Elofty Direct Drive

Absolutely true. If using pneumatics, either keep it casual( can go intense but only for short durations), or go 4WD.

I believe even 4wd, if pushed hard, will over heat quickly.

It’s a simple mechanical disadvantage, and the only really solution is a bigger diameter stator for these larger diameter wheels.

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Umm, really? Say you have identical motors and have 2 setups.

  1. 2wd with 83mm wheels, with Kv
  2. 4wd with 166mm wheels, with Kv

Simple math tells me that both of these setups can produce equal force, but the i^2R losses will be doubled in the second case. However, since they are distributed over 4 motors(and not 2) so motors in both the setups will heat up equally when each setup produces the same force.

So they wouldn’t heat up more. Am I wrong somewhere?


Now if we consider the case below(same size but different Kv), I have an intuition that both setups will be equivalent in terms of heat production and force production. But math has to worked out to say for sure.

  1. 2wd with 83mm wheels, with Kv
  2. 4wd with 166mm wheels, with Kv/2
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A lot really does depend on the motor itself and what it’s built with. It’s hard to generalize too much.

They may be capable of producing the same torque, but what your forgetting is how that torque is applied. The bigger wheel has a longer distance between the stator teeth and magnets (where the torque is being created) and the contact surface of the wheel.

It’s like trying to close a door by pushing the hing side of a door vs pushing the handle side. Your proposing a linear increase in torque when in fact you need a quadratic.

You can change the kv, and it will help, but it’s not equivalent to using a larger diameter stator. This is why even Dexter himself said the current DD’s with pnuematics is not a permanent solution.

We can handwave around concepts all day but to do it the right way we have to write down the math. I fear this thread will devolve into a devin style volt-amp posts. So we can take it private if you want to get into the math. Promise I am good with physics and won’t take you on a wild goose chase.

In case you misunderstood me, I’ll say one thing though: notice that I didn’t use the word “torque”, but rather force. Where Tau=f*r

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Lazy test build. Will put some sort of an enclosure before I take it out. No wheel bite with the TKP setup. image IMG_20190419_051323

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I miss Devin. Saw him irl the other day. He is genuinely a nice guy, hopefully @mods will let him come back some time soon.

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Assuming your motors have a constant efficiency over the whole rpm range, that’s correct, however this example is misleading. @evoheyax is talking about “motors getting too hot” and here you imply same heat production but overlook heat dissipation, which doubles in your 4WD case.

Another way to see it is “you’ll get at the same speed with both setups with the same battery, but second case will keep cooler motors”. But no matter how you phrase it there will always be side cases where equivalent setups become better or worse, mostly because the temperature depends on :

  1. heat dissipation which is function of surface, speed, and a small correction factor k*rpm

  2. other thermal factors that will systematically be overlooked as thermal conductivity of the truck/axle/bearings/connection to the wheel, and heat capacity of all these elements you’re slowly cooking - that is likely a happy mix of various metals and thermoplastic polymers covered by a fine dust or a heavy mud layer :smiley:

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Finally. Someone who understands. Yep, you are right. The 4WD will actually run cooler because it has more surface area & heat sinking mass.

When you say misleading, it’s quite the opposite. Isn’t it? I was making a case for 4WD and didn’t show everything that’s in favour. :smiley:

Absolutely agree. Just didn’t want to make it into a huge wall of post that people ignore, which they do anyway because they don’t really know who’s rambling and who’s making sense. Haha.

at least he is wearing a helmet

Since you want so bad to have them with pneumatics, please be the test subject to statorade :grin:

My bet is that the effect will be big, it won’t solve the consumption problem, but will increase the heat dissipation capacity

We have the same problem as ebike hubs motors. The only direct path for the heat to escape is the axle, and even then we don’t have much surface area to dissipate the heat on the hanger

We can build a big direct drive, but once everything is heat soaked it doesn’t matter

I will have more numbers to back that soon, figuring out how much heat can be transferred by the air gap to the can, and then doing the same thing with statorade

https://www.ebikes.ca/shop/experimental/statorade.html

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The Km of the motor which tells heat to torque relation is regardless of kv or kt so the kv doesn’t matter as far as efficiency in the motor n heat produced. u would need a higher current controller to do the higher amps needed for a high kv motor to get the same torque but as long as has the same amount of wire would be same km

With the double long lever of the pneumatic wheel it will need double the ft/lbs from the motor for same output at wheel and 4 motors would do and then could rid of heat easier.

