MAC GMAC Hot Rod Info

[Bullfrog]

Started this thread so fans of the MAC/GMAC (like me) can share information about hot rodding the motors. Below is some of my experience to date...please share your experiences so we can all learn .

One reason I really like the MAC/GMAC is that it produces more torque per amp than any other motor which means more acceleration and more FUN IMO.

I have an 8T MAC I am currently using for a build and I have done most of my work so far with a 12T MAC. The maximums I have run so far with my 12T MAC that I bought Jan 2017 are:

A. Max Voltage: 58.8v...but I hope to try a 20s (72v) battery in the near future.

B. Max Amperage: 60A battery and 180A phase...but had to drop to 50A/180A settings due my BMS limitations. I ran a 12 FET 3077 Infineon controller for a long time and used an 18 FET 4110 Infineon controller when I went above 40A. No problems with the clutch or gears. I greased the gears using Mobil SHC 100...same base stock (oil) as Mobil 28 but it uses a Lithium Soap thickener instead of the Clay thickener in the Mobil 28. The Engineers at Mobil suggested the SHC 100.

C. Largest OD tire: 750mm...it was a Maxxis Hookworm 29x2.5".

I weigh about 210 lbs ready to ride and my bike weighs 62 lbs. The bike was born as a Mongoose Terrex from Walmart...steel frame hardtail :wink: .

There are potential problems with the MAC clutch if you ride off road and beat the crap out of the motor which I documented here: https://endless-sphere.com/forums/viewtopic.php?t=104226

I tried liquid cooling my MAC with both Low Viscosity Automatic Transmission Fluid (ATF) and later with a mix of distilled water and Motul brand "MoCool" corrosion inhibitor...both worked but have potential problems...leakage of the ATF will make your brakes stop working and although the water/MoCool worked and I had no issues, I only ran it for about six months so the long term affects are TBD plus you need to check the fluid level occasionally to ensure that you are thermally connecting the motor to the shell...this takes about 4.5 ounces of fluid. My experiments with the Low Viscosity ATF are documented is this thread on page 77: https://endless-sphere.com/forums/viewtopic.php?f=2&t=48753&p=1337584&hilit=atf+mac+terrex#p1337584 I did the same thing with the water/MoCool mixture after a little ATF got on my brake disc and my brakes quit working .

ANY AND ALL MAC AND GMAC HOT ROD INFO IS WELCOME AND APPRECIATED...PLEASE SHARE YOUR EXPERIENCES AND INFORMATION .

 

[john61ct]

My interest is in the torque, not speed or "fun"(at all) just hauling big heavy cargo up long steep slopes.

So a "slow" wind, means a higher "T" is that right?

Smallest tire I can get away with on unpaved roads, thanks for that link

And not much point going over 52-60V ?

Grin controllers seem too limited for phase amps, but I'd like FOC, any suggestions to max out the motor? Yes battery will be huge. . .

And yes, I plan to use overtemp limiting and fluid, thanks also, why not Grin's Statorade?

Difference between regular MAC and Grin's version I assume are worth the extra?

 

[Bullfrog]

john61ct...I did my best to answer your questions below in red. Sorry for the length but I get a little passionate when discussing the MAC :lol: .

So a "slow" wind, means a higher "T" is that right? Nope...for a given motor, the winding speed only affects top speed. All versions of a given motor are capable of the same torque per amp from the battery. I'd suggest you play with the motor simulator to see how different parameters affect the big picture. Here is a link to it: https://www.ebikes.ca/tools/simulator.html

Smallest tire I can get away with on unpaved roads, thanks for that link Going to a small diameter tire will increase the thrust...torque remains constant throughout the system regardless of the wheel diameter. With equal torque, you get more thrust or "Force" at the wheel/ground interface which in laymen's terms equates to "lower gearing". I went to a 20" tire with a 27.5 front and two problem areas...lack of ground clearance and slow steering.


And not much point going over 52-60V ? The same thing that makes the MAC the highest torque per amp motor also makes it have higher losses if you spin it real fast. IMO it isn't worth going to a higher voltage unless you have a 12T MAC and plan to limit your rear wheel diameter to 26" or smaller....otherwise the motor temps start to get too high. My answer is VERY subjective...it all depends on how much internal loss you are willing to accept...in other words, there is no exact answer on this question. A 14s (52v) battery is easier to find and usually less expensive than a higher voltage so that is an issue for some. On the flip side, you can get more "power" with less amperage if you increase the voltage. Power=volts x amps. Lots of things to consider.

