Transmissions vs. Dual Motors

I’ve been messing around with motors lately, and stumbled on something that I think explains the slightly different nature of electric motors, power curves and transmissions.  This time I’m not using graphs, I’m using actual performance.  It works with three configurations of the same bike.

The first configuration was with the Motenergy ME0709 with gearing that gave me a top speed of around 70mph.  It was capable of throttle-blip wheelies.  If I geared it slightly taller, it would possibly do a higher top speed but about the fastest I think I could get it to go would be around 100mph.  The top RPM is around 3200.

I then put in an ETEK.  This motor is lighter, by something like 12lbs.  It was using the same gearing, but with a top RPM of over 5000, the top speed looked like it was around 110mph.  However, it didn’t have the low-end torque to do wheelies with this gearing.  (One of the tests I want to run is to compare the performance of the two motor geared for the same top speed, to see how the power distribution goes, and see if, first, the ME0709 can pull the top speed for high mph gearing, and see if the ETEK can pull wheelies at lower mph gearing. )

So, with the ETEK, I have the top speed I want, light weight, but not enough low-speed torque.  If I gear it down I may get the torque, but lose the top speed.  Perfect application for a simple two-speed transmission, right?  Maybe so, if there was such a beast.  But here’s where it gets interesting.

Take your ETEK, keep the gearing the same (for high top speed), and add another ETEK. What do you get?  You get the same top speed, but double the torque at any given RPM.

Running two motors in parallel keeps your voltage the same, but feeds twice the current (assuming you’re able to feed that kind of current).  It adds the weight of a second motor, in this case, 21lbs.  I suspect you couldn’t build a two-speed transmission that’s going to be lighter, so we’re even there.  It also puts less strain on each motor, than you’d have for a single motor set up with a transmission, basically being asked to pull hard at low speeds, and pull hard at high speeds.

Basically, you’re adding thermal mass and torque at the same time.  And that, my friends, is the secret behind getting your head around the concept of why adding motor capacity is different, and maybe better, than adding a transmission.

It gets back to the basic difference between gas motors and electric.  Gas motors represent an entire system that delivers power, similar to the entire electric drive system.  An electric motor is only a part of that entire system, and it’s basic function needs to be power handing capacity, rather than thinking about it as power delivering capacity. See what I’m doing here?  The system delivers the power to the motor, and it has to be able to handle it without blowing up, to be a balanced part of the system.  (…where gas motors ARE the system.  Think in terms of the piston, if you’re a gas-head.  The piston has to be able to handle the power delivery of the gas motor without melting, whether you’re running a normal motor or a turbocharged nitrous configuration.  The more power in the combustion chamber, the more stress the piston’s going to get.)

So adding a transmission to a motor is going to stress it more.  If the motor is big enough to handle the stress and the system can deliver the amps, then it will work.  There’s parasitic loss, but that’s probably not enough to worry about.  Adding another motor spreads the torque curve, by doubling it, and adds thermal mass.

Only by looking at the entire drivetrain system, can you really answer the question…  will additional motor capacity work better than a transmission.

The end result is only a little more weight- roughly 42 lbs of motor, not counting a few pounds for the mounting, and twice the torque.  The ME0709 is what, 34lbs?    Also, twice the current handling capacity.  The ME0709 handles 300amps peak.  The peak current for the ETEK is hard to find, and I don’t believe some of the numbers out there, but if you take a conservative 250amp peak and double it, then you’re looking at 500amps peak.  Well above the ME0709.

As I’m becoming fond of saying, it’s all about the system.  As remotecontact is fond of saying, it’s all about finding the bottleneck in the system.  Rather than simply adding juice to one component or another, you have to think in terms of the entire system and how all the components work together.  And one more thing, maybe the most important of all.  It all depends on what you’re designing the system to do.

ETEK Video- (Lemco)

Continuing my ETEK anatomy thread, just found this video showing the Lemco motor:

Skip to 4:38 to see the inside bits.

The ETEK Exploded

Well, view.  The exploded view.

Them are the partz.  This is how they go together:

The two collars are what holds the rotor.

So, yeah, in the process of discovering how to take the thing apart, I broke a 12-ton press and damn near busted my thumb with a sledge.  Broke my BFH too.  Had to cut the collar nut off, then realized it was coming off the wrong direction, over a collar that was just a wee big too big.  If brute force doesn’t work, you’re not using enough.

