MAC-BMC Motor, planetary gearbox efficiency study

[mrbill]

I recently compared system efficiency using a MAC-BMC "600 watt" motor (adapted for external control) without a gearbox, with the older Currie gearbox that uses a 12mm output shaft and 1/2" brass bushing, and with the newer Lashout gearbox that uses a fatter 18mm output pinion shaft and ball bearing on the outer housing to support the shaft.

Conclusion: some gearboxes are more efficient than others. Specifically, the Lashout gearbox with its output shaft supported by a ball bearing rather than a brass bushing, is the most efficient.

Efficiency estimates:

Lashout planetary gearbox: 93% at <20A, 95% 20-33A, and 97% >33A
Currie planetary gearbox: 88% over most of the band, creeping up to 90% at 33A

http://bit.ly/j6tFS3

If you are planning to use a gearbox with one of these motors and want the highest efficiency, I recommend using the Lashout as sold by Scott MacGregor at EVDeals.com.

 

[neptronix]

I know that the currie consists of straight cut notchy gears.. noisy as hell.. and can't be all that efficient.

Do you have a picture of the lashout setup?
Hell.. do you have a picture of your entire setup?

 

[mrbill]

I know that the currie consists of straight cut notchy gears.. noisy as hell.. and can't be all that efficient.

Do you have a picture of the lashout setup?
Hell.. do you have a picture of your entire setup?

The Currie and Lashout use the same planetary mechanism, and, yes, they're straight-cut gears.

http://www.electricscooterparts.com/SPR-P360.htm

They do make some noise, about as much as the Headline/Cyclone system. Whether it's too much is up to the listener. Adding some thicker grease (thick, sticky molybdenum disulfide is best) quiets them down somewhat. Straight-cut gears will usually be more efficient than helical gears since the teeth of the former are sliding less as they engage and disengage each other.

The following link points to an album of photos I've taken over several years of adding electric assist systems to this bike.
http://mrbill.homeip.net/albums/power_gold_rush_build/index.html

The gearbox with the higher efficiency is the Lashout gearbox that is sold by EVDeals.com with the 18mm output shaft and ball bearing support at the end. There may be other sources of this gearbox, but I believe that the planetary gearboxes that use the brass bushing to support the pinion have lower efficiency and wear faster with use.

Here's a photo of this gearbox disassembled:
http://mrbill.homeip.net/albums/power_gold_rush_build/pages/page_83.html

Here's a photo of the Currie gearbox housing showing wear at the bushing after only 1000 miles of use.
http://mrbill.homeip.net/albums/power_gold_rush_build/pages/page_81.html

 

[neptronix]

Interesting, thanks for the education, hehe.
I read up on wikipedia for a bit and now i understand the difference.

BTW sorry for the OT but i see that you're in the central coast? that is where i grew up.
Did they ever complete that trail from Avila to Los Osos ?

 

[amberwolf]

What's the most power you've run thru one of those Matex (lashout) planetaries, and have any of them ever broken/failed in use for you?

I ask because I have two of them (new from All-Electronics) that I plan on eventually making up shaft adapters for, to run off of some radiator fan motors I've got for a small drive system, probably friction, along the lines of the first successful DayGlo Avenger ebike setup I made.

 

[mrbill]

Interesting, thanks for the education, hehe.
I read up on wikipedia for a bit and now i understand the difference.

BTW sorry for the OT but i see that you're in the central coast? that is where i grew up.
Did they ever complete that trail from Avila to Los Osos ?

Don't know. I live near San Jose, CA, which is generally considered to be north of the "Central Coast". Back in 2007 I rode the Bob Jones Trail into Avila Beach on my way from San Luis Obispo, but I don't recall seeing a branch heading off to Los Osos. San Jose is about 200 miles north of San Luis Obispo. California is a long state.

 

[mrbill]

What's the most power you've run thru one of those Matex (lashout) planetaries, and have any of them ever broken/failed in use for you?

I ask because I have two of them (new from All-Electronics) that I plan on eventually making up shaft adapters for, to run off of some radiator fan motors I've got for a small drive system, probably friction, along the lines of the first successful DayGlo Avenger ebike setup I made.

I've run about 1250 watts in (for about 850 watts out) at 24 volts for up to 30 seconds when testing. That's about 50A at the motor for whatever torque you get out of the motor (MAC-BMC "600 watt" or "Powerpack" style motor) for that current. The planetary didn't fail or make any untoward noises. What is starting to fail is the bushing where the pinion is held at its outer end as in the photo linked above. I also noticed that the planets in the carrier were a little looser in the gearbox I had used than in the new gearbox. How loose is too loose before replacement is necessary, I have yet to discover.