Grin controllers seem too limited for phase amps, but I'd like FOC, any suggestions to max out the motor? Yes battery will be huge. . . Check out "Table 2" in this paper: https://pdfs.semanticscholar.org/40ac/06d3db0b82242038c2dcd20c433d5d1c74f6.pdf
The paper has some good info but it may be a little complicated for some to understand :lol: . Every type of controller has advantages and disadvantages, including cost...IMO the advantages and disadvantages are summarized nicely and succinctly in "Table 2". I personally like the Infineon Trapezoidal Controller from EM3ev IF your objectives are Low Cost, Simplicity, and High Power. FOC is nice but more complex and expensive plus I have never used one so I have no personal experience with FOC. And yes the Grin Tech controllers are not capable of what I call "High" power but they are great for other applications up to their power limits. Like you said, batteries are a factor and right now the highest amperage BMS I know of that comes in a 14s battery is 50A continuous from EM3ev...so the BMS is even more of a limiting factor than the battery. Some forget that you not only need cells capable of high amperage but also the BMS as well as the controller.

III. COMPARISON OF GENERATED TORQUE

And yes, I plan to use overtemp limiting and fluid, thanks also, why not Grin's Statorade? Statorade offers no advantage if you are not running a Direct Drive Hub Motor...because it uses magnetic particles that help it stay where you want it i.e. in the narrow gap between the stator and the housing. It is also fairly expensive. You'll need at least 4.5 ounces of fluid in a MAC to thermally connect the stator to the housing. My experiments with ATF are on page 77 of this thread: https://endless-sphere.com/forums/viewtopic.php?f=2&t=48753&p=1337584&hilit=atf+mac+terrex#p1337584 I also did the same thing with distilled water and Motul brand MoCool (corrosion inhibitor). Warning...if you use any type of slippery substance like oil, ANY leakage may make your brakes completely quit working...that is why I went to the water/MoCool :lol: .

Difference between regular MAC and Grin's version I assume are worth the extra? It depends on your objective and how much you have to spend. MACs cost less than a GMAC, GMACs have regen, the rear freewheel MAC has a larger/stronger axle, GMAC axles can fit in the dropouts without grinding on your frame, etc. etc. Same power potential.

 

[Bullfrog]

Here is "Table 2" mentioned above:

 

[john61ct]

> So a "slow" wind, means a higher "T" is that right?

I was asking about the relationship between the two. Is 12T for example, fast or slow wind?

Lower amps at slow rpm, extremely overloaded weight going up steep slopes, lower top speed is great.

I've been repeatedly told by many very smart members that slow windings do make some difference **in that specific scenario**, even if only a slight advantage.

And for my purposes, torque vs thrust is I think a too-fine distinction, as stated I cannot go down to "too small" a wheel anyway.

_______
For controllers, cost & simplicity are not relevant, except for ability to program as motors are swapped out, so Sevcon is out, maybe non-Grin ASI too?

BMS current is also irrelevant for me.

Given all that, do you have any straightforward suggestions?

 

[Bullfrog]

12T has the slowest top speed. 6T has the fastest top speed.

Go with a 10T MAC if you don't want regen and a 10T GMAC if you do. I like a 12 FET 3077 Infineon controller and a 14s6p battery.

That combination will cover about 90% of the scenarios.

If you plan to ride off road...go with a BBSHD.

If you want to go over 30 mph go with a direct drive hub motor.

 

[john61ct]

but a 40A current limit?

How close does that get to maxing out the low-rpm torque of those motors?

 

[Jenming]

Difference between regular MAC and Grin's version I assume are worth the extra?

I think Justin mentioned that the gmac was properly sealed for liquid coolant. So if you plan to cool it, then probably yes worth the money? No atf on your brakes.

Also it has a locked clutch witch allows regen. Worth considering for coming back down those hills.