Will Ted be able to put it back together?  Will the ETEK ever run again?  Don’t change that channel…

(Sorry about the abbreviated posts, I’ve got two story deadlines this week…  had to get these posts up though to keep me honest.  I’ll be back and flesh them out a bit after the stories are done.)

Here’s how the collars go together:

ETEK Motor Teardown: 10 Minutes (Video)

Here you go.  Start to bitty parts, how to tear down an ETEK (or Manta) motor.   (Even sparing you the tacky voiceover or obnoxious music.  Don’t thank me, no, you’re too kind…  )

ETEK Motor Repairs

OK, I ran my ETEK for a bit and the rotor started binding on the brush-side magnet.  So I started looking for slop.

The magnets are located on the two housing halves.  The rotor is located between them with the bearing and the shaft, along with some shims and a bearing lock plate, on one end only- the sprocket end (as opposed to the brush end).  So, there’s where I figure there has to be some slop.

As far as I can see, the shims and the circlip seem OK.  The shims measure out at a perfect .010 each, and the circlip fits snugly in it’s little circlip groove.  The bearing has a bit of slop from side to side, so I’ve ordered a new one.  I’m going to hazard a guess that it’s moving .015 or .020, at the most.  I figure it can’t hurt to just plop a new one in.

But here’s what I found that may actually be significant.  The bearing locking plate, on the inside of the housing, doesn’t seat up against the housing.  Here’s what I mean.

This is the bearing sitting in the housing.

The outer diameter of the bearing is flush with the face of the housing.  Here’s the plate, sitting over that face:

That, once it’s bolted in, should hold the bearing flush with the face.  The problem is, it doesn’t.  The plate is slightly larger in diameter than the faceplate relief.  Here’s what it looks like from the other side, with the bearing removed, showing the space between the plate and the face.  It measures out to about .035.

…corresponding to the same depth of the relief on the inside between the outer casting (where the plate is sitting) and the inside face (where the plate should be sitting):

So, it should be a simple fix to just grind down a little of the edge diameter of the locking plate so it has a better fit. I’m not at all convinced that this will be enough to keep my rotor from binding, but it certainly isn’t right.   Stay tuned.

For the record- this is a “Manta” ETEK motor from eBay- reportedly never used, and “remanufactured”.

Briggs and Stratton ETEK Teardown: via TeamHurtz.com

Want to open up the ETEK?  Piece of cake.  Here’s a great 3-step post on it, via TeamHurtz.com.  Great suggestions on when to mark the positions of the parts you’re taking off, too.

Also found this manual: etekmanual Form #275225 ETEK Manual

Now.  Here’s what I did.  I don’t have photos, because, frankly, I was more interested in doing the repair than showing how to do it.  Sorry.

First, I pulled the cover as shown above.  I can’t rave too much about the sweetness of having a good puller.  The one I have is a basic three-leg gear puller, and by taking everything off except two of the brackets, I was able to reach below the legs of the face plate here and toss a pin across the two puller bracket holes.  The cover came off in a heartbeat.

All you’ve done at this point is to pull the cover off.  The magnet got sucked into the rotor when you undid the bolts.

Going to the other side, undo the circlip on the shaft.  There are a few shaft shims, take them out, and then, with a rubber mallet give the shaft a bunch of hard whacks (after you’ve undone the bolts on that side too).  The shaft should move out of the bearing at that point, and the rotor will come out, with the magnets stuck to it.

I then reconfigured my puller with a couple of brackets bolted to the magnets, and used that to pull the magnets off.  I had a few pieces of wood to stick in there between the rotor and the magnet as it separated, and once it got to about an inch and a half away, I could grab the magnet and pull it off.

Watch your fingers.

I was pulling the thing apart because there was some significant binding when the motor turned.  The first thing I saw was something that looked like this, which freaked me out:

The corner of the rotor was all ground off, on one area.  I figured my motor was toast.  I then found this video, showing the same thing, and so I figured that grinding was done in the factory to balance the rotor.  Remember to breathe.

I cleaned everything, checked stuff, noticed the rubbing was on the brush-side magnet from the outside of the rotor, and checked the rotor for wobble.  Sure enough, there was a little run-out, and I tried tapping it gently with a rubber mallet where it was a little proud.  It brought it in, remarkably, and it ran fairly true.  I have no idea why it was like that, and no idea if the problem will come back, but after reassembling the motor it seems to have taken care of it.

