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Learning how to build Lotus Seven replicas...together!
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PostPosted: January 8, 2019, 2:52 pm 
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You explained it pretty well, but your MS paint skills really clarified it for me! :lol:

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PostPosted: January 9, 2019, 7:39 am 
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You could maybe use something like a with rope boat steering. Have a cable wrapped around a shaft so it pulls in both directions. Use threaded end mounts and a very stout cable and you should be able to eliminate all slack. Your design would be similar to what you show with a rod. It would have the benefit of no notching as the sprockets mesh. You would likely need to anchor the center of the cable on the spool

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PostPosted: January 10, 2019, 12:54 am 
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Joined: July 4, 2006, 5:40 pm
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Location: Novato, CA
I built a scaled down Locost with chain steering. Worked great, which surprised me a bit. I also expected play and notchiness, but I built in an adjustment using Heim joints and the steering was smooth and direct.


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PostPosted: January 10, 2019, 4:11 am 
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nocones, yeah, I was trying to think of a way to wrap the chain around a full 360+ on some sort of mandrel, like I think you are saying with a cable. It would be a pretty nasty helical sprocket thing for sure. I think the idlers could be eliminated from my design then since you could start wrapping the cable on the bottom side so the cable would be straight with the tube. It would be flipped over to steer the right direction. Hmmm...I guess if you attached the chain to the mandrel in the single spot, it wouldn't need teeth. Not sure if that would be notchy. I'd be a little worried about a cable fraying and fatiguing on the mandrel.

nick47, I was thinking about something like that. I like your design, that is a hefty chain tensioner! A lot of RC cars have a "servo horn" directly connecting to the tie rods. On RC cars that can be a good way to adjust ackermann, by mounting the tie rods higher or lower and closer or further apart. Only thing I would worry about is bump steer since the tie rods are so long.

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PostPosted: January 10, 2019, 7:33 am 
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Joined: December 18, 2010, 3:29 pm
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Would this steer the wheels? Yep. Is it clever and ingenious? Yep. Would it feel good in a steering system? No.

(corporate required GM disclaimer) I've worked as an integration engineer at GM for 10+yrs so I get the unique opportunity to do really well controlled A to B experiments on every component related to ride, handling, steering, and many other factors, hopefully this is helpful feedback and not just a knock on your really clever mechanical device.

Steering system stiffness is absolutely critical at both the front and rear of a vehicle (called toe stiffness in the rear). The kind of deflections that you can feel as a human driver are pretty mind blowing, thousands of an inch to be certain. Yes, thousands, even going through a tire contact patch that moves around a bunch. One thing I learn at work every day is that humans are truly amazing.

Look at the evolution of intermediate shafts on modern cars (the shaft from the column to the rack with joints and sliders for crash). As the industry has learned how critical the system stiffness is the i shafts have grown from rag jointed, slip fit, 3/4"DD shaft to monstrous >1" splined shafts with special coatings to engage tighter splines and huge u-joints. Some cars still have dampers but a lot have ditched those as well. Lots of manufacturers are bragging about steering system stiffness increases of > 1000% lately and it's because you can feel it directly.

That need for stiffness goes right on out through the rack and into the knuckle. Deflection on a cast iron knuckle is a real thing that you can feel in an A to B test of two differing components, that's how stiff a system we're talking about.

So, the chain, even in tension, not to mention the sprocket components, is really going to let you down on feel and handling. If it were a perfect system with zero slack it would still not be stiff enough due to chain stretch. Given a zero slack chain system would have huge friction some slack would be required and that would completely ruin it. If you don't care about feel and handling why on earth are you building a car like this? It's basically a hugely compromised car just to get you road feel and good steering!

Alex


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PostPosted: January 10, 2019, 9:05 am 
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Joined: September 22, 2005, 8:12 am
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Location: 4AGE in S.E. Michigan
Alex hit the nail on the head! :cheers:
I can personally tell you that I could fell .003" play in one inner tie rod, in the my steering system. I'll say it again, unless you are only going less then 35MPH, you need a REAL steering system.
Your life just might depend on it. These cars are made to drive, you need to have confidence in wheel placement.
DaveW


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PostPosted: January 10, 2019, 6:00 pm 
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Joined: April 19, 2018, 2:02 am
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Alex, thanks for the info. I do have a cheap Ebay rack ordered which will need to be extended. Maybe if I get time I'm make the chain version and see if it feels as weird as you say.

Good info!

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