George,
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Do when you say "raised and lowered" do you mean so that in the raised position the tripod will roll and in the lowered position the tripod feet will contact the ground?
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That is a huge range of motion, especially if you have decent (needed to traverse rough ground) sized wheels. Like four to eight inches.
And given the weight of the tripod you'd need something in the design to give you the mechanical advantage needed to move the wheels with the load (mount+telescope) present.
And to avoid tipping you'd ideally want them all to raise and lower in sync over that kind of range of motion (4 to 8 inches). Or to be able to move the individual wheels up and down in small increments so you could work your way around the tripod, raising and lowering the tripod incrementally.
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I think this is why George Cushing couldn't find any.
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The usual solution is to make/buy what is called a tripod dolly (JMI makes what are known as "Wheeley Bars") that have jack screws (with pads to spread the load) to slightly raise the wheels off the ground.
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If you are handy with working with metal (nuts and bolts or even welding) you can readily make one. Otherwise, spend the money. Or make something out of plywood.
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The advantage of building your own is you can use proper jack screws (it is a special square section Acme thread). The commercial astro-specific models use a standard, triangular, National Coarse thread which, over time, will strip under the load of going up and down. I know this because I maintain the Wheeley Bars our local Park District has. And whenever I set it up for them I place metal pucks (they now sell as an upgrade pads but that reduces the ground clearance) under the screws so they don't punch thru the blacktop. And we replaced the (cheaper) pneumatic (billed as providing a "soft ride") tires with marginally more expensive solid ones that never need inflating and actually give a better ride.
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Best regards,
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Mark Christensen