The one trick to re-assemble the motor is to bolt the magnets into the housings before you put it back together.  If you don’t you’ll be trying to place the magnets on the rotor and get them centered.  That ain’t easy.  Then when you try to bolt it together again you’ll have a reach to get to the threads, and be pulling the magnet off the rotor with your little bolts and not a lot of thread.  Not easy either.  If you place the magnets in the housing halves, bolt them in, then assemble them, the magnets get firmly seated, the bolts don’t get stressed, and the magnets help you by pulling the whole thing together.

Yeah.  On that.  When you’re putting the brush side housing on (after you’ve put the output side on and replaced the shims and the circlip) keep your fingers out of the way.  It doesn’t go in gently.  It snaps it right in…

Total ET of the teardown, without messing with the puller for the first time?  About 5 minutes, including sipping coffee.  Reassembly?  About 3.  Don’tcha love a motor with one moving part?

Sneak Peek at EnerTrac TTXGP Motor!

EnerTrac sure knows how to tease…  but it’s the best kind of excruciating pain.  Here’s the first peek at his TTXGP motor for Team Catamount:

Why a Badass Hub motor for a race bike, you may ask?

From EneTtrac:

“It’ll let the bike hold less expensive larger format batteries and still be able to hold the full 7.5KW.

It’ll allow the batteries to be lower, much lower on the bike.

The motor is cooled by the wheel.

This is a high voltage lower current motor design so less copper cable weight, no chain weight or sprocket, no added metal for motor mounting.  Better streamlining- again no need to have protruding motors in the air stream.

This motor’s power band is optimized for high speed- it really shines at speed and is worst in off the line situations. She’ll be forced air cooled, solving one of the design challenges with wheel motors, no brushes, thin silicon steel design for low eddy currents allowing the unheard of high RPM.  This motor is capable of the MHM 600 series motor, has got to be the first direct drive hub motor capable of over 2000 RPM, that you can actually buy. Well that’s the short list.

Our goal is to get teams who can’t afford the really pricey batteries and still be able to compete.”

…but as Mark is fond of saying, we’ll let the track prove the claims. 

EnerTrac/ZEV/Kelly – the Hub Motor Spec Matchup

	EnerTrac MHM602	ZEV 7000	Kelly Hub Motor 72V 6KW(13-inch)
Price	$1,295.00	$575.00	$599.00
Availability	In Stock		In Stock
Contact Info	enertrac.net/contact.php	sales@zelectricvehicle.com	sales@kellycontroller.com
Website	http://www.enertrac.net	www.zelectricvehicle.com	www.kellycontroller.com
Warranty	1 year workmanship	2 year	One month refund, one year warranty.
Power Output- continuous	10KW @ 700 RPM @25ºC ambient	7kW @125ºC	6KW
Power Output-peak	30kW @25ºC ambient	15kW @125ºC	N/A
Voltage Range	144V	96V	96V
Current Max	250 amp max	150 amp max	N/A
Weight	55 pounds	42 lbs (incl. tire)	50 lbs
Diameter	10 inch	11.32	N/A
Width	190 mm	200mm	193mm
Mounting details	see PDF file	see PDF file	see PDF file
Brake mounting	EnerTrac intergraded Disc	Disk  – 220 mm	3 hole disk brake
Housing construction	Aluminum	Aluminum	Aluminum
Cooling	Air	Oil/Air	Air
Wheel diam.	16 to 21	13″	13″
Tire size(s)	recommended 110/90 X 18	130/60 -13	130/60-13
Max Speed@tire diam/bike wt.	65mph on Lifan project bike- 118mph (est) on Volta custom- see links below	80mph in a crouch, 74mph sitting up from a dead stop in 1/4 mile trap speed on the drag strip	120km/h on 96V (75mph)
Options	16, 17 , 19 , inch rim sizes
Additional Comments	The motor uses a higher voltage, lower current design to minimize losses from wire heating.The motor is thermally protected when using the recommended Kelly Controller to prevent overheating and burn out. The Hub motor is designed for motorcycles weighing less than 400 pounds with the batteries (dry weight, no rider).The Hub motor will come laced to DOT compliant rim, WM3 style 36 hole, 18 X 2.15, other sizes available on special order, or order just the motor and have a rim of your choice laced onto the motor.

EV Album link for details of Lifan conversion with EnerTrac.

The Hammarhead Volta page for details of EnerTrac in an ’09 Royal Enfield Bullet base chassis. More details with top speed theoretical calculations here, on Autopia.

The ZEV 7000 product page, here.

