Looking for a better hill climbing setup with my gmac / baserunner

[frk1206]

Hi folks!
I recently took the plunge and upgraded? from a BBSHD to a GMAC + Baserunner on my Cargo bike. The first thing I notice is while I have significantly more top speed my hill starts are painful specially when loaded with my kid + cargo (roughly 350lbs with bike). Anything over 5% becomes painful and 10%+ is just not possible (if you stop, its impossible to start).

My battery can do 60A peak (52V 18ah Panasonics). What can I do to make hill starts and hill climbing better? My options are:

1. Upgrade to a frankenrunner
2. Upgrade to a bigger battery / BMS to match the frankenrunner max amps (96)
3. Add a geared front hub motor (ideas welcome on which one)
4. All of the above

I'm climbing hills in the SF Bay area (I live in Oakland) all day and don't like being limited by grade. I had no problems with my BBSHD cuz gears but wish to replicate something similar with a hub motor. The BBSHD was nice but 1 chain, 1 derailleur and 1 clutch later I'm done with that setup.

Thanks!

 

[E-HP]

Hi folks!
I recently took the plunge and upgraded? from a BBSHD to a GMAC + Baserunner on my Cargo bike. The first thing I notice is while I have significantly more top speed my hill starts are painful specially when loaded with my kid + cargo (roughly 350lbs with bike). Anything over 5% becomes painful and 10%+ is just not possible (if you stop, its impossible to start).

My battery can do 60A peak (52V 18ah Panasonics). What can I do to make hill starts and hill climbing better? My options are:

1. Upgrade to a frankenrunner
2. Upgrade to a bigger battery / BMS to match the frankenrunner max amps (96)
3. Add a geared front hub motor (ideas welcome on which one)
4. All of the above

I'm climbing hills in the SF Bay area (I live in Oakland) all day and don't like being limited by grade. I had no problems with my BBSHD cuz gears but wish to replicate something similar with a hub motor. The BBSHD was nice but 1 chain, 1 derailleur and 1 clutch later I'm done with that setup.

Thanks!

More amps. It looks like the frankenrunner is equivalent to a 42A controller (with 96 phase amps), so if your battery can provide 60A, you can go with a lot bigger controller, if the GMAC can handle it.
https://ebikes.ca/tools/simulator.html?motor=GMAC8T&batt=B5220_GA&cont=cust_41.9_96_0.03_V&hp=0&axis=mph&frame=mountain&autothrot=false&throt=100&grade=0&wheel=26i&mass=110&cont_b=FR&motor_b=GMAC8T&batt_b=B5220_GA&mass_b=110&hp_b=0&bopen=true

 

[frk1206]

More amps. It looks like the frankenrunner is equivalent to a 42A controller (with 96 phase amps), so if your battery can provide 60A, you can go with a lot bigger controller, if the GMAC can handle it.
https://ebikes.ca/tools/simulator.html?motor=GMAC8T&batt=B5220_GA&cont=cust_41.9_96_0.03_V&hp=0&axis=mph&frame=mountain&autothrot=false&throt=100&grade=0&wheel=26i&mass=110&cont_b=FR&motor_b=GMAC8T&batt_b=B5220_GA&mass_b=110&hp_b=0&bopen=true

Don't think the GMAC can handle it - 5 minute power is 2600W max (~50A). Btw how did you figure out that its a 42A controller? It says it peaks at 96A Battery and 96A Phase current

 

[frk1206]

If you are steadfast in your position not to change back to the BBSHD to climb your hills more effectively, then for your very special circumstance...big weight + hills, I would add a front geared hub motor for getting up the hills. That is my vote.

A last note and question please. Your 52 volt battery has an unusually high amp rating...or uncommon to an off the shelf, on-line store bought 52 v battery. Can you share if you purchased this battery?...and if so from what supplier?...or did you make this battery and source the 60a BMS? Dp you know what brand and model cells you have inside the battery?

Thanks! I've tried all the mid drives so looking for something cleaner and different. Hubs are definitely cleaner and cooler - if only I can make it climb hills!

Custom battery with a 60a daly BMS. panasonic ncr18650bd - which aren't great for discharge but are able to do 1.5c discharge which is around 60A.

 

[E-HP]

More amps. It looks like the frankenrunner is equivalent to a 42A controller (with 96 phase amps), so if your battery can provide 60A, you can go with a lot bigger controller, if the GMAC can handle it.
https://ebikes.ca/tools/simulator.html?motor=GMAC8T&batt=B5220_GA&cont=cust_41.9_96_0.03_V&hp=0&axis=mph&frame=mountain&autothrot=false&throt=100&grade=0&wheel=26i&mass=110&cont_b=FR&motor_b=GMAC8T&batt_b=B5220_GA&mass_b=110&hp_b=0&bopen=true

Don't think the GMAC can handle it - 5 minute power is 2600W max (~50A). Btw how did you figure out that its a 42A controller? It says it peaks at 96A Battery and 96A Phase current

I matched the torque curve, but the actual spec page says 40A for battery, 96A for phase.
https://ebikes.ca/shop/electric-bicycle-parts/controllers/bundle-frankenrunner_mt.html

Grin and Kelly list their current for phase amps. Others use battery amps. You never can take any of the values as a given until you drill into the specs.

 

[frk1206]

Interesting - ofcourse. However if you dig even deeper into the frankenrunner manual it says 96A battery amps. Maybe theres is a mistake somewhere: https://ebikes.ca/amfile/file/download/file/218/

Even deep into the BAC855 manual and it says 84A

 

[E-HP]

Interesting - ofcourse. However if you dig even deeper into the frankenrunner manual it says 96A battery amps. Maybe theres is a mistake somewhere: https://ebikes.ca/amfile/file/download/file/218/

Even deep into the BAC855 manual and it says 84A

Make sure to pay attention to peak vs continuous. The Grin manual says 55A continuous phase. All the other specs are peak.

 

[frk1206]

At thermal rollback you mean? Yeah. Otherwise none of the docs have a nominal current seems like. Run it to 96a till it overheats.

But in any case - I guess run at 96a peak and see what happens? How do you generally decide the “melting point” current on these motors?

 

[E-HP]

At thermal rollback you mean? Yeah. Otherwise none of the docs have a nominal current seems like. Run it to 96a till it overheats.

But in any case - I guess run at 96a peak and see what happens? How do you generally decide the “melting point” current on these motors?

I think Grin models it through destructive testing; at least I seem to recall seeing that on one of the videos. Besides current/power, there's a time element for a motor heating up to the melting point. Grin says stay below 110C, and 150C for a short periods to keep the motor from melting.

Another way to look at it is to check the motor's efficiency. If the motor is 80% efficient, and you feed it 500W, then you know 100W is generating heat, which is a lot, if you've ever tried to see how long you could hold onto a 100W incandescent bulb.

 

[frk1206]

Thanks! Super helpful in making me think through it. I think I’m gonna first fix my battery so it can provide more amps (it starts sagging over 30) and then possibly look towards a dual motor setup to help the initial start. Or just pedal a little haha.

 

[999zip999]

Use your John CR motor temperature gauge.
Take your hand and put it on the motor. Now how hot is it ? To hot ?
E-hp I like your light bulb test for a hundred watts of heat