Simple Electric Bike

What is it and how well does it work?

This is a very simple electric bike. A geared DC brushed motor is mounted in the triangle of the bike and turns one of the crank sprockets (the gears that your feet directly turn).

It works quite well. It’s easy to put together and it’s cheap and effective. Not as much power as a brushless motor, but it still provides a very nice boost especially when going uphill or when your legs get tired. The effective power band is much narrower than on the other bikes I’ve built, but since you can still use the rear derailleur it’s easy to change gears to match road speed and inclination. The one caveat I have so far is not to use heavy power assist while changing gears. This tends to throw the chain off.

Intro

After tooling around with recumbents, I decided I wanted to make the simplest electric bike I could imagine, as I still had some work to do on the actual bicycle building part of creating an ebike.

So I took an old chromoly frame MTB and decided the simplest electrification would be to use a brushed DC motor. These have just two wires and can use cheap brushed DC motor controllers (costing approx. $25). The brushes do wear out over thousands of miles, and they are less efficient than 3 phase brushless DC, but they are so cheap and easy to use that I figured it’s worth a shot. The MY1018z I used on the serial hybrid bikes is internally geared down so that when it is attached to a crank set it approximately matches a human pedaling cadence. I decided I would mount the motor inside the main triangle of the frame and dedicate a gear on the crank set to it. This would mean losing the front derailleur but I never use it on the street anyway…

Check out bike elektro antrieb for a refined version of this idea. In comparison mine is a total caveman conversion.

Parts

  • MY1018Z motor
  • Half twist hall effect throttle (I prefer these to the full twist, they don’t turn on if you lay the bike down or lean the handlebars against an object)
  • brushed motor controller (YK42-3 in this case)
  • 1/8″ single speed bicycle chain OR a grinding tool and 3/32″ multispeed bicycle chain
  • Master link for the bike chain
  • 36v worth of batteries (4x Makita 3.0Ah power tool batteries)
  • wires
  • 1/4″ washers, bolts and nuts
  • 3 large 1/4″ u-bolts -> UPDATE: I have found that good quality hose clamps work much better, and are easier to install. The best are the kind that are tightened using a nut and a bolt; but stainless steel plumbing clamps work OK too
  • >=1/8″ thick sheet metal, square foot
  • Tools: Sharpie, ruler, sawzall, chain tool, grinder (optional, but very nice), drill, wrench, pliers, soldering iron, duct tape

The Plan

You’re going to attach the motor to a piece of sheet metal. This sheet metal will be ubolted to the frame (so you can just remove it later if need be). The motor attaches to a front sprocket with some bike chain. The idea is to approximate the position of the motor, throw some chain on, and then position the motor so the chain isn’t loose and falling off. Then drill holes in the sheet metal to run the u-bolts through. You’ll likely need to do some more drilling to get it just right, unless you’re the sort of person who measures things really well.

Instructions

  1. Place the sheet metal against the bike frame
  2. Roughly trace the bike frame tubes with the sharpie onto the metal
  3. Place the motor in the triangle, and trace its outline on the sheet metal
  4. Cut the motor hole out using the sawzall; grind down the sharp bits
  5. Verify your cutting by placing the sheet metal back against the frame
  6. Drill the screw holes to mount the motor; this takes some work. Start with one hole, then add another, then the third. I never get the third one spot on, so I dremel out the hole.
  7. Now throw the bike chain onto the smallest front sprocket and use the chain tool to shorten the chain. This is critical. If the chain is loose and sloppy, it will fall off. If its too tight, you will wear out the bearings on the bike and motor and generally make your life difficult. Put the chain on the front sprocket, place the motor/ sheet metal in the triangle, and raise the motor/sheet metal until the chain is tight. Then give it just a little bit of slack. Use the sharpie to mark where the hose clamp holes should go
  8. Drill or dremel the hose clamp/u-bolt holes. I used a Dremel cut off wheel and cut slits in the metal. For U-Bolts, use a small bit to make a pilot hole, then follow up with the 5/16″ bit
  9. Attach the motor using the u-bolts
  10. The position is probably off a little, so do some more drilling :)
  11. Mount again
  12. U bolt the motor controller on
  13. Take a hand grip off and place the throttle on the bike
  14. Wire up the throttle (this could be a nightmare if the color coding doesnt match)
  15. Attach the batteries to the frame– I ubolted a $3 Big lots trash can to the handlebars and put the batteries inside
  16. Follow the controller instructions for hooking up the wiring; I soldered washers to each wire and use bolts and nuts to hold the wires together; I insulated the connections with duct tape
  17. WITH THE CHAIN DISCONNECTED, try out your new bike
  18. Fix the wiring, which is inevitably incorrect the first time around
  19. If it now works, put the chain back on
  20. Voila

Photos

Test fit of the motor in the frame triangle

Sheet metal with the rough shape traced with a sharpie

I used the sawzall to cut the metal

Now I traced the outline of the motor on the sheet

Ready for cutting and grinding

Please wear gloves! I cut and smashed 3 fingers before I put mine on…

Looks good!

Now the slightly annoying task of drilling the motor holes… look closely, you can see I had to redrill some holes…

Here I’m marking on the sheet where the U bolts should go. Actually, hose clamps work better and you can be sloppy with the holes

Here is the motor mounted onto the frame. Time to add the chain

Throw the chain on and see how many links you need to remove

Masterlinks will make your life so much easier, and they only cost a couple of bucks. The other tool you need is a chain tool. The cheap Walmart ones are awful but will do; a proper $30 chain tool will do the job 10x faster (since I do this often I bought one)

Here is a masterlink installed on the chain

And two shots of the final product. The motor kept shifting downwards over about 5 miles so I added some hose clamps and it hasn’t needed readjustment since.

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