The New Design Scooter System
copyright 2005 by Dave Broyles
My previous scooter tow system was called Scooterzilla for various reasons including that it is UGLY. This is a full dress scooter, not in perfect shape because of the rigors of police work, but retaining all of the expensive plastic. It is an '88 Honda Elite 250 with only 3500 miles previously used by the Dallas Police Department for various functions, but not including chasing speeders. Not because it couldn't catch them ( these scooters are fast, unless compared to a 600 cc Ninja) but because of the possible conversation with the judge. "If I was speeding, HOW could I have been caught by a motor scooter?"
So when I built a scooter tow system using this scooter and I wanted to come up with one of my typical annoying names for it, I just decided to call it Copzilla. Now, Copzilla is special, not because of it's body work but because of the new tension measuring system. My previous tension measuring system depended on Newton's third law, "For every action there is an opposite and equal action". The scooter sat on a frame with wheels so that it could roll "freely" and was restrained by a hydraulic cylinder used as a pressure gauge. Because the mass of the scooter, frame and operator had to be overcome by the tow force to register at the hydraulic cylinder there was a lag in the display of tension. Because of the friction of the wheels on the axles, and the inevitable dirt on the trailer floor there was often an error in the tension reading.
Sometime back, a Greek genius named Sotos Christoforou looked at my pictures and articles on the Kite-Enterprises website. Sometime after that, I got his website URL, and was able to view his scooter tow system at http://www.flycyprus.com/scootertow.html with clear illustrations of how it worked (but not measurements). To keep my conscience clear, instead of copying it, I reverse engineered it. That's a computer weasel word saying that I didn't steal the intellectual property but just the idea. Actually, I bought a length of 2" sq. steel tubing, a length of 4" sq tubing, started dismantling my old system, pulled out my MIG welder, ran to Northern Tool to buy more tools and parts, and started cutting, welding, measuring, cutting and etc. I ran down to the bearing store, bought 100 R6-2RS ball bearings and went to the machine shop. I wanted to eliminate all sources of error, thus the ball bearings. Below is what I came up with.
First tension frame
This is the prototype tension frame. The right side faces forward. You can sort of see the 4 bearings at the top of the tension arm on the rear view picture at the left above. The center and right pictures shows the pressure cylinder, but it is not the Bimba Hydraulic Cylinder, which I retrofitted when I found the Clippard air cylinder I started with leaked, probably because I wasn't using air, or because the original air cylinders though unused, were 10 years old.
The tension frame has 14 R6-2RS ball bearings and is designed to work with small diameter rope without chance of the rope being trapped between the pulleys and the swing arm. Both of the pulleys are ball bearing mounted, as is the swing arm. A Bimba h-093-DUZ hydraulic cylinder is used for pressure sensing and a brass, glycerin filled, 400 psi Noshox pressure gauge for readout. The frame and the wheel drum are black power coated. This one was the first one I built, and I extended the frame by 4" after I first welded it. The pulley on the lower part of the tension arm is positioned to compensate for the size of the hydraulic cylinder.
This is a full dress scooter tow system made with the ex-Dallas Police Scooter. Actually,I sell this system with a different scooter, that is equally functional but not so pretty. This is good news for anyone who wants a scooter tow system that looks really nice and has Dallas Police on the side.
On the other hand, this is what I use myself!
I don't want to mess up my full dress scooter, so I actually tow with this system, which is REALLY ugly but tows well. It is a '86 Honda Helix 250 I bought from a motorcycle junk yard. I used the frame with an engine I bought off EBay. It has all the special features that make it tow well. There are kill switches on the rear wheels to stop the engine if the rope gets off of the drum and a Tiny-Tach to monitor the engine RPM and time. It is mounted on the trailer with the front axle through the tension frame. The seat is really comfortable, and since the scooter is longer and the rear shocks are angled back rather than straight down, the rope is easier to work with.
Close up of the tension frame with the Helix
The tension frame showing the path of the rope
The rope comes through the guide rollers in the front, goes back through the 4" top tube and around the pulley at the top of the tension arm, down around the pulley on the tension arm, and back the to wheel drum. For accuracy, the tension arm is adjusted to be vertical, and the rope between the rear wheel and the pulley needs to be approximately level. Hydraulic cylinders usually do not come with piston sizes of exactly 1 in. sq. which turns out to be good since it would be hard to attach the hydraulic cylinder exactly at the center of the pulley. The chosen hydraulic cylinder is .88 sq inch in area, so the pulley is located at 88% of the distance from the top pulley to the attachment point of the hydraulic cylinder. This causes the output of the hydraulic cylinder to be 100 psi with 100 lb of tow tension. I use the German made NoShox pressure gauge because it is very solid and durable. The pulleys are designed for 1/8" rope or smaller, so spectra is recommended.
Helix scooter tow system showing rope entering the front,
exiting the tension frame and going to the rear wheel drum
The tension frame is obscured by the retrieval winch. For more information on the retrieval winch read scooterzilla.
The winch drum holds approximately 3000' of 1/8" Samson Amsteel12 rope.
For more information, call 972-390-9090 or email to firstname.lastname@example.org Dave Broyles.