MAC 8T on 16S lipo?

[teklektik]

how about a request?

System A: 26" wheel, 12s Lipo, Limited to 35A
System B: 24" wheel, 12s Lipo, Limited to 35A
System C: 24" wheel, 18s Lipo, Limited to 25A

Sorry about the hijacking!

Ya - but since we already chatting about another build, what the heck.....

The 18s example you wanted is in a bad range for the experimental estimator so here's the results using Justin's simulator - not exactly a MAC 8T but close. I thought it made more sense to have everything from the same source for purposes of comparison.
Settings for your examples:

• 8T ~= BMC V2S
  12s2p = custom battery 3.8v (mean) x 12 = 45.6v 30mOhms 10A ('2p' only affects range estimate)
  18s2p = custom battery 3.8v (mean) x 18 = 68.4v 45 mOhms 10A
  35A limit = custom controller - 35A
  25A = custom controller - 25A
  adjust weight for 230lbs bike+rider
  adjust wheel size
  set for mph instead of kph

I used 3.8v as the mean discharge voltage for LiPo - it obviously will be higher HOC... I hi-lighted some of the more commonly interesting results. Remember that these plots are at WOT - if you look at lower speeds that's not what happens with changes in throttle - it would be from changes in load.




The MAC 12T is sort of like the BMC V2T - there's nothing really there for the 10T.
Anyhow - this is a little OT but should get you going for your own guesstimations for an 8T...

 

[Observator]

Thank you! I tried using the grin simulator earlier today, but messed up when entering the battery internal resistant. Couldn't get it to plot anything. Your elaborate example cleared that right up. Much appreciate the effort you put in to helping!

Hijacking is hereby over!

 

[teslanv]

Digging a little deeper on my Configuration.

I modeled a MAC 8T on a 20" Wheel and a MAC 12T on a 26" Wheel, 16S Battery and 250 lbs Bike & Rider.

I get very close to the same data, so I am thinking apart from the shorter wheel base and no suspension, the BMX should perform roughly the same as a Mountain Bike with the High-Torque MAC.

Anything I missed?

 

[teklektik]

the BMX should perform roughly the same as a Mountain Bike

Seems reasonable.

The various bike configurations (eg Mountain Bike) are composites that account for aero drag and rolling resistance. So - 'Mountain Bike' is really pretty much appropriate for any forward-leaning posture for a bike of about the same seat height (hence frontal area) and semi-fat tires with mildly aggressive tread - it's really about the drag that is typical for certain classes of frames - not the frames themselves. For instance, 'Road Bike on Tops' might be an option that would have more aero drag and less rolling resistance than 'Mountain Bike' - primarily due to the upright posture and narrow tires - but 'Road Bike on Hoods' would have less aero drag due to posture. You can go into the custom config for that selection and jiggle the drag and rolling resistance, but this can be a bit of a crap shoot without real measurement so the major selection options there seem a workable solution. These are, after all, estimates....

As for the wheel sizes and the shift in motor types, you are quite right - very similar. The interesting thing is to add some grade and watch how 'similar performance on the flat' diverges under load.

 

[teklektik]

Thank you! I tried using the grin simulator earlier today, but messed up when entering the battery internal resistant.

Glad you were able to get it working!

The battery resistance plays to voltage sag and so the effective battery voltage reported in the summary tables. I have had a hard time finding good LiPo IR info and so am presently using 5 mOhm/cell as a mean value. So for an XsYp battery, the total battery resistance Rbatt = Rcell * X / Y. It would be good to get proven product-specific values, but that's not in hand today... These values are relatively small so any IR error from this guesstimate should be minimal for most moderate powered builds.

Apologies - last OT post for me....

 

[neptronix]

You should get better results than that with the upgraded stator, for sure.

 

[srtgumbee]

Thank you everyone for your input with regards to the 16S lipo and MAC 8T. I will consider using 14S or probably just go with 12S and suffer some top end speed. I manage my commute ok with no motor at the moment, so even with a the 12S it will be better than just with my legs!

Interesting info on the simulator and various configurations. I learnt some things from that too

Steve

 

[Danos]

Where in NZ are you Steve? I'm in Wellington, I have a Mac 8T in a 26" wheel. I have a 16s LiFePH4 and it tops out at 50kph. It's a great set up but I don't ride it much now as my commute is 30km compared to the 5km that it was.

 

[srtgumbee]

Hi Danos,

I'm in Nelson. Good to hear you enjoy the MAC 8T....I assume living in wellington that you had some hills to deal with when you did use it for commuting? if so, did the Mac 8T go well on the hills?

Steve

 

[Danos]

Hi Steve,
No I was in west Auckland and had a couple of hills but now in Wellington. The MAC was awesome on the hills, they were about 500m long and about 10-12% gradient from memory and it just powered up them at about 40kph with my assistance. I cruised at 50kph on the flat for the rest of my short commute. Was just as quick as the car from door to door!
Cheers, Danny

 

[srtgumbee]

Hi again Danny,

Last question...... what size controller do you use? 9fet or 12fet?

Cheers

Steve

 

[m52 power!]

EB2 on a higher than average RPM wheel with the most difficult to drive hub motor? no way, it'll run like crap!

I run my Mac 8t on 16s lifepo4 with a Lyen9 fet. I've always been unhappy with the sluggish throttle response, is this eb3 issue the reason why?