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Old 02-18-2018, 09:39 PM   #11 (permalink)
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Quote:
Originally Posted by oil pan 4 View Post
What are you going to be using for a wheel?
I don't think I have ever seen highway service bearings and tire on a caster.
If I understand "Caster" correctly, I'm not using that geometry. I'll be using either a motorcycle wheel, or a standard trailer wheel in one of two configurations:

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Old 02-18-2018, 11:13 PM   #12 (permalink)
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What's your plan for grease seals and bearing preload?
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Old 02-19-2018, 04:15 AM   #13 (permalink)
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I haven't worried about that yet, but I have repacked a trailer wheel bearing before on the road. I would probably use a wheel with sealed lifetime bearings. The trailer is not for cargo, but for aerodynamics, so it will not be heavy.
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Old 02-19-2018, 05:57 AM   #14 (permalink)
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Oh I thought you were eventually going to put stuff in it.
Why not a Reese hitch caddy boat tail caddy?
That way no wheel related problems.
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Old 02-19-2018, 10:06 AM   #15 (permalink)
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The boat tail is too long to hang off the back of my car. It needs to b a trailer.
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Old 02-19-2018, 02:26 PM   #16 (permalink)
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Quote:
Originally Posted by Angel And The Wolf View Post
Why would a two wheel trailer not have this problem?
1) Two wheel trailers have free movement in all three axis. On military equipment where this Roll center difference between trailer and truck can be very severe they use a pintle hitch where the ring is on a swivel(can spin 360)on the Y axis.
2) roll from the tow vehicle is only seen as a change in Direction not a steering input such as in the y-axis lockout causing the tire to roll up on its side / lift one corner of the tire by changing the amount of weight on that section of the tire it changes the diameter / circumference from one side to the other. Somebody correct me if I'm wrong but I think that's why aircraft tires are so balloony, so that when the plane lands with excessive yaw the tires physically getting smaller where it wants to grow and the tires getting physically larger where it wants to shrink the circumference counteracting the tendency to Be a steering input.
The effect should be minimal and only a consideration. Motorcycles do not have to lean but 5 or less to change lanes no steering inputs involved.
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Old 02-19-2018, 10:34 PM   #17 (permalink)
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OK, I think I have it now.The reason I need a single wheel is that my trailer will taper from hatch and bumper profile down to a 12 inch by 12 inch square tail plate, and I need to keep the wheel within that 12 inch transverse dimension. A standard ball hitch presents a problem in that the trailer is all too likely to fall sideways given the least angular change in forward travel. The U-Joint hitch solves this, but introduces lean steer in the wrong direction when the tow vehicle leans to the outside of a turn at speed. I've added servos where the trailer frame ties in to the tow bar to provide a correctional limited number of degrees opposite to the lean, using input from steering angle sensors on the steering arm of the tow vehicle. Properly calibrated, this should lean steer the trailer to track the tow vehicle in turns, rather than trying to steer the trailer (and push the rear of the tow vehicle) outside the turn circle. When the tow vehicle is traveling in a straight line, the servos will hold the trailer straight up, as if the rotational linkage were locked.

What do you think, Gumby?
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Old 02-20-2018, 08:59 AM   #18 (permalink)
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If the trailer has any freedom of movement to roll about its center axis, you're going to get roll-induced steering lift when the trailer gets even a little bit sideways. Next thing you know it's going to be bouncing violently while lurching from side to side. At certain speeds it'll hit its resonant frequency and beat itself to pieces.

You ever see a sport motorcycle suddenly get a bad case of the wobbles? Seriously, google "motorcycle wobbles" and click on any video that comes up. Your trailer is going to do that. You say you want a servo to counter-roll in turns, that could help and maybe you could control it, sorta, and maybe you could install one MOTHER of a steering damper and that would help, but any - ANY play in the linkages means it can hop. It doesn't even have to be play in the linkages, you could develop a hop just from flex in the hardware. And it doesn't need to hop much before it beats the linkages to pieces, cooks the seals in the damper, and then you have a cleanup project by the side of the road.

Somebody said it: there's a reason why the single wheel, two-attachment trailers are a thing.

If you build this thing, shoot video of the testing. I think it will be very educational.
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Old 02-20-2018, 11:00 AM   #19 (permalink)
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Quote:
Originally Posted by elhigh View Post
Somebody said it: there's a reason why the single wheel, two-attachment trailers are a thing.
Even a two attachment system wont contain roll steering. That's why I added the servo controlled counter roll system. And hopping straight up and down with the servos controlling the attitude isn't going to morph into wobble, Those motorcycles don't have a three thousand pound anchor in in front of them holding them vertical. I wish I had the spare change to prove you mistaken, but right now, this is a thought exercise

Last edited by Angel And The Wolf; 02-20-2018 at 11:07 AM..
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Old 02-20-2018, 07:08 PM   #20 (permalink)
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the idea is ok but your going to need a bigger joint the one from a drive shaft is to small to handle the torque from cornering at speed
the force trying to twist a trailer is large think about how stiff a sway bar is

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