 

[john61ct]

OK, bit of searching, looks like 1500W is only sustainable in the low-rpm highest torque scenario for maybe 15-20min

800-1200W continuous depending on weight/slope, just how slow, as well as ambient, cooling hacks etc

So maybe I shouldn't be looking at more than 40A, and if that's the case Phaserunner + CAv3 is a good fit for me.

And if I need more oomph then start looking at a second motor, maybe Grin's All-Axle to get even stronger drag braking on the down side of the long steep hills.

 

[john61ct]

I think Justin mentioned that the gmac was properly sealed for liquid coolant. So if you plan to cool it, then probably yes worth the money? No atf on your brakes.

Also it has a locked clutch witch allows regen. Worth considering for coming back down those hills.

Yes def need as much of both, cooling and drag braking, as possible

 

[Jenming]

B. Max Amperage: 60A battery and 180A phase...but had to drop to 50A/180A settings due my BMS limitations. I ran a 12 FET 3077 Infineon controller for a long time and used an 18 FET 4110 Infineon controller when I went above 40A. No problems with the clutch or gears. I greased the gears using Mobil SHC 100...same base stock (oil) as Mobil 28 but it uses a Lithium Soap thickener instead of the Clay thickener in the Mobil 28. The Engineers at Mobil suggested the SHC 100.

That's a ton of phase amps for that motor
I'm running 40a battery and 85a phase on a 8t gmac. I guess maybe some room to up the phase amps.

If you want to go over 30 mph go with a direct drive hub motor.

My 8t goes 40mph with 5a of field weakening with a 14s battery. Is still at 35mph near lvc cutoff (42v). Though perhaps the constant 2kw will over heat when summer comes around.

 

[Bullfrog]

The table below is from the Grin Tech web site: https://www.ebikes.ca/product-info/gmac.html



If you are riding along on flat ground, it is roughly saying you can push 1000 watts through a MAC/GMAC once you reach steady state without the temperature increasing any higher. 1000 watts equates to somewhere between 28-30 mph depending on all of the variables and that is why I say if you want to go over 30 mph then the MAC is not the best choice and you need to go to a Direct Drive Hub Motor. It is a lot easier to just use a nice round number like "30 mph" than to explain how I came to that conclusion :wink:. The MAC can run at temperatures well above 110C without any problems but 110C is a nice safe temperature to use if you are speaking to the general public. For short periods of time you can push a LOT more than 2,600 watts through a MAC. The shorter the time the higher the power you can use without over heating...they are inversely proportional when it comes to motor temperatures. It is important to remember that it can take a long time for a motor to reach steady state...over 30 minutes for me when I am riding along on flat ground.

On the phase amperage settings...having my controller set to 160A max phase amperage is probably NOT the best idea for everybody :lol: . It can make the hit very hard when starting. Something like a 90A (or less) phase amperage setting would be much more reasonable and be a lot easier on all of the drivetrain components as well as the electronic/electrical components. Starting and stopping anything including electrical current is hard on the components. A 90A phase current is very doable with the Phaserunner :wink: and there are multiple ways to soften the impact when starting if you are running a Cycle Analyst and/or a programmable controller but the simplest IMO is just to lower the phase amperage.

As far as the torque per amp being the same for all MAC windings...the primary factors that determine torque for a particular motor design are the diameter, width, and the number of poles...these parameters are the same for all MAC motors. A good understanding of how Pulse Width Modulation works and the differences between Phase and Battery amperage will help you understand why different windings of the same motor are all capable of the same torque per battery amp.

 

[Jenming]

If you are riding along on flat ground, it is roughly saying you can push 1000 watts through a MAC/GMAC once you reach steady state without the temperature increasing any higher. 1000 watts equates to somewhere between 28-30 mph depending on all of the variables and that is why I say if you want to go over 30 mph then the MAC is not the best choice and you need to go to a Direct Drive Hub Motor. It is a lot easier to just use a nice round number like "30 mph" than to explain how I came to that conclusion :wink:. The MAC can run at temperatures well above 110C without any problems but 110C is a nice safe temperature to use if you are speaking to the general public. For short periods of time you can push a LOT more than 2,600 watts through a MAC. The shorter the time the higher the power you can use without over heating...they are inversely proportional when it comes to motor temperatures. It is important to remember that it can take a long time for a motor to reach steady state...over 30 minutes for me when I am riding along on flat ground.

