Range question about adding a geared kit on top of a direct drive kit

zeddrick

1 mW
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Mar 6, 2020
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I have a DIY ebike with a 1200w rear direct drive hub motor and two 48v20ah batteries that I swap between manually (both batteries are attached and secured to the bike, I just unplug one from the controller and plug in the other when one gets low). I'm tempted to get a bafang front geared kit so I wouldn't have to swap between batteries and so I could get more torque up hills while using both motors and possibly have more range? I love the direct drive but I hate having to crawl up some of my steeper hills with all the cargo I sometimes carry at like 5mph while I spin away in my lower gears. It just feels wrong having the throttle maxed out while still peddling and only going walking speeds.

My main question is range, would I possibly get slightly better range by adding a geared motor up front and having both 20ah batteries split between the two motors if I use them right? If I used the geared motor for hills, the direct drive for flats, and both at once for steep hills, wouldn't I get better range being that I'm no longer stuck to having to push the direct drive to 100% all the time doing the thing it isn't suited for? I live in a very hilly area and usually have 5-10 pounds of cargo on the rear rack but sometimes up to 20-25 pounds.
 
Range question about adding a geared kit on top of a direct drive kit
by zeddrick » Sep 22 2021 6:31am

I have a DIY ebike with a 1200w rear direct drive hub motor and two 48v20ah batteries that I swap between manually (both batteries are attached and secured to the bike, I just unplug one from the controller and plug in the other when one gets low). I'm tempted to get a bafang front geared kit so I wouldn't have to swap between batteries and so I could get more torque up hills while using both motors and possibly have more range? I love the direct drive but I hate having to crawl up some of my steeper hills with all the cargo I sometimes carry at like 5mph while I spin away in my lower gears. It just feels wrong having the throttle maxed out while still peddling and only going walking speeds.

My main question is range, would I possibly get slightly better range by adding a geared motor up front and having both 20ah batteries split between the two motors if I use them right? If I used the geared motor for hills, the direct drive for flats, and both at once for steep hills, wouldn't I get better range being that I'm no longer stuck to having to push the direct drive to 100% all the time doing the thing it isn't suited for? I live in a very hilly area and usually have 5-10 pounds of cargo on the rear rack but sometimes up to 20-25 pounds.

I have a little bafang front geared motor on a trike. Think it is rated for 4-500w, pushing it to 650w but would not try to push a cargo bike up hill by itself in fear of over heating it.

Using it in front with your rear motor for hills would be better. In this case you would not save any watts with access to more power.
It may not use that much more if you climb the hill faster and did not lose watts to heat.

You stated that you swap batteries. You can gain usable Ah from your batteries if you ran them in parallel and lessen the demand on one battery. Need to make sure they are charged 0.1V of each other.

Then split off of the paralleled batteries to run both motors up hill then only use the DD on the flats. So two throttles. One for assist of the DD. Just keep the batteries parallel even for the rear motor only.
 
Yes your total Ah available is greater with one big battery rather than swapping.

You will also get a lot more burst power when needed, lots less voltage drop and stress on the pack.

And by halving your average C-rates, get much longer cycle lifespan out of both sub-packs
 
Seems lighter/simpler/cheaper/better to use a controller that can deliver more amps to the one motor you have, and put your two batteries in parallel after charging them both fully. Treat them as a single battery, as long as they stay connected.
 
I have my DIY ebike with a rear DD hub motor and I'm looking for the cheapest way to upgrade my torque power for all the steep hills around me. Would adding something like a 500w/750 bafang mid drive kit on top of my direct drive ebike make sense? Or would it be better for weight/efficiency to ditch the direct drive in the rear, put a regular bicycle rear wheel back on, and just use a mid drive?
 
zeddrick said:
I have my DIY ebike with a rear DD hub motor and I'm looking for the cheapest way to upgrade my torque power for all the steep hills around me. Would adding something like a 500w/750 bafang mid drive kit on top of my direct drive ebike make sense? Or would it be better for weight/efficiency to ditch the direct drive in the rear, put a regular bicycle rear wheel back on, and just use a mid drive?
The only things a direct drive motor gives you are 1) regen and 2) power if your chain breaks. However 1) is pretty small (a few percent increase in range per Justin's tests) and 2) can be mitigated by carrying a spare chain.
 
zeddrick said:
I have my DIY ebike with a rear DD hub motor and I'm looking for the cheapest way to upgrade my torque power for all the steep hills around me. Would adding something like a 500w/750 bafang mid drive kit on top of my direct drive ebike make sense? Or would it be better for weight/efficiency to ditch the direct drive in the rear, put a regular bicycle rear wheel back on, and just use a mid drive?

Rear hub motors are known to break at the root of the freewheel thread from pedal forces. I would not expect one to tolerate mid drive input for long.

The cheapest way to increase your torque would be to use a controller that can supply more current to the rear hub motor you already have (if your battery and connectors can take the extra load). Torque is in proportion to the number of amps.

Second cheapest would be to add a low cost front hub kit.

Using a mid drive system by itself should improve your bike's hill climbing ability, but is not a very cheap option to implement or to maintain in the future.
 
JackFlorey said:
The only things a direct drive motor gives you are 1) regen and 2) power if your chain breaks.

3) reliability
4) longevity
5) low maintenance
6) low purchase cost
7) parasitic drag when coasting. :(
 
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