, but I know this isn’t my PTSD or depression at work, the only mental illnesses I have that I can’t blame this thinking style on. Maybe my ADHD, yes this is undoubtedly what happens when genius meets butterflies and squirrels. And since I just noticed my word count has tripped the 1K mark for this post I think this is a good spot to put this post to bed.

Still thinking about the steering on the Sprint-T

I have been told that thinking is a bad thing for me to do, and bad things come from it. But someone sent me a link to a rack and pinion steering system that was supposed to replace a Vega steering box and I got started thinking, did it really? From the initial blurb it certainly fit in place of a Vega box, but did it function like a Vega box?

Note to Siouxy, this can be used for advanced adult education in math.

First to get apples to apples we needed to get common units to determine functionality. The Vega box is spec’ed in box ratio and turns lock-to-lock, the rack and pinion is spec’ed in turns lock to lock and throw. So we have to figure out the throw of the Vega box, which boils down to the chord of the arc swept by the Pittman arm going from lock to lock. But first we have to “cipher” the angle of that arc, or convert ratio and turns lock to lock into the angle swept by the steering arm.

The Vega box has a ratio of 20:1 or 20 turns of the input shaft equal one turn of the steering output shaft, and 5 turns lock to lock for the input shaft. Reducing the fraction gives us 1:4 or the steering output shaft has turned ¼ of the way around, or 90°.

The formula for the length of a chord when you know the angle it sweeps is 2(sin(½Θ)*r) or in English 2 times the quantity the sine of half the angle times the radius of the circle. In this example we already knew the radius of the circle as the center to center distance of the Pittman arm, is 6.25″, and the angle as 90°, so half the angle is 45° and the sine of 45° I know as 0.707 from our friend Pythagoras and his theorem as 1/√2. So throwing all the numbers and functions together in the right order and rounding to the most significant digit we get a throw of 8.84″ for the Vega box and the Pittman arm that comes in the kit.

So now we have common units with which to compare the rack and pinion to the Vega box it’s supposed to replace. From the web page we know 3.75 turns lock-to-lock and total stroke of 5.25”. Right away we can see that while there aren’t as many turns lock to lock, it doesn’t move the front wheels as far as the Vega box, and comparing the throws and the turns lock to lock as a ratio we find the Vega box is 26% quicker than the rack and pinion in a head to head apples to apples contest, and gets 68% more steering angle at full lock. Now which one wins depends on what your criteria for the system in the car are, but for the Sprint-T application where the idea is to get the wheels changing direction as quickly as possible so the car can go fast on a slalom or get around a single pylon turn as quickly as possible having a greater steering angle at the wheels is better. Corollary to that is getting to that angle faster is also better. Conclusion : I’m not buying the rack and pinion kit, even if it was cheaper instead of about $80 more. I get more steering angle quicker for less money, and adding the steering quickener and the electric power steering assist just builds on that.