December 17, 2012

Improper Use of Machinery

With the arrival of some parts from Surplus Center and Monster Scooter Parts, I was able to finish the differential and assemble most of the drivetrain.  

Since I don't know where to find a proper broach on campus (maybe the Edgerton shop has a set?) I had to horribly abuse the poor MITERS tools use some unconventional machining techniques to make keyways in the differential's output gears.  I basically followed this guide, but used the mill instead of the lathe, and using a tool I  ground out of some tool steel blank.  I tried using the lathe at first, but found that the tool holder would twist if I accidentally tried to make too deep a pass, so I switched to the mill, locking the output so the cutting tool wouldn't turn.  The keyway isn't perfectly the same depth all the way down the gear, since the tool flexed some, but it works well enough.  I imagine this method would work much better on aluminum than steel.  

Yes, I chucked a piece of square metal in a 3 jaw drill chuck...

I widened out the bore of this 15 tooth sprocket, and bolted it to the output adapter I made for the hub gear.  All the hubless sprockets I got had teeth numbers that were multiples of three, so I could easily widen their bores on the lathe.  I totally thought of that beforehand.

And here is the assembled drivetrain.  I was not as lucky with the left side as the right side, so I had to make a chain tensioner to take up the slack in the chain.

Here's where the trike lives when I'm not working on it.  ALL The Bricks below it, Hat Coil to its right,  and parts from MITERS plane behind it.

When I started building the fork, my plan was to attach the front wheel via two blocks of aluminum that would clamp to the legs of the fork.  I made these two clamps, but I managed to sheer off one of the tightening screws in the process of clamping the block to the fork, making the piece useless.  I decided to go a different route rather than remake the broken part, and just weld on some steel supports for the front axle.  I cut the supports out of some scrap steel bar, and bolted them together at the correct spacing for welding.  I'm not sure what alloy of steel it was, but it made almost gold colored shavings on the mill, along with lots of unhappy noises.

Tacked in place:

This weld made me really happy.  The others weren't quite as nice, but they still didn't need much grinding.  I seem to be improving at this MIG welding thing.

The axle is a random stainless rod I found.

I may replace the rod later with a threaded rod, so that I can turn the axle holes into proper dropouts like on a bicycle, so that the wheel can be easily removed.  A threaded axle would also provide a convenient way to attach foot pegs to the fork.  The foot pegs could even double as the nuts that clamp the axle in place.

To stop the front half of the trike from falling over without a person on it, I attached some air springs from SEGFAULT.  They don't provide nearly enough force to lift up the frame when it has been tilted, but they do stop it from falling over.

To interface the rear wheels with the differential and drive shafts, I first pressed out all the bearings, and removed the stock sprockets and band brakes.  I milled one side of each of the wheels flat, so I could bolt on these hubs with 1/2" bores and 1/8" keyways, also from the now disassembled SEGFAULT.  Later on, disk brakes will also be bolted to these hubs.

I made some little aluminum inserts for the opposite side of the wheel, to guide and support the axle through the entire wheel.

And now it rolls!  One possible issue I've noticed now that it's assembled is the questionable steering geometry (rather like the first edition of my scooter's steering, but not nearly as bad).  Because of the alost 90 degree head tube angle, the steering has negative trail, which may make leaning difficult.  I guess I'll have to ride it to find out.  If it is a problem, I could either simply flip the fork around 180 degrees, or cut and re-weld the head tube at more of an angle.

Two sets of parts I forgot to take any good pictures of the making of are the two bearing blocks and the two outer vertical plates.  Each of the bearing blocks has a pair of bearings pressed into it.  They are held in place by two screws from below, as well as two screws each through the vertical plates.

Cutout for the end of the motor:

The protruding corners of the bearing blocks wil be removed:

This is roughly what the top plate will look like.

I split the top plate into two parts.  The smaller bit will be the cover to the battery compartment.  I plan on making two battery packs for the trike, so that I can quickly swap them out when one dies, and I did not want to have to take off the entire top plate each time.

Since I had to oversize the chain between the hub gear and the differential, I made a chain tensioner to take up the slack.  I started with a rod of some sort of round plastic stock, nylon, I think, cut it to the proper diameter on the lathe, and bored out a hole to press a small bearing.  I then used the indexing head on the mill to drill out ten holes around the perimeter of the plastic cylinder, corresponding to the low spots in the sprocket.  Since plastic is soft, I just used a coarse file to sharpen the teeth.  It rolls quite smoothly, and since it is on the low tension side of the chain, it should not wear too much.

Battery pack time.  I pulled out one of MITERS's many boxes of A123 28650 cells, to see exactly how many I could cram into the battery compartment.

I can fit about 36 cells, with room for wiring, which will give me a 12S3P pack. I also did some test fitting with some 18650 cells (the size commonly found in laptop batteries) and found that I could fit 96 cells, for a 12S8P pack.  In A123 land, this means around 28% more capacity, at the cost of much more labor to make the packs.  Also, there are way more of the larger cells freely available, so I'll probably just use those.

This is the last update until early January, when IAP starts, and I will have as close to unlimited time as I ever will here.


  1. stop being awesome >:o

    Also, how will you assembly that pack? Usually, "bounding-box" battery pack arranging causes a oddly shaped configuration which is difficult to solder. Did you try putting cells in sideways? It looks like you can fit 2 'bricks' oriented front to back.

    1. I think I'm going to solder it into two 6s packs, which will then be connected in series externally. The problem with assembling the pack with the cells in any other orientation is that I want to be able to lift the pack out vertically. The nut that holds the gear hub in place sticks into the battery area, so I have to leave a vertical gap all the way down the pack where the nut is. If I orient the cells any way other than vertically, there is a lot more dead space around the nut.

  2. here i got all the modern tools used for cutting and drilling purposes

    Keyway Broaches