I do not have experience with 2WD yet, but I am building one, so I just wanted to share some of my thoughts. More experienced ES-members can correct me at will.
This is a very useful thread. I am determined to build a dual front motor tadpole trike, for various reasons but also because I can
Obviously with dual matched front motors they'd have to be matched in speed and throttle and so on. Meh? If they don't match, I will just point the wheels a different way and go. It'll work even if it wears out one tire. I'd probably set it up so the batteries are amidships, right next to each other on either side of the frame, and make all the connections super short between them. Controllers also mounted close. With 'Bents you have a lot more room to put things where you want them, and since it is a custom frame, the options are endless.
Here are the questions I come away with:
1. One motor per battery, or two batteries in parallel? It seems it has been done both ways, which is best?
Probably depends on the expected amps per motor and the c-rating of your batteries. As I use Lipo, I don't have to worry about the discharge rate, therefore, I find 1 large pack more convenient. Especially as I have rear- and front driven motors that are expected to draw different currents at the same time, using one pack leaves me with one worry less that there may be a difference in discharge between two packs. I guess the same counts for 2FWD, but less so, as the expected current should be more or less the same for both motors (unless you are driving circles or use different motors...)
llile wrote:2. I'll be using a Cycle Analyst. Will I need two CAs, or one? ( I guess that depends on the answer about number of batteries..?) Two is more expensive, but that is still in the budget. Maybe two CAs check the health of both batteries? two CAs monitor individual motor power more closely, allowing fine tuning of match? I am still a little concerned about how to hook up the CA to this hack.
I agree this is depending on the number of batteries, but more importantly, what do you want with it. If you use the CA only to monitor voltage, then there are much cheaper ways to do that. If you want to check the used Wh, then having two battery packs and two CAs means that you will have to do a lot of counting. It is one more reason to go with one battery pack, one stand alone CA with a separate shunt to measure current from the battery pack BEFORE the split to both controllers.
However, if you expect currents higher than 45A continuous, you may need a bigger shunt. I went with a 200A shunt from Ebay
(expecting 100A per motor), which is on the high side.... better safe than sorry, though. To use it with my CA, I need to modify the CA (I have the DP) and recalibrate it for the new shunt. I am still working on that. If you get the stand alone CA, connecting the new shunt should be piece of cake.
llile wrote:3. One throttle. Definitely. The controllers and batteries will be physically close, grounds will be heavy and short between the systems, throttle wires will be short and symmetrical. I guess if the throttle is powered from the cycle analyst there isn't a problem with the 5V power supply? If there is any interface electronics needed, can do. 5V Dc-Dc converrter if necessary to get the throttle working right. Instrumentation amp? Hell it is all 5V stuff, I might use a PIC or an Arduino instead of an instrumentation amp. I do that shit for fun anyway. But that seems overcomplicated. Can the throttle just be hooked parallel to two controllers or CAs?
I am no electronics guy. Therefore, I went with the easy way out, as shown by ~Methods, and inserted another hall sensor into my throttle (see here
). Took me 45 minutes. No high-voltage peak will mesh up my throttle signal.
llile wrote:4. I will probably be running at 72V. With a faring. I hope to build something with a 40 MPH speed on the flats. Don't tell the cops.
I guess that is 20S? Looks good to me, cause that is what I use now! On the flat, my HT3525 gave me 36mph. A faster motor (HS version) should give you more than 40 mph, but if you go that route, you will use more amps when hill climbing, increasing the risk of melted wires inside your motor.
llile wrote:5. I ride a long way in rolling hill country. 2WD will be a good thing for those hills. Some are killer grades, short sections of 20% are encountered on most rides. 50 Mile round trip is also not uncommon. Battery requirements will be serious. I am thinking about two 30 AH batteries. Ping. Is that too much battery? This is 4X the battery I use now, at 20MPH same distance.
I have no idea yet. Is also very much depending on which motors, max amps used, etc. You need to give us a bit more details about those, in order to give a better estimate. My rear HT3525 eats 20% hills at 20mph at 84V (20S lipo hot of charger) and between 20 and 30Amp. I guess, at a certain speed, you just need to 2kW energy to manage those 20% hills. However, with a consumption of 100Wh/mile, your mileage may vary..
Two 30 Ah batteries (72V?) sounds very heavy to me and gives you >4kWh. But with >4kWh you should be able to climb a 40 mile-long 20% hill at 100Wh/mile (assuming your motors don't melt). So, a 50 mile round trip sounds very manageable without hitting LVC.
llile wrote:6. I'll still pedal. I love the feeling of exertion, I love being in shape, and it takes a good 1-2 hour workout to get there anymore. I hate sitting in a car, wishing I was getting some excercise. I'll probably cobble together a transmission that can still allow pedaling at 40MPH - maybe a 7 speed rear and a 3 speed intermediate hub. I've built crazier transmissions than that. Geared high, the pedals will be useless at normal non-Ebike speeds but who cares? I have never run out of juice before, due to good planning.
Looking forwards to see that.
llile wrote:7. The other innovation I am seriously considering is a leaning frame. Front wheels don't lean, but the rear wheel, me, and the heavy batteries do lean. My friend has had his trike up on two wheels, doesn't sound fun. Leaning should improve cornering. But that is a whole 'nuther thread.
How about the 'lectric details, am I on the right track?