It’s gonna be the 35/20 split angle. Coming from 30/30 that’d make a huge difference
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1 good m4 drill tap kit would do it dude… Can’t be that much.
So got back from today’s session.
Couple thoughts:
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The frame is super stiff. Torsional stiffness is great, but zero flex length wise, I am not sure. Some flex would help me increase truck angle when pushing hard into the board, helping turning.
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120cm / 47" wheelbase doesn’t help turning either. I did compensate for the wheelbase in angles, but I didn’t compensate for the angles in bushings.
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Below axle height standing platforms adds progressiveness to the truck feel at lower speeds, but when turning with high forces this progressiveness gets less. That said, there’s progressiveness which I don’t really like. But tuning bushings should be able to get rid of it I think. I would also benefit from extra angles to compensate for the lack of flex while we are at tuning bushings. That said, I am quite deep below axle. Good bit deeper than the V6.
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Power feels lacking, and it’s quite significant. But also, I just plain don’t understand my data.
This is the previous session on 22T.
Note the frequent dots suggest an acceleration of roughly 0.5G. Felt weak, but decent enough. This would gear me to close to 90 mph, whereas 22T gives about a 50mph gearing for supernovas.
This is the last supernova session:
Note the lot of dots at roughly 0.8-0.9G. So far data checks out.
Then there’s today session, kart wheels on 12T. Gearing is about 5% off from the novas… Yeah kart wheels should probably accelerate slower for the same gearing, more rotating mass, I totally get that.
Frequent dots maybe around 0.5G again. About the same?? I did do multiple low speed (nearly standstill) full throttles. The racebox must have picked up at least some of that, right??? Right???
What the hell?
Also top speeds shouldn’t really be compared between two different tracks I get that, but roughly the same length of straight, and I was reaching roughly the same top speed? Whereas on Novas I’m now 59 in the straight so way faster? I just really don’t understand what’s going on here. Changing gearing directly impacts torque. Except… What the hell just happen here? Did I manage to break physics next to my gears???
And I also fully wore down a set of 12T pinions. Before I even wanted to finish the session. Probably shitty quality. Backlash was set good. There was no weird resistance from anything. I did run them dry though. But I ran my 22T dry too and I’ve got maybe 10 sessions on those by now with basically no signs of wear…
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12t moving such a big wheel… seems like a lot of work
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It wouldnt be too hard to do the math to figure out just how much energy rotating those wheels up to speed is taking from your setup, might be worth looking into.
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A quick rule of thumb is that, at most, a rolling mass has twice the inertia. That comes from the rotational inertia for a hollow cylinder, which is the worst case. I don’t know how much he weighs, but the wheels are 12 kgs, so if you figure 24 kgs of inertia for those, that is considerable, but shouldn’t make that big of a difference in acceleration of the board+rider as a whole, especially since there was probably at least 4 kg giving up to 8 kg worth of inertia before.
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Wear rate is proportional to applied force and to surface area. A smaller gear will have less teeth (duh) but also experience higher forces at the teeth, so you should expect 4x wear rate for a gear 1/2 the size (as long as I’m not making a mistaken assumption here). It could be simultaneously true that those ones are made of cheese too, ofc.
Rotating or not, the mass of the board and rider is dominant here. IIRC the difference in KE between a rider and normal esk8 wheels is something around 2 orders of magnitude, so mabye we should expect this board’s tires to be closer to 1 order difference.
Maybe what you need is a wooden deck with a lot of bias ply composite layers? Or a metal deck built like a really flat torsion box.
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Just ran some calculations with chatgpt then I realized something.
If we simplify the model by taking the worst case scenario (wheel modelled as a ring, all weight on the outside diameter), then the effective weight will basically be vehicle weight + wheel weight.
I just remembered that i ran some calcs in CAD and the kart wheel is 2400g + gear (I assumed 300g for now).
Then effective weight will be 34kg board + 85 kg rider + 2.7x4kg wheel inertia, vs 1.3x4kg wheel inertia.
So 129.8kg for the kart wheels and 124.2 kg for the supernovas. So I lose maybe 4-5% of my power to the inertia, and remember this is worst case scenario assuming all weight is on the outside diameter of said wheel.
