Introducing... Plush Hub Motors

I don’t think I understand what you are trying to say. What do you mean by small in diameter? The goal of this is to create a motor similar to a trampa hub (without a motor). The ride height will be based on the diameter of the tire you use, so you can use a 6 inch tire and get lower to the ground or an 8 or 9 inch and get higher from the ground. The inner diameter of most penultimates is about 93.5mm, with walls around 110mm to keep the tire on. Then there is about 30mm inside of the walls (width of the tire). This is the constraint of pnuematic wheels, and making a motor with a smaller diameter would mean you need to make custom pneumatic tires and tubes and that even wouldn’t necessarily get you closer to the ground, unless the diameter of the tire is less.

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I think your confused about torque. The torque between a hub and DD motor with the same sized stator and same winding pattern and same esc and battery will be the same. The location of the motor doesn’t matter, since the gearing ratio stays the same (1:1).

Unless you mean by you can use a much larger diameter stator (since the stem doesn’t get in the way). This would make sense, and is a reason I thought about it. It’s a nice idea. But I believe I can still get good performance from this stator (it’s much larger in diameter than most stators used in eboards).

Thus if it can be fit in wheel to have the performance needed, why not fit it in wheel?

Nah, not like that. Imagine if you have a motor which both sits inside the wheel (like a hub motor), aswell as on the hangar (direct drive). Lest say you have a hub motor which is 40mm in length, and you have a direct drive motor which is 40mm in length. Now combine these, and you will have an 80mm long motor. Make sense now?

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Yea Buddy. At 50v looking at 9kw per wheel.
Screenshot_20190211-105117 https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F183638309572

I understand what your saying and I understood it before.

Basically, you end up with a bigger stator. That won’t give more torque still. It will just run cooler, unless the original stator is so small that the stator saturates and can’t give the torque it’s designed for.

At some point, all of the power is useless without A) bigger contact patches B) a way to hold on for dear life.

You know that 10kw across the board is insane, dangerous really, which is why you throttle back the watts.

So at some point, it comes down to what is practical. I’m aiming for 8kw total (2kw per motor x 4 if you want power) or 4kw total (2kw x 2 for sane people who still want crazy power).

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I think that it’s just not necessary to make it much longer. If I can not get the performance I’m looking for from this in wheel design, my next option would be to extend it outward until it is large enough.

The questions that you will hopefully answer once these are tested is: Is a stator narrow enough to fit just inside the tires capable of producing sufficient torque?

After that we can debate if a bigger stator is needed or not

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I might have missed this earlier in the thread, but will these have a wide enough range of torque/speed to run well with a range of 6-9 inch tires? Say it has great torque on 6 inchers, would it have enough to be acceptable running 9 inchers? Seems to me like you’re asking a lot for it to be ideal with such a potential difference in wheel sizes but I don’t know enough yet to make any assumptions.

That is the goal here. 2wd should be great on 6 and 7 inch tires, and 4wd should be great with 6, 7, 8, and 9 inch tires. I listed projected top speeds in the first post.

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Sorry, misunderstood. But I think you mean length, and not diameter here?^^

Anyway, wouldnt a 6374 produce more torque than a 6355? This is my experience atleast from riding both on same vesc settings.

In theory, no.

Torque (km) is proportional to kv and the watts you put into it. The issue is when a motor’s stator is too small for the amount of watts you push into it, your stator saturates, and loses torque and efficiency.

If you take hummie v1 hub motors, you could the same torqure as the v4 motors (double the stator length than v1).

You can take a really tiny motor and get the same torque as a big motor. The difference is the little motor will get hotter than the bigger motor. Thus the bigger motor can take more current and provide a stronger acceleration. If you only change motor size and no amp limit settings, you should experience the same torque, unless you saturate the stator in the smaller stator.

Bigger stator = more copper in the motor = lower winding resistance (since you can fit more copper in each wind). Lower winding resistance = less copper losses = less heat generated from the resistance of the copper wire. It also means more steel in the stator (which is important for flipping the poles) and you also have more magnets.

Thus, bigger motor = bigger elector magnet and permanent magnet = can handle more watts without heat issues = more powerful acceleration. But do not confuse this for torque. Torque is a constant value. The actual rate of acceleration is a different story.

