Two motors in series?

[offGridDownUnder]

My current build uses a GMAC as a 'stoke monkey' motor, with a Gates belt connection from the left side of that to the left side of a rear ("dirt jump") hub - there is no cluster or chain on the right side of the rear hub. The rim is 26".

I have a wheel with a Grin All-Axle front with a 26" rim. What would be the general outcome of putting that in place of the "dumb" rear hub I have now?

I understand each motor would require it's own controller, cables. Grin sells cables to connect two controllers to one Cycle Analyst.

But generally, what would be the outcome? Would each motor shine at what it does best, or would they "fight"?

 

[amberwolf]

Well, they aren't actually in series, they're still in parallel, since neither motor actually drives the other motor, even if they are driving the same wheel. If the mid motor has any freewheels in it's beltline to the hubmotor wheel it won't be backdriven by the hubmotor if that's running faster, so no power loss there at least.

Also, you'd need to modify the GAA to install a sprocket on it, or if you want a shiftable drivetrain for the GMAC / pedal drivetrain (if you have pedals) you'll need a way to bolt a shiftable gear cluster to the GAA.

The results are no better power/etc wise than having them power separate wheels, except that now there is twice as much stress on the single powered wheel's structure (spokes, rim, tire, etc), only 1WD isntead of 2WD (so less chance of traction control via motors and there is no redundancy in traction either).

To put them in series you'd need to have one motor driving the other and then that one separately drive the wheel; not sure how you could do that with these.

I think that since it's a "front" GAA you would be better off using it in front; it's much simpler and easier to do, and gives you the various benefits of 2WD.

 

[gromike]

What do you want to achieve? I suppose you want the best of a mid-drive and the best of a hub motor. As amberwolf has written the hub motor on the front and mid-drive rear makes more sense. That being said, it would be an interesting experiment. Simplicity is your friend, complexity is the enemy.

 

[offGridDownUnder]

What do you want to achieve?

To find out if someone can suggest what will happen if I did this.

The machine is in my signature - it's a Greenspeed Magnum Big Wheel trike. The GMAC is coupled to the rear hub with no freewheel, as the connection is Gates sprockets and belt on the left side through the ISO 6-bolt brake rotor mounts. Trikes don't use rear brakes except as parking brakes, so no loss.

The rear wheel regenerates the motor now. There is a cluster on the right side of the GMAC to decouple from the pedals (and me) and permit me to adjust my pedaling input for my comfort.

I'm not asking if I should or should not do this. I'm asking for an analysis of what will happen.

With a conventional 2 wheel bicycle, and front and rear motors, and the same rim size, they will spin at the same speed. This arrangement will too, except that there can be a ratio introduced using the Gates cog on the output of the GMAC and on the input of the rear All-axle. But the connection of ISO brake rotor mount to ISO brake rotor mount is absolute barring catastrophic failure - the motors will spin in lock-step, just as with a 2 wheel bicycle.

I've read a suggestion from Grin about using a DD and a geared motor on the same 2 wheel bicycle to provide the efficiency of the DD, and the hill capability of the geared motor. I'm wondering if this is different - the motors are still locked at the same speed as with that 2 wheel bicycle.

Will it work the same? Will it be different? What will happen? I'm asking for knowledge about motors.

 

[gromike]

So, if I understand it, you will drive one rear wheel of a trike with a "Stoke Monkey" ungeared mid-drive, and the other wheel wheel a DD hub motor. How is power shared between the wheels. This is way out in right field, but General Motors built a bus for Greyhound that was named the Scenic Cruiser. It was powered by twin 6-71 diesel engines. With the technology of 1950's GM could never get those engines to share the load in any beneficial way. Greyhound soon replaced all those twin 6-71's with one 8v-71.

 

[amberwolf]

You won't get any more power or capability doing it the proposed way vs separate wheels.

You just get more stress on the single wheel.

You can setup your system in the ebikes.ca simulator and see what will happen for each motor, setting it up as 2WD.


Just like separately-powered wheels, if the two motors are not identical in properties and/or controlled by a smart enough system that doesn't just feed them identically, then whichever one has a higher kV (vs gearing/wheelsize between it and road to give final RPM) will be trying to spin faster than the other and taking more of the load, assuming they are controlled by speed-modulating controllers.

If they are controlled by torque-modulating controllers, then whcihever one has a higher kT will take more of the load (again, dependiong on specific gearing/wheelsize)

If they are identical in properties and controlled identically, then they will both supply equal speed / torque in lockstep.

If the controlling method takes the kV / kT and gearing / wheelsize into account and produces throttle inputs to each controller along a curve specific to that, it could keep the speed / torque the same on both so they both share equally in driving the system.

