Low Cost Footpedal for Electric Pottery Wheel

***WARNING *** Read all of this Instructable before starting work. Obviously if you are not completely confident with wiring mains powered appliances safely, do not use an AC/DC universal regulated switching DC power supply as your power option for this Pottery Wheel, and reduce the electrical risks by providing the 36V DC power supply needed by your Pottery Wheel and any ancillary devices (such as foot pedals etc,) from a 36V ebike or hoverboard battery instead, or link three 12 V motorcycle or car batteries in series, but in all cases, make yourself aware of the potential hazards associated with AC and DC electricity.

If you are competent working with 240 V AC and 120 V AC and plan on using an AC/DC universal regulated switching DC power supply to power your Pottery Wheel, always run it from an RCD-protected mains outlet. Whist the description below will work satisfactorily and safely when followed by a competent person, any work with mains power requires good knowledge and awareness of the electrical hazards likely to be encountered with AC and DC supplies. If in any doubt about these, always consult a qualified electrician before starting work on this project.

*** DISCLAIMER ***

The author cannot accept any liability for any harm, personal injury, damage to property, or loss experienced as a result of following this Instructable in an unsafe manner.

Background

This Hall Sensor (HS)-based Footpedal has been developed to work with the "Simple Electric Pottery Wheel" Instructable I have published, but it will almost certainly work as a replacement for the broken footpedals of commercial pottery wheels that employ a 3-wire potentiometer rotated by gears and/or levers. This is because the Hall sensor supplies a variable voltage to the output pin which is generated from the input voltage supplied to the Vcc and Ground pins. It uses the position of magnets to alter the magnetic field which in turn causes the voltage output to change in a similar way to that caused by the rotation of potentiometer. Benefit is the HS has no moving parts and is still very cheap, whereas Potentiometers need mechanical parts to rotate them, wear out with usage and are damaged by water, dust, clay, etc.

MATERIALS

MDF (plywood, chipboard) sheet material

Screws

Hall Sensor 49E (linear type as used in Ebike throttles)

Wires for the lead and a connector to suit your wheel

Magnets (common ferrite type work just fine) or 6mm neodymium discs

Aluminium wire or strip

Steel strip or wood batten (optional)

TOOLS

Pliers or side cutters

soldering iron

Hot Glue gun

Drill and bits

Saws, screwdrivers,

Cut Out Footpedal Parts

Cut your sheet material MDF to the dimensions in photo. The top angle of the trapezoid side plates sets the inclination angle of the footpedal in the stopped position, you could change this angle from the 25 degrees used here to suit your preference.

Make Hall Sensor Lead

Solder wires onto the 3 terminals of the HS to make a lead (photo) which has a multi-pin connector at the other end that connects to your speed controller (ESC). These wires must connect the HS pins to the Red, Black and Coloured wires of the throttle connector on your Ebike Electronic Speed Controller (ESC) in the correct order. With the face of the HS that has the serial numbers on facing towards you, solder the wires as shown in diagram (photo). Now insulate by covering with hot glue.

Carve back the hot glue to create a cylindrical stem of 5mm diameter (or whatever hole size you plan to drill in the side plate, Step 3) just behind the HS component (photo).

Make Adjustable Magnets

If not using 6mmNeodymium disc magnets, cut the ferrite magnet into small cube shaped pieces (5- 6mm approx) using pliers. The exact shape is not critical as seen in the photo. Find the poles (sides) that repel each other and mark these with a marker pen as it is critical that the same poles always face towards the HS. Attach this small piece of magnet onto the end of an 80mm length of aluminium wire using hot glue. Aluminium was used as it is not magnetic but steel wire may also work and is easier to find. You will need 2 of these adjustable magnets. They are "adjustable" as we can bend them to get the magnet in exactly the right place in the final step. For now, bend the aluminium wire into an approximate C shape (see photo).

Assemble the MDF sheet materials as follows. Attach the trapezoid side plates in the middle of the long edge of the base (photo), note the smaller vertical square of MDF on the base is added in the last step but unfortunately is shown already attached at the start in this photo sequence. Then screw the movable pedal to the side plates so the top face is flush with the top edge of the side plates (photo). This requires holes to be drilled through the side plates the same size as the fixing screws which then screw further into the side of the movable pedal (down a narrower pilot hole) to create the hinge. Now add the square piece of MDF seen in first photo that acts as the pedal travel end stop (stops pedal at horizontal and sets the working operation angle (photo).

