21-01-2003 14:13

Madison

which sprocket rotates the crab module?

I've never finally understood how these crab modules are built, but it is something I'd like to try to improve upon in the future.

21-01-2003 14:19

Jnadke

Just when you think the crab module can't get any better... someone goes and proves ya wrong...


Though... I do see some problems that need to be addressed...


1. What will keep the bevel gears together, other than gravity? Won't the drive shaft want