The grin tech motor simulator incorporates the whole system and shows running a high kv is inefficient but I guess that inefficiency happens in the esc n wiring only.

Here’s the ‘Bajaboard’ style suspension, btw. This one will be a de facto standard in 2020 yet you can expect the smaller vendors to all start selling this in two months or so.

And yes, we have a couple of similar drivetrains incoming for science. 6 weeks or so.

I can tell you right now they’re junk - yet I can also predict that one of us will CNC a precision version of these trucks and they will be amazing.

I still owe Winfly and Sofu parts on the Lofty; my real life work took precedence this week.

It also appears that 90 MM is where our brakes are, per China. Curious if the Boas make a difference; no word yet on how the Baconators brake. They have an AWD ESC in production, no deets provided.

If brakes are 90 MM or nothing, it’s hardly the end of the world. I already love their thane.

I’m just curious how brakes will play out with the other, larger Lofty wheel choices and AWD. That seems to me where they are headed.

If I had to guess, their AWD Carbon would be $1999.

Hope this helps!

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Can’t people just increase the brake current and get stronger brakes that way? Doesn’t make sense that they can accelerate fine but not brake.

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that’s not the problem. It’s full short these motors seem to not be very strong as of now, unless it’s actually a unity issue. I haven’t hand spun them yet and haven’t compared them to the TBDD yet.

I will say, if eLofty wants people to use them for high power applications, they really need to increase the gauge of the phase wires. They’re incredibly thin and every time I throttle hard I worried about wires getting too hot and melting the rubber around them…

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whats interesting is that. when I had my Hyperbeast working with the Raptor hub, unity and nano remote, it soft breaks at low rpm if I calibrate the nano correctly. If I forget to calibrate the remote and break, it perhaps clips under the lower bound of the pwm signal and I can definitely feel stronger break. that’s why I suspect it’s an unity issue. I’ll bring over my dual ESCape for testing.

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I can give it shot if heating becomes a huge problem for me.

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@sofu, I tried the current (not current-no-reverse-with-brake) mode and braking is as strong as you want it to be. Even on a downward slope. Give it shot. The issue is that if you keep braking even after it has come to rest you start going backward. Haha.

@trampa, has there been any discussion regarding addition of a control mode mode where a reverse current can be applied to brake harder but still not go into reverse? That would give much stronger brakes to these direct drives and hub motors.

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Yes that’s been the solution for carvons too. But it shouldn’t have to be is my point. I know it’ll work :stuck_out_tongue:

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Then it’s more of a VESC firmware issue. What you describe is a normal effect that any motor will show to some extent, for instance if you short the phases of a running motor you’ll get less and less counter-torque as the rpm goes down. It doesnt matter if you have gears or a belt drive system, because the motor is still turning fast enough until you reach a speed low enough to consider that you can step on the ground. But if you turn it slowly enough, any shorted motor will become extremely easy to rotate.

So what you need in order to get a more or less linear decceleration until you stop is to have the VESC shift from regenerative braking to active braking (what is the VESC “backwards mode”) under a pre-set rpm (typically when you switch to sensored mode) but you want to backwards mode to stop before you actually start moving backwards. Ideally the VESC would then shift to an active “stationary mode”, keeping a low current flowing to stabilize the wheels in a fixed position until you release the remote’s brake. This is the same kind of modification that has been implemented on Ackmaniac’s firmware version, but with a slightly different algorithm. This would be a super cool feature actually… Couldn’t anyone just find a way to blackmail Ackmaniac or something? :yum:

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