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One advantage of having more than two wheels on a recumbent cycle is that you can stop at junctions and other obstacles and not have to put your feet down. This means you can leave your feet clipped to the pedals and hill starts are much simpler, with no set-off wobbles. The other advantage with recumbents (depending on the configuration), is that you push against the seat to extert pressure on the pedals and don't just use your body weight. This means acceleration and top speed are increased.
The perception that recumbent cycles are less safe than a normal cycle is misplaced. The very nature of the seating position means that your head is supported and relaxed in the position required to look at the road ahead, rather than the standard 'head down' cycling position. The low centre of gravity means that accidents are less likely and you are better protected in the event of a crash, through a feet forward riding position. In slippery road conditions a skid is also much more likely to be recovered, before you make contact with the road.
Why have I chosen four wheels and not three? A good question that everyone asks. I have no doubt that trikes are lighter, faster, have less rolling resistance and a lower centre of gravity. A trike is also naturally designed to keep all of its wheels on the ground over varied terrain. If speed is your only goal, then a recumbent bike or trike is the solution.
A quadricycle is slightly more stable and has better all round balance. It is also shorter in length and offers greater manouverability (depends on design though). The main reason for me though, is that it has the right handling characteristics, in that it matches my experiences of car and kart racing. It is something that I can throw into corners with confidence. It has two driven rear wheels for good traction. As designed, it also has more storage space. Another factor is that it simply looks better with matching small wheels. My final reason is simply that I like engineering challenges and the elegant drive of my quadricycle avoids the huge chain lengths, chain tubes/tensioners and carriers I've seen on recumbent trikes.
My goal has always been to keep it relatively light and to build from readily available parts. This almost explains why it has taken so long to design and build my quadricycle. Even now I have had to resort to some custom made parts but, these are fairly generic in their application. The breakthrough in terms of implementing my plan was the discovery of go-kart component suppliers on-line. Go-kart parts are superbly engineered and fairly light-weight. They are also very cheap, since they are made in large numbers.
Efficiency is not a critical design issue, as one of the reasons for commuting by pedal power is that it involves some exercise. Having said that the quality components and bearings used mean rolling resistance is very low. The quadricycle is as light as possible but sturdy enough to withstand some reasonable off-road use. I've compromised with the tyres which are not going to be road going slicks but fairly chunky. The reason is purely because of a non-functional requirement, in that is must look good. The 16" black wheels with chunky black tyres will give it a fairly aggressive look. I'm also using black wheel hubs, chassis and transmission parts. The go-kart parts are all gold annodised and the steering and seating is all metallic red.
My quadricycle is 160cm long to allow me to fit in the steering, chainset, seat, rear axle and storage space. It could be shorter but this length guarantees my feet can't foul wheels, the steering, the chassis or the ground. It could be made narrower but I've constructed it to be 90cm wide for improved stability on cornering. The downside is that it may not fit between some bollards found on some cycleways. The size of the wheels affects the look but it also affects the ground clearance and the turning circle. Ground clearance is pretty good, being nearly 6".
I can't confirm the final weight until the quadricycle has been completed, but it will be fairly light. My target weight for the completed quadricycle as described here is less than 24Kg (~54lbs). This is based on estimates and actual weights of components and includes everything from chassis to wiring for the lighting.
The design is a fairly simple and conventional space frame chassis, largely made from 1" x 1" square section tubing.
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A front wheel with brake disc attached. (1338 x 1410 pixels, 538KB) |
If I have one concern with the design of this bike, it is the use of a 9mm axle for mounting the front wheels. I have added collars to increase the effective diameter of the axle but longer term I am going to try and find a thick axle on which to mount the front wheel. A 12mm diameter axle is the recommended miniumum for recumbent trikes but then they have a much worse front:rear weight distribution, placing much greater loads over the front wheels.
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A rear wheel based on a kart hub and a 36-spoke 16" rim. (1024 x 768 pixels, 538KB) |
I use Shimano RT-60 160mm discs. The front ones are mounted on Shimano Deore XT front disc hubs. The rear discs will be mounted in-board on custom shaft mounts. I'm going to see how I get on with front brakes only and add rear brakes if required. This will save weight and about £200. There wil also be a parking brake.
My quadricycle uses Shimano V-brake levers. The right one operates on the front brakes and the left one will operate the back brakes, if they are added. The brake cables run a BMX bike adaptor which converts one cable to pull on two cables. These connect to the two rear cable-driven, Shimano Deore disc calipers. It is worth noting that these brakes are designed to stop 26" wheels and I'm using them on much smaller wheels. The reduced torque on the brake disc will mean the stopping power is going to be pretty awesome and I'm going to get through front tyres very quickly.
I did consider hydraulic brake calipers but the costs are much higher. A cable calliper is £45 and a hydraulic calliper is nearer £100. The levers are also more expensive. Hydraulics have the advantage of in-built self-balancing but at the cost of twice the brake lever travel. My cable solution will require a harder pull on the lever and careful balancing by manual set up. I'm also investigating the use of a balance bar to ease adjustment of the brake bias.
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The centre hub. (1221 x 1101 pixels, 358KB) |
The centre hub is mounted in a lightweight frame, which is attached to the chassis via bolts. This can be rapidly dismantle to remove the chains, if required. The centre hub drops down into a guide channel which provides fore/aft movement to tension the rear chains. For now, I've retained the quick release hub to acheive this but this will probably be replaced by a pair of nuts, which will be much lighter.
