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High quality, lightweight disabled trikes that inspire independent riding

High quality, lightweight disabled trikes that inspire independent riding
19th March 2018 Bob Griffin

 

A Weighty Problem

Whilst I’m not a great believer in coincidence, it’s astonishing how seemingly unrelated events so often cross paths.  You might dream about a long lost friend, then the next day they call you out of the blue, or the washing machine breaks down just as ‘Which’ publishes an article on “best buy” washing machines.   Spooky!

Just recently, we received two trike orders on the same afternoon from opposite ends of the globe; one from the UK and one from Australia.  Both were ordered by mums and both said that after extensive research, their overarching reason for choosing Tomcat was its lesser weight.

Now weight is something that I have been passionate about over the years and for very good reasons too, but it’s actually quite rare for a customer to recognise its importance, and that’s what’s prompted me to pen this blog.

So what is weight?  Well basically, its gravity, and gravity is a very mixed blessing.  Without gravity, all our possessions would float away and the air would be full of frozen peas, but on the downside, if you try to fight gravity by lifting something, you’ve got the very devil of a fight on your hands!   Think of it this way…

Next time you see a boat on a lake, try pushing it away from the quay.  It’s amazing how big a boat you can push because the boat is floating in gravitational equilibrium and only water friction can stop it moving sideways.  But what if you tried to overcome gravity by lifting that same boat out of the water…!

Tricycles too, move relatively easily on a flat surface like a school hall or show arena but unfortunately, only Terry Pratchett’s Discworld is flat.  Where you want to be if you have a disability is outdoors, but there are hills outdoors and lots of them.  If your school is 30 metres higher than your house, then no matter how far away the school might be, little Jack or Jill will have to raise the entire weight of their trike and themselves up 30 meters if they are going to get to school!  Did I mention school…?  Let us do some sums.

It takes 10 joules of energy to lift a weight of one kg through one meter. A Tomcat without accessories is about 14kg and that means the school run will require 14kg x 30m x 10 joules of energy or 4200 joules.  Now add their body weight of 28 kg and the energy required rises to 12600 joules, which is the equivalent of measly 3kcal of food energy.

That’s a surprisingly tiny amount of food energy for all that work, so let’s imagine it as physical effort instead.   A house brick is on average 3kg in weight, so imagine putting five bricks in Jack or Jill’s pockets and asking them to climb a church tower!  It’s a frightening thought, but it’s exactly the same effort as pedalling a Tomcat trike up that 30-meter hill.

From that analogy, it is easy to see that weight is tremendously important when strength is impaired and every 3kg over and above the weight of a Tomcat is like dropping another house brick in their pocket and who would vote for that!

When Tomcat came into this industry two of our competitors’ trikes were an astonishing 43kg and 45kg respectively.  That’s about 30kg or 10 house-bricks, heavier than a Tomcat.  Little wonder then, that the revolutionary new, outdoor Tomcat worked so well and achieved such miraculous results.  It might have appeared to be sprinkled in fairy dust, but of course, it was just old-fashioned science, engineering and gravity at work.

Pushing the limits. 

Our latest design is a stunningly versatile machine for teenagers and adults called the “Bullet” and we are immensely proud of it because although it has a payload of 120kg with a rider height of up to 188cm’s, it weighs just 19kg!  Compare that with say the Van Raam Easy rider at 43kg or the Draisin Slider at 46 kgs.

Over the next few months, the BBC will be following the story of an Afghan conflict veteran (who is suffering from serious spinal injury and Post Traumatic Stress Disorder – PTSD) as he cycles from Lands End to John O’Groats.  The programme will air in November.  There are many hills to climb between Lands End and John O’Groats, so we are very pleased that he and his team have chosen the Tomcat Bullet with which to face this demanding challenge.

Very soon, he will be measured at the Biomechanics lab of Gloucester University with whom we work closely, and with whom we are conducting a study into the health benefits of cycling for the disabled.  Following those measurements, we hope to custom build him a sports Bullet “Flash” that reduces that weight by another 1.5kg.

But how can you keep or improve on strength and rigidity but also reduce weight?

