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 Post subject: Roller Chain Steering?
PostPosted: January 5, 2019, 3:54 am 
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I'm building a BEC and am looking for a steering rack. Somewhere along the way I went down the rabbit hole and started thinking about some sort of roller chain setup. I found a Nexen roller pinion thing for CNC linear motion.

Not sure what the upside or downside would be. I'm thinking the upside would be it might be easy to build yourself, downside might be that the chain stretches. I can think of a couple configurations. One being similar to how belt drives work on 3D printers.

Thoughts?

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PostPosted: January 5, 2019, 10:00 am 
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The roller chain is the pinion, like you mentioned. The rack is a linear sprocket so no chain to stretch.

The primary issue I see with wide engines in narrow cars is the pinion ends up very close laterally to the inner pivot, leaving little room for rack travel so center tapped racks with a fabricated plate "center link" make a lot of sense.

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PostPosted: January 5, 2019, 10:04 am 
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John
Get a real steering rack. You do not want any play in your steering system. Unless you use large sprockets, you get a notchy motion from each tooth as it loads and unloads.
You can find used English sport car racks on E-bay, for the price of 2 sprockets and a chain.
The rack shim kit are peanuts, to bring them back to factory spec. Plus the rack can be shortened without any welding. The only machining new threads on one end.
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PostPosted: January 5, 2019, 12:45 pm 
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Yeah, it was late and my mind was wandering, I will probably get a conventional rack, just wondered if anyone else had thought of or tried this.

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PostPosted: January 5, 2019, 7:30 pm 
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John, you are not talking about traditional sprockets and chain right?

https://www.nexengroup.com/nxn/products ... on+System#

I don't know how cost effective it would be for the amount of work involved for the housing.

Some of the english racks I've found information on did not have a threaded end for a removable ball socket but my spitfire does. I believe those were mg racks. If you have enough room between the pinion and the inner pivot for the necessary travel, it is hard to beat the value. The rack is not hardened so that helps too. Just make sure the rack you get is not bent. It will have inconsistent resistance to turning the pinion along the bent area and the housing diameter is very small, so it is easily bent.

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PostPosted: January 6, 2019, 12:55 pm 
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Miatav8,MstrASE,A&P,F wrote:
Some of the english racks I've found information on did not have a threaded end for a removable ball socket but my spitfire does.


The Cortina and Capri racks were like that. They had a soft steel blind pin driven into a hole drilled between the socket cup and the jam nut, which had to be drilled out to adjust the tierod slack or replace the inside bits.

I never bothered drilling for a new pin after taking one apart, relying on torque to hold the jam nut, and figuring if the cup started to back off the slack in the steering would be very obvious long before it came off the rack. YMMV, etc.


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PostPosted: January 6, 2019, 7:10 pm 
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This is what I came up with the parts I had laying around. Then a housing of two main plates and spacers would hold everything together.

It's probably too quick though, it's 2/3 of a turn lock to lock (4" travel). With an 8 tooth pinion it would be one turn lock to lock. The two idlers would be fixed and the center pinion would need an adjustment to take up chain slop/set tension. Or one end of the chain could be attached to a stiff spring. Idlers could be smaller.

The #40 chain says about 4000 lbs max strength. Going to a smaller pitch chain would allow a smaller pinion.

I don't want my formula car to look like it's got tractor parts on it, but I think it would work. I could laminate the outside with carbon fiber to throw off the doubters. :wink:


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PostPosted: January 7, 2019, 7:20 am 
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I guess we are not talking about the roller pinion anymore.

Nobody doubts sprockets will work, it’s just a question of how well for the extra effort. Both sides need to be tight (consider the inside wheel in a turn) so I don’t think a spring for the slack side is going to work well. Any slack is sort of a built in anti-ackermann. I think chain steering has come up before and not just for quickeners.

Just stack a 3:1 reduction on the front away from the engine. Center drive sprocket then use the reduction to put the pinion input where you need it. This way the pinion location and tie rod pivot location are isolated and don’t limit rack travel. I look forward to seeing what you come up with. :cheers:

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PostPosted: January 7, 2019, 5:45 pm 
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I'm essentially using the chain as a gear rack mounted to the tie rod tube, but there's extra length to go over the top of the drive sprocket for more engagement. The chain would be entirely inside the housing, the only parts sticking out would be the tie rod tube (1" square tube in the above picture) and the input shaft to the pinion. The chain ends would be bolted or welded to the tie rod tube. And the pinion could be in a vertical slot to adjust chain tension. The idlers are there to keep the chain in a straight line to keep chain tension constant through it's travel. If the chain were angled it would tighten and loosen through its' travel.

With the amount of chain engagement I don't think there should be any "notchyness".

I've got some UHMW poly laying around that would make good bearing surfaces for the tie rod tube.

