Motor comparison spreadsheet

[crossbreak]

As you pointed out the losses for a jack shaft can be as high as 10% per stage ! hence what use is a 95% efficiency motor if you need a triple stage reduction that has 10% losses per stage or 30% total losses !

If gearbox loss was 10% per stage, a tripple reduction has an efficiency of .9³=0.729, so it's ~27% not 30%. Anyway, a MAC geared motor that has a reduction of 5 gets 85% efficiency including reduction loss. If this reduction loss was really about 10%, the MAC motor efficiency (without gears) would be in the high 90s :lol: :lol: :lol: in fact is has around 88%, as reduction loss is~3%. Not more, not less.

If we there really would be 10% loss per stage, people would start using water cooling for their gears The only gears that have such horrible efficiency that i know are badly aligned bevel gears in chinese made andgle grinders. these gear boxes indeed get hot. But this is fixable by adjusting gear alignment, then even these cheapo tool gearboxes have acceptable efficiency

 

[Punx0r]

a MAC geared motor that has a reduction of 5 gets 85% efficiency including reduction loss. If this reduction loss was really about 10%, the MAC motor efficiency (without gears) would be in the high 90s :lol: :lol: :lol: in fact is has around 88%, as reduction loss is~3%. Not more, not less.

What documentation is there to support these efficiency values for the MAC motor?

 

[crossbreak]

http://www.ebikes.ca/tools/simulator.html
choose the eZee 300rpm(choose ideal battery and ideal controller). I made measurements with the 6T MAC which is identical, arrived at little more then what the calculator shows at equal rpm

 

[crossbreak]

here is an updated sheet.

BTW: Revolt told me the exact same Data for the RV-120!? Who measured these figures? John or Revolt?

 

[liveforphysics]

Picture your favorite RC motor. Now unroll it's stator about its axial center, and re-wrap it around the inside of your rim, repeating the pattern as needed, at say 4x the radius if previously you were going to use 16:1 gearing reductions (because motor torque grows at the square of radius). Now you have a motor capable of equal specific torque

Interesting point. Specific torque doesn't equal with specific copper loss, does it? It doesnt:

A motor with 4 times the radius has 4 times lower Kv, if all the 4 parts are connected in parallel. Then it has 1/4th of the resistance. Km² = (60/2π)² * 1/(kV²*Rm), so the new motor has 1/(1/4²*1/4)=4³ = 64 times lower copper loss per Nm of torque. Not the same as the small motor that has 1:16 reduction, as reduction raises Km² quadratic, it has 16²=256 times lower copper loss per Nm!!!

Sorry Luke, gearboxes are unbeatable awesome!!

Both must be wound to have the same wheel speed range so its apples to apples. At which point your kinda silly calculation is mute.

 

[crossbreak]

math can be silly, indeed

Km² tells you how many Newton-meters of torque you get for a Watt of copper loss. the gear drive has an advantage of 300% here, so your comparison is obviously not apples-to-apples

 

[liveforphysics]

Somewhere we may have a conceptual issue. Let's look at what gearing does.

Picture a statically loaded cog/cog interface. Trim away all the teeth that aren't engaged right now (typically just 1 tooth at a time is carrying torque). So it looks like a pair of lever arms interfacing with each other, whatever ratio between lever arm lengths happens to be is the amount of additional rotation needed by the shorter lever, and also the amount of force increased by the leverage on the longer lever. In a gear box with a bunch of stages, it's a bunch of lever arms pushing on lever arms, so we can make a bunch bunch of input motion on the lever become a tiny amount of motion on the output lever with proportionately increased force.

All I'm advocating, is rather than getting your 'gearing' through a bunch of external series lever arm arrangements (which each add mass that isn't copper or iron and hence not helping convert electricity into what you ultimately wanted, torque at the rear wheel over a speed range), to instead just use single stage lever geometry that permits achieving the same amount of leverage you wanted, but in a single stage that has no additional moving parts (failure modes) and weight.

 

[speedmd]

These little levers are both pushing and sliding. The higher the torque and poorer the lube the greater the losses and wear from the sliding.

 

[Arlo1]

It's worth noting that all the gearing reduction stages do not increase KW or HP which is the ability to do actual work in fact they reduce the HP because of the efficiency losses from friction ect. You will see an increase of torque with a loss of HP and a loss of RPM (speed).

 

[cwah]

So are geared motor better than dd?

 

[liveforphysics]

So are geared motor better than dd?

If you prefer to stack a series arrangement of little teeter-totter levers that each cause loss rather than just starting with the lever length you wanted to begin with.

 

[Arlo1]

So are geared motor better than dd?

If you prefer to stack a series arrangement of little teeter-totter levers that each cause loss rather than just starting with the lever length you wanted to begin with.

I think there is a balllance here. With rpm vs weight vs size of the package and I bet 1 stage of reduction is optimal. But maybe a really big diameter with a hollow center where the controller would sit..... If only someone was working on a round controller

 

[liveforphysics]

So are geared motor better than dd?

If you prefer to stack a series arrangement of little teeter-totter levers that each cause loss rather than just starting with the lever length you wanted to begin with.

