NEED HELP - Geometry for Skateboard Truck Design

[drakem4]

Hey everyone!

So I'm trying to design a surf-style skateboarding truck for my electric skateboard.

It is a pivoting design unlike a traditional kingpin.

I've read and heard that other designs have been created so that when the truck is turning, the center of gravity lifts up on the board, so that gravity acts as the "restoring force", and therefore at higher speeds it is more stable.

I've been experimenting with angles on the various components but am having trouble getting it to lift under turning.

https://files.engineering.com/getfi...-4d7d-af57-bf0c0b3f31c2&file=Skate_Trucks.png

Here is a video of what I'm trying to do

https://youtu.be/Vko2VqubfpY

Can anybody help point me in the right direction?
Thank you so much in advance!

 

[3DDave]

I expect that a change in board height won't make very much difference; the change in the bend angle of the rider's knees will far exceed what the suspension on the board can do, and the rider's upper body inertia will damp out any moderate frequency inputs anyway. Most of the skateboard stability is due to that inertia - as the board shifts to the side, the board surface tilts, turning the truck to steer back under the rider.

 

[drakem4]

3DDave thank you for your input!

I think the main consideration for having the boards COG lift under turning is to prevent speed wobble.

I want the board to be really stable at high speeds, from my understanding, the faster the board goes, the more stable it is with this condition (a rising COG under turning).

I'm going to be 3D Printing the prototypes to test them out, so it might take a couple of tries. But getting an idea of what to look for would be awesome when considering the geometries of all the moving components.

Thanks anyone in advance for any input they may have!
Myles

 

[3DDave]

The component that is missing is damping. Any energy input that is conserved will tend to push back and then overshoot the other way. If you've seen a Weeble toy then you see that there's not much stability to be had by raising the CG. That energy just gets released back into the system.

 

[BUGGAR]

I think what you have in mind is camber (or is it caster) on a conventional wheel spindle where each wheel rotates and lifts by rotating about an angled axis (terrible description, I know).

 

[Strong]

Basic wheel axle definitions here:

https://www.intercotire.com/caster_camber_and_toe

Not a good idea to copy grocery shopping cart front wheel suspension!

Walt

 

[chicopee]

Now I could be wrong from past recollection about the French car Citroen which has a suspension system that remains level when cornering. See if you can dig out info about that car suspension system.

 

[BUGGAR]

The Citroen was an active system with pumps. I remember watching a big guy get into a Citroen. It squatted for a moment before rising to level.
For the skateboard, I was thinking you might need to put in another degree of freedom: Think of a car with conventional sla suspension links with extreme negative camber, and with anti-steer links "misaligned" to induce roll steer. Will that work?

 

[SwinnyGG]

Regular skateboard trucks already have a return-to-center force, which is controlled primarily by changing the rake angle.

It might be possible to design a truck that does what you're saying.. but I know of no truck on the market that does this. The end result is going to be a lot more complicated than a normal skateboard truck, which is an elegantly simple device.

 

[dgallup]

I can tell you for a fact that normal skateboard trucks have a very strong proclivity for speed wobbles.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[SwinnyGG]

Depending on how they are adjusted, sure they do.

Speed wobbles on a skateboard are a product of setup and rider skill (or lack of both).

 

[MintJulep]

My first impression is that the additional degrees of freedom introduced will offset any intended stability gains.

 

[BUGGAR]

I spent some time talking to neighbor kid who rides a skateboard around the neighborhood. He rides a longboard. He said anything that will raise the board relative to the pivot point will make the board more sensitive and it will wobble at a lower speed. We discussed rear steering being inherently unstable, and reducing the steer at the rear truck increases the speed to wobble. I have to think about all this.

 

[SwinnyGG]

Raising the ride height (by adding spacers between the board and truck, for example) increased wobble tendency because it reduces the centering moment provided by the busing arrangement. (the centering force applied by the bushings is the same, but it is applied against a lower mechanical advantage as ride height increases)