Two motors, one throttle, good idea?

leisesturm

100 W
Joined
Aug 28, 2014
Messages
205
Greetings- I am new to this site. I've heard of it of course and my research has led me here before. I'm mainly a geek who likes to know a little bit about everythihng. Now I have an actual need for an e-assist and a budget amount to complete it. We are a car free couple who must use tandems as our commute and grocery/cargo biking needs because one of us is blind. The tandem most likely to be the platform for the e-assist is the lower quality of the two. We have been using it for six years in Hillsboro to pull a Bob Yak which can easily carry 100lb and larger loads despite its modest 70lb manufactures rating.

We recently moved to S.E. Portland and the hills up Hawthorne and Holgate as well as the bridge approaches are daunting. We are fit but some days and some occasions (date night) you just don't want to give your all on every trip on the bike. I hope someone knowledgeable will help me organize my energies and help me make wise decisions and purchases. I will look at the FAQs but I have some offbeat questions that I have never seen tackled by the mainstream sources of information, to wit:

Two motors. Why or why not. I think it would be a good way to get the torque we need from simpler to install hub motors. I could do a mid-drive but tandems are not the easiest platform. The Eco-speed will do a tandem but they are $3,000 and I'm not even certain if that includes the battery. I've recently (very recently) learned of the 2-speed hub motors available. I think one motor in each hub driven off a common battery with either one or two controllers managed by a pedal sensor or throttle would be better than one huge motor (1,000W) in the very thin and cheap dropouts of our grocery getter tandem.

Any thoughts anyone?? TIA

H
 
Have you tried using the search function found in the upper right corner of this forum?

https://www.google.com/search?sitesearch=www.endless-sphere.com&q=+two%20%20+motors%20%20+one%20%20+throttle Using the check box, "Using google search" will probably yield you better results.

I say this not to be offensive, but because your question suggests you haven't read anything about the topic. It's been done more than once.
 
I don't think a mid drive would be a good idea on a tandem, too much hassle and fabrication to get that working.

I wouldn't worry about your dropouts either, as long as you fit torque arms you'll be fine.

I'm presuming your forks are rigid on the tandem?

If so the absolute simplest conversion you could do would be a front wheel hub motor, any one would do.

I would start there and then if you really feel the need for two motors, which i very much doubt you will, then you can add a second.

A good example would be :

http://em3ev.com/store/index.php?route=product/product&path=36&product_id=138

As for your battery you don't specify how far you want to go, at what speed on what terrain....

Kudos
 
It seems to be as simple as connect the controller's throttles outputs in parallel to the matching wires and then connect to the throttle
 
There have been several 2WD builds featured. Everything that can be tried pretty much has been experimented with, so...the good news is you don't have to spend any money trying out something new. Teklektik arranged switches so that he could run on either the rear motor alone, or both.

One throttle works just fine, but...you need two controllers. If one of the motors is in the front wheel, I HIGHLY recommend that the front motor is a geared hub, which has an integrated freewheel. I don't know what configuration interests you most, but the three comprehensive 2WD builds that I know of are each using two identical controllers and two identical motors, geared hubs front and back. Of course there are other options:

1. Geared front hub, DD rear hub (regen braking from the rear hub, near-silent sine-wave rear DD hub is slightly faster on the flat terrain, and the front-geared only helps on hills when the DD slows down a little?)

2. Mid drive + DD rear hub? Near-silent sine-wave DD hub is good for 30+ MPH on the flats, Mid drive is noisy, but good on slow uphills.
 
I've made several 2WD bikes and even a bike with three motors that had insane acceleration. It's very straight-forward. First, you need a very powerful battery because you'll be pulling a lot more current than normal with two motors. next, you need two controllers. Finally, you only need a single throttle and PAS. From them, you only connect a branch from the signal wires to the second motor, not the 5v, otherwise you get problems. If you use two batteries, the grounds have to be made common if you want to share the throttles. There are some controllers that work two motors, but I've never tried one and I have some reservation detailed below.

When you have two motors, you have to consider the power very carefully. It works really well with typical 250w geared hub-motors and not bad with heavy direct drive motors with low start-up torque. The problem you get if you have a high-torque rear motor is that it unloads the front, so you can't get any traction with the front one, and if the front one also has high torque, it doesn't get a chance to use it because of the lack of grip.

After all my experiments, I came to the conclusion is that 2WD is good for off-road and riding in snow with two small motors, but it has no advantage for normal riding on the road, where a single rear motor can give you everything you need. I would generally advise people not to fit a front motor unless there are no other options because it has so many disadvantages over a rear one: Lack of traction; it locks suspension forks when under high torque; it upsets the bike's handling; safety issues from spin-outs and broken drop-outs.
 
d8veh said:
I would generally advise people not to fit a front motor unless there are no other options because it has so many disadvantages over a rear one: Lack of traction;

Nope. Works fine for me on my bikes with 1600-1800 max watts and slow windings. It rarely slips, and when it does, it hooks right back up again. When it does slip, it’s not like an unpowered front wheel skidding, which usually results in a fall. The wheel still pulls in the direction it’s pointed, even during the instant it’s skidding.

it locks suspension forks when under high torque;
That’s one of a few reasons not to use suspension forks on a streetgoing e-bike.
 
Balmorhea said:
d8veh said:
I would generally advise people not to fit a front motor unless there are no other options because it has so many disadvantages over a rear one: Lack of traction;

Nope. Works fine for me on my bikes with 1600-1800 max watts and slow windings. It rarely slips, and when it does, it hooks right back up again. When it does slip, it’s not like an unpowered front wheel skidding, which usually results in a fall. The wheel still pulls in the direction it’s pointed, even during the instant it’s skidding.

It depends mainly on the motor's torque. Some direct drive motors aren't so bad as geared motors because they don't make so much torque on take-off, but something like a Bafang BPM or Mac running at 1200W from the battery will spin the wheel on take-off. That's on the flat. As soon as you go up hills, you get a weight transfer to the back of the bike, and even one of those 250w 15A 36V hub-motors will lose traction if the hill is very steep and the surface not too good.

There are always people that say that they have this or that and they're very happy with it. I've built many bikes with front motors, rear motors, mid motors and all permutations of them. I give my opinions freely and as unbiased as I can for the benefit of others.
 
There is a controller on aliexpress that has 2 sets of phase wires/hall connectors coming out of it. Unfortunately it is very underpowered, only 13 amps per motor, or 26 amps total.
 
Back
Top