There are many ways, but here are a few of the more significant…

TIG Welding

Customers are often surprised to hear that a Tomcat frame weighs just 2.5kg of the trikes 14kg.  Clearly, that’s where we achieve a large proportion of weight saving over heavier trikes, but how is it achieved?  In a nutshell, it’s all about the welding process.  Most manufacturers favour an M.I.G welding process for its production speed, ease and cheapness, but M.I.G welding is easier with thicker steel.  A Tomcat frame is made of very thin steel but this requires the neater, more delicate and much more skilful T.I.G welding process but the payback is a stronger weld and a lot of weight saving.  As with all things, you get what you pay for…

Hollow Axle

Tomcat axles are another invisible example of how we save weight.  Tomcat axles look very robust, but in fact, they are hollow like the prop shaft of a car. The missing 16mm core of the axle loses very little in strength but saves a hefty ¾ of a kilogram (or a ¼ of a house-brick) in weight, so well worth the extra engineering involved for the rider.

Material choice. 

Look at a Tomcat design and you will see lots of intricate components built into the frame or accessories.  These are made of aluminium, which is three times lighter than steel and more expensive to produce, but give the trike its obvious superior quality and the weight reduction we are looking for as designers.

Good Design.

In addition to good production techniques, we use advanced CAD (Computer Aided Design) and FEA (Finite Element Analysis) software to get the very best from the materials, not to mention the good old-fashioned principles of triangulation.  The strongest 2D shape in nature and science is the triangle and the strongest 3D shape the pyramid.  Use these shapes in a supportive frame and like an ant, it can carry many times its own weight.  Everywhere you look on a Tomcat frame will be bounded by a triangle to get that strength and rigidity we are looking for at minimal weight.  The only exception is the main frame tube where we use an oval shape that is specially made for us, not for appearance as many think, but for the exceptional vertical plane strength and resistance to twist the oval tube gives.  It weighs next to nothing but gives the Tomcat its distinctive high tech looks.

Computer-Aided Design

All these techniques are brought together by CAD design software that allows us to play with our ideas until we get the very best aesthetic and engineering solution for the rider, then we test the design with FEA to computer simulate the stresses and strains the frame will be subjected to in use.  In this way, we can check a designs strength and rigidity before it is ever built, and identify high-stress areas that might only show a weakness after years of use.  All these things, when put together, result in a trike that looks good, is immensely strong and rigid, yet weighs far less than most alternatives.

Transportability is quality of life.

Weight is also an important consideration for parents who often have a lot of equipment to deal with but because most Tomcats dissemble into two or three parts, those parts are rarely more than 10 kgs each.  That’s a very manageable weight for most adults, not to mention very much easier for transportation than a folding frame.

In fact, the Tomcat is so manageable a machine, that it can be hung out of the way on a garage wall (using the Tomcat “Trike Tidy”) and I don’t think any other trike in the world is able to do that!

Is a lighter trike easier to pedal on a flat surface, or does it make no difference?

Unsurprisingly the answer is yes, but the reasons why, are immensely subtle and worthy of its own blog, but let me summarise as follows.

Riders with greater than moderate learning difficulties will always require a fixed drive.  This is because they understand the “one o’clock” to “five o’clock” “push” element of pedal rotation, but don’t understand the 5 o clock to 7 o clock “drag backwards” element of the rotation (that you have been doing all your life without even thinking about it…!)  Without the 5 o’clock to 7 o’clock bit, the non-pushing leg doesn’t get to the one o clock position where it can push in turn and keep motion going.

How does weight affect that fact?

If you push a cannonball and a tennis ball across a parquet floor with the same force it is obvious that the cannonball will quickly slow down and stop, whilst the tennis ball may roll on for yards.  Trikes are just the same.

Manufacturers of heavy trikes, compensate for weight by lowering the gearing ratio, as that makes the trike easier to move but at the price of speed.  That robs the trike of a phenomenon, essential to overcoming the 5 o’clock to 7 o’clock problem – momentum…!

As you will realise from this blog, we put an awful lot of importance on reducing weight so that first push can create speed and momentum that works like a flywheel to pull the trike through the 5 o’clock to 7 o’clock dead zone.  A Tomcat has a success rate in the high 90%’s,

so we know from years of experience that most children will excel on a Tomcat where they may not do so well, or fail entirely, on a heavier machine,

 

 

so I think the best advice I can give you is always imagine yourself lifting a trike into a car and always insist on a Tomcat assessment to give yourself a benchmark.

When I watch athletes, jumping higher, turning quicker and running faster than I can, I look in the mirror and think to myself – “Hmmm… time you lost a bit of weight, Bob”.

 

 

 

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