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Step 3Make the tow arm
Do not use PVC as originally described and shown when this instructable was first published. Why not? PVC is no where near strong enough to prevent flex, even with an empty trailer. Although it may take a moderate load and several miles before breaking, even if filled with hot melt glue, the flex allows low frequency occilation which is extremely unstable and dangerous and prevents speeds over 3 MPH.
If you are concerned at all about tow arm strength, plan a trailer for use with an industrial bike or an electric motor move up an even furether notch to 1-1/4" or 1-1/2" steel conduit and pay to have it bent on a machine. My usage under moderate loads and over rough terrain with lots of ramps that jerk and pull the tow arm considerably suggest 1" conduit is not sufficient for industrial or motorized usage but minimum for regular to heavy loads of blocks or groceries.
Approximate dimensions are shown in the first drawing. Cut a 40" to 60" length of 1" steel conduit depending on trailer width and trailing distance you select.
To line up the bike and trailer center lines take the following measurements.
1. Trailer axle width (TW)_(27.5)
2. Frame at dropouts width (FW) (5.25)
3. Distance from frame to pivot point (PP)_(1.5)
4. Quick connect length (distance from pivot point to the begining of the conduit) (QC)_(1.75)
Use the formula below to determine where to bend the conduit.
Calculate rise of Quick connect:
HQC = .5 * .52 * QC
Calculate rise of tow arm less rise of quick connect:
rise = (TW/2) - ((FW/2) + PP) - HQC
Calculate length from beginning of conduit to end of axle: (Point A to point B)
AB = sqrt(rise2+rise2)
Calculate and deduct take-up and mark the conduit. (Point D)
AD = AB - (r * (1-cos( c * pi / 180)) / sin( c*pi / 180)))
Note: Use a disposable piece of material like a coat hanger to test the results of your measurements and calculation.
Once you are satisfied the results are correct place the arrow on the mark facing the beginning of the conduit and make a 45 degree bend.
If you are concerned at all about tow arm strength, plan a trailer for use with an industrial bike or an electric motor move up an even furether notch to 1-1/4" or 1-1/2" steel conduit and pay to have it bent on a machine. My usage under moderate loads and over rough terrain with lots of ramps that jerk and pull the tow arm considerably suggest 1" conduit is not sufficient for industrial or motorized usage but minimum for regular to heavy loads of blocks or groceries.
Approximate dimensions are shown in the first drawing. Cut a 40" to 60" length of 1" steel conduit depending on trailer width and trailing distance you select.
To line up the bike and trailer center lines take the following measurements.
1. Trailer axle width (TW)_(27.5)
2. Frame at dropouts width (FW) (5.25)
3. Distance from frame to pivot point (PP)_(1.5)
4. Quick connect length (distance from pivot point to the begining of the conduit) (QC)_(1.75)
Use the formula below to determine where to bend the conduit.
Calculate rise of Quick connect:
HQC = .5 * .52 * QC
Calculate rise of tow arm less rise of quick connect:
rise = (TW/2) - ((FW/2) + PP) - HQC
Calculate length from beginning of conduit to end of axle: (Point A to point B)
AB = sqrt(rise2+rise2)
Calculate and deduct take-up and mark the conduit. (Point D)
AD = AB - (r * (1-cos( c * pi / 180)) / sin( c*pi / 180)))
Note: Use a disposable piece of material like a coat hanger to test the results of your measurements and calculation.
Once you are satisfied the results are correct place the arrow on the mark facing the beginning of the conduit and make a 45 degree bend.
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