72V Motorcycle Wheels Mac 6T Motor Street Ride

[Bullfrog]

Yea I know this is an old thread...just wanted to hear the latest from "mainsource" and others on their related projects. Hopefully some are still around and get notices about new posts on this topic.

A little additional info....
I am currently running a 12T MAC at 58.8 volts (14s battery) in a 27.5" rim with a Schwalbe Supermoto 2.8" wide tire. I cool it by using a mixture of distilled water and Motul Mocool...in the motor. Four ounces total with 5% Mocool by volume. Sealed the MAC hub/cover interface with Permatex Ultra Gray and have never had a problem with leaks. Previously used low viscosity Automatic Transmission Fluid (ATF) and it worked great for cooling but a tiny bit got on my rear rotor and my brakes quit working so trying something less slippery. The Mocool is a corrosion inhibitor. You can add fluid thru one of the brake rotor bolt holes or drain some out by leaning the bike on its side with two of the brake rotor bolts removed. Four ounces is enough to thermally connect the motor to the hub and transfer the heat so it can be rejected to the atmosphere and it is below the axle seal when the bike is upright so leakage is less of an issue.

I have been running the MAC at 40A for several years and have not had any problems to date with the clutch (I rarely pedal). Plan to install an 18 FET (60A) controller and slowly increase the amperage...after I get a battery that can supply the power. EM3ev is supposed to be developing a 20s (72v) triangle battery in the near future and I may try the MAC at 72v if the battery is available before I kill the motor. Grin Tech currently has a 20s2p (72v) battery available if anyone is interested. I plan to lace a MAC hub to a 24" rim and run a Duro 24x3.00 tire...as opposed to my current 27.5" setup.

Totally agree with the comments on a DD motor being a better option for high amperage applications but I just want to play around and test the limits of the MAC. Grin Tech now has the GMAC which is a new and improved version of the MAC and it has a locked clutch and is capable of regen...I may try a GMAC and/or the locked clutch if I break anything.

Why a MAC...well I went through every motor listed in the Grin Tech Motor Simulator (great tool by the way) and the MAC produces the most torque per amp than any motor listed (I geared the mid dirve motors 1:1 for comparison purposes). Well except for the Bafang G60 but the G60 design is a little less robust than the MAC and I am afraid it would not survive similar experiments.

Is anybody else pushing the limits of a MAC and what results have you had?

I may start a new MAC thread to discuss the limits of the MAC depending on interest..what do you guys think?

 

[neptronix]

The mac is never going to handle 50mph speed

Oh come on, i hit 47mph on mine in a 26 inch wheel with the old 0.5mm lam motor back in 2012 or so. I also weighed nearly 300lbs.

The only problem you'll have with hitting those speeds is the magnets flinging off the rotor.. :lol:

A more realistic safe continuous cruising speed for a 20inch ish wheel is maybe 35mph, but the torque should be amazing.

 

[neptronix]

Bullfrog, I'd love to see a video of your setup going all out ! And pics of how you sealed it, etc.

DD is way better but you can't beat this low weight and high power density today in hubs. The Mac would perform better in more like a 26 inch wheel if you can handle some rear drop!

The Mac is a less than ideal motor for 20 inch wheels because high RPM is known to fling the magnets off. I forget what Paul told me but it may be around 500 wheel rpm where this starts being a problem. So this is an ideal motor for 24 inch wheels or above.

 

[Bullfrog]

When I sealed my MAC, I did do it with the motor cover separated from the motor housing (off the bike)....just ran a very small bead of Permatex Ultra Gray on the interface, partially assembled the cover to the motor housing, let it sit for a couple minutes and then tightened everything down...just basically following the directions on the tube. Never had an leakage of the ATF or the water mixture via the cover/housing interface.

I will attempt a video if I ever get the bike together with the 24" rim/MAC set up.

Here is a pic of what I ran long before I started trying any liquid cooling. I was trying to gear the bike as low as possible to keep the MAC from overheating. It was a 20" rim that was 57mm internal width and a 4" wide tire. With the 14s battery, the speed was about 20 mph on level ground. We called it the "Clown Bike" because it looked like it should be in the circus with three or four clowns on it instead of on the trails with me on it.