Draw lines on one side plate that show the perpendicular from the hinge pivot (screw hole) when the pedal is in the inclined (stopped) and Horizontal (full-speed) position. Mark a line to bisect this angle (see photo) and drill a hole for the HS about 45mm from the pivot hole. The image here shows another large hole below this HS hole in which a "tuning" magnet has been added (see later section on tuning). Now drill holes into the underside of the pedal just above the HS. These should be about 6 - 8 mm from the edge and 50mm either side of the centre line of the pedal so they are positioned equally either side of the hinge pivot. Insert magnet wires into these holes and glue in place with hot glue or make a tight fit with pieces of paper packing if required.

Insert the HS through its fixing hole so its head protrudes a few millimetres. Now bend the magnet wires so that the magnets come to rest 2mm from the HS in both the Stopped and Full-speed position. This requires several attempts at bending the wire without knocking off the magnet and is best done with a dummy HS in place (e.g. the end of a 5mm drill bit) to avoid damaging the HS itself at this stage. Although not critical, in their closest position to the HS, each magnet should be square on to the flat face of the HS so that the magnetic field is also perpendicular to the HS face.

Setup

Having established the approximate position for the magnets in Step 3, insert the HS through its fixing hole so the face with writing on faces the magnet which closest when the pedal is in the inclined (Stopped) position and attach the trailing lead firmly to the side of the base with hotglue or a cable tie so the HS is not pulled by the cable when transporting. Connect the footpedal lead to the speed controller of your pottery wheel and switch on. The wheel should not rotate until the pedal operated, and increasing pedal movement should give corresponding increments in wheel speed. If nothing happens try pushing the pedal fully down (to the horizontal) and then move back slowly to the inclined (stopped position). If the pedal operates the wheel like this, i.e. the wrong way round , turn off and simply pull out the HS, turn it 180deg before reinserting so that the writing now faces the other magnet (or you could turn both magnets through 180 degrees which requires more effort).

Troubleshooting

If the wheel does not start at all the magnets may be too far away from the HS when the pedal is at each extremity, as the Speed Controller may not be getting a low enough (zero) voltage in the stopped position to initiate its function.

If no rotation can be achieved after trying the above, take the HS and lead out of the Footpedal and disconnect the lead from the Speed Controller. Now turn on the speed controller without HS attached, and then plug the HS into the speed controller with the pedal in the stopped (inclined) position. If the HS, your wiring to the HS pins, or your wiring of the multipin connector are all OK, the wheel should spin at half speed as soon as the HS lead is connected to the Speed controller. If this does not happen then its one of these three areas which is to blame.

If you are at a complete loss to identify the problem buy a twist grip or trigger type ebike throttle and check it operates your wheel normally. If not then the problem is with the Speed controller. If it does work normally you can dismantle it and pull out the HS which is inside (and the magnets too) complete with lead and connector, and engineer it into place in the footpedal instead of the parts you tried first.

Tuning

If you make the footpedal as described above it will function perfectly adequately at all operating speeds. However to gain slightly more precise speed control at the very lowest rotation speed, i.e going from stopped to its slowest speed (~ 5rpm) and then from 5rpm to 10 rpm you can improve the sensitivity slightly by adding a "tuning magnet" as seen in the earlier photo. Basically this seems to deflect/supplement the magnetic field of the "slowing" magnet, so that it requires greater travel distance of the pedal to get the whell up to 5 - 10rpm. You will see the magnet is at an angle to the plane of the HS and other magnets and that position was simply identified by lots of trial and error. This is a minor refinement and is optional, but if you feel you would like more slow speed control then you can explore this refinement. It was relatively easy to do with the long ferrite bar magnets i used, and maybe a neodymium button magnet would need attaching to a wood or Aluminium strip to give it greater length to assist testing different positions.

Horizontal Foot Bar

You will see one photo in the Assembly sequence that show the metal bar attached just forward of the pedal rotation axis. This is a worthwhile optional extra (a strong wooden batten/strip would probably do the job equally well) as it allows you to rest your leg weight on that strip and use a more relaxed twisting of the ankle to apply toe or heel pressure on the pedal. Most commercial wheels have a fixed pad for your heel which achieves the same resting/twisting action to be applied to the movable pedal and get precise speed control. This or any pedal would be difficult to operate in a standing position if you didn't have some kind of "rest" for your leg weight. A few bricks or blocks of wood positioned to the side of the footpedal near the pivot would do the same job.

This really needs little description. Its rather basic but works. Just secure an ebike Thumb Trigger Throttle to the bottom plate and position the end of the pedal plate on the trigger. The position is quite critical so it doesnt slip off the trigger but once found hot glue the throttle body in place and add a cable tie for good measure.

I found the best position was slightly angled to the lengthwise dimension, about 45 degrees, see photos.

the one shown was simply a length of 10mm Correx fluted polypropylene with a hinge formed by cutting away one flute sidewall.