Open Source Precision Trucks and Hub Motors Project

ESK8 Innovations
1

Hi All,

I am in the process of building my first ESK8, and I am very interested in fabricating my own precision trucks and hub motors much later down the road. I have built 3D printers, drones, and other projects in the past, and I recently taught myself how to use Fusion 360, so I have some amateur experience with engineering and fabricating. I am creating this topic to share my ideas, designs, and to take advice and inspiration from other ESK8ers who are perhaps more experienced than I am.

My goals for this project are:

  • Create precision trucks that are designed with ESK8 in mind and hub motors to go with them
  • Build upon and address issues with current truck and hub motor designs
  • Share my designs with the public via thingiverse.com
  • Design with the amateur hobbyist in mind, so that anyone with access to a metal CNC mill can make it themselves

My current ideas for this project are:

  • Make precision trucks that use the same bushing and pivot cup dimensions as an existing precision truck (possibly Surf-Rodz RKP) so that instead of having to make custom bushings of dubious quality, people can buy bushings from a tried-and-true manufacturer like Riptide.

  • Make Hummie style hub motors rather than Carvon style motors. I know this is a FIERCE topic of debate in the community, but I want to go with Hummie style hubs. Here’s why:

    • Stress is more evenly distributed across the motor

    • They make use of space much more efficiently

    • It seems like just about everyone in the unpowered downhill scene uses much shorter width trucks. I think having shorter trucks might increase stability at high speeds, because it essentially makes the wheelbase longer relative to the truck width. Also, the longer your trucks are, the more your leaning is converted into turning, which can lead to instability. I think we can learn a lot from the guys going 50+ mph. How does this relate to hub motors, you might ask? Well, with Carvon style hubs, the trucks need to be SUPER wide to accommodate the motors in between the kingpin and the wheels. But with Hummie style hubs, since the motors are in the wheels, you have a lot more room to shorten the trucks.

    • Stealthy as fuck. Not nearly as important as the other things listed, but I know some people care a lot about looks.

    • As for the issue with thin urethane on in wheel hub motors, I think there is an easy fix. Bigger wheels! Why stop at 90, 97, 107mm? Since in wheel hubs require casting urethane, why not use that as an opportunity to cast some bigass wheels? I’m thinking 120, maybe even 130mm. That would allow the motor to be bigger as well, which would increase power and cooling.

  • Make the truck a giant heatsink. The biggest issue with in wheel hub motors is that they have a hard time cooling down. Duh. You can’t stick a motor capable of pushing a human being over long distances at speeds over 30 mph in a nice blanket of heat insulating urethane and expect it to be cool as a cucumber afterwards. So why not make the truck a giant heatsink? After reading @Minim’s awesome post about his custom Raptor 2 hangers (link: https://www.electric-skateboard.builders/t/raptor-2-custom-hanger-for-better-cooling/61104) I had a eureka moment. USE THE TRUCK AS A HEATSINK! Minim had to design the hangar to be compatible with all of the Raptor 2 measurements, but if I am making trucks/motors from scratch, I can design it to be one large, incredibly effective heatsink. Perhaps I could use thermal paste where the motors attach to the hanger to augment the heat transfer even more.

Anyways, those are my ideas so far. If you have any suggestions or advice, please comment below.

Thanks,

Harry

5 Likes
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Seems like an interesting topic. Why not try to make something new, like a mix between Carvon style motors and regular hub motors? :grinning: That would have been very cool IMO

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I believe Carvon actually did that a while ago with their V2s. Like half of the motor went into the wheel.

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A suggestion for your design: A queen pin, like on Ronin trucks

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FYI

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For the record, what are precision trucks? :slight_smile:

I am very interested in how your hubmotors will be designed because I am also interested in building my own but don’t know where to find information about how to design them

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Larger wheels do affect the acceleration curve (decrease in gradient). They also can reduce or even prevent the ability to push kick the board although I suppose the USP of the larger-urethane wheel hubs would be top speed.

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Interesting. Can’t the decrease in acceleration be counteracted by a lower-kv hub motor? Also, I know a lot of people use pneumatics which are even bigger than the wheels I want to make.

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Yeah, designing trucks/hub motors is tough because there is hardly any information on the internet regarding dimensions, sizing etc. Probably because everyone wants to buy them :joy:. I’m getting a lot of info from Hummies thread about his hub motors.

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Thanks for the link! That is super interesting.

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UPDATE: I came up with a few more ideas I’d like to implement in my design.

  • Built in split angles. For example, I can make the powered rear trucks 40 degrees and the unpowered front trucks 60 degrees. This way, no wedges will be required. I’m thinking of going with a 60/40 split because it is sort of a middle ground. Maybe I could design some baseplates with different angles for people who like to experiment, but for now I think 60/40 will satisfy 90% of everyone’s requirements.
  • A hexagonal hanger. I was thinking of doing a round hanger at first, because without the need to mount belt driven motors, a round hanger distributes load more evenly than a square one. However, making it round would drive up machining costs by a lot, so hexagonal seems like a good compromise.

That’s it for now. One thing I am really struggling with is finding the right dimensions of pivot cups and bushing seats for precision trucks like Surf Rodz. If anyone has a Surf Rodz RKP truck and some calipers, I would really appreciate it if you could give me the diameter/depth of the pivot cup and bushing seat. @Alphamail, perhaps you could help me out?

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I would not copy the SZ RKP bushing seat as it is substandard many levels! Here are good basic seat cross sections in mm and Inches. basic%20bushing%20seat%20dimensioned%20mmbasic%20bushing%20seat%20dimensioned

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The Pivot Axis should intersect the center of the bushing floor spacing

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If you work in solidworks,2012 or older, i can look at the part file, otherwise send me a .step file and I can convert it to help you with the pivot cup placement and dimensions. My email address is [email protected]

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One other thought is a 20 degree split is great but i think you are on the highside with the 60 degree front. I think you will be happier with a 50/30 configuration

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Thanks for all the data! It’s interesting that the SZ RKP bushing seat is substandard. I’ve heard some people complain about SZ trucks being too tight or “sticky”. Does that have to do with the bushing seat at all? Right now I’m trying to find the best pivot cup to use. I found this handy diagram about your different pivot cup dimensions here:all-pivot-cup-specs-to-scale I don’t know if the above image is precise at all or just an approximation. I want to use existing pivot cup dimensions so that people can buy Riptide pivot cups for X truck that will work perfectly with my trucks instead of having to make custom sized pivot cups. Which would you recommend? Is bigger better? Also, what tolerance should I go for when designing the pivot cup and bushing seats? For example, if I decide to go with your Caliber II pivot cups, should the hole be 18.1mm? 18.2? 18.05?

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These details should be discussed confidentially

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Do you design in Fusion 360?

How about adjustable angle baseplates?

I’d love to help out with this project in some of my spare time… I have some experience designing longboard trucks, testing prototypes, and have had some of my designs manufactured in the past.

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I do indeed use Fusion 360. That’s super awesome! Once I get my first revision done, maybe you can take a look at it and tell me how I can improve. I’ve never heard of adjustable angle baseplates, but that is a very interesting idea. I’ll look into it.

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You should rewrite this so anyone with access to a knee mill or CNC can make these trucks.

Do you mean hanger width? Becuase if it is, this concept is already proven in Motorsports with regards to vehicle track width as wider is more stable, but you run into problems to is a choice for a specific width in design.