The Electric Chair

 

Background

I started this vehicle in 1993. It was designed to improve on a 4 wheel loco based on the going electric articles in Model Engineer Mar 1989. The first loco worked well but wasn't powerful enough to pull more than two adults at a reasonable speed, hence it could not be used as a passenger hauling loco at the club track. The options were to rebuild it with twice the power or build a single seat fun vehicle. The more powerful option was dropped because of its size and weight and a single seat design started. Much head scratching produced the vehicle shown below.

Originally a car battery was used but this proved very short lived so a leisure battery was used instead. This picture was taken during the reconstruction required to fit the larger battery.

Details

The chassis is supported on two 4 wheel bogies. They are not sprung but transfer the weight of the body via rubber blocks. The rear bogie has a Sinclair C5 motor driving both axles via a toothed belt. The padded seat is secured by two screws and is removable for ease of transport. Under the seat is a compartment for the drive electronics. The battery compartment is in the middle and has a hinged lid on which is mounted the power control knob, direction switch, horn button and current monitor display. Above the front bogie is a foot rest under which is the horn. Only the rear bogie is braked via a lever behind the seat.

Front and rear lights are fitted and change colour according to the direction selected. The control system was design to enable multiple unit operation. as yet I have not built the second unit!

Being a lazy individual the position and angle of the seat and footrest were very carefully calculated for maximum comfort. The only problem was where to put the controls. Their final position between your knees is not too ungainly and is much better than the alternatives. The design works, I know because it is rare that I get a ride on it without having to prise someone else off. The only complaint is that the very low seat is difficult to get down to and even more difficult to get back up from. Generally this is a complaint from older or wider drivers.

Battery life is about 4 hours on a full charge of 85Ahr , around 6 miles on our track. Top speed is around 10 mph on the flat.

Changes made 2018

A requirement came up for several track meetings with young people as guests (8-11year olds). It was thought a modified chair could be used by the children to drive themselves in safety on our long siding. Two changes were needed one was to reduce the top speed to say 2mph and the second was to find a way for much shorter legs to reach the footrest.

Changing the top speed sounds easy but as the electronics has no input for rotational speed a major change to the way it works would have been required. Probably not acheivable in the time available. The next thought was to reduce the power from the motor. This didn't seem easy to acheive without aditional electronics so changing the motor to a lower power unit was tried. A number of suitable motors were checked but all ran too fast so a small geared motor was tried. It is an old 18V drill motor/gerbox. The drill was a cheap one and the batteries died within a very short time. The keyless chuck was also useless so I salvaged the only parts that might have further use. An alternative mount was made so that the 18V motor could be substituted fairly easily.

Next was to try and make the seat more small user friendly. The first change was to add a second mount point for the seat about 50mm forward of the original position. That was only possible if a smaller battery was used. A visit to the local battery shop produced a pair of golf buggy batteries. They are quite a bit smaller in dimensions and capacity (2 x 22Ahr) but should be quite adequate for the intended use. The batteries are connected in parallel for normal operation but charged separately. This allowed the top of the battery box to be lowered and the length of the box to be reduced making it easier to get short legs over the top of the box. There is still the option of making an alternative foot rest closer to the seat.

Initially the motor was changed to see if it was powerful enough to move the load and how fast it would run. That seemed alright on a short length of test track so the battery box was modified and everything put back together. A repaint was required to hide all the changes and it was ready for a test run. A 16stone test driver was quite amazed that a drill motor could shift him. The top speed may be slow but it reaches that speed very quickly so there must be plenty of torque available.

Improvements required

Reduce the weight of the chassis. (Easier to transport to and from the track) The bogies could also do with less weight.

Make a removable addition to the foot rest for shorter drivers.

Change the single drive motor to a smaller motor on both bogies. Probably brushles DC motors. Incorporate electric braking as the current mechanical brake behind the driver is difficult to find in a hurry.

Change the spower control from a rotary pot with a separate switch for reverse to a single linear speed control with a detent position for stop.

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