Pumilio Tiempo RMC
Pumilio Tiempo RMCClick here for the inside story on the design and development of the Pumilio Tiempo
Click here to go directly to 'The Learning Curve' a short video clip of a practice session with the Pumilio Tiempo
The Pumilio Tiempo RMC is designed and manufactured in Finland. It's a rather exotic 1/6 scale shaft driven machine that uses hub center steering and is designed to be powered by a 3.5cc nitro engine, making this a fast bike for sure. Unlike other bikes currently being produced, the Pumilio Tiempo’s frame is fabricated from laser cut and polished stainless steel and the swinging arm and gearbox housings are made from CNC machined billet aluminum. All of the fasteners supplied with the bike are stainless steel. We are talking about a very durable frame designed to withstand pretty well any punishment that can be meted out by an experienced RC bike enthusiast, or an inexperienced enthusiast working their way up the control learning curve. The combination seat and tank is made from thick Lexan with the fairing being made from slightly thinner gauge material. The one thing lacking with the Pumilio Tiempo is that it doesn’t come with a rider, for me though this is amply compensated by the extremely good-looking sports style exhaust system. It’s worth noting that the rider figure included with the Thunder Tiger FM1e fits the Pumilio Tiempo quite nicely; my TT rider quite happily volunteered to have a go on a different bike! The Pumilio Tiempo, right down to the box it arrives in, comes across as an example of high tech precision engineering that manages to be both stylish and elegant. The bike looks and feels like it could have escaped right out of a BMW design studio!
(PT box)
Introduced at the Helsinki Hobby Show in 1999, the Pumilio Tiempo is the product of several years of research and development by keen RC’ers who also happen to be experienced 1:1 motorcycle enthusiasts. The PT’s frame is fabricated from polished stainless steel and is comprised of three pieces that bolt together to which the gearbox, engine, suspension and steering subassemblies are added to produce a very sturdy and durable machine. The quality of the supplied components is absolutely first rate; they definitely have a ‘tool-room feel’ to them. From first hand experience it has to be stated that the Pumilio Tiempo is a pleasure to build from the clear instructions provided. Every assembly step is clearly shown in the assembly instruction book. Pumilio Design even included the Allen keys required during the bikes assembly, a very thoughtful touch. Here's a couple of pictures of the bike frame under construction.
(bike frame under construction)
The hub center steering features two radial bearings. The whole idea behind this system is to permit the PT to lean into corners like a full sized bike. The PT’s suspension is handled very nicely by a couple of oil filled coil over shock absorbers, with ride height being easily adjusted by sliding each shock’s top connecting bolt to the desired position along adjustment notches machined into the bikes frame. The range of adjustment allows the bike to be set up to handle a variety of surfaces from normal road through to sand or dirt tracks. Unlike other RC bikes, the PT makes use of 1/8 scale buggy wheels and tires, while this may sound somewhat strange at first, this wheel and tire combo permits the PT to handle surfaces that many other RC bikes cannot. To use the lightweight buggy wheels in bike service, Pumilio Design needed to get some additional mass into the front wheel for the required gyroscopic effect. Pumilio’s answer to this was to wrap and glue a strip of lead around the inside circumference of the front wheel before fitting the foam insert and tire, a clever engineering solution.
As already explained, Pumilio Design forewent the usual chain drive method of getting power to the rear wheel and opted instead for a shaft drive system not unlike those found on full sized exotics such as BMW. The PT’s universal jointed drive shaft is securely located inside the CNC machined aluminum swinging arm which pivots on smooth acting bronze bushes. The CNC machined aluminum gearbox is a fully ball-raced dual reduction twin shaft design, incorporating hardened gears to ensure durability and trouble free operation.
The PT’s design requires the use of a rear exhaust type nitro engine (not supplied with the kit, but Pumilio Design will supply one if you ask them nicely). The major aesthetic benefit to using a rear-exhausting engine is that it allows the manifold to protrude slightly through the front of the bikes fairing for a very scale effect. The PT’s exhaust system is a thing of beauty, very sport bike, it’s almost a shame to use it in anger.
The Pumilio Tiempo does not arrive with the required 3.5cc engine, engine mounts, flywheel / clutch assembly and 14 tooth bell housing, although as stated earlier Pumilio Design is willing to supply these parts if you ask them. In my case I wanted a full kit of mechanical parts and Pumilio Design happily supplied everything required to satisfy my requirements.
I installed a Futaba Model S9204 servo for steering duty, and a Futaba Model S3003 servo to take care of the throttle department. For a receiver I selected a Futaba FP-R122JE from a defunct 1/10 car. The PT requires a 4.8 volt flat NiCad battery pack 250 mAh (Futaba NR-4K) which fits neatly under the bikes frame. This posed a slight problem for me because I live in a part of the world where I couldn’t quickly rustle up the required battery pack. So initially I cut up a slightly larger flat pack and reconfigured it to fit above and behind the rear wheel, not the best position I’ll admit, but it worked out as a temporary measure. I carefully protected the wiring with fuel tube so as to avoid any possibility of the wires becoming trapped against the metal frame and cut through (even though the frame is free of any ‘burrs’).