If the controlling method takes no account of anything and simply drives them identically, then if they're just speed controllers the faster motor will really be doing "all" the work (depending....). Torque controllers will share the load in some proportion at least.

Trikes don't use rear brakes except as parking brakes, so no loss.

Yours might not, but it's not a universal thing.

In case it's something you just didn't know about (and might affect future trike-purchase or design considerations):

For delta trikes, my SB Cruiser used to (but they were crappy and ineffective junk so I took them off, someday will have disc rear). Trucktrike (or triketruck?) uses disc rears. Various pedicabs have rear brakes, as do a number of other delta trikes and trike kits to add to bike frames. Those with a single live axle often use a rotor on the axle rather than the wheels, but some use them on the wheels instead.

For tadpole trikes, I've seen various pics showing rear brakes (rim or disc) on at least some over the years, though don't know which ones they were.

 

[offGridDownUnder]

This suggests (with some different parameters) that one motor will drive the other sometimes. I don't know, but I am wondering if the Grin suggestion points to "When one of the motors sucks, the other will still drive", such as on hills. Perhaps I'll ask them.

Note for this I specified a 12" wheel on the GMAC to simulate the ratio reduction between the two Gates sprockets, roughly,.

All-Axle + GMAC in some ways

 

[offGridDownUnder]

one rear wheel of a trike with a "Stoke Monkey" ungeared mid-drive, and the other wheel wheel a DD hub motor. How is power shared between the wheels.

This trike has only one rear wheel. If you look at the build in my signature, you'll see how it's driven now with just the GMAC.

 

[amberwolf]

This suggests (with some different parameters) that one motor will drive the other sometimes.

That's correct in that as I noted previously, without a special control system to force sharing, non-identical systems will operate differently in different parts of their speed/torque curves.

That's the same whether they're chained or belted together as you're asking about, or as separate wheels.

 

[gromike]

This trike has only one rear wheel. If you look at the build in my signature, you'll see how it's driven now with just the GMAC.

This trike has only one rear wheel. If you look at the build in my signature, you'll see how it's driven now with just the GMAC.

My bad. Looking at your build you are over my paygrade. Your idea would be a great experiment, but I would question the added weight. That, and the added complexity.

 

[offGridDownUnder]

I also purchased an SX2 to try in place of the GMAC. I haven't mounted it yet.

Using this simulation, and toggling between using the SX2 and the GMAC, I notice the GMAC shows negative motor power, but the SX2 never does.

Is this real? What does this mean?

Dual drive

 

[offGridDownUnder]

Overall, I tend to look at what I have, and consider what I could do with it. From time to time, I spot a synergy and I win, or I spot a black hole, and I avoid it.

When I sold the Cruzbike (see sig), the buyer didn't want the motor, etc. (that fool!), so I have it taking up space. I built a model All-Axle rear and saw I could fit that where the GMAC is (and may someday try that, but it's not someday yet - I'll see about the SX2 first, as that's road-legal here in Oz). But I have the All-Axle front, with replaceable axle mounts (and I can make my own to customize - I already did this to mount it on the Cruzbike to prevent the brake rotor from sawing through the motor cable).

So, I think about it. Where you (generic you) say "redundant", I say "spare". I have to keep it somewhere - perhaps in the rear fork is the best place.

I do have a goal: to keep moving as my body fails out from under me, and to enjoy it. I'll reach full age pension next year. I don't want to own a car. The battery on the trike is large enough to run a computer, lights, and maybe a radio. 'offGridDownUnder' is real.

I want to tow a trailer up hills even when I'm weaker. I want to ride into the bush (nothing too gnarly, but that leaves plenty). It's not muscles - my joints are already failing - that progression of electric bikes in my sig is my joints catching up with me over the past few years. I should be able to ride a boosted trike for a long time even with my current and future problems.

Grin advocates adjusting the motor controller to provide a trickle all the time to overcome motor cogging, and insists I'll recover more by regen than I use up on that trickle - "electric freewheeling" is their term. The Cycle Analyst provides support for three saved custom profiles - one could be "All-Axle on trickle only (no added power from PAS or throttle), but SX2 on PAS/throttle", one could be "SX2 on trickle only, but All-Axle on PAS/throttle" and I could switch by pressing the button on my hand grip.

Yes, it weighs 4kg more than not having the second motor. But if it makes enough of a difference riding in hills, or off-road, it's only 4kg, and I can stand to lose that much (and some more). And a "free" spare motor in the outback can be useful (but hopefully not too often).

And the other possibility would be that there is some way having both operating would be useful, which was the start of this thread. The simulator says the All-Axle will drive the GMAC, but that second URL I provided just above says something will be different with the SX2. Perhaps the difference is just that the SX2 isn't properly parameterized in the simulator.

But the "one or the other" configuration in the Cycle Analyst is practical anyway. Interesting to find if there is a better way by having both active at the same time.

