Mk IV

Frame

     The main things I wanted to accomplish with this trike were the following:

1. Lower the frame another 2"
2. Lower the boom 2½"
3. Drop the steering arms to the horizontal again (like on the Battleship)
4. Use a 27" rear wheel off of a racing road bike
5. and add a mid drive

     The bike was built out of the same material as the other trikes and I'm starting to look into some 4130 as I think 45 lbs is about as light as I can make the bikes with my design.  While they handle fine and don't really "feel" heavy to ride, I'd like to see what they would handle like with 10 lbs off of them.  This trike came in at about 52 lbs because of all the extra weight of the mid drive.

     Dropping the frame and the boom were pretty simple jobs.  The steering arms went back to the horizontal with the handlebars coming out the end of them to lighten and simplify the front end.  The tie-rod was also modded to connect directly to the steering arms instead of to small, separate steering linkages like on the Mk III.  Again, lighter and simpler.  Extending the chain stays wasn't required to accommodate the 27" wheel because the Mk III had a little room to spare so the 27" wheel went in fine.  The tough job was the mid drive.

     First of all, let me say, that adding a mid drive isn't difficult, but it was made difficult for me because of two things - my "twin rail" frame design and the fact that the frame bottom is only 4" off the ground.  To "properly" and/or simply mount a mid drive, I needed a minimum of about 7" clearance between the mid drive's axle and the ground.  I realized this AFTER I'd already welded up the frame and I wasn't cutting up the frame to accommodate the mid drive, so that meant I either had to mount the mid drive up high on the trike behind the seat, or I modify my mid drive design.  As for the "twin rails" frame design, I had the choice of mounting the mid drive on the outside, in which case the cluster didn't line up with the rear wheel OR the bottom bracket, I cut the frame . . . AGAIN, I mount the mid drive up high above the frame rails to get it INSIDE the frame, or I modify my mid drive design.  I HATE cutting things up after I've welded them together so I decided to come up with an alternative design.  I figure that if I have to figure out a work around, any effort is pennance for not paying attention in the first place.  So, the work around . . .

     First, I had to rearrange the 5 cogs on my mid drive cassette to get the big cog lined up with the rear wheel's cassette.  I had to change my plan so that the pedals would now drive the left three cogs on the mid drive, the largest cog would be moved to the second cog from the right on the mid drive, and the small outer cog could still be used to screw everything tight, but I wouldn't be able to use it as I had planned.  I added two large washers as spacers between the mid drive's "front cogs" and the 28 tooth "rear cog" so the chains wouldn't hit each other.

       As I didn't have room for a rear derailler both because of the small ground clearance and the frame rail being in the way, I took another front derailler, turned it upside down, and flipped it 180 degrees.  You can see it in the top right corner of the picture above, where it is mounted to a small tubing stub I welded to the right frame rail.  Below, is a right side view of the mid drive showing the front derailler mouted inside the frame and low in front of the mid drive.  As I only had 3 gears on my mid drive now, I reasoned a front derailler should work fine, which it does.

     The mid drive is mounted to the frame by a 3/8", standard length axle and is secured to two small drop outs I made and welded to both frame rails.  The derailler cable runs back and loops around to the other side of the frame through two cable bosses, and then runs forward and is fastened to the mid drive gear level that is mounted to the left side of the seat mount.  The near chain, on the big sprocket, is pretty much standard length and runs to the rear wheel.  The rear chain drives the three smaller cogs and runs forward to the cranks.  I ran the power side of the front chain through a piece of chain tube in case it should ever decide to rub or slap the bottom of the seat or the nylon cords holding the seat mesh tight.

     In the picture above, you can see the left side of the mid drive and a clearer view of the derailler orientation.  The piece of square tube pointing up in the middle of the picture is the rear seat adjustment/support tube.  At the suggestion of a friend, the mid drive's axle also serves as the mounting point seeing as how it was already in generally the right spot - a good idea :)  The silver nut and painted tube that are just below and forward of the mid drive's axle are the cable support and guide for the center-pull rear brake.  Just below the rear brake, and in the bottom left corner, are the two cable bosses for the mid drive's derailler cable.  On the far side, and just behind the cog set, is one of the two water bottle mounts.  The near bidon is in the bottom right picture corner.

