Pashley Tri-1 with 'pronto' electric assistance

The objective was to build a tricycle that can fold in order to fit a 5-door car and be light enough to lift into the car (battery removed). The Pashley Tri-1 is the lightest trike around that can be supplied with a fold. It is also stiff - unlike the di Blasi.

For many riders the trike has to be sufficiently powerful to work with little or no assistance: the 'pronto' approach can be used with various gear reduction ratios, and there is a choice of 3 motors to achieve the necessary torque. A low gear reduction will be achieved using a small drive sprocket ~15-17T with a large chain ring ~48T. The Tri-1 is supplied with a 44T sprocket onto a 7-speed derailleur.

The basis for the 'Tri-1 pronto' is a 36V nano (2.3kg) mounted in a cradle. The chosen mounting point is the seat-tube support triangle.

The cradle will be 'upside-down' so the drive-side motor axle must sit in a hole, not a slot or it could pull out! Using treadplate as the cradle makes it lighter but it needs reinforcing to be sure that the motor won't twist

Tri-1 pronto

The finished item with polycarbonate chainguard (not shown on other pictures) minus the battery

Tri-1 pronto

The rider's view showing the power switch, battery gauge and thumb throttle. This model is also fitted with a 12V accessory supply powering a 4 Watt iC headlight

With the following ratios:

  • 250Watt 36V 210rpm motor with 15T cog
  • 44T driven chain ring
  • 42T drive chain ring

The Tri-1 pronto:

  • easily climbs 14% slopes including hill-starts!
  • In 1st gear the top speed is ~8mph
  • In top gear the pronto easily holds 15mph
  • A 15Ah LiFePO4 battery achieves > 20 miles on mixed terrain

Weight increase

  • Motor & cradle 2.3kg
  • Chainset 2kg
  • 15Ah LiFePO4 battery 4kg

Link to all photos here

The sprocket is fitted to the hub motor using button-head bolts to keep the overall width as small as possible with the sprocket aligned with the outer chain ring The inner chain ring must be used for the derailleur to allow it to move across all the gears without fouling.

This shows a 15T cog, the smallest that can be fitted (resulting in the lowest gear ratio). For higher speed 16, 17, 19 or 22T cogs are available.

In addition there are different motor speeds: 175, 190, 210 and 260rpm.

pronto
pronto

The motor cradle is folded out of treadplate to 155mm width. The offside motor support is a hole strengthened with steel to prevent pull-out or rotation. The nearside is slotted to allow the motor + cable to be fitted.

A 4mm hole is drilled to accept the tab washer that prevents the nearside axle dropping out of the slot

The clamp comprises a 15mm-thick shaped filler of ABS and a matching stainless clamp ensuring no movement.

The top view of the cradle. The mounting holes are slots to allow the cradle to be exactly aligned with the chainwheel.

A stainless plate makes a neater finish as well as a bearing surface for the mounting bolts (fitted with nyloc nuts).

proonto
pronto

Working on trikes can be easier when flipped vertically!

The original 44T chainwheel is replaced with a dual-freewheel chainset with 44+42 chainrings. The final chain ring can be 32 for lower gearing (but higher cadence).

Some bottom brackets are to narrow to accept the freewheel chainset, but they are easily upgraded.

This shot shows the motor, chain tensioner and chainset. The tensioner is spring-loaded and allows for wear and adjustment in the chain. pronto


pronto

This shot shows a 15A/hr Lithium Iron Phosphate battery strapped to the rear triangle. If the wire basket is used them the battery is moved up towards the seat. Smaller batteries can be fitted under the rear loadspace.