 

[gromike]

As they, it's all about the battery.

 

[amberwolf]

Using this simulation, and toggling between using the SX2 and the GMAC, I notice the GMAC shows negative motor power, but the SX2 never does.

The GMAC is clutchless, so it will turn as a generator if forced from teh outside, regenerating power out of it.

If the SX2 as created in the simulator (or reality) has a clutch (internal freewheel), that will prevent housing rotation from passing back into the motor inside, so it won't act as a generator (unless you were to spin the housing backwards).

 

[offGridDownUnder]

If the SX2 as created in the simulator (or reality) has a clutch (internal freewheel), that will prevent housing rotation from passing back into the motor inside, so it won't act as a generator (unless you were to spin the housing backwards).

I didn't think that through. Yes, of course.

I'll spend more time looking over that profile. I bought the SX2 with a welded locked clutch, as alternative for the GMAC. I also thought I may need to lower the ratio (embodied in the two Gates cogs - I can manage down to 3:1 in this build), and then wondered about over-driving the SX2 - with the consequence of thinking I might replace the welded clutch with the factory one to provide freewheeling and avoid over-driving.

If that profile shows any great advantage (hill climbing?) I could replace the locked clutch, still have the All-Axle for regen (avoids brake wear) and efficient flat long runs. I would also have two motors. Perhaps there isn't any great advantage.

 

[amberwolf]

Overall, I tend to look at what I have, and consider what I could do with it.

<snip>

So, I think about it. Where you (generic you) say "redundant", I say "spare".

<snip>

I do have a goal: to keep moving as my body fails out from under me, and to enjoy it. I'll reach full age pension next year. I don't want to own a car.

I'm pretty similar, though I'm much farther from "pension" age (though I have none coming). So I understand the idea.

Grin advocates adjusting the motor controller to provide a trickle all the time to overcome motor cogging, and insists I'll recover more by regen than I use up on that trickle - "electric freewheeling" is their term.

That's very likely true--the FW current is typically very low, since it is not driving the motor, it is just enough to cancel out the "cogging torque" of the magnets vs the stator teeth. A few dozen mA, most likely. Can be determined experimentally by increasing the FW current until it is possible to manually spin the wheel offground about as freely as a bicycle wheel.


As long as you are using regen braking to do as much of your slowing down as possible, to maximize the input, you'll probalby see 2-5% back in regen.

The GMAC will probably provide better braking force than the GAA because of the gearing multiplication (that's been my experience with the SB Cruiser so far. I don't have the GAA, but it's the case with the Ultramotor vs the GMAC in the same wheel and position on the trike, both using the Phaserunner with the same settings vs the motor type/capabiltiies/etc.

The Cycle Analyst provides support for three saved custom profiles - one could be "All-Axle on trickle only (no added power from PAS or throttle), but SX2 on PAS/throttle", one could be "SX2 on trickle only, but All-Axle on PAS/throttle" and I could switch by pressing the button on my hand grip.

You can't do that with a single CA unfortunately, as it only has one throttle output, that controlls both motors at tje same time, if you're using it for throttle manipulation.

But you could use a separate device (arduino, PIC, ESP, discrete components), to generate two throttle signals, and a button to toggle between whatever modes you want those to obey. One signal would just be a FW current amount, generated to the level that whichever motor controller is receiving it needs to do that. The other singal would be a direct passthru of the CA's throttle output.

Another consideration is each motor will need a different amount of throttle signal to do the same job, so you will also need to scale the CA's throttle output for each one, and that device can do this, too.

If you are using controllers like the Phaserunner, then it has it's own throttle scaling built in and so you would not need another device to do that part. You can also setup the FW current in the PR itself so that it always does this anyway, removing the need for the device to switch the CA's output between systems (a simple physical switch could be used for that instead).

 

[amberwolf]

I would also have two motors. Perhaps there isn't any great advantage.

To me there's "always" an advantage in two motors for redundancy if no other reason, but for that purpose I prefer them to be separate drivetrains so that one cannot directly affect the other, and also prefer the pedal drivetrain to be separate from both for a trike (which is why my future SB Cruiser replacement would have the pedals running the front wheel, and motor(s) on the back ones). even though I can't really pedal the trike faster than about 1mph for any distance, and couldn't climb a slope with it that way without motor help).

Your trike is not delta like mine, but tadpole, so to have front drivetrains they have ot either deal with steering angle changes or be hubmotors in the wheels. (one of hte reasons I built delta; the other being cargo hauling is far easier to design in). So a front motor is complicated enough to avoid. Unlike every other motor, the GAA actually wouldn't be difficult to do that way, though, so it is at least a potential option if you found it would work better or suit some other need.