I think there is a balllance here. With rpm vs weight vs size of the package and I bet 1 stage of reduction is optimal. But maybe a really big diameter with a hollow center where the controller would sit..... If only someone was working on a round controller

Eventually the residue of thinking inside the confines of the ICE limitations will pass, and people will embrace understanding the torque/power they wanted was only a single lever arm and active material of the correct geometry away.

It's true most hubmotors are non-stellar performance. If an RC motor was made around the same labor and materials budget per motor mass afforded to most hubmotors, it would suck too.

This doesn't mean hubmotors dont have the capacity to be amazing, it means that RC motors have been developed around achieving high performance through optimized design and good materials, and hubmotors have been optimized for being the lowest cost solution to make a bicycle/scooter move.

 

[Arlo1]

What I'm saying Luke is there is most likely there will be a problem getting the torque over the speed range with out gearing it down to get the rpm up or increasing the diameter/size/weight of the motor to something unrealistic. I'm very interested in experimenting in this area. But I do agree multiple stages of reduction and multiple years are a waste of energy and have more failure points making the system less desirable.

 

[liveforphysics]

What I'm saying Luke is there is most likely there will be a problem getting the torque over the speed range with out gearing it down to get the rpm up or increasing the diameter/size/weight of the motor to something unrealistic. I'm very interested in experimenting in this area. But I do agree multiple stages of reduction and multiple years are a waste of energy and have more failure points making the system less desirable.

Direct drive has the potential to be both lighter, and the most efficient if the wheel diameter permits packaging the radius needed. If not, a single stage is the best compromise.

 

[speedmd]

When something like a lightweight - porous high flux magnetic iron (or semi metallic) reaches maturity and light weight conductor options to solid copper come on the scene, it will be a whole new day for large diameter DD wheel type motors.

 

[liveforphysics]

When something like a lightweight - porous high flux magnetic iron (or semi metallic) reaches maturity and light weight conductor options to solid copper come on the scene, it will be a whole new day for large diameter DD wheel type motors.

This is coming inevitability. The EV technology of today will seem as crude as model-T cars seem to us in another 20 years of development.

 

[John in CR]

here is an updated sheet.

BTW: Revolt told me the exact same Data for the RV-120!? Who measured these figures? John or Revolt?

The only thing I measured was resistance on the RV-120, and that was confirmed by Weasel's measurement.

 

[crossbreak]

ah ok, thx. would you mind doing some no load tests?

 

[crossbreak]

Somewhere we may have a conceptual issue. Let's look at what gearing does.
[...]
All I'm advocating, is rather than getting your 'gearing' through a bunch of external series lever arm arrangements (which each add mass that isn't copper or iron and hence not helping convert electricity into what you ultimately wanted, torque at the rear wheel over a speed range), to instead just use single stage lever geometry that permits achieving the same amount of leverage you wanted, but in a single stage that has no additional moving parts (failure modes) and weight.

sure you missed something. Your large motor with 4 times the radius only has 1/4rd of the lever the 1:16 reduced small motor has. The big one may have 4 times the copper, still it cannot win. The 1:16 small one will have a much better efficiency over the whole rpm range, especially at low to mid speeds and high torque. I'll try to draw a contour map of both using the TP-100 (my favorite RC Motor) data as an example if I find the time

 

[Arlo1]

Torque goes up at the square of the increase of the diameter. And with the added copper of the bigger motor the continuous power will be higher.

 

[liveforphysics]

Somewhere we may have a conceptual issue. Let's look at what gearing does.
[...]
All I'm advocating, is rather than getting your 'gearing' through a bunch of external series lever arm arrangements (which each add mass that isn't copper or iron and hence not helping convert electricity into what you ultimately wanted, torque at the rear wheel over a speed range), to instead just use single stage lever geometry that permits achieving the same amount of leverage you wanted, but in a single stage that has no additional moving parts (failure modes) and weight.

sure you missed something. Your large motor with 4 times the radius only has 1/4rd of the lever the 1:16 reduced small motor has. The big one may have 4 times the copper, still it cannot win. The 1:16 small one will have a much better efficiency over the whole rpm range, especially at low to mid speeds and high torque. I'll try to draw a contour map of both using the TP-100 (my favorite RC Motor) data as an example if I find the time

The lever arm radius is one of the two factors making the torque grow at the square of radius, the active perimeter length is the other factor which together make the X^2.

As you grow radius, you have a longer line of magnet/coil assembly pulling on a longer lever arm.

 

[crossbreak]

i totally agree on torque abilities. Just not on copper loss. The geared motor has an advantage here

 

[liveforphysics]

i totally agree on torque abilities. Just not on copper loss. The geared motor has an advantage here

The geared motor is capable of being arranged in an equivalent model as an RC motors stator teeth on a radius of proportional length to become equal to the gearboxes net equivalent lever length. It just looks like a big hubmotor then that has a sparce ring of teeth and magnets.

 

[Arlo1]

i totally agree on torque abilities. Just not on copper loss. The geared motor has an advantage here

With more copper you have potential for less losses. More copper always wins. You are comparing a small motor to a big one. Bigger motors with the same design just scaled up are ALWAYS more efficient at the same power level.