Later on I managed to find the correct battery pack, however with only 250 mAh I found that after 20 minutes of run time the pack was into the ‘medium’ range on my battery condition tester. Without a failsafe device I was a little nervous about this state of affairs so I fitted a 1500 mAh pack (Japan Battery 4N1500), this time in the correct location in the bikes frame just under the engine. This entailed cutting the underside of the fairing so that the pack would fit in place. Being slightly larger than the correct battery pack, the 1500 mAh pack almost but not quite touches the ground when the bike is leaning heavily into corners. To protect the pack I fabricated a prototype battery cradle out of aluminum angle and secured the cradle/battery pack assembly in place with a zip tie.
(250 mAh pack and imposter!)
The PT’s instruction book is a first class document that clearly and easily guides the constructor through the 23 step assembly process. The instructions indicate exactly which components need to be assembled with Loctite, which don’t, and which components need to be lubricated during assembly. Pumilio Design had thoughtfully pre-installed bearings and bushes, and provided a couple of Allen keys necessary for the bikes assembly. The clearly marked parts bags included extra parts … just in case they were needed. I didn’t have to file anything or fiddle about to fit the parts together. The only thing I did that wasn't mentioned in the excellent instructions involved fitting the small bevel gear (part 0204) into the rear swinging arm tube. To help with installation I put it in a ziploc bag, popped it in the freezer and about 10 minutes later the bevel gear was suitably shrunk and easily fitted into the swinging arm tube. I can honestly report that assembling the Pumilio Tiempo was a straightforward and enjoyable experience. The finished bike looks great with or without the seat/tank and fairing, it looks fast just sitting there! With the correct battery pack my finished ready to go Tiempo weighs in at 2550 grams, a reasonable weight for such a sturdy design. The 1500 mAh pack added another 200 grams (ouch!).
I test fired the engine and ran half a tank of fuel through it. The engine, a Novarossi Crono Le Mans started easily with the aid of the 12v electric starter. After the initial engine test run I spent some time adjusting the throttle servo connection until I was happy with it.
Once fired up the PT was easy to launch single-handedly, all I did was to hold the bike level and build up enough revs to get the back wheel going and the bike was off to a flying start. The bike accelerated like the proverbial Bat out of Hell and I managed to keep it upright but dropped it when I attempted a turn. At this point I need to confess I was a little nervous, this being my first try at operating a nitro-powered bike, or nitro anything since I was 12 years old … and that’s more years ago than I’m ready to admit to. I’m definitely on the learning curve with it. The PT features a clutch bell braking system that some enthusiasts might criticize a seeing a little old fashioned, but I can report that in practice it works extremely well and is an efficient design to say the least.
Fast forward several weekends and I’m beginning to feel more at ease with nitro engines. For more convenient starting I modified a model airplane field box so that the fuselage cradle holds the Pumilio Tiempo over the electric starter’s wheel. The modified field box (known affectionately as the Birdhouse) works very well and allows me to sit in a lawn chair to fuel up and start the bike. Not necessary, but extremely comfortable!
(the Birdhouse)
I also fitted a neat Thunder Tiger fueling valve which allows me to hand crank fuel into and out of the fuel tank without a spill, all without removing the Lexan tank/seat cover molding. I reached the stage where I could make a few ‘wobbly u turns’ but definitely need more practice. I altered the bike’s ground clearance from medium to maximum and this helped in making my ‘learning curve’ turns. At this point I was still dropping the bike more than I was happy with so I bit the bullet and cobbled up some training wheels!
For the training wheels I used Thunder Tiger 45 mm diameter model airplane wheels, attaching them and their axles to an aluminum plate with epoxy, which in turn was attached to the PT frame just ahead of the flywheel guard. When I tested this setup it was immediately obvious that the training wheels didn’t allow the bike to lean enough and the resultant turning circles were nothing to write home about. Back to the drawing board! My second attempt has each training wheel/axle assembly ‘epoxied’ to extruded aluminum angles, which in turn are secured to both sides of the PT’s fairing in place of the standard black plastic crash strips running along each side of the fairing. The pictures below illustrate the crude but functional prototype training wheel assemblies.
Both training wheels are inclined at an angle so that when the bike is leaning to the maximum extent possible, the wheel will just touch the ground. In practice this setup has worked really well and is allowing me to log more time exploring the bikes handling without constantly ‘wiping out’ at every turn. In hindsight I wish I had come up with this idea sooner, it would have saved the PT’s fairing (yes I trashed the Lexan fairing … I have a second one in the works) and I think I’d be further up the learning curve. To get the max possible wear out of the original fairing I ‘armor plated’ the sides of the fairing with flattened out aluminum beer cans, not very attractive but lightweight and somewhat functional while learning to control the bike!
Running the Pumilio Tiempo is a lot of fun and practice makes perfect, so my plan is to log as much run time as possible and develop my handling skills to the point where I can ditch the training wheels. Go to PT Running Reports for the latest updates.
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