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sidecar wheel position Answered

i've looked up sidecars on google and found lots of information for sidecars on vehicles that have front steering only in which case the sidecar wheel tends to be positioned parallel to somewhere between the midpoint and the rear of the vehicle, however if the vehicle has both front and rear steering would the sidecar wheel be best positioned parallel to the exact midpoint or not?

9 Replies

Toga_Dan (author)2017-12-16

with a motorcycle, and 1 wheel steering, if the sidecar wheel is not in line w. The back wheel, there will be tire scrubbing ( sideways sliding). With yer skateboard, if front and back steer equally, then the sidecar wheel should be at midpoint.

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gmoon (author)2017-12-16

Seems like it's very implementation dependent. A skateboard has tilt designed into the steering (like some three-wheel motorcycles) so that would have a non-trivial effect. Would your design not tilt due to the side car?

My cousin, BTW, owns a Ural sidecar motorcycle. Both back wheel (the bike and the sidecar wheel) are drive wheels. They are locked together without a differential -- but the dang thing still works fine. I think the newer models can on-the-fly switch between one and two-wheel drive...

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ambientvoid (author)gmoon2017-12-16

the points on my doodle marked as 'pivot' will be a bolt through the sidecar arm and into a block mounted over each skate truck, just loose enough to allow the skateboard to tilt but let the sidecar remain nearly perfectly level on the ground. i made a crappy scale model (think bits of card and cocktail sticks ¬¬) that showed that there should be a near imperceptible tilt to the sidecar in hard turns but considering my balance i probably will have tipped off the side well before that :D

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Downunder35m (author)2017-12-15

A sidecar construction usuallyonly has three wheels with one for steering.
How do you want to keep it stable with two turning wheels?
You change the center of the circle and the fulcrum point depending on the steering position...
I don' see it working...

On a normal sidecar the wheel is positioned to give maximum support while turning to the side the sidecar is mounted.
Too far in the front and the backwheel lifts, too far in the back and the same happens, both mean a lot of damage to the bike and people involved.
Also helps to know the weight distribution between front and rear wheel.

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ambientvoid (author)Downunder35m2017-12-15

in this instance it'll be a sidecar style platform attached to a longboard skateboard carrying an 18kg to 20kg load spread out as evenly as possible, effectively 2 parallel skateboards with a hinge/pivot where it attaches to the skateboard to let the skateboard lean/steer. my own weight will be spread across the majority of the skateboards length.

i've previously used an especially long board with the load on the rear and then a conventional trailer on a shorter board, in both instances i caused damage to the load by accidentally kicking it when i was pushing hard so it seemed worth trying to mount the load on the opposite side of the board to my kicking side. a shorter and slightly wider setup will also be easier to get on public transport then the old really long one when i need to, and hopefully will turn better with the shorter wheelbase...

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Downunder35m (author)ambientvoid2017-12-15

Details make so such a difference... ;)
I experimented with similar things when I was less than half my age and skateboarding was just becoming a thing.
When I spread the idea of a "shopping basket" attached to the baord some had their usual fun while others started thinking with me.
We never got the design to a fully working stage due to some problems.
I will list them so you can avoid them:
1. Fixed hinge...
You don't want a rock solid attachment for your pivot mechanism.
When you steer the board a fixed pivot point will cause very uneven steering.
Our most successful connection was made with an air hose connector so it can twist that was mounted to a ring nut to allow for sideways movement as well as some up and down for the pivot.
Getting two springs either side to work correctly to stablise it all was what killed the mood.
But mind you, we were very young and only had the most basic tools available...
2. Load swing...
If the board ever started shaking due to too high speeds, worn rubbers or whatever then the attached board often caused fatal instabilities.
You want to create your pivot mechanism so it allows for a certain amount of freedom for your board.
3. Vibrations...
This was our actual problem back in the day.
With really good connections everywhere and allnice and solid the laminated sections of the board were under too much stress.
Sp only way out would have been to use a mounting plate right over the back axle but that would have made the board useless for any fun use.

On a long board you certainly have more options an with modern glues it would even be possible to avoid drilling holes into the board.
If you can tolerate it than I still think the back axle is the best connection point.
And nothing against a sidecar but I think you find in the end that a longer connection between board and load and the load behind you makes life easier.

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ambientvoid (author)Downunder35m2017-12-16

so i made a little pic of roughly what i have in mind. a one piece U shaped bent tube frame with a plywood sheet bolted (or zip tied) to it attached to the board on each end by mounting a small block on top of each truck baseplate with a hole through them lengthways for a bolt and washers to let the board swivel/lean. i figure mounting the arms at both ends right in the middle will reduce the strain on the board steering and stop the sidecar from tilting/flopping as much as possible. it also means i'll be able to remove the board from the sidecar fairly easily and won't have pointy bits sticking out each end if i want to use it separately.

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ambientvoid (author)Downunder35m2017-12-15

it was this video that got me thinking about it even working in the first place:

my side platform would need to be longer, and i'd rather have a single fixed soft sidecar wheel than use hard casters on the probably rougher roads i'd be using it on...

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