     I still needed some form of chain tensioner so I could use the 3 chainrings at the front, and the three small sprockets on the mid drive, so I added a rigid mount for a second rear derailler just behind and below the cross member.  It provides enough tension and slack to allow gear changes front and rear and has the low gear screw turned all the way in to help line it up with the dearailler and the mid drive behind it.  It only clears the ground by about 2½" at it's lowest point, but I won't be taking it off-road or doing any curb jumping so don't think it'll be a problem.

     While the mid-drive didn't go in like I originally planned, the work around functions better than I thought it would and I have 54 (later changed to 72) gears to play with, so I am quite pleased with the end result.

Seat

     I shortened the top of the seat back by an inch, and shortened the front by an inch as well.  I moved the top seat support down an inch and moved the bottom seat support forward an inch.  The seat frame is very stiff and I'm very happy with it - no more seat frame mods required.

     I went back to the same seat material design as the Battleship in an effort to reduce the seat sag a little, and let the material and the seat frame take some of the load instead of having to adjust the seat strings so much.  It seems to be working great and the rider's butt doesn't hit the lower seat support any more.  I think the seat design is pretty much nailed down now.

     The seat was made out of the same steel tubing and mesh and used 30 grommets.  For cosmetics, I decided to get the frame powder coated with the bike frame this time.

Wheels

     The rear wheel is a 27" wheel with a 6 speed cassette on it.  The front wheels are heavy duty 20" wheels with 48 spokes and 14mm axles.  I put 65 psi Kendas on the front and am running them at 70 psi and they roll MUCH nicer than at 60 to 65 psi.  The rear tire is a 100 psi racing bike tire so it was already good to go.

Brakes

     I decided to try three sets of brakes on this trike and use only two brake levers.  As such, I needed to come up with a method of operating both front brakes with a single lever.  On the net, I came across a number of methods but they all seemed either too complicated or not within my ability to manufacture them.  On the other trikes I used the heads off of 1/4" hex screws as cable guides and stops, so I thought I'd try using them to build my dual-pull brake system.

     I took two 1/4" cap screws, cut the threads off and welded them upside down on opposite sides of a 5/16" cap screw.  The large middle cap screw threads right up inside the housing of the brake lever and nicely holds the two smaller cap screw heads in the proper position on each side of the brake lever housing.  I took a 1/4" drill bit and drilled through both sides of the brake lever where the brake cable's large round end slides into it.  I cut a piece of 1/4" steel round stock about 1/2" wider than the brake lever (1/4" longer on both sides) and drilled small vertical holes near each end of the rod for the brake cable to go through.  I used small washers on each side to shim out any end-to-end play in the rod once the cables were in.  To balance the brake pull, I adjusted the longer cable's brakes so they are a little closer to the rim than the short cable.  By the time the short cable's brakes are starting ot contact the rim, the long cable is stretched and braking about the same.  I don't notice any real brake-steer from uneven brake pressure at any speed.  The dual-pull was simple to make and gives very satisfactory performance.  I'm quite happy with it.   I doubt I will add a rear wheel brake on any other trikes as it is pretty un-neccessary and with heavy front braking, it un-weights the rear end and causes premature rear wheel lock up any way.  Just my two cents though :)

Misc Hardware

     The brakes, levers and deraillers were all salvaged parts.  The only store bought items were the front wheels, tires and water bottle carrier.  The paint job is a candy apple purple powder coat done by the Powder Shoppe just north of Toronto, in Barrie.  The bar end shifters are off the same racing bike that donated the rear wheel, derailler and chain and the shifters are very nice pieces of kit.  I might even consider buying a pair of bar end shifters for the next trike :)  I added a safety flag mount like on the other trikes and will install the second water bottle carrier when I go pick one up.

Specs:

Modifications:

• added a rear fender to keep the spray down.  Want to add front fenders too.  Either buy some like this which are only $11 US for a 20" front, or possibly make something myself.  The rear fender was a plain old 26" rear out of a 24/26" set that I bought for $20 Cdn.