If you want to see this, take two different size motors on the same truck (different wheels). Put one into a vesc at a time, same settings (set them lower so you don’t saturate the stator) and do an acceleration test. You should feel a similar acceleration. But the smaller motor (assuming they are the same motor kv’s, same winding and winding pattern, same brand, just different stator size) will be hotter (easy to measure with cheap hobbyking laser thermometer). Now up the amp limits some more, and you’ll see the heat difference between the motors more drastically.

On the hummie hubs, the one piece that made a difference is the wider wheel base, which gives more traction. At 30a per motor (50v), wheels would slip on the hummie v1. On the hummie v4, it takes over 50a per motor to get the wheel to slip. Thus I get better acceleration on the v4’s than the v1’s, even though the torque is the same.

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dont think wheelbase would determine if the wheel slips.

the peak torque output of the v4 is much more than the v1 as its over twice the stator size.

why the new wouldnt slip but the old would given the same esc amp settings is likely because the v4 use a bigger softer tire. otherwise they should slip more as they’re lower kv and more torque per amp.

The forum must have been hiding this topic from me, noticed it only today :thinking:

First of all: THIS SEEMS AWESOME! Lowering the amount of parts for AT builds is much needed. Secondly: Small pneumatic wheels like the Bergmeisters seem to be a hot trend right now. Assuming these hubs would fit sixshooter tires, they would also fit Bergmeister tires (same core/internal wheel size I believe). Only problem is that at 5" and just 40KV, top speed is significantly lacking. Seeing as a lot of people prefer the 30mph sweet spot, was just wondering if you’d be open to having a 55kv motor option as well.

Thank you for the very detailed post! :yum:

I guess I used the word torque wrong. so you should only experience better acceleration with a longer stator if the smaller gets hot enought to be become saturated, right?

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Never said wheel base, I said contact patch. Larger contact patch = more grip, that’s just basic science. And I’m not just talking about the new wheels, but also the v3 motors too, which those crappy poured wheels.

Formula?

Everything I’ve seen (online calculators and other topics on this forum and from what you’ve told me personally), is that the torque is a constant, called kt, which is propositional to kv, which is decided by the wind. https://calc.3dservisas.eu/ for example calculate torque without considering magnets or stator size.

First v1 hummie hubs were all under 85 kv, most where just over 80 kv. My v4’s are 80 kv, 85 kv, and 2 at 90 kv. So they are not a lower kv for me, actually, the opposite.

Wheel base. [quote=“evoheyax, post:33, topic:83082”] On the hummie hubs, the one piece that made a difference is the wider wheel base [/quote] But a larger contact patch isn’t always better grip and you can get fast wearing soft sticky tires with better traction or hard n long lasting n bad traction

I agree the kv/kt reveals what torque the motor will put out with general use but if you’re overloading the motor trying to get as much torque as possible the bigger stator won’t saturate and get extra hot, as you said.

I don’t disagree with this either. It’s totally possible this played a role in my experience also. But generally speaking, same wheel with a longer contact patch = more grip.

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Wow - thanks so much for this - really happy you are determined to create a proper hub motor for 6-8” pneumatics.

I agree with your measurements 93.5mm or about 3.75” for tire rim plus the height of walls sticks up from that to hold the tire on. I do think you could increase the width a little - perhaps 40-50mm rim width between walls.

The trick/problem is that stem to inflate the tire takes up so much space below the 93.5mm rim so you might lose 10mm for that (though you could also use that space to attach tire rim to motor). You would probably end up with a max motor diameter of about 80mm (at least that’s how I have it pictured in my head - wish I could think of a way to get a larger diameter motor)

I have been trying to figure out pneumatic hub motors for my current project. Was considering buying TRAMPA superstar rims (plastic) or more likely megastars (aluminum) without the hubs and stuffing your existing hummie hub in there and finding someone to mill out a simple interface between them. Seems do-able - am I missing something - why hasn’t this been done before?

A few other ideas:

if you’re machining your own rims, you could create/machine a rim profile that is similar to some automotive or bicycle rims. The rim profiles sometimes incorporate a “hook” (small recess as well as a bump) that hold the tire bead on more securely. . . This in conjunction with a permenantly installed (and strategically placed valve stem) might save some space allowing increased diameter of motor and have the added benefit allowing tires to be run tubless. Tubless tires save a lot of weight and have other benefits.

Speaking of weight - please count every gram as you design this thing - a heavy weight will dissuade majority and really take the fun out of it.

Regarding your decision of 40kv. That is PERFECT for me - in fact could go even lower!