New Hi Power Off Road Fat Tire Build Need Advice

[tjgaryiv60]

Need advise or opinion please read. You guys are the experts. Not me.
I am building a new fat tire hi power off road machine. My goal is to have enough power to tackle most terrain including
Florida sugar sand. I want to be able to get deep in the woods for hunting and possibly pull a hog out with a small trailer.
The motor is a Mxus rear direct drive rated up to 5000 watts. The battery is 20s 4p 26650 3.7v 5000ma cells 72v nominal
40a bms continuous 120a maximum. The controller is a " vector " chinese 24 mosfet 80 amp maximum output. It is questionable.
I have not powered it up yet. It is huge and heavy 300 mm long and about 2 kgs plus. I will try this with your advice without a cycle
analyst. Just wired directly with a simple digital volt meter and thumb throttle. No power switch. I wired the little red main ignition
wire from the controller directly to the controllers main red positive. Power on off is just a simple connection directly to battery with Anderson
50 amp connectors. On the bike I did install a Grin Technologies torque arm. Please advise. My previous build had all the above except the
controller was only a 40 amp and it did not have enough power thru deep sand. The controller would get hot and shut down. Let it cool down
and go again. Thanks

 

[MadRhino]

Looks sound, except for a few small things.

Battery/BMS: 40A continuous doesn't feed a 80A controller. It will shut off. You say 120A bursts, how long ? I ask because your controller will pull 80A pretty long when you are accelerating in the sand, and your battery need to deliver enough to feed it.

I believe that you didn't need such a big controller to feed 80A. A 18 fet 4110 can be upgraded to feed 150A reliably.

I'd use 75A Andersons, and 8 ga silicon wires

 

[tjgaryiv60]

MadRhino

Thank you for your reply.
That was my concern too. The battery. Here is what I hope will happen. I not talking plowing up and down sand dunes just
patchy sugar sand places on trail 50-100 yards. I plan to use use the extra power to get momentum thru the stuff, some float speed , then
back off enough to keep the momentum going. That was the plan. Same for thick middy patches . I'd say maybe 10-15 second
bursts. Then back off. I have not built a battery before but I have two 20s 4p 26650 3.7v 5000ma with 40a bms continuous 120a max
batteries. Any suggestions on combining them ? Or ripping them apart and building one large one ? Or use a cycle analyst to limit power ?

Jack

 

[MadRhino]

I am not familiar with building batteries with round cells, and I don't know the cells that you have. Yet I believe that you need to build a bigger battery, or use higher C rate cells. Your BMS must not trip at lower Amp draw than you controller is set to pull.

 

[dogman dan]

If the whole pack does not get all hot when you run it, you aren't pushing it too hard.

But with a 40 amps battery, and 80 amps burst, bet you heat it up nice. Warm to the touch quite normal, but if it feels actually hot, you are flogging the battery real good.

It should be the other way around, 40 amps capable battery, use it at 20. If you have an amp meter/ watt meter on the bike, then at least you will know what amps you actually pull, as you ride through the thick sand.

BTW,, thick sand worse than hills, a lesser motor you'd melt it.

 

[John in CR]

What kind of all up load (including bike, rider and hunting equipment) are you talking about. Without that info accurate input/feedback is impossible. Tough conditions at low rpm and big diameter wheels are 2 strikes against you, so the plan might work for a cyclist weight guy, but a large person would need a 2nd motor on the front for 2wd. You're talking about a motorcycle/quad replacement, not something that could be done on a pedal bicycle except at extremely low gearing. Low rpm high load is a hubmotor's nemesis, especially with large diameter tires that are a good gearing only for the street.

 

[tjgaryiv60]

Thanks for the reply Here is my scenario with the links for motor controller battery or two batteries Advise or Opinion greatly appreciated


My current bike 72v 40a controller 3000w motor with 2.5 in balloon Maxxis
tires was struggling to power thru the soft sand. It was almost where I needed it to be. I weigh 220 lbs, rifle / backpack 30 lbs.
The motor and wheel is about 24 lbs, battery 18 lbs, controller 4 lbs, bike about 40 lbs I come up with about 85 lbs total. Heavy beast.
The current bike would bury deeper and require more power to pull thru it. I thought the fattie tires and more amps would do it
The bike can only go "fattie" so far 4.5 in tires and is heavy. A light setup could float right over the sand but I need raw pulling power.
This width is definitely better than the 2.5 in balloon Maxxis tires I am currently running. But I have added weight to the new bike.
My goal was more raw pulling power to get me thru patches of the deep stuff. I'm not talking climbing sand dunes just 100 yard or so
stretches. I was informed my battery rated at 72v 20ah with a BMS 40a continuous 120a instant is under amps for this controller.
I have two of these batteries. BIG QUESTION Can I connect these two battery packs in parallel to increase my amps or will the BMS still
limit it to only 40 amps. Will it pull 40 amps from one and 40 amps from the other and give me 80 amps combined ? If yes now I got to
configure how to mount the second battery inside the triangle part of frame. Weight now would be 105 lbs. Big Heavy Beast.
If I can run two batteries and get 80 amps of power without pushing the system my next idea was to configure a small flat trailer
with balloon tires to pull a hog up to 150 lbs out of the woods during hunting season. I leave the deer alone if any Bambi readers.

Here are the links for the controller battery and motor I have chosen.

controller
https://www.aliexpress.com/item/72v-84v ... 0.0.k8rPGJ
motor
https://www.aliexpress.com/item/MXUS-V3 ... bbe7&tpp=1
battery
https://www.aliexpress.com/item/Powerfu ... 0.0.k8rPGJ

Thanks if any reply from you guys.

 

[MadRhino]

I believe both batteries can be paralleled using each their BMS, and it will be capable of 80A continuous.

John is right about the wheel size. Life would be easier with smaller diameter wheels. If your bike can ride 24", it would be a big improvement already. Fat tires are wide but also high, making 26" about 28.5", and do require considerable power.

 

[tjgaryiv60]

We will leave the 26" wheels since they are already built. Now I got to figure out where to mount the second battery.
Hopefully I can construct some sort of mount to fit inside the triangle. Both in the back is too much. Thanks for your advise
I will let you know how it turned out and send a pic. Once I get the vehicle right the next project is the trailer for hauling a pig out.
Thanks
Jack

 

[Chalo]

Once I get the vehicle right the next project is the trailer for hauling a pig out.

Be sure the police officer is completely dead before you transport the body. Wounded cops are extremely dangerous and likely to lash out without warning.