As far as convective cooling...I saw the duct work pictured below a while back when I was researching everything that people had done to add additional cooling to a MAC and it is the best option I have seen for forced air cooling. You could even add a filter so that you don't pump dust and dirt into the motor. The dust/dirt entering the motor is probably the biggest reasons I never tried adding vent holes to my MAC. I passed on the ducting and forced air because it was a little more complicated in the long run than liquid cooling and required a fan, filter IMO, and a power source to run the fan which could easily be the same battery that powers the bike but it would decrease the energy available for riding.



Been running the water/mocool mixture in my MAC for two months and no problems yet...I plan to open up the motor after about six months or if it has any issues and do an inspection to see if/how much the water/mocool are harming the motor internals.

 

[The Stig]

As far as convective cooling...
...
Been running the water/mocool mixture in my MAC for two months and no problems yet...I plan to open up the motor after about six months or if it has any issues and do an inspection to see if/how much the water/mocool are harming the motor internals.

What do you think about the idea sticking cooling fins to the housing of the mac? I think I remember seeing a post of someone who put their heat sinks around the perimeter of the hub - in between the spokes. They should probably be wire tied AND glued with heat sink glue

 

[Bullfrog]

As far as convective cooling...
...
Been running the water/mocool mixture in my MAC for two months and no problems yet...I plan to open up the motor after about six months or if it has any issues and do an inspection to see if/how much the water/mocool are harming the motor internals.

What do you think about the idea sticking cooling fins to the housing of the mac? I think I remember seeing a post of someone who put their heat sinks around the perimeter of the hub - in between the spokes. They should probably be wire tied AND glued with heat sink glue

As always I have to qualify my answer with "It Depends"...and when I say that it is because there are a LOT of variables. Once you define all of the variables any good engineer can give you a Yes or No answer :lol: .

Convective heat transfer is proportional to the area of the cooling fin...in this case the "heat sinks" AND the velocity of the air across the cooling fins. Without some good modeling, a smoke test, a wind tunnel, etc....it is hard to say exactly how much it will help but in theory it should help a lot. One of the challenges is getting the heat to the fins...if you have an air gap between the motor and the housing then you can bolt on huge fins and flow massive amounts of air across them and they won't help much because the air gap is basically disconnecting the heat flow path. A good analogy is electricity...almost all of the time if electricity will flow through the path with little resistance then heat will also, that is just a different way to think about things that helps me sometimes.

So what I am trying to say is...thermally connecting the heat source (motor windings) to the motor housing will help the most, followed by increasing the surface area of the motor housing. Without some testing/modeling it is hard to say how much the cooling the fins will add because if they are in a "dead zone" with little air flow they won't help much but if they get a lot of air flow they can help significantly...assuming the heat can get to the motor's housing .

All this theory I throw out is nice but sometimes it is better to just try something and measure the results. Please don't let me be inhibit anybody's enthusiasm or ideas...everybody out there knows something I don't and could make a great discovery.

A few things that have helped me measure my results for my cooling experiments are an Infrared Thermometer like this: View attachment 1

AND these temp plates that have a response time of a few seconds:


Having a temp sensor (thermistor) in your motor is another good measurement device but remember where and how it is mounted can significantly affect the temp measurement so be careful if/how you compare temperatures.

 

[neptronix]

I'm impressed and would like to see long term results on how the internals handle cooling.

If you want to replace the rim, check out those 22" BMX rims that are becoming popular. Some of them have the same erto as 18" motorcycle tires. IMHO that would make for the perfect compromise between getting a Moto tire, keeping the bike geometry relatively sane, and having the power advantage of a small wheel. I started a thread about this somewhere..

 

[Bullfrog]

Good suggestions and ideas neptronix...Thanks.

I am way to "thrifty" (wife says cheap)....I bought a 24" wheel for a Mongoose Bering bike directly from Pacific Cycles and the entire wheel was around $20. Removed the hub, spokes, and nipples and plan to lace the rim to my MAC after I order 13G Sapim spokes/nipples. The rim is dual walled, pretty heavy duty, and should survive anything I can dish out .

 

[neptronix]

24" is good too and you'll see a minor power bump vs 26". Motorcycle tire fitment is out the window, but any MTB has better geometry and less risk of the pedals smacking the ground.

This can be a tough choice!

best wishes with your build tho, and wow if that isn't a cheap solution :thumb:

 

[Bullfrog]

Wellll, after running approximately 4.5 ounces of distilled water and Motul MoCool at 5% by volume in my MAC for three months and a 27.5" rim, I pulled my it open...only because I am changing over to a 24" rim/tire.