An amateur Kelly hub motor conversion here.

Disclaimer: All specifications are from manufacturer’s published sources, and are unverified. Although every reasonable attempt has been made to confirm specifications with manufacturers, The Electric Chronicles will accept no liability for false claims or errors.  Readers are cautioned to confirm details and requirements with the seller.

This information represents all available information at the time of publication.  Data will be updated and corrections made as available.

Water cooled motors…

Check out the MotoCzysz D1-10 Dyno vid- awesome awesomeness.

Whether the output is worth the weight increase of all the cooling stuff remains to be seen… but this MotoCzysz motor will certainly tell the story one way or another.

I’m consistently impressed by what these guys are doing. I just wish I could spell it.

A Short Primer on the History of the Etek Motor, and Other Tales

It doesn’t take more than a few hours of looking into building your own electric vehicle before you see the name Etek. The original Etek motor seems almost legendary, and the fact that the Briggs and Stratton name is associated with it makes it all the more interesting. After a while, though, a few things become apparent… the original Etek is pretty much not available, it seems to have been replaced by two newer models, the Etek R and RT, and as you delve a little deeper the confusion mounts.

Cedric Lynch designed the original Lynch motor, started LMC, which appears to still be around, went on to found Agni Motors, and there are rumors about technology from Lynch’s design being licensed to Briggs and Stratton for the new Etek R and RT. Depending where you look, you can find Lynch “LEM” motors listed, Agni motors, original Etek motors, new Etek replacements, even listings on Ebay in the Briggs and Stratton Outlet store for Etek motors. Then, there’s Mars.

Through a conversation with Steve Lorenz at Sevcon, I got in touch with John Fiorenza at Mars Electric LLC. John was a great help in answering some of my more pointed questions- in particular, solutions to the old “permanent magnet DC motors running regen and blowing up” issue- (John’s answer- “Sevcon MilliPak 4Q control was developed for PM motors. It will not blow up.” ) but in the meantime, we got into a conversation about the history of the Etek motor and the current situation. Yeah, I can’t stop myself from making that pun. But here’s the deal.

The original Etek motors were developed by Briggs and Stratton for OEM use, and actually, they were not allowing sales of the motors to any 2 or 3 wheeled vehicles capable of over 20mph for some reason known only, probably, to the lawyers. The early motors were purchased by EV guys resourcefully, through the Service channels. This is how legends are born.

The so-called Etek R and RT are actually Mars motors, designed by Mars (John, actually) without Briggs and Stratton or Cedric Lynch, either. There’s no licensing from Agni going on. Originally there was licensing from Lynch to Briggs and Stratton for the original Etek design- obviously a major source of the confusion.

The Agni, as well as the original Etek, by the way, is an axial air gap motor- see the previous post. The Mars is a radial air gap- a much more traditional basic design. The names, Etek R and Etek RT are names coined by some of the resellers- actually discouraged by Mars and probably an infringement of the Briggs and Stratton trademark.

The bottom line is that the Mars ME0708 and ME0709 motors are what you want, and what you’re going to be sold, if you’re looking for a new motor of “Etek” design. You want the best deal on them? Buy them from John, at Mars Electric LLC. If you want a kit or a package, and the support that comes with that, and are willing to pay a bit extra (usually only $25-50 more) then go with the resellers. (I’m a big supporter of dealers, and the service they provide- but you should know what you’re buying.)

As a little aside- you have, no doubt, heard about the Perm PMG 132 motors? Well, there’s a dirty little tale there, too- that company started as Cupex and was working to help act as supplier for Lynch. Instead, the company got their hand into the cookie jar- they started producing their own motor, the 132- an axial air gap design- and have been accused of infringing Lynch’s patent. The story goes that they don’t deny the design, they argue that the patent is invalid. As far as I’ve heard, it was never resolved in court, and they continue to produce the motor. (Update from Travis: the patent ran out in April of this year…)

From John:
“As to Mars Electric LLC, we are a niche motor designer and distributor for low voltage, high efficiency motors and controls. We design the motors in the USA, and have them made in China to reduce the product and tooling costs. We have been in business since 1997. Our core focus is to develop specialty motors for OEM applications, but we also sell motors to a few dealers in the EV markets. Our warehouse is located in Mequon, Wisconsin, and most of our orders are drop-shipped directly to the customer.”

Oh, and those motors on Ebay sold by Briggs and Stratton? Those are some leftovers from a failed outboard motor project- and with some questionable specs listed, to boot.