Hand Throttle (May 24, 2006)

BACKGROUND:
A cable actuated hand throttle has been around for some time now. There are a number of ways to install one as well as a number of ways to utilize. Putting one in an automatic transmission rig is the same procedure. However, it doesn't offer as many advantages as putting one in a manual transmission rig. While many installations utilize a gear shift lever and cable for the rear de-railer on a bicycle, I chose to use a vernier cable from an aircraft. The difference being that the vernier cable can not only be pushed and pulled like the gear shift lever, but can also be spun for a micro-adjust (CW - decrease rpm and CCW - increase rpm). The uses for a cable throttle include:
  • cruise control
  • throttle control on an incline when the engine stalls seemingly requiring feet on all three pedals simultaneously
  • setting RPM to operate:
    • an onboard welder
    • onboard air
    • operation of a PTO winch
  • setting a minimum RPM for climbing obstacles

OPERATION:
Once the cable throttle is installed, it is simply adjusted to whatever RPM the driver needs. Keep in mind that small adjustments in throttle without engaging the transmission result in large RPM changes. Once the transmission is engaged the cable throttle has a much smaller effect. Getting a feel for the approximate settings of the hand throttle is key to operation in a sticky situation.

IMPLEMENTAION:
I had my fabricators at work fab the bracket to attach the vernier cable to the stick shift. Reason being that I needed a stout bracket that had both a 7/8" and a 1/2" hole. I had them weld 1/2" ID set screw locking collars on both sides of the bracket so I could ensure that the bracket would not move under heavy use. The 7/8" hole was for the hand throttle (3/4-16) and the 1/2" for the stick shaft. I used my vise at home to bend the angle into the bracket so the knob would clear my 7-ball shifter.

I had read on another hand-throttle writeup that the cleanest way to attach the carb linkage to the cable is with a wire and ring connectors. After breaking a small wire in my driveway and breaking a large wire halfway up a trail, I decided to fabricate my own bracket.

PICTURES:
Mockup Picture 1
Mockup Picture 2
Final bracket with tension on the hand throttle
Both linkages disconnected for clarity
Disconnected linkages #2
Hand throttle final location. Ends up right where the thumb and index meet!
Final position profile view
Both linkages hooked up to throttle
Notice the extra return spring on the left and the tape to prevent chafing