I've not been able to find a reasonably priced rack that I like. But then I may not be looking in the right spot. This would be a super cool rack, but not $670 cool. http://www.kaztechnologies.com/fsae/steering-rack/ I suppose anything that has FSAE in it's name is 10x overpriced.

Needs to be center input and 21.5" center to center, or there abouts and 4" of travel. Literally I'm used to making things that I could buy, if I have materials laying around the shop. It could be 2am and I need a pulley, I just make one.

It's a long way out before I'll need it, I would prefer to buy something, but not for an arm and a leg, I mean I wouldn't even be able to drive it after that!

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PostPosted: January 7, 2019, 5:56 pm 
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So when you make a turn, one side of the chain is in tension (pulling) and the other end is in compression (pushing) the TRE's? Clarify this for me, I keep picturing trying to push a truck up a hill with a rope. It's just I've never seen a roller chain used in compression.

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PostPosted: January 7, 2019, 6:58 pm 
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It helps to use a rack that uses a common cheap joint.

https://www.ebay.com/itm/RACK-PINION-ST ... ondition=3

Drill the ends for 7/16-20, weld a 7/16 bolt to a ½ tube end, weld a U flange for a rod end on the other end of the tube. Tubes would be around 3 inches long to get you to 21.5. You can use a jamb nut or have flats on the tube. You could also use allen bolts through the center of the tube with a washer welded on the end for the rack side leaving the end open. You could also thread the tube to accept a rod end with an id greater than the allen head. The boots stay where they are and the tubes stock out.

Another method is to run a cross tube 21.5 eye to eye behind the rack, with linear support bearing attached at the rack mounting holes that put the supports about 16 inches apart. Use flat stock to replace the rod ends on the rack spaced 14 inches apart

My experience with these type racks:
viewtopic.php?f=36&t=11384&start=105

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PostPosted: January 7, 2019, 11:33 pm 
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horchoha wrote:
So when you make a turn, one side of the chain is in tension (pulling) and the other end is in compression (pushing) the TRE's? Clarify this for me, I keep picturing trying to push a truck up a hill with a rope. It's just I've never seen a roller chain used in compression.


I know, it's a bit hard to describe, but I hear ya, and maybe here's a better way to visualize.

What I'm calling the "tie rod tube" would be akin to the typical round rack with teeth cut into it. Maybe it would be called a "gear rack".

So imagine just welding a length of chain to my "tie rod tube" all the way along. Now put that into a housing and drive it with a sprocket.

All I'm thinking is only attaching the chain on the ends, putting a bit more chain in to wrap around the sprocket to avoid notchyness.

The idlers are mounted inside the housing and keep the chain tight all the time. Mind you my picture is not the entire rack system. There is no housing pictured.

The "tie rod tube" is the solid piece connecting the actual tie rods. So that will be a solid connection between wheels. If the chain is properly tensioned by the idlers there would be no slop. The idlers will be fixed and I'm thinking the pinion will have a vertical adjustment, which will preload the chain, say to 100 pounds or so.

In my picture if the steering is turned to the right (clockwise) the left end of the "tie rod tube" will be pulled by the chain and move to the right. My car is front steer. Mount it upside down for rear steer.

It works in mockup.

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PostPosted: January 7, 2019, 11:38 pm 
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Miatav8,MstrASE,A&P,F wrote:
It helps to use a rack that uses a common cheap joint.

https://www.ebay.com/itm/RACK-PINION-ST ... ondition=3

Drill the ends for 7/16-20, weld a 7/16 bolt to a ½ tube end, weld a U flange for a rod end on the other end of the tube. Tubes would be around 3 inches long to get you to 21.5. You can use a jamb nut or have flats on the tube. You could also use allen bolts through the center of the tube with a washer welded on the end for the rack side leaving the end open. You could also thread the tube to accept a rod end with an id greater than the allen head. The boots stay where they are and the tubes stock out.

Another method is to run a cross tube 21.5 eye to eye behind the rack, with linear support bearing attached at the rack mounting holes that put the supports about 16 inches apart. Use flat stock to replace the rod ends on the rack spaced 14 inches apart

My experience with these type racks:
https://www.locostusa.com/forums/viewto ... &start=105


That ebay rack doesn't look too bad. It would probably be easier to modify that. I might just grab one to see how feasible it is to extend it to the length I need.

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PostPosted: January 8, 2019, 12:49 am 
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Small Cessna planes, like the 150, 152, 172, use chains and sprockets in the aileron connections to the control yoke which is a system sort of like the steering controls on a car. The system is reliable and without any slack as long as the sprockets and chains are in good shape. I once had to change a sprocket because the bolt hole that fixes the sprocket to the shaft had elongated but that airframe had over 11,000 hours on it.
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PostPosted: January 8, 2019, 7:01 am 
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A picture is so much better than all my words. You can see how straight forward both methods are.


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