Yes, that is a useful table. 40mph is over 500 rpm (on a 26 wheel) so that might get you a couple hundred more watts. The time to steady state is also important. At 50 F outside temp I am able to drain a 15ah battery before overheating running at high rpms and 1500-2000 watts pretty much continuous. Enough to go to 40 mph. We'll see how that holds up in the summer. You are right, 30mph is something this motor will do with no concerns. 40 mph is more of a watch your heat and depending on outside temp, distance, etc., you can pull it off.

When you were liquid cooling did you have any trouble pulling 2kw continous at high rpms?

On the phase amperage settings...having my controller set to 160A max phase amperage is probably NOT the best idea for everybody :lol: . It can make the hit very hard when starting. Something like a 90A (or less) phase amperage setting would be much more reasonable and be a lot easier on all of the drivetrain components as well as the electronic/electrical components. Starting and stopping anything including electrical current is hard on the components. A 90A phase current is very doable with the Phaserunner :wink: and there are multiple ways to soften the impact when starting if you are running a Cycle Analyst and/or a programmable controller but the simplest IMO is just to lower the phase amperage.

Yes, if you want to stay pretty much in spec a phaserunner should be plenty. At 80 phase amps I haven't had any problems with the baserunner.

As far as the torque per amp being the same for all MAC windings...the primary factors that determine torque for a particular motor design are the diameter, width, and the number of poles...these parameters are the same for all MAC motors. A good understanding of how Pulse Width Modulation works and the differences between Phase and Battery amperage will help you understand why different windings of the same motor are all capable of the same torque per battery amp.

It is fun to play around with the simulator to see the effect of different windings.

If you run an 8t and a 10t at the same watts and proportionally scale the volts and amps the motors will perform very similarly.

And even if you use the same battery, but adjust your phase amp settings to compensate for the wind, the controller can cause the motors to behave very similarly up until voltage becomes a limiting factor for the slow wind.

But the 8t will require more phase amps to do the same torque, which likely causes more losses in your controller (accounting for some of the differences in the simulator). And if you are hitting the phase amp limit of your controller then the 10t will have more torque. Which leads to the scenario of pairing a GMAC with a specific controller at max phase amps and battery (say phaserunner at 90 phase amps and 52v battery), in which case the 10t will have more torque at the slow end and the 8t will have more speed/torque at the fast end.

 

[Bullfrog]

With liquid cooling i.e. about 4.5 ounces in my MAC, I never got over about 160F/70C so you can run a LOT more power without overheating BUT it did have its own challenges like leakage with any fluid which meant it needed to be replenished and brake loss with ATF. I sealed the cover/housing interface with Permatex Ultra Gray...no leakage there. I did get some leakeage between the copper stranded wires and the insulation that covers them...capillary action. Also got leakage between the axle and wires where they exit the axle...not much you can do there without disassembling the motor and sealing it where the wires enter the axle.

Jenming...Good explanation on the torques...I just want to point out that the scenario where one wind had more torque than the other is because they are "controller limited". And yes it takes more phase amperage to get the same torque from an 8T as it does a 10T but the same battery amperage and battery amperage determines "efficiency and power". I am guessing that the losses through the controller, like you said, are why there is a very small difference at the same battery amperage. I honestly don't know but I plan to ask Justin because curiosity is killing me.

I also plan to ask what about the GMAC makes it better suited for liquid cooling than the MAC.

Report back when I have answers .

 

[Bullfrog]

Played around with the controller resistance and if you drop it to .001 for both scenarios, the difference between an 8T and a 12T torque, assuming you are not controller limited, is about 1%. I'd guess that 1% is due to a slightly different copper fill factor between the motors.

As far as sealing for liquid cooling, the newer MAC and GMAC are the same. They both have an o-ring seal on the motor side plate and a shaft seal over each bearing.

Justin provided both tid bits above .

The MAC I used for my liquid cooling experiments was the newer version with the same sealing as the GMAC...so leakage is a concern with virtually any MAC/GMAC IMO. Two factors help a lot...don't tip your bike over too far, that way the fluid never comes in contact with the sealed interfaces and only use about 4.5 ounces of fluid...it is all that is required to thermally connect the motor to the housing, any more and you run the risk of having the static fluid height above the sealed interfaces.

