Friday, May 20, 2016

Two Motors for more Hill Climbing Power

Mid Mount Motor Mod
I think I have finally found the best way to have a stump pulling gear for my MtGoat CycleTruck; use a direct drive hubmotor with the mid mounted Cyclone mid-drive motor with a single speed gear reduction ratio behind the seat post on a rear extension. This will use the hub motor as the high gear. Then torque will slowly shift to the mid mount motor. Yet still use power from both motors.

That way I will not have to use a absurdly slow gear ratio to climb the steep hills. But I will need to figure out exactly the right gear-ratio to use from the mid-mount motor mod. If your hills are steeper than an average geared hubmotor can deal with a mid-drive motor can be geared down lower than any geared hubmotor. A 3000watt cyclone motor is just barely strong enough to climb our 16% grades with 400lbs total combined weight. So you could use the larger cyclone motor. But without the higher gears to cruise with, a DD hub will help better than using the human powered drive chain and sprockets.

To find the right gear ratio I would need to start with a 42t sprocket cassette because it is almost too slow with a 40t chainring on the crank using my 17inch tire [my front wheel is even smaller; 20”]. Justin says the direct drive hub motor should be running at the same time for hill climbing so the mid motor so it won't fight the core losses from the hub motor. The low geared mid-motor should have a little more power than the hub motor at the steepest part of the climb; because the hub motor is very inefficient when climbing the hills.

It maybe good to mount the direct drive hub motor in my [16” rim] front wheel. But I may also need a larger battery pack because I will be climbing the steep hills faster. I don't know how much extra power will be needed by the extra controller etc.

You need two controllers. So learn to build them:

These two lectures tell all about how to use two motors for better hill climbing.

The full version of the lecture is here: “A guide to multi-motor (2WD and 3WD) ebike drive system"

Two hub motors; one geared

                           Two motors; one mid-drive:

2WD Yuba Mundo V4 (Build Thread) 

Two stage reduction (for single hill climbing gear):

2" diameter pulley ÷ 12.5” rim pulley (on the drive wheel)= 6.25:1 ratio x 7:1 ratio (primary reduction) = 43.75:1 ratio = close to 12 mph

This thread tells a lot about how 
to rig two motors to one bike:

Dual motor

You can do this with One battery pack, One throttle, One 3-Way & Cruise & EBrake using Two controllers paralleled, Two motors individually tied to each controller, and Two CAs - one for each.

The overall power is divided somewhat arbitrarily between the two controllers depending on load.
  • Going uphill, both will pull evenly.
  • On somewhat of a flat whilst in Cruise Control, one will take the lead and the other will go into "slip mode"; pull enough current so that it essentially freewheels... however on the slightest increase in load - it will pick up the slack until Cruise cannot be held.

I don't measure Amps; I measure pack Voltage because the shunts have been modified by trace-beefing and I do not have equipment capable of measuring scant ohms accurately, so I just measure voltage. I know the battery capacity, I know from experience how to set the amount of theoretical current to the wheels, and thus am able to calculate roughly the overall power consumption. The CAs validate this by using Miles per charge; I know how many miles I should have covered by x-amount of voltage drop - which is not exactly linear, but then I understand that too.”


1 comment:

siemens said...

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