Two motors also has the advantage that it's usually cheaper to get two smaller controllers than one big one to provide the same power (the two motors may be more expensive than the one larger one, however if you already have them.... ) so for situations you need higher power....

 

[offGridDownUnder]

If you are using controllers like the Phaserunner, then it has it's own throttle scaling built in and so you would not need another device to do that part.

I have:
V3 Phaserunner L10 bought with the All-Axle front - no idea about reverse.
V4 or 5 Baserunner L10 bought with the GMAC - tested to politely reverse by grounding wire in 'mains' plug.
V4 or 5 Baserunner Z9 bought with the SX2 - probably does reverse, not tried.

Reverse mentioned as I want it. The trike is 2 meters long and I don't like dismounting to get out of tight spaces, particularly with my joints and/or in traffic. A fun thought about that is to have a hidden switch for reverse, and leave it set when stopping, so if someone tries to steal my trike I can catch them at a walk...

I understand the FW (Free Wheeling) current is set up in the Phase|Base-runner, and each would have it's own. I also vaguely recall two schemes Grin provides for two motors - I'll have to look at the details again to see if one helps (I only had this 'serial motor' thought this morning).

Another approach is to, say, connect the All-Axle to the PAS/Cycle Analyst, and use a throttle only for the (unlocked) SX2 with FW current. Only use the throttle on the SX2 for hills when the All-Axle drags.

Or connect one motor at a time according to terrain/load. Just switch the connectors.

Not obviously apropos, but another scenario I've had in mind for a while is some day when the motor fails. Then, or for other reason, I can install a regular rear hub/cassette with Gates sprocket on the rotor mount in place of the GMAC or SX2 and keep pedaling, albeit without assist. At least I still am not dragging my chain/derailleur through the mud, and I will still have whatever deep ratio I select for the two Gates sprockets.

 

[Papa]

Somewhat akin to your situation, I too am off-grid (by choice for several yrs now).

But more to the point. I'm curious...
You've obviously owned a verity of spendy HPVs, but I see no Delta trikes mentioned. Why not? You are aware, I suspect, that Greenspeed has/had? a Delta offering. Yes?

 

[offGridDownUnder]

a verity of spendy HPVs

I hoped each would see me to the term of my life. Deteriorations introduced themselves and forced me to move on to the next approach. I've sold each as I did to recoup some of my loss, and it has been a loss.

But not being able to get around, or out to a natural setting, or being able to buy or rent outside of town gives me incentive to keep going. I won't be earning after next year, and I experienced what happened to the supply chain due to the pandemic. I am solving my problem now, rather than some hoped-for later.

I'm happy to have found out the problems my body is throwing up while I'm still in a position to do something about it. If I can't ride a recumbent trike, I probably can't ride anything. I need the motor, as I can't build up my joints. The motor also gives me heart - hills and wind are not reasons to stay sedentary, nor is a large load. I don't want a car - this machine may be the way I evacuate from a bushfire, and I've already ridden it over 60 km in one go.

I know of no trike dealers here in Perth with stock.
I've never seen a video of anyone riding a delta off-road.
I've not seen or read of anyone with a folding delta.
Rear drive on a delta is complex, or compromised if only one rear wheel is driven.
My Tern S8i was front wheel driven, and easily broke traction on uphills - worse on dirt.
The Magnum Big Wheel model is the only Greenspeed I know of that can mount a 4" rear tire (although with my drive train I'm likely limited to 3"). There is a dealer here, although he had to order it in.

 

[Papa]

Rear drive on a delta is complex, or compromised if only one rear wheel is driven.

Anura - GreenSpeed Trikes

Anura A delta with a difference, the Anura sheds the traditional tadpole style, offering a unique and comfortable ride. The higher, more upright seating position is preferable to some riders, and the Anura can also be used in a tandem format. Specifications Frame Material 7005 Aluminium Alloy...

greenspeed-trikes.com

The Greenspeed Anura pictured below, note the differential

 

[Papa]

I've never seen a video of anyone riding a delta off-road.

I've not seen or read of anyone with a folding delta.

Most production deltas separate mid-frame. While not considered a genuine 'fold' feature, it allows main frame separation creating a smaller, transportable package. However, an Hase Kett EVO, is, in fact, a folder:

Also: (note the impressive near 'zero' turn-around radius @ 1:33)

Please remember, 'Tis NOT my intentions to convince you or anyone else to purchase a delta trike. It IS only my intention to address occasional misconceptions.

 

[offGridDownUnder]

I was afraid of this. You weren't asking me because you wanted to know my answer. You were asking so you could pretend you had a reason push your opinion.

If you wanted to inform people about this or any other approach, you can start your own thread. Nothing was stopping you.

I've already bought my trike, and I don't have "misconceptions", and I didn't ask your opinion about it. Say your own opinions in your own thread - no one was asking.