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What I am considering is a radium style swingarm implemented on a stiff metal chassis. Potentially even willing to give up ride height adjustment for that if the kart tires do well on our indoor tracks, although I do need to see in CAD if I can keep wheelbase relatively under control with that. I really like the idea of being able to finetune exactly how much extra truck angle I want just by changing another bushing or two.
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I’ve done some small personal development around radium style swing arms! I’d love to share some of my preliminary work with you if you’d like. Haven’t done a lot of testing yet though.
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I’m probably not putting much work into it until end of June (after my upcoming exams), but I’d love to see it!
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I just made the skidplate. Did a couple deep cuts in the ABS sheet with a carpet knife, bent it at the cut, and it looks pretty darn clean. Much better than my jigsaw jobs that’s for sure! Decided to just put some foam on there towards the steel chassis and mount it with 4 zipties. It’ll be easy to service lmao.
Also upped angles:
The front now has a riser stack of 12.5 degrees, totaling in a 47.5 degree total truck angle. The rear now has 17.5 total angle. Standing on it in my room, it does seem to feel better. Have to see if I can get new bushings in time to tweak it, but this now feels like it will be doable to race on even for the super short track of Pitland.
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Had a conversation with chatgpt. My Bridgestones are not considered stiff sidewall, and that apparently eats up a huge amount of power.
It came up with these numbers after I told it about my tires and use case. ASSUMING the 12T acceleration wasn’t a fluke and the 22T was, this would be fairly believable going off my not very scientific data.
Switching to the Lecont LPMs, which are even grippier and are considered a hard sidewall tire in karting, I can expect better acceleration.
Then I also told chatgpt about my seemingly unexplainable dilemma of the gear swap not creating more torque like it should have.
If anyone agrees with chatgpt and thinks that tires can act as a saturation point of torque transfer before slipping on the ground, PLEASE enlighten me how that works without any other effect that I can feel. I sort of want to put the 22T back on the rear, and do bluetooth logs along with drag times, then put on 12T or 11T again and repeat. If my current (not very scientific) data is correct, and this is a real phenomenom and not just chatgpt being sky high, then I may be in trouble.
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I can’t imagine how the tire could be stopping torque beyond absorbing a couple degrees of rotation.
If you think the hub could possibly be spinning separately to the tire put a little mark on each part and see if it moves.
You are using a really huge wheel and very small gear, I don’t know much about this but could there be strong enough forces pushing apart the gears that they get angled sideways a bit or create resistance internally in the wheel hub or motor?
Please be aware that whatever misconceptions/urban legends/armchair physicist nonsense that random people have transmitted around the internet about how tires work will be reflected in LLMs. They don’t represent truth, just the average of all prior things written on the web.
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I have specifically asked it to find me research papers that talk about this issue. It did tell me a few to look at but I’m too tired today to really dive in deep into them.
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In my experience, asking chatGPT anything technical leads to it hallucinating stuff. Stuff that sounds really good and knowledgeable, but as soon as you dig into it deeper it’s just passable technobabble. It’s good at identifying search terms too look into deeper, but that’s about it.
Idk anything about tires so I can’t say if that’s what happening here, but it definitely makes me think it’s a possibility.
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This is definitely not the case. The tire is super tight on the rim. So much so that it’s borderline impossible to remove without a tire press.
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Yeah I am sceptical against chatgpt too. I don’t see how this is possible. But on the other hand I also don’t see how it wouldn’t increase my torque if I change my gearing so significantly… Something weird is definitely going on, either with the data I am working with, or with the tire itself… But I don’t think it’s the data… 
maybe that shitty 12t gear also contributed something. I really can’t wrap my head around all this.
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The Chatgpt explanation makes no sense to me either. Even ignoring other issues I have with it, if you were somehow losing kWs of energy into the tires, they’d be overheating pretty quickly, I think. I’d definitely go with the A/B testing with Bluetooth logs to make sure you’re actually getting the expected power and everything. Another thing I guess you could try if you have one available is looking with a temp gun to see if something is really hot, but if something were providing that much resistance, I think it would be obvious and melting or getting red hot.
I kind of wonder if you’re not deforming the gear and/or motor shaft and causing that to lower efficiency, but again, I think stuff would get so hot so quickly that you’d know about it already.
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