View Full Version : Differential ?

05-16-2008, 04:29 PM
Ok, the reason I am buildint (or planing to build) an Atomic-Zombie vehicle is my current PCV quad torque steers something awful when I apply power to the hub-motor, or come off the power.


(yes its fun, but at 25Mph is wiggles too much)

SO...on this version I am going to put in a differential...

Saw lots in my research, but they all have problems with twin drives...

Hum... what about a torque limiter instead? Question is at what point to you want to let it slip, and would it slip in turns vs when just one rider was pedalling? Industrial shaft-2-shaft torque limiters are easy to find...

The problem with a differential is that it expects a Single drive point... and unless I built a jackshaft to consolodate the two pedallers, and THEN went to the differential, I can't have 2 sources, or 3 if I add a motor other than a hub-motor up front...

Jackshaft to differential...hum.... things to thik about....

05-16-2008, 07:06 PM
Someone bought the plans off ebay for the PVC Quad i almost did till i found this site. Sorry your having steering trouble.
But glad i didnt build one lol

05-16-2008, 10:07 PM
The good old American Speedster. I had more problems with that thing, from the flimsy 1/4" kingpins which I had to beef up after a couple of days, to the PVC warping with the changes in weather. By the time I was done correcting whatever problems I could, the thing weighed over 80 lbs. It got to the point that I had to stiffen up every piece of PVC with EMT, ands even with that, the tracking went so far off I could hardly pedal it anymore. I finally scrapped it after many hours of wasted time and energy.
Your torque steer is caused by the physical properties of PVC. It doesn't like to be stressed in any way. Vinyl siding is PVC. Installers will tell you you don't nail it, you hang it. PVC siding has to slide back and forth freely, or it will become undone when the weather changes. It's the reason why many homes are still using aluminum siding in the midwest.

05-17-2008, 09:58 AM
Yup to all the above..that's why I am looking at the KC...

I have a 2HP hub motor on it which probably doesn't help... and the Motor on the KC would be centered in the front wheel which will help greatly.

The side kick is GREAT for slow speed touring...what it was designed for... However at SPEED for a quick trip to the store.. with power assist and SPEED, it has issues. Again that is why I will be building the KC....

I am trying to make sure that All I learned from the SK I put into the KC... Torque Steer was the big one...

Brakes came next. I assume that disk brakes address that.
Gearing came next. The availability of more clusters addresses that
Last was comfort I will want a Nice sling seat... again easy on the KC.


05-17-2008, 11:25 AM
The brakes are well taken care of with the discs. I built the tadpole in my avatar with disc brakes, and believe me, they are more than adequate, even with a lot of weight on those front wheels. A front brake on the KC to be used as a parking brake is an asset.
As for gearing, if you use front chainrings of 22-32-44, and a 7 speed mega freewheel 11-34 teeth, you'll have a gear inch range of 12 - 80. That's low enough for any hill, and with 2 people pedalling at 60-80 rpm, it will give you a speeds ranging from 14-19 mph. The standard longer cranks on the KC will also give you more leverage.
Bear in mind, with the KC, there are 2 separate gear sets, unlike the SK with 2 people pedaling the same gears. That setup just added stresses to the PVC. Like you said, the hub motor on the centered front wheel will also prevent torque steer, but the inherent design of the KC takes care of that all by itself.
Don't let the wheel building scare you off, it's a lot easier than you may think. I can tell you this. I built a of couple of steel bikes after wasting my money on the American Speedster, and steel beats PVC by miles.