• took the old 26" rear wheel from the Mk3, and put it on the purple one.  I found that at 50kph+, the 27" rear wheel started getting some weird kind of gyroscopic twist/torque in it and the trike would actually start to crab sideways.  I guess the 27" wheel was far too light for even the lightest lateral loading.  The 26" wheel makes the trike much more stable and it has the added benefit of lowering the rear end a bit and increasing the castor which makes the steering a little heavier - more to my liking.
• moved to a new house and there are a TON of hills.  For peace of mind, I hooked up the rear brake again.  When I switched to the 26" rear wheel, that meant that the brake pads would no longer reach the rim, so I made adapters that lengthens the caliper arms so the pads can bite the rim again.  The rear makes a nice drag brake now with the majority of the braking still being done by the front wheels.  I made the adapters out of welding small pieces of 1/8" mild steel together.

• with the mid drive, the trike would occaisionally throw the chain off the mid drive sprocket if I changed gears too fast, so I added a guide roller to keep the chain on track.  I used the tried and true roller blade wheel and a short piece of 1/8" x 1" mild steel.  Side and rear views are shown.  It's only supported on one side as it is not under any kind of tension from the chain.

• added bar ends, like I did on my white one.  Very relaxing to ride while using them on long hauls where brakes and gear changes are not needed.

• added a fish eye rear view mirror that I picked up for a whopping $4 at Wal-Mart.  It's actually a pretty good little mirror with very little or no vibration.  It's most effective at checking my left rear for approaching vehicles.
• after putting close to 2,000 Km on this trike, I realized two things. One, I'd never ever likely get the chance to wind it out in top gear so the mid drive and all the 72 gears were little more than extra weight. And two, I was REALLY getting tired of the convoluted and "draggy" chain line.  So, I pulled the two chains off and replaced them with a single.  I removed the rear brake, and the dual pull front brakes and converted the trike to normal dual front braking.  I removed the front chain's tension derailleur and the mid-drive's inverted front derailleur along with the cabling and shifter for the old mid-drive.  I took the mid-drive cluster completely apart and left all the cogs off except for the threaded 14T and spun it all the way in to bottom it out the threads ended.  I took the guide roller that had previously been on top, and just flipped it around and mounted it to the end of the old rear brake cable stop's long mounting bolt so it could guide the power side of the chain onto the mid idler cog and prevent it from skipping off at extreme chain angles.  Lastly, I took my ruler and measured the chain distance from the boom and side rails, shimmed the two main guide pulleys, and now the chain runs perfectly straight from the middle chainring all the way back to the middle of the cassette.  I can actually feel the difference when I pedal now due to the much "cleaner" chain line.  Additionally, it trimmed about 6 lbs off the trike's weight.  The new, cleaner mid-section of the trike is below. :)

• along with the white trike, I was riding more, and for longer, and I was tired of slinging various bags, packs and pouches over the seat back.  I took a plain old aluminum bike rack I had, and used the same round stock, 1/8" steel, and 1/8" angle iron to make front rack mounts for this trike too.

I added small tabs to the frame rails just in front of the rear wheel when I built the trike, so I could later add some kind of fairing or rack, so that's where I mounted the bottom of the front rack supports.  The 1/4" steel rods were about 19" long and bolted to the rack at the top with 1" angle iron, and to the frame tabs at the bottom using 1" square steel tabs.  The rack is very stiff, no rattles, and the day after mounting the rack, we went on a 85 km trike ride on a converted rail line.  No rattling or problems at all.  Again, a simple and straight forward project that could be applied to just about any bike rack on just about any trike, I think.

• some friends and I started riding to work when the weather was nice, but as the fall approached, the 24 km ride was getting pretty dark when we started out at 6 AM.  I needed lights.  Encouraged by other DIY lighting systems I'd seen on the web, I built my own 12V system.  Details on the light system is here.

Wish list:

• will build an aluminum rack for the rear which will incorporate a trailer hitch at the middle, top, rear for a trailer or tag-along bike/trike.
• want to add cloroplast fairing/storage for the rear for trips to the store and longer distance bike trips.  Planning to do some randonneuring with it :)

Next time . . .

• want to incorporate everything learned from last two bikes.  Will likely be much like the MK 3 with lower boom, horizontal brake arms and the Mk 4 seat
• want to try a flying cross too

Final Update:     As of Sept 2005, with a total of about 6000km on it, the trike was sold.