DM01 fitment for tandem

[polyglot]

I am trying to put a DM01 on my tandem (Avanti Tandem 2017) but having issues because there are chainrings on both left and right sides of the crank. The bottom bracket is 68mm, so we tried to fit a DM01 this afternoon but the left chainring interferes with the left end of the motor (first picture).

It *looks* like the DM01L should clear the left chainring but I am not sure because the diagram provided by toseven is incompletely dimensioned. The pictorial representation seems to be 1000W (127mm motor) assuming it's drawn to-scale, but who knows?

So I have two questions:
* does anyone have a more-complete CAD diagram of the motors, and
* has anyone fitted a DM01L using sleeves to adapt it to a narrower bottom-bracket?

Alternatively if you have DM01L, could you measure that clearance for me? At the very least if someone can confirm that the motor face does not protrude beyond the end of "Decorative Ring (3)", then I think I'm all good.

I could machine up sleeves totalling 32mm length so that the DM01L can grip a 68mm BB but is that going to cause me problems e.g. an insecure fitment? I haven't yet worked out whether my chain paths will be too wonky with the longer crank shaft length but I think I can make them work.

Any suggestions welcome as to options/experience. I could consider other motors e.g. hub, but I particularly want torque sensing with no separate throttle, and there's someone near me who is a toseven evangelist who would help with non-fabricating aspects of the installation.

Or if you are from toseven, please message me

 

[polyglot]

Second request for suggestions: battery. I am considering a LiFePO4 for a number of reasons:
* I have extinguished two shed fires this year due to ebike charging so do not want that for myself,
* I want huge capacity (2 fatties want to go for long rides like 100km) e.g. 2kWh,
* I don't think the extra 10kg of LiFePO4 vs NMC will actually matter on a 250kg bike, though we have no suspension...

The guy doing my install reckons I'm an idiot for fixating on LiFePO4 instead of just getting an NMC pack like normal people and maybe he's right.

My main problem is *where* to put a bulky 20kg battery. There's a cargo shelf over the back wheel but it's not as low as I'd like. There are not a lot of big triangles available in the middle and using one or both of those would mean no water bottles in reach, which is no good. The battery also needs to be easily removable, because the bike needs to on a bike-rack on the car.

Theoretically I could split the pack into two halves and mount them either side of the rear wheel? That makes wiring and charging and assembly a massive hassle though.

Has anyone built an e-tandem with long range? With unusually heavy battery?

 

[amberwolf]

Regarding battery chemistry vs fire, anything can catch fire--if the battery doesn't, the charger, bms, or wiring could (which could burn the battery itself once the fire gets going, even if it doesn't start with the cells).

It's much more important that you start with a properly built battery / etc, made of quality matched cells that have *identical* properties, that is correctly spec'd for the usage it will see with room to spare in capacity and capabilities.

If they start out identical in resistance, capacity, capability, etc, then there won't be problems with them being unbalanced, and thus having cells that either drop too low in voltage and get damaged during discharge, or charge too fast or too high a voltage, heat up too much during charge, etc., and end up starting a fire in the cells.

If the battery is properly built, then interconnects between cells won't fail allowing some cells to take more load than they should, and wiring won't pinch or crush and short, etc, insulation between cells and wiring and bms wont' fail allowing shorts and damage and fires, etc.


If it's possible, I'd recommend using used EV modules from places like Greentechauto, batteryhookup, etc., as the worst of those are almost certainly built better than any ebike, scooter, etc battery you can buy premade, and of better cells that are much much more closely matched to each other.

They may be so good and so closely matched that you won't even need a BMS if you set the controller LVC and charger HVC properly, and occasionally verify the cells are all still equal both at full charge and before charging. (this has been true of the ancient EIG NMC cells I've used, with only a couple of cell failures in about a decade and a half).


Regarding placement, I'd recommend panniers front and rear, on good quality racks designed for mounting on the type of bike you're using, designed for carrying more than the weight you'll be using in them.

The packs could be built so that they are separate parallel units that are each individually protected (if you use a BMS, use one on each, and make sure they are all common-port types so charge and discharge si thru the same port), then connected directly in parallel at the controller. (not using one of those "battery paralleling" devices, often called "smart" or "balancer" of which they are neither). THen always keep them parallel for charge and discharge like this.

Removing the panniers individually would be easy enough, if you choose a rack and pannier system designed for that. You can use secure but easy to deal with Anderson SB seires connectors for plugging the batteries into the bike's wiring harness at the rack. Tehy're bulky, but that makes them easier to handle and plug/unplug with no risk of accidental misconnections or shorts or reverses, etc. Others like XT-series could be used, but tehy're small and while keyed against reversing, can still be touched together backwards in some instances, shorting them and causing arc damage to the connector and reverse-voltage damage to connected devices.

 

[amberwolf]

using one or both of those would mean no water bottles in reach, which is no good.

If necessary, there are camelpaks for the water/liquids.

Has anyone built an e-tandem with long range? With unusually heavy battery?

No, but CrazyBike2 was a heavy cargo bike similar in some qualities to a tandem; there's a long thread about it's evolution around here if interested.

 

[amberwolf]

I could consider other motors e.g. hub, but I particularly want torque sensing with no separate throttle,

There are other ways to get torque sensing.

You can use any of a number of standard TS BB spindles, which would allow mounting your chainrings just lke any regular spindle.

Or there are hubmotors with torque sensing cassette mounts. Stancecoke just posted today about a new Yosepower kit that comes with one of those.

There are some controllers that can directly read various TSes, and there is also the Cycle Analyst or Grin Smartharness (not sure aobut the exact name) that reads various TSes and creates a throttle signal to feed any controller's throttle input (without you needing an actual throttle).


Additionally, depending on the setup and situation, true cadence sensing may work without torque sensing; I use this on the SB Cruiser trike (via the Cycle Analyst, but there are other ways like the Lishui open source firmware project) to control it's 2WD setup, and really only use the throttle on it as a "go button" for the instances where I can't push enough with my legs to get the cranks moving (when they hurt too much or I am too heavily loaded).


(Most controllers can't read any PAS sensor other than seeing that you are or are not pedalling, and just turn the motor on full for whatever assist level has been chosen, but the Lishui OSF and the CA are two of the few possible ways to get actual cadence control so that how fast you pedal controls the motor assist amount).