GM BLT motor internals?

[Neptronix]

Hey there, I just wanted to post up here because y'all seem to have more golden motor experience than endless sphere..

http://goldenmotor.com/SMF/index.php?topic=4432.5

I'm wondering what this motor looks like on the inside? could someone crack the back cover and show us it's butt?  I'm thinking that if it's a low pole count motor, it could probably be spun up to a good RPM on high voltage and make maybe half the power of the HPM-5000B, which would be fun :]

Let me know if anyone has taken pics..

[Neptronix]

I have done some bench racing on this motor, which is why I am excited about it ( and want to see if it has a low pole count so that it can be ran at higher voltages ):



This motor is looking better the more I look at it  :lol:  now that i've had some sleep, i've done a bit 'o math..

I do plan on using a 4.33:1 reduction by running the 9T sprocket the motor comes with to a 39T sprocket..

http://www.goldenmotor.com/hubmotors/BLT-800W%20Performance%20Curve.jpg

So the constant loaded torque when reduced 4.33:1 for the 800W x 48v would be 39.57n-m. ( 29 ft-lb ) at 234rpm ( 80% efficiency )

Let's compare this to golden motor's pro-kit motor ( not the Magic Pie ): 18.6n-m ( 13.7ft-lb ) at at 266rpm ( 77% efficiency on 36v. Not so impressive huh.. 

If you adjust the RPM / torque for equal windings, the BLT-800 produces about 2 times more torque constant... wwwow.

I can't find any dyno testing numbers on the Magic Pie, but I know it is a total torque beast as well because I built a hill climbing race bike out of one.

So let's compare the BLT-800W to a Crystalyte HS ( per the dyno test on crystalyte.com ):

4:33 GM BLT-800 motor on 48V: 39.57NM constant at 234RPM - 80% efficiency
Crystalyte HS3540 on 48V: 26.53NM constant at 271RPM - 83.2% efficiency

Since the Crystalyte HS is running 14% faster, let's take 14% off the BLT-800's torque figure..

BLT-800W: 34nm constant, HS3540: 26.5nm constant.

By these numbers, the BLT should produce 33% more torque constant than the Crystalyte HS 3540.

So maybe the BLT-800 can perform more like a Crystalyte 53xx or 54xx?

This thing seems like a torque beast; as most GM motors seem to be :]..
If you want a high power bicycle speed motor from GM ( the HPM-5000B is waaaaaay too much ), this bad boy might be the ticket.

[Bikemad]

Hi Neptronix andto the forum.

I've just been doing a few calculations of my own to compare these two motors at an equivalent power consumption and output speed.

The Crystalyte (34.87V @ 26.02A) uses 907.6W to produce its maximum power output of 755.2W with a speed of 271.9rpm and a torque of 26.53Nm

The BLT-800 with a 9T to 38T gearing (4.222:1 reduction, 48V @ 18.96A) would require 910W to produce an output of 767W with a speed of 273.6rpm and a torque of 27.02Nm

These output figures are within 2% of each other, but the BLT-800 would probably loose more than 2% of its delivered output due to the mechanical inefficiencies of the chain driven gear reduction mechanism.

It's also interesting to mote that with a 26" wheel, the no load speed of the Crystalyte would be 27.13mph, but the unloaded speed of the BLT-800 would only be 24.41 mph.

If the Crystalyte was running on 48V instead of 36V, the recorded measurements of the two motors would be easier to compare.

Alan
 

[Neptronix]

Nice to hear that someone else is nerding out on this motor . I have seen it multiple times but because of how the spec sheet presents the info, it looks like a weak motor. Only until you think about it at higher voltages and gear it down significiantly, does it look remotely appealing.

Are you comparing it to the Crystalyte HS, or the 5300 series?

Also, the figures I was using were 'max power' figures given by both motor companies. Max efficiency numbers seem to be quite different, and sometimes max torque on hub motors is calculated at below 50% efficiency ( yeahhh.. that's real useful - for about 5-10 minutes ).. so that seems to be the most accurate number.

