Idea for an electric push trailer... let me know what ya think...

Discussion in 'Electric Bicycles' started by bigkat650, Aug 20, 2009.

  1. bigkat650

    bigkat650 Member

    My idea to make an electric push trailer was to make something economical and functional. The idea is to use it as a peddle assist more then a motorized bike. My girlfriend lives on a massive hill out of town, and I'm a big guy (over 300lbs)... So simply peddling up the hills would be extremely difficult. With the assist of the silent electrical motor, I think I would use my bike alot more, which will help me get back into shape. Anyways, The idea is to use either a 500 or 600 watt electrical motor, and 4 12v 12ah batteries wired to create a 24volt 24ah reserve. Unlike most electrical bikes, I had planned on using an external electrical motor as apposed to the hub style motor. The main reason I chose to do this is cost, and keeping the back wheel around 12inches.

    All in all, I think I could build this for less then $300... The batteries are $93 shipped... the motor will be around $60 shipped... Then I would need a thumb throttle, and control unit... which is about $75. Plus scrap metal I can get for free to create the frame.

    Below I created some 3D pictures on a basic autocad program which shows basically what it would look like. The 4 batteries are in grey, the motor is in gold, and there is a simple chain that would attaching the motor to the black gear which is attached to the rear wheel. Ideally, above the batteries and motor your could tie down anything such as camping equipment, a basket, or a cooler.

    Lastly, if you click HERE you can see what gave me the idea, I wanted something a little smaller, that I can make myself, without being a hub style motor, that would be less then $300... Let me know your thoughts folks... Thanks!

    Attached Files:

  2. bigsugar999

    bigsugar999 New Member

    looks really awesome to me .. you could even add a generator for range extension... perfect
  3. bigsugar999

    bigsugar999 New Member

    .. or solar a panel...
  4. bigkat650

    bigkat650 Member

    I guess I do have a couple questions...

    Is it better to mount to the back axle, or under the seat?

    Would a 500 watt motor be sufficient? Or would something like a 300, or a 600 ok? I don't mind peddling, but I want to know I have a decent amount of thrust in case I wanna just cruise for a bit (i don't need to go more then 20mph) The best deal on batteries I found was 4- 12volt 12Ah batteries for about $93 shipped... SO figure either 24v & 24ah, or 48v & 12ah... Either way it calculates to just over 500 watts continuous for an hour. If a 400 watt would be sufficient assist, that may be better... I do have about 25 miles up and down hilly roads to go between my residence and my girlfriends house, and it would be nice to to able to get there on one complete charge.

    Lastly, what gear ratio should I use? The 500 watt motor I am looking at is 2500rpm's with an 11 tooth sprocket. Again, i'm a big guy, and I can peddle, I am looking for some assist going uphills and perhaps a decent cruising speed of around 20mph on flat ground (a can peddle to reach that speed if need be)... Lastly I would like to be able to use it for about 25-30 miles while assisting.
  5. bigkat650

    bigkat650 Member

    Found THIS: 24 Volt 450 Watt Direct Drive Electric Motor & Rear Wheel Assembly Which I think would work very well with this design... 450 watts should be a good combination of power and Ah usage. All the scooters run on about 10ah and are rated around 15 miles on a single charge. With peddle assist, and a 24ah battery, I think 30mile range is a practical thought.

    Again, I am very new to this, and I have never done a motorized bike... so if you think my calculations are off, please let me know. Thanks
  6. bigsugar999

    bigsugar999 New Member

  7. safe

    safe Active Member

    I'd just buy it, build it, then run it.

    However, I think there might already be some push trailers around... it's a very common idea actually.
  8. bigkat650

    bigkat650 Member


    Its a cool bike, but it doesn't fit my needs at all. I live in NY, and motorized bikes are illegal... Which is why I need an electric one, which is silent, and I can hide fairly well within a trailer.