Never had any issues or malfunctions whatsoever in the three months and visually the motor looks just like it did when I put it together except the copper windings are a tiny bit dull in appearance as opposed to bright shiny copper when it was brand new.

As soon as the bike shop finishes lacing my 24" rim to the MAC hub, I plan to put the motor back together, add the cooling fluid mixture, and do some off road riding to see how it accelerates with the smaller wheel as well as how the temps do. Using a Halo Contra 24x3.0" tire and if everything works OK, then I'll swap the controller from a 40A to a 60A. Just ordered a 14s battery that can supply the 60A...so the battery will get installed when/if I install the 60A controller.

More insanity to follow.... :lol: .

 

[The Stig]

MACs can take 60A ???

 

[Bullfrog]

Don't know, we are going to find out :lol:...I'll definately be adding some auxiliary cooling.

Been running my 12T MAC on a 13s/48v battery, a 27.5x2.8" tire, with a 40A controller for several years without any problems...mine runs about 105 degrees C in the summer time...when cruising on flat ground with the throttle wide open at about 23 mph...it takes approximately 1,000 watts/20A for me to cruise at 23 mph so I rarely push the full 40A through the motor.

When I go to the 60A controller, I plan to run about 4.5 ounces of distilled water and some Motul MoCool for corrosion protection.
Motul recommends 5% by volume and that is what I have been using for the last three months as a trial before changing to the 24" wheel/tire and changing over to the 60A controller.

Why am I doing it you might ask...I want to see if I can get as much torque out of the MAC as I am getting out of my BBSHD when riding off road. And if I can, I want to see if the MAC will survive...my biggest concern is the clutch since I'll be monitoring the temps closely and won't exceed 105C.

A lot depends on how you use it...I am real easy starting off and keep a close eye on my temps plus I have my Cycle Analyst programmed to start decreasing the power if I reach 105C. You could probably destroy a MAC with a 30A controller (or lower) if you abuse it enough.

 

[Bullfrog]

Haven't gotten a 72v battery yet but I am running an Infineon controller set for 40A battery and 112A phase current. The bike is a little quicker (more acceleration and top speed) than my stock BBSHD with a 28F/22R gearing and a 727 mm OD Maxxis High Roller 27.5x3.00 rear tire. In addition to the controller, the MAC powered bike below has a 24" Halo Contra rear tire that is 652mm OD mounted on a 49mm internal width rim from a Mongoose Bering (kids bike)...the rim was laced to a MAC hub using 13G Sapim spokes. Top speed of the bike is about 23 mph...running a 12T MAC and a 13s4p (48v) battery with 30Q cells. I plan to convert it to street tires, install a 60A battery/180A phase controller, and install a 14s4p (52v) battery with HG2 cells. Eventually go to a 20s/72v battery. Converting it back to "street" because the top speed is too fast for the single track trails where I ride and if something has a throttle, I don't have enough sense NOT to keep it turned WFO...that is wide open for anyone that isn't an old MX racer :lol: . Head tube angle is 70 degrees with the configuration as pictured...so the steering is fairly quick and just the way I like it. With the 20" fat tire...pictured somewhere above, the steering tube angle was several degrees less and the steering was too lazy/slow for my liking.

 

[rockstar195]

Looks like a fun bike to ride. I know it's rigid, but how does it ride?

How come no pegs?

 

[Bullfrog]

Looks like a fun bike to ride. I know it's rigid, but how does it ride?

How come no pegs?

rockstar...on pavement, it rides great...also notice the suspension seat post. Off road, not so smooth...I run about 14 psi in the rear tire to give it a little cushion and that is as low as I can go without getting rim strikes on roots. I have the same frame/forks with a 27.5x3.00 Maxxis High Roller in the rear (BBSHD powered) and it rides noticeably smoother off road. I plan to convert the bike pictured to pavement only use and run a 24" Maxxis Hookworm or a Schwalbe Crazy Bob AND go to a 24" front wheel as well. You might think the bike pictured looks a little weird but it is nothing compared to the bike I called my "Clown Bike"...same frame and forks/front wheel with a 20" rim and Kenda Slant Six 2.6" tire with a MAC motor in the rear...looked like it should be in the circus with 3 or 4 small clowns riding it :lol: . The bike pictured has a 24x3" tire which has a diameter about equal to a regular 26" tire...it works good for one clown...ME . The pic several post above was running a 20x4.00 tire...which is a lot wider and larger diameter than the Kenda 2.6" tire. I did a lot of miles with the little wheel and never had a problem with magnets coming off...not sure why they would since the MAC currently has them glued to the inside surface of the ring they are on and the faster you go, the more force there is to push them into the ring. MACs may have been built differently in the past so take my lack of historical knowledge into account .