 

[Bullfrog]

> So a "slow" wind, means a higher "T" is that right?

I was asking about the relationship between the two. Is 12T for example, fast or slow wind?

Lower amps at slow rpm, extremely overloaded weight going up steep slopes, lower top speed is great.

I've been repeatedly told by many very smart members that slow windings do make some difference **in that specific scenario**, even if only a slight advantage.

And for my purposes, torque vs thrust is I think a too-fine distinction, as stated I cannot go down to "too small" a wheel anyway.

_______
For controllers, cost & simplicity are not relevant, except for ability to program as motors are swapped out, so Sevcon is out, maybe non-Grin ASI too?

BMS current is also irrelevant for me.

Given all that, do you have any straightforward suggestions?

Check this video starting at 2:16:40 to 2:22:40 for Justin's comments on climbing ability of different Kv motors:

https://www.youtube.com/watch?v=c96n0Ma2rLY&list=PLH8T1SX8ZJv-gD2g-oLo_LBDnXP2PjNnR&index=2

 

[Jil]

Hi,

I currently ride a Surly Krampus with GMAC 8T + Phaserunner controller + 52V (14S) battery, and 29" wheels, mainly for off-road use (beaches).
It's nice but I find it a bit limited in max speed, and the controller gets limited also quickly due to high temp at max speed and power (around 1600W with my setup, it goes down to around 1000 W in case of overheating). On the other hand, the motor has never shown any sign of overheating, even in summer it is barely lukewarm after a long ride.

My questions :
- what are the options to limit the overheating of the Phaserunner ?
- using a 72V battery will raise the max speed + limit the amp (and so controller heating) at equivalent power, do you confirm ?
- should I except troubles when using 72V battery ? Will it limit the ability of the bike when climbing hills (already a bit limited with my 29" wheels).
- what is the maximum continuous power at which a GMAC can generaly operate (on flat land), controller set apart ?
- If I want to be able to ride around 55-60 kph continuous without overheating, will it be better to simply change the controller/the motor ? If yes, which models would you advise ?

Thanks !

 

[neptronix]

I put 4kW peak into an 8T MAC in 2011 and established what it was capable of. I peaked at 46mph. That was with the version that has 0.5mm laminations and struggled to hit 80% efficiency. It has had many generations of refinement and improvements in efficiency.

With the removal of the clutch and the thinner lams, the motor is certainly capable of more. I'd like to see someone hit it's limits and beat my record. Bring a spare set of gears, lol...

 

[Bullfrog]

The MAC/GMAC is capable of high amperage and very high torque...more torque per battery amp than any motor BUT you can't do it continuously or it will over heat.

I have run 60A, 58.8v, ~3,528 watts and I currently have my controller set for 55A since my BMS cuts my battery off if I go any higher. I have never had any problems with the gears or the clutch. I weigh about 210 lbs. and my throttle has two positions...wide open and off so I constantly hammer the motor. BUT I am limited to about 29 mph on flat ground if I want to ride continuously or my MAC gets too hot. I ride standing up due to arthritis so there is a lot of wind drag. A smaller/lighter person could run a little faster continuously but IMO the MAC is limited to roughly 30 mph continuous and there is a long laundry list of variables that affect that :wink: .

There is a big difference between what a motor can do for a few minutes and what it can do continuously...the Grin Tech Motor Simulator is the way to go for predictions . You can drag things around and see what happens at low speeds and wide open throttle to just hit "simulate" and see what happens for continuous operation.

I tried a 5T MAC in a 26" wheel with a 52v battery and went high 40s mph (GPS) on flat ground but I was scrunched up in a ball to get my drag as low as possible and it was NOT a lot of fun so I sold it. I didn't even document the top speed because I never planned to do it again since it took me a few hours to unfold my knees/body after doing it :lol: .

I'll let Neptronix have the record...he is a good guy, has been doing this a long time, and tries to help everyone :wink: .

 

[Bullfrog]

Jil...IMO a 8T MAC in a 29" wheel has an effective gearing that is too high.

Even if you solve the Phaserunner overheating by mounting it on an aluminum/copper block (heat sink), you will then have a problem with the motor over heating IMO. You could add about 5 ounces of low viscosity ATF to the motor to help it stay cool if you wanted to stick with your current set up but the ATF has unique challenges like making sure you don't leak any on your brake rotor :lol: .