I got my higher figures using that number.

[GM Canada]

Here you go. Please keep in mind this motor was in use for a while then I believe the hall sensors failed. It was sent back and a new one sent out. This motor then sat for about 8 months before I opened it today. I was really surprised at how strong the magnets are. It took a lot of force to pull it apart. Hope what you are looking for can be seen in these pictures.

Gary

[Neptronix]

Gary; that thing sure isn't a lightweight, lol! I see what they did with the 650w, bit of a cheap move there. Then again, you've got a ton of thermal mass to dissipate heat there for the 650W motor. So the extra steel/aluminum is just a bonus heat dissipator for when you're really hammering it climbing hills and maybe room for fans too.

I like the low pole count, it looks like it may spin up on higher voltages pretty good. I wonder if the magnet/axle assembly is hollow on the inside or what. Maybe it could drop a little weight that way.

This motor looks like quite the chunk of magnet and copper, I can't wait to get my hands on one.

Thanks a lot for the inside look; I really appreciate it. Maybe more people will get hip to this motor once I hot rod it :]

[Bikemad]

There appears to be a lot of empty space inside that motor, I reckon there's just enough free space to accommodate 650 grams of Bacon, Lettuce and Tomato, hence the BLT-650 label.


With a bit of machining, that motor could be made a lot shorter and significantly lighter too, but still have exactly the same power output.

Alternatively, they could have placed dual in-line rotors and dual windings to make the motor a lot more powerful, and the casing looks thick enough to enable grooves to be machined around the main body to increase the surface area for improved heat dissipation and even more weight reduction.

Are you comparing it to the Crystalyte HS, or the 5300 series?

Also, the figures I was using were 'max power' figures given by both motor companies.

I was using the maximum power figures for the Crystalyte HS3440, and simply used the point on the BLT-650 graph where the power consumption was pretty much the same:



I thought this would be the fairest way to compare them.

Alan
 

[Neptronix]

I hope that the 800W motor doesn't have dual rotors because the benefit of such a loooong motor is that you end up with less copper at the ends of the stator ( is it still called a stator in an inrunner? ) basically sitting there doing nothing but making heat.

That's why these square sized / long motors are so dang efficient. more of the copper is actually doing work than in say, a hub motor where you have tons of copper hanging out on the edges. That's a waste.

I ordered up a 650 and an 800. The 650 has a bit higher efficiency than the 800, which would not make any sense.. I hope it is not due to dual rotors 

The case could definitely be machined a bit for more heat dissipation.. or you could add some heatsinks to it!



RE your calculations.. you said BLT-650 but that's the BLT-800 graph you have there, so I figure you are comparing the BLT-800 with the HS3540.

But your calculations are very pessimistic because you are comparing the max efficiency number on the BLT-800 to the max power out number on the Crystalyte.

The difference in RPM makes things harder to calculate - also, these motors have different performance curves, so the RPM to RPM comparison may not be the best way of doing it. I don't know which way is best, so i'm not saying your way is wrong.

Max efficiency point on the Crystalyte would be only 13.42NM though. Max efficiency on the BLT-800 is 6.180NM ( needs to be adjusted per RPM difference of course.. )

However -
Max power out on the Crystalyte is 26.53 NM, Max power out on the BLT-800 is 10.53NM.

So if we consider the 'max power' figures only, then the Crystalyte is putting out 26.53NM, and the BLT-800 is putting out 36.69NM after the reduction.

The Crystalyte HT comes close to comparison:

http://cy.wjisc.com/www1/Crystalyte%20Ht%20Rear%20Motor%2025KM%20Max%20speed.pdf

Max power out would make 37NM at 170RPM at 35v. But it would only run at 74% efficiency which is rather low.

That's good torque, but low RPM. I bet you would need to run this motor at 57V to get the same RPM x Torque as the BLT-800 on 48V. You would have to run a lot of volts to get good speed on that motor.

Are you convinced that the BLT is a torque monster yet?