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These are the carriers that allow the single freewheels to drive the 25mm kart axles. (1525 x 803 pixels, 261KB) |
The half-shafts are mounted to the chassis using custom made bearing hangers, go-kart bearing plates and 25mm go-kart bearings. These are fairly heavy but offer a reliable, low friction means to mount the axles. The bearings have twin grub-screws to stop the shafts sliding sideways in the bearings.
Sources of bearings found so far are:
web site.
The shafts have standard go-kart, gold annodised hubs on the ends, which have a three 8mm wheel studs for the rear wheel mounting. These also have a key-way.
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These are the gold anodised kart wheel hubs. They are an amazing bit of engineering for the £14 they cost each. (1146 x 1074 pixels, 293KB) |
The front steering uprights are acheived using a Cane Creek C2 headset on each side with a custom fork column tube, to which the front axles are fixed. Nuts are welded to this tube and the axle runs through them at 23° to provide the centre point steering action. The upright also has fixing points for the disc calipers and fixing for the steering pivot. The upright is also inclined backwards by 12° to provide a self centering action.
The tie-rods are installed based on Ackermann steering geometry to ensure that the inner wheel turns more to optimise grip on cornering. Because Im envisage lots of high-speed cornering, the wheels will be slightly more parallel than pure Ackermann geometry dictates. This counteracts the bikes basic nature to continue in a forward motion due to momentum. There is no toe-in, toe-out or camber angles on my design.
There are a few web sites worth looking at about steering:
Having measured up the front wheels and steering geometry, I need a king-pin inclination of 23° to get full centre-point steering. This is quite a bit more than the recommended maximum of 15° for a recumbent trike. I'm going to go with this though because the weight distribution on my quadricycle is very different to that of a typical recumbent trike.
The reason for limiting the kingpin angle is because an angled kingpin means that the bike is actually lifted when the wheels are turned. The more it is inclined, the more it lifts the bike and the more effort is required to turn the wheels. Based on measurements from a friends recumbent trike, the front:rear weight distribution is typically around 70:30. Based on my measurements with two set of scales my quadricycle has a weight distribution of 45:55. Simple maths shows that my weight distribution and a kingpin angle will require less effort to turn the wheels, than a recumbent trike with a 15° kingpin inclination and 70:30 weight distribution.
The seat is in two parts. The base is a small, contoured, solid foam with an easy clean/dry, black vinyl finish. The seat back uses a light-weight aluminium tubular frame, covered with a tensioned polypropylene, black mesh fabric, as used on trampolines. It provides comfort, lateral support and ventilation. All exposed metal is painted deep metallic red. The seat is bolted to the chassis at four points. The angle of the seat base and back are adjustable. The seat back is shaped and incorporates an angled head support. The position of the seat can be changed if required but a fully adjustable mechanism was dropped to reduce weight.
A recumbent seat has numerous advantages as outlined in this article.
The LED lighting is for normal use and allows the bike to be seen. Three, very high intensity, 10mm white LEDs are used on the front of the bike and three similar red LEDs are used at the rear. These are mounted through 40mm diameter, circular reflectors, directly to the chassis and indicate the extremities of the bike. A further red LED is also mounted at the rear of the bike, at the top of the seat.
The halogen spots are for lighting up the darker bits of my route to/from work. They are mounted to the handle bars and thus turn with them, allowing the lights to 'project around corners'. A convenient, handle bar mounted switch allows them to be flashed momentarily or switched on permanently.
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Another aspect of the enclosure is under investigation. Ideally, I would like to enclose the underside of my quadricycle to keep water and dirt out of the transmission components. This is likely to be in the form of a very light nylon covering.
At the rear of the quadricycle will be a towing hitch. This is so that I can mount a towing bar and pull my children along on the unpowered go-kart I've built them. This also doubles up as a handy point from which to suspend the completed quadricycle to weigh it.
Since I'm using standard go-kart components at the back end, I've also brought a spocket carrier, to mount on one half-shaft. This would allow me to add electric power to the quadricycle very easily if I wanted to.
I've maintained a list of all the tools used to build/maintain the bike, so that I can carry a light-weight toolkit around just in case. So far, it's a few allen keys, a screwdriver and a 10mm spanner, plus the usual bike toolkit parts (tyre levers, chain splitter, etc.).
http://www.edwards200.freeserve.co.uk/diary.htm#latest%20news
. Looks very good and is very strong. Ordered 1m at £13.50/m and the fabric is 1.8m wide.
to use as the hubs of the rear quadricycle wheels. These are 120mm wide and have a large rim so I will get them machined down to about 90mm in width and then get the rear wheels built with spokes coming out radially from the hub. These are specials, requested off the production line before the valve holes were drilled in the rims. These 'hubs' will also be painted black.
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The Kart wheels as delivered. (1024 x 742 pixels, 129KB) |
tyres in 16" x 1.75" size. Ouch, they are expensive (£15 each) but seem to offer good compromise on size, looks, etc. and are puncture resistant. They can also go to 70psi which means lower rolling resistance on my cycle paths. Slight shift from the chunky looks I envisaged in favour of on-road manners. Now I can work out the rolling diameter and finalise the steering design and sort out the centre point steering.
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A rear wheel hub after machining. Yet to have the spoke holes drilled in it. The blue ink is to hilight where it was marked for machining on a surface plate. (1024 x 768 pixels, 181KB) |
make recumbent trikes and sell spares which would be suitable for this project. Not very cheap but reasonably priced considering these are custom parts, hard to obtain anywhere else.