Are you running a Cycle Analyst so you can monitor your motor temps? If you are, you can set it to roll the power back at a given temperature and keep the motor from being damaged. The highest I'd recommend is power roll back starting is about 130C and motor shut down if you exceed 140C. The MAC/GMAC can run continuously at 150C but you don't want to exceed 150C and as the motor temp increases the resistance increases so it gets hotter...quickly.

If you want to stick with your Krampus (29" wheel), IMO you need to switch to a Direct Drive Hub Motor...and there is no bigger MAC/GMAC fan in the world than me .

My recommendations for everyone are...

If you want to ride 0-20 mph on any surface and/or you constantly need to stop and start then a BBSHD would be a good choice.

If you want to ride 20-30 mph on a hard surface then a MAC/GMAC is a good choice.

If you want to ride over 30 mph then a Direct Drive Hub Motor is a good choice.

There are a boat load of variables that could affect my recommendations :wink: .

 

[neptronix]

The larger the wheel, the lower the rpm per mph, the lower the continuous power capability.
..until you reach an inflection point where too small a wheel, too high a rpm = exponential power loss due to gear friction or eddy currents.

Where this inflection point lies is dependent on the motor design.

And yes, that 4kw figure was a peak figure. The plastic gears lasted 5 minutes before melting due to heat.

A more realistic continuous current for a MAC or GMAC is 1000-1500W in an ideal wheel configuration.

 

[Bullfrog]

The larger the wheel, the lower the rpm per mph, the lower the continuous power capability.
..until you reach an inflection point where too small a wheel, too high a rpm = exponential power loss due to gear friction or eddy currents.

Where this inflection point lies is dependent on the motor design.

And yes, that 4kw figure was a peak figure. The plastic gears lasted 5 minutes before melting due to heat.

A more realistic continuous current for a MAC or GMAC is 1000-1500W in an ideal wheel configuration.

I agree...and Justin has some good data on wattage the MAC/GMAC can handle here:

https://ebikes.ca/product-info/grin-kits/gmac.html

Neppy...approximately how old was your MAC and did you grease the gears any? I have not had any problems with the newer gears and I cover the ring gear teeth with Mobilith SHC 100 when I get a new MAC. I know there have been some improvements in the gears but not sure when they occurred .

 

[neptronix]

Mine was from 2010, so yeah.. weaker gears, lossy stator, worse cooling, etc.

I'd love to see what you could squeeze out of an 8T today.

 

[Bullfrog]

Mine was from 2010, so yeah.. weaker gears, lossy stator, worse cooling, etc.

I'd love to see what you could squeeze out of an 8T today.

Wow they electric bikes back in 2010 :lol:...you were just ahead of your time IMO .

There have been a lot of improvements to the MAC since then thanks to Paul at EM3ev and the GMAC with Justin at Grin Tech.

I wish EM3ev still sold the MAC. I bought an extra 10T and a 12T rear MAC directly from MAC so my next order has to be at least 8 motors...I don't see that happening. I don't know of an easy way to buy a MAC at this point in time and I may want to use a front (100mm) 12T MAC in my Schwinn Shuffle kick bike due to arrive 11 Jan...guess an eZee or a Shingyi SX may have to suffice .

 

[neptronix]

Shengyi SX is a very good motor for a small wheel like you have if you need large power. Due to the lower reduction ratio and 1 pole less than the MAC/eZee.

Peak efficiency seems to beat a MAC .. i have tried to pull details of where this efficiency comes from out of the Shengyi people and cannot get them. My guess is super thin lams..

The MAC/GMAC is still the ticket for high powered geared motor action tho.

You may not know this, but i was the one who named EM3EV with Paul back in the day and i made his first web store. He introduced me to the MAC when everyone on this forum thought it was a piece of garbage. I think my high power tests had something to do with that perception changing... 8)

I like businesses started by engineers because they typically won't bullshit you about their products. EM3EV is still one of my favorite vendors for that reason. I'm sad to see that Paul stopped selling the MACs ( the reasons are a big head scratcher ), but luckily ebikes.ca has filled the gap there.