In use I tend to peak about 1000 watts or less into the motor, about 1HP out, peak. Running at higher voltages won't increase the maximum torque, but will increase the RPM. I haven't tried higher voltages than the 28 or so I get from a fresh battery. I know that these motors and planetaries have been used at up to 48 volts (e.g. Ecospeed), but I don't have first-hand experience.

 

[amberwolf]

Thanks--that helps. The bushing wear wont' be a problem on mine, as I'll end up using a bearing, probably also a pillow bearing on teh other end of the output shaft from the planetary.

The planets are probably not on bearings in the Matex carrier, but I can change that if excessive wear becomes a problem. At $10 each plus shipping (from AE) they're a bit expensive for me to change out the whole planetary, assuming they even still have any by the time I need some.

 

[Ham549]

I have been running 1,000 watts at 48 volts through these and recentely after a few years of use the sun gear broke. Now I had another planetary gear set and put that in and just about a mile into my ride the sun gear on that one broke. The first time I wrote it off as wear and tear but haveing it happen twice in a row something is up. I am wondering if the roller clutch that has started making a clicking sound.

 

[mrbill]

I have been running 1,000 watts at 48 volts through these and recentely after a few years of use the sun gear broke. Now I had another planetary gear set and put that in and just about a mile into my ride the sun gear on that one broke. The first time I wrote it off as wear and tear but haveing it happen twice in a row something is up. I am wondering if the roller clutch that has started making a clicking sound.

Hi Ham549:

Sorry to hear about your troubles with your gearbox.

The roller clutch and sun gear are two different parts. But, if the roller clutch is making strange noises, then maybe it's about to go. These things usually fail all at once, but I've had some that start to show tell-tale signs of wear before they actually break. In particular the carrier for the rollers starts to crack in a few places. Take it apart and look for tiny flakes of metal or for cracks in the plastic or phenolic roller carrier. Use a magnifying glass or loupe if necessary.

Are you using the EVDeals/Scott McGregor version of the planetary housing with the 18mm pinion and clutch, or are you using the older 12mm pinion and clutch? The latter is much more likely to fail. Moreover, the efficiency is rather poor as its outer end is held only with a brass bushing that gets quite hot in use instead of a nice, smooth-rolling bearing.

As for the sun gear breaking, can you tell us where got your spare planetary gears? Last time I checked All Electronics was no longer carrying the Matex planetary gears, but you can still get them from EVDeals.

http://mrbill.homeip.net/albums/lashout_planetary_gearbox/index.html

 

[Ham549]

I am using the EVDeals/Scott McGregor version, the spare gear set up was from the older gear box (the gear assembly looks the same though). It's haveing them go one right after the other that has me puzzled). You can get more Planetary Gear Assembles here http://www.electricscooterparts.com/specialtysprockets.html The thing is I am constantly fixing this bike and am considering a hub motor but it dosen't look like there is one that would give me the same speed and torque.

 

[mrbill]

I am using the EVDeals/Scott McGregor version, the spare gear set up was from the older gear box (the gear assembly looks the same though). It's haveing them go one right after the other that has me puzzled). You can get more Planetary Gear Assembles here http://www.electricscooterparts.com/specialtysprockets.html The thing is I am constantly fixing this bike and am considering a hub motor but it dosen't look like there is one that would give me the same speed and torque.

Drive parts and bike parts do eventually wear out with use. Unless you've recently changed something about the way you ride (e.g. increased current limit, increased the gearing of the motor to the drivetrain, increased weight of bike, riding harder than before--more jackrabbit starts), you're probably just unlucky and got a bad planetary gear set.

I do find that running at 48 volts and input power less than about 600 watts is less efficient than running at 24 volts for the same power. At 48 volts the efficiency curve gets pushed to the right, the peak being around 1200 watts in. If you're average power is in the mid-100s range, then you're losing some energy to heat by running at 48v instead of 36 or 24. That reduced efficiency manifests as heat. Heat can stress parts more, even if the torque (effective input current) is the same.

http://mrbill.homeip.net/albums/mac_bmc_600w_motor/efficiency_curves/M1_delta_Inf.pdf

I've got a few thousand miles now on my first planetary gear set, running at 24 volts, roughly 1000watts peak input power, sometimes a bit more.

 

[StudEbiker]

I am running peak watts around 1300 at 12s LiFePo (39v). I had one planetary fail where the roller bearing shaft enters the planetary, but I think this is because the bronze bushing was failing and getting out of round causing bad stress on that section. I replaced that planetary and went with one of the EVDeals upgraded housings and everything has been fine since. The noise level went down significantly when I replaced the housing as well as the performance increased. That little thing is a pricey little booger, but it is a much better part than the stock piece for sure. I just wish we could find out what that bearing is, I have about 3-4 more housings lying around I'd love to be able to convert myself.