Speed vs Torque -- Margin of Safety

[dhlee3]

Does anyone know what the motor size is for the Firewheel? I have an F260 and contacted them to find out what the motor size was and they responded "Rated power 550W, maximum output power 1350W".  I'm not sure how to compare that to other glidewheels - like the ones below. Do all manufacturers have a rated power and a max output power?  Is the value they publish the rated power? 

Brand & Model	Motor (Watts)
AirWheel X3	400
GotWay M0	400
GotWay M10 260	400
GotWay M10 340	400
Ninebot One C	450
Ninebot One C+	450
AirWheel X5	500
GotWay MCM 14	500
Ninebot One E	500
Ninebot One E+	500
Firewheel F779	550
IPS113	650
AirWheel Q1	800
AirWheel Q3	800
AirWheel Q5	800
AirWheel X8	800
IPS132	800
IPS133	800
GotWay MSuper	1000
IPS121	1000
IPS122	1000
IPS123	1000
IPS181 Lhotz	1000
IPS191 Lhotz	1000
IPS192 Makalue	1000
IPS131	1300
Solowheel Classic	1500
Solowheel Extreme	1800
Firewheel F132	550?
Firewheel F260	550?
Firewheel F528	550?

 

[Gimlet]

I think there is a problem here in that rated power is what the motor can produce continuously for a decent period of time and peak is what it can deliver for a short burst when called on to do so.

The IPS132 actually quotes 1300 but I'm fairly sure that must be a peak reading. Having said that it actually climbs very long hills very well so I think the continuous rated power must be fairly high as well. I would put it slightly above my MCMV2S on a long climb but obviously the MVM can go faster up the hill in short bursts.

I believe Jason McNeil  of WheelGo is trying to sort out a dynamometer that is suitable for testing eucs. Should he succeed then we will gradually find out the true ratings of all the wheels he gets to test.

 

[dhlee3]

The IPS132 actually quotes 1300 but I'm fairly sure that must be a peak reading. Having said that it actually climbs very long hills very well so I think the continuous rated power must be fairly high as well. I would put it slightly above my MCMV2S on a long climb but obviously the MVM can go faster up the hill in short bursts.

​Thanks Gimlet.  BTW, on the IPS site, they reference the IPS132 as 800W (http://en.iamips.com/products.html).  IPS Electric Unicycle Co.,Ltd. says 800 as well. http://ipselectricunicycle.com/bbx/222147-222147.html  Maybe as you said1300 is the peak reading and 800 is the rated power.

 

 

[Gimlet]

That makes a lot of sense. I'm afraid I don't read Chinese and I find the Web site translators only tend to translate a fraction of most sites but the second link is good for me.

I even spoke to Jason about the 1300 claim which is quoted on several sites including his WheelGo site. But even he admitted that it was probably peak rather than rated power.

800 rated would explain it's phenomenal climbing ability though.

[Jason McNeil]

It's a good topic: until there's comparative dynamometer testing, the peak/sustained wattage is going to be mired in exaggeration & controversy. 

As was discussed on another thread, the three elements that determine both sustained/peak power is the battery-pack/chemistry, control-system & motor. Historically, most manufacturers have gone with the assumption that battery-pack is in always going to be what defines the peak/sustained power, but the story is more complex than that. A well-designed control-board & BMS system should actually regulate the current that's feed into the control-board, as the experience of the likes of RW has demonstrated, is that if there's 100% battery power-delivery to the CB without any battery safety margin, the risk of cut-outs or power-brown-outs under high sustained loads is considerable. The lifespan of the battery is also adversely effected by continual operation at the maximum power output design limits of the cell.  

At the control-board level, the number & type of MOSFETs plays an important role in power-delivery. Cheap MOSFETs—the type that are found in most of the generic CBs—apparently only have an efficiency of around 70%, the remaining 30% is converted into parasitic heat, which presents a real problem in a hermetically sealed space.  

For brief periods anyways, there is quite a bit of margin for temporary high currents to be feed into the hub motor, but the mechanical power efficiency drops away as more current is feed into it—as with most things in life, the law of diminishing returns is a force to be reckoned with. 

Since there's a tacit unofficial formula in the industry for rating power (= battery pack sustained output = V x A x cells), it's difficult to see how this will change. For example, AirWheel, IPS & Ninebot use this rating system. The latest most egregious example of blatant exaggeration, even within an industry which lacks any sort of standards/definition is the SoloWheel Xtreme: all the evidence suggests that Solowheel are inflating their peak output stats by at least 50% above other manufacturers. Of course time will tell when it is subjected to the rigors of the dyno. 

 

[Jason McNeil]

Here's the datasheet that IPS provided a couple months ago with the 1300W peak output claim. 

[dmethvin]

I just thought of a good analogy for the motor torque-vs-speed problem, and that is a row boat.

When you are rowing, you can choose short oars which give you really good leverage (more torque) and will get the boat going quickly. However, at some point you are going so fast that you cannot physically put the oars in the water, stroke, and pull them out effectively because the water is moving by quickly. You have hit the max speed.

The way to get higher speed is to use longer oars. Now you can get the oars into the water for a very long stroke at faster speeds. However, the drawback is that you have lower leverage (less torque) since the oar is attached close to you on the boat and most of the oar is sticking out over the water. This makes it harder to get started at low speeds, and also makes it hard to slow down in a controlled way--try to hold the oar still in the water while moving quickly and it may rip out of your hands!

This is the problem the EU motor designer faces. They have to choose the length of the oar that gives the best performance trade-off. They can't cheat and put a bunch of different-length oars in the boat! 

[esaj]

This is the problem the EU motor designer faces. They have to choose the length of the oar that gives the best performance trade-off. They can't cheat and put a bunch of different-length oars in the boat! 

...unless they use some sort of transmission/variator   

​

[dmethvin]

...unless they use some sort of transmission/variator   ​​

Okay @esaj I'm throwing you overboard!  True you could  use a transmission but that brings a bunch of other issues like weight, noise, and reliability. Plus it would seem to be hard to switch gears on a unicycle without the risk of throwing you off balance. 

[esaj]

Okay @esaj I'm throwing you overboard!  True you could  use a transmission but that brings a bunch of other issues like weight, noise, and reliability. Plus it would seem to be hard to switch gears on a unicycle without the risk of throwing you off balance. 

​True, I was thinking automatic transmission or variator, but anyway, I doubt such things will ever be made for EUCs...   So pretty much just trolling   I think I already pissed off half the forum members by being deliberately (although maybe unnecessarily) provocative and said that the (maybe?) mandatory helmet usage that's in the law amendment for EUCs and other light electric vehicles in Finland was a good thing, because then the "idiots wouldn't get (any more) brain damage" in another topic...  

[Eryk88]

Most of boards I've seen have shunt resistors to sense current (power is calculated = current x voltage). The Firewheel's board too. GW is rather unique in having a dedicated current sense IC (but the PCB has a double layout for a shunt resistor based sensing scheme).

​

Not True - Solowheel uses the allegro sensor and so does Firewheel - in the matter of fact fire wheel uses a copy of solowheel board!