Gearing down is more efficient in terms of power consumption, in exchange of lower top speed.
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But just during acceleration, not at constant speed. But yes in most AT situations that’s right.
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Let me ask, for the same battery and wheels, is the 200kv motor mated to a 1:3.5 gearbox less efficient than a 100kv motor mated to a 1:7 gearbox?
One has more losses in the copper winding, one has more losses from a more complicated gearbox…
Edit: I had the kv’s mixed up
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All I can say is I didn’t notice a significant difference in consumption when switching from 1:3 geared 190kv motors to 72kv direct drive and that’s one hell of a difference in gearing. So I’m thinking that maybe the difference is actually negligible and nothing to worry about?
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@Marsl187 this looks great. im just curious, why mount the motor so far out? if you have a 2 stage reduction you get a lot more flexibility for the motor to wheel distance, so why have the motor so far from the axle?
Not this again, do you really need someone to explain how power works one more time?
Higher KV motors are more efficient so a larger reduction allows the motor to be higer KV whilst giving the same speed at the wheel.
Think your mixed up here, 200kv motor is twice as fast as 100kv, and 1:3.5 give less reduction than 1:7 so output is faster. 200kv motor with 1:3.5 gearbox is 4 times as fast as a 100kv motor with 1:7 gearbox so not a far comparison to discus efficiency.
also seems to be mixed up.
A low Kv motor has more winds of thinner wire. A high Kv motor has fewer winds of thicker wire. the thicker wire means lower resistance and therefore less heat generated and less copper losses.
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Whoops I mixed them. Thank you, I’ll fix in your honor.
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So are they or not? You guys keep confusing me.
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These videos are great. i wish we had the equipment to make these sorts of graphs for eskate motors.
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in theory, yes they should be.
BUT in reality were arguing over tiny percentages of efficiency. In reality belt tension, bearing quality, tyre pressure and a good gear ratio (that puts you in the efficient point of the motor at cursing speed) will make orders of magnitude more difference to overall efficiency.
yes I messed that up, let me try again
is the 100kv motor mated to a 1:3.5 gearbox less efficient than a 200kv motor mated to a 1:7 gearbox?
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In theory yes. Also the 200kv motor will also be rated to a higher current so you can more total power out of this setup if you wanted to push it 
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You can’t say this in general. It really depends on your gearing and your riding style. Like I said before, at constant speed high kV is more efficient. If you accelerate often and hard a lower kV is more efficient. Same with gearing.
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If you imagined the pulley was exactly the same size as the wheel, then pick whatever wheel size, and the torque is the same.
In your example btw, a 90T HTD 5M pulley would have a circumference of ~450mm => diameter of 143mm, or around 5.6 inches. Not bad for a 9 inch wheel or whatever.
I do see the appeal of this drive though: achieving higher torque than you could ever get with like a 14T motor pulley and idlers, or whatever is the realistic minimum we use.
However I don’t think adding another belt and pulley is worth it just to use a higher kv motor. (Extra inefficiencies from more moving parts) Would love to be proved wrong though.
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im not sure your understanding whats being discussed here. Were not talking about changing the torque output of the system by changing the kv. Were saying that if you increase the motor kv and change the gear ratio so that the torque and speed at the wheel are the same, then the system is more efficient. it makes no difference if your at constant speed or under acceleration.
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Very interesting build idea and looking forward to real world results.
Makes me wonder about the rolling resistance increase now with twice the amount of belts and pulleys involved.
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Yeah 90t was just arbitrary number. You have to also factor in how many teeth on the motor pulley you can fit.
*click to expand chart
I don’t follow your logic here…you can’t just change the pulley diameter without affecting tooth count.
that was just a hypothetical example to show that “in an imaginary world where we didn’t need teeth / teeth were small enough to always fit”, if you scale the wheel up along with the pulley, the torque stays the same, because it’s literally just the torque your belt is experiencing 
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Thank you guys
Basically I just love to build stuff. I also sell an ordinary motor mount for belt drive. It’s completely fine bet yeah looking at the gearing 1:5 is almost the maximum there.
I would say 14T is the minimum you can really go at a mountainboard.
I’m not so after efficiency, nice to have if it is but thats not the main goal for me.
Thank you, really! 
So a little story to tell from my first mountainboard. I got those Turnigy 6374 190kv motors and a gearing of 16/72. The motors are claimed for 100A and 4400W. But torque was not enough for me. So went down to 14/72. But I wasn’t very happy with the clearance and the the belt skipped sometimes. Installed idlers, but still to less clearence, broke some pulleys and belts from time to time. Also it is not a feeling you want when something of the board touches the ground and you loose contact to the ground with the wheels. So I decided to buy the same motors again but with 150kv so I could change the gearing to something like 15/66 or so, have similar torque and better clearance. But the 150kv motor can “just” push 80A. So i was disappointed because I did not get as much torque with this setup. Both (150&190) ran at 80A, but the 150kv performed worse. And the 190kv could push even more. So basically thats the story behind. May not be applied to general, just my experience with kv and gearing.
Trampa uses 1:6 gearing in the spur gear drive. I wanted something like that, but with better clearance and silent 
Rolling resistance will be kinda very high, especially in contrast to a gear drive.
Thank you @ducktaperules! You always need some space between the two pulleys. You should not have less than 6 teeth in mesh of a pulley. Thats why you add idlers. Going back to the axle with the motor is not possible because it would touch the truck and the truck adapter, this also needs to be somewhere. The motor is not that much more away than in an ordinary belt drive. Maybe like the Trampa Urban Drive. Increasing the angle between the two stages is possible (45° at the moment) but then it could really touch the deck while turning when using a 35° Long from Trampa or so. With the most mountainboard decks it shouldn’t be a problem, but will definitely check it out. @brown5tick
BTW I did not really plan to make it a product. But when people are interested and if it works and performs well we can definitely find a way It might take some time (hopefully not that long) because it firstly have to build the mountainboard itself to test
It is definitely not the best option. The designed gear drive is a lot smaller (fits in the diameter of the wheel) and with helicals would als quiet. But I think this is a good, easy to build and inexpensive system.
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If you want to reduce the drag slightly you could reduce the belt width of the belt closer to the motor. This belt is under less load so can be thinner than the other
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