    Do we think 24v and 24ah is sufficient for a 450watt motor to assist me for about 30 miles, some of which is over hills? If need be I can purchase 2 more batteries so its 24v and 36ah to be sure I would have enough power.
  9. machiasmort

    machiasmort Active Member

    What part of NY? I run a gas bike here and don't get much flack in Buffalo. The burbs are where you get your problems!

    I've got lights hooked up to run off of the motor. If I get pulled over, I'll tell 'em the only reason you heard the motor run was because it powers the lights!
  10. bigkat650

    bigkat650 Member

    hahahaha thats a good one! If a cop believed it though, maaan they are dense! I think I would let you off just for thinking up the clever response!

    But to answer your question, I am in upstate NY as well, Ithaca actually... (cant wait to watch the Bills beat up on the Packers tonight!). But back to the topic... I researched it last summer, and any bicycle that has a motor attached to is, has to be registered as a motorcycle--regardless of the size of the motor. Its a state law, so I'm sure it is technically in effect everywhere. But weather or not the cops know about the law, or would even bother to enforce it... is another story. I just assume not draw the extra attention. I wanna be ultra sleek, so that no one suspects a thing! bwahahahaha.

    If I am wrong about that law, let me know... But I believe its one of the top 2 toughest states on motorized bikes.:shout:
  11. mrspock

    mrspock Guest

    I think you are way over estimating the range you will be able to get. If you use a 24v motor and two 12v 12ah batteries, your total ah (amp hours) will only be 12, not 24. Batteries are wired in series. No matter how many you wire in series, you still only get 12ah. 25 miles is a very long way on most ebikes. If you even carry extra batteries, look at the weight you will be toting around. Pedaling won't be near as easy as you think when pulling that much extra weight, especially up hills. With the distance you say you need to travel, an electric scooter would be better but with most current models, you'd still need to recharge while at your girl friend's. But since your budget is $300, an electric scooter would be out of the question since they run closer to $1000. However, for around your price range, you could buy a Currie Ezip bike ($300-$400 range). They are currently $398 at my local Wal-Mart. They come with one battery pack and you can add another. But 50 miles round trip would still be pushing it. Weighing 300 lbs would be a major strain on the batteries. I've driven this bike for almost 2 years with no problems except the battery contacts wearing out from the constant vibration of the road. I really think your best bet would a small gas scooter, which would carry your weight and be a miser on gas too and you would have no worries about running out of juice. You could get your exercise from a mountain bike on the side.
  12. mrspock

    mrspock Guest

    You can't use any type of generator to replace the power you're using while the bike is in motion. This is getting into the perpetual motion scenario. An ebike gets all its power from the batteries and some from pedaling. The bike is using too many amps too quickly to replenish. You could strap a gas generator on the bike but it still could not charge the batteries as fast as you were draining them. Plus, the extra weight of the generator, even if a lightweight one, would just make the batteries drain even faster. And there's a lot of variables that make solar charging a bike very inefficent also. The best comparison is a cordless lawn mower. They typically are 24 volts with two 12v batteries, just like many electric bikes. At least one cordless mower manufacturer offers a solar panel option but they tell you up front that under ideal conditions, it takes 3 sunny days to recharge the batteries and of course, that's with the mower turned off while recharging. 5 days or more for cloudy days. It would take a lot of square footage of solar panels to carry around on the bike and that's just hauling them and not using them. No way you could set them up to use on the bike while running it unless the bike was 10-15 ft long. Would be very awkward on a bike. Just like a gas generator, the solar panels couldn't keep up the charge while the bike is in motion. I'm not referring to the experimental vehicles that run directly off the panels and sit on the ground. I'm referring to a bicycle.
    A lot of people bring up the generator or solar thing with ebikes but you need to realize that this would already be being done if it was at all feasible.
  13. bigkat650

    bigkat650 Member

    Well the original plan was to use 4 batteries total, not 2... wired to create a 24v 24amp load

    Honestly I should kill this thread because I have completely rethought the idea, and a simple hub drive is the way to go with LiPo batteries instead of SLA... just debating on geared or non-geared now