Pegs...where I live your bike has to be capable of being powered by a human to be classified as a "bicycle", otherwise it requires a tag and registration which means $$$. The crank arms in the pick are 120mm (Sinz crank) and I may try an Answer Mini Crank with 100mm arms. I run 75mm unicycle crank arms on my BBSHD powered bike. I ride with the crank arms horizontal and the short crank arms allow me to drop my outside foot quickly when cornering and get better weight distribution and handling.

 

[rockstar195]

How do you think it would perform if it could hit 50mph?

Could you also post any pics of the other bike. I've always thought of doing something like the bike you just posted. Nice how you found a spot for the controller on such limited space.

 

[Bullfrog]

The bike with the 24" rear wheel is in my post on this page...posted Dec 26 2019 6:50pm.

The same bike with the 20" wheel is several posts above that on Nov 04 2019 12:26pm.

IMO it would do OK if I could get it up to 50 mph...I have been down a local hill hit low 40s. It gets interesting when you are riding a bicycle over about 30-35 mph IMO...not something I care to do with traffic around.

Getting to 50 mph is another story...and why this thread was started, I think :lol: . Using the Grin Tech Motor Simulator, if you take a MAC and run it with a fully charged 20s/72v battery which would be 84v, you'll be pushing 69 amps through a 6T MAC and going roughly 49 mph with a 722 mm OD rear tire (27.5x2.8 Schwalbe Super Moto-X). The problem is once you get over about 60 amps, parts get more challenging and expensive...you need a controller that isn't available everywhere, some of your wiring may not be large enough and insulation might melt with a resulting short, you need a BIG battery to avoid voltage sag and overheating the BMS...LiPos are an option but have their own unique challenges, the 6T MAC will overheat so you'll need some auxiliary cooling if you want to run it for very long, etc., etc., etc. All that doesn't mean you can't do it, just that it isn't simple or easy.

 

[rockstar195]

I meant the other bike you named the "Clown Bike". Any pics of that one?

 

[Bullfrog]

The "clown bike" with the 20" wheel is pictured in my post above...Nov 04 2019 12:26pm.

In the pic it has a 20x4.00" rear tire. I do not have any pics of it with the 20x2.6 Kenda Slant Six tire.

 

[Bullfrog]

MACs can take 60A ???

Stig...I told you we were going to find out if a MAC can take 60A and it turns out it can...at least for a little while :lol: . l Just finished putting my 12T MAC together with a 14s4p battery that has HG2 cells and a 18 FET 60A Infineon controller. It has survived a couple runs up and down the street so far .

It is NOT something I would recommend. At some point, you can keep turning up the amperage and all you'll get is more heat and very little if any increase in power. From my seat of the pants dyno, I'd say 60A is past that point.

At about 45 amps, it feels like the acceleration has pretty much leveled off and increasing the amperage any higher just turns your stator into a heating element :lol: .

Of course with a 72v battery it would accelerate a little faster but IMO a MAC on 72v starts to exceed the point where eddy current losses pile up quickly...assuming you spin the motor at full speed. That is why I decided NOT to try a 72v battery with my MAC. If you use just throttle and don't pedal, a 12T MAC with a 24" or larger tire will over heat on a 1% grade according to the Grin Tech Motor Simulator with a combined weight of 264 lbs. and any of the faster winds will overheat on a 0% grade under the same conditions. I define "overheat" as exceeding 110C which is where my Cycle Analyst is programmed to start rolling back the power to make sure I don't melt anything. So you can run a MAC on 72v but IMO there are much better ways to go fast if that is your objective.

AND you CAN run a MAC on 60A but it is not very smart to do so IMO since you just produce a LOT of excess heat and not a lot more power.

For any new MAC owners out there...I have had the best results for my 12T MAC with a 52v/14s battery, a 12 FET 40A controller, and a 26" rim with a Maxxis Hookworm tire.

Doesn't mean you can't run a MAC on 72v or 60A...just not something I would recommend .