Blog Post #4: Preliminary bench marking and mold prototypes
We asked a lot of riders on what they wanted to change about their Boosted Board if they could bolt on a wheel. Here is what riders said:
We got a good amount of data entries, but always looking for more. If you want to cast your vote, then enter it here: https://docs.google.com/forms/d/e/1FAIpQLSe_0pczK7zKszclZMb2c7gOUIu3XXqYQI_AgQfpBhyL-sssdw/viewform?usp=sf_link
New Focus on: Comfort and high speed
Let's give people what they want, but at what trade off?
However, we're not sure what trade-off people are willing to take if they get a wheel that is more comfortable with capability of higher top speed. Adding comfort means more rolling resistance and a much softer durometer. So here is another poll designed to ask what would you be willing to trade? Enter your vote here: https://docs.google.com/forms/d/e/1FAIpQLSeNob28YN9VG6AE8JWYVOQ3ZmNfC2wiMelSyPspMSdRJP_4pQ/viewform?usp=sf_link
Bench marking durometer
One thing that affects ride quality is softness of the wheels. So let's measure the durometer and deflection of the popular wheels on the market. We measure the Caguama (Kegels data coming soon). These are the 83A durometer wheels and it consistently comes in at 90.5A on all four wheels that we have. These are sold as 83A shore, but polyurethane does have a tolerance variance. We'll be comparing our design to the Boa Constrictors and Kegel in the following blog post.
Deflection Vs. Force Curve
Comfort is also attributed to compliance of the wheel. So we measured that too for a bench mark. For Boosted Board riders, Orangatang are the key choice here. We'll be performing this same test on the Kegel and other wheel choices, then overlay the data.
Simply put, the Caguama wheel is pretty stiff. When you're on your board, you're traveling at 22mph. You're 200lbs. You and the board is 215lbs. Each wheel has a distributed load, each wheel is under a load of 54lbs. It takes nearly 75lbs for the wheel to deflect .1". These wheels pretty much have no give to them.
By comparison, the Momentum wheels deflect a lot more when the same load is applied.
Caguama: 75 lbf and deflects .7 inches.
Momentum: 75 lbf and deflects .137 inches.
Momentum deflects 2 times as much as the Caguama. That can translate to a lot more comfort.
Based on our engineering software (we solid modelled each wheel), our inertial calculations relative to each wheel is as follows:
Kegel 80mm is 2.0, our wheel at 100mm is 3.0, and BOA 100mm is 5.8
This would mean that we'd be able to achieve a higher top speed, around 26mph if you're on a Boosted Board V2, but with similar acceleration of the stock Boosted Board Kegel wheels. Exactly how much less acceleration? We will have to determine that when we start testing in a couple of weeks. Basically, the current design can accelerate nearly twice as fast as the BOA and a little slow acceleration than Kegel.
First prototypes and 3D printing
We're using a 80mm polyurethane of our own resin and the results look good. We don't have any testing on acceleration, top speed, or comfort yet, but that will be coming in the next blog posts. Mostly, we just have one wheel so far and we have to spend the next couple of days creating the wheels. They typically take a day for us to hand make each wheel.
The specs of these wheels are 100mm diameter with a 40mm contact patch. Stock Kegel Wheels are 233g and our wheels are currently 197g. We think the weight of our design will increase closer to the Kegel weight, but not sure exactly how much right now.
We will be testing soft durometer and different levels of grip. It's still early to say and these our first prototype wheels. Based on our motorsport experience, softer compound means higher grip, so we can get away with less contact patch. If the wheels are more compliant with softer durometer, then that means a more comfortable ride. However, we're still figuring out all the sensitivities in the design.
Dynamic and Static Testing Metrics
What dynamic and static testing metrics would you like us to measure when comparing our design to the other wheels? What other wheels should we test against?
Bumpiness, acceleration, top speed, range, grip, surface transition. Anything else?
Weight, durometer, inertia, Deflection vs. force. Anything else?
We're planning for a big testing session on the 7th of November. Who in Austin, Texas wants to join us and have some beers and go riding (when we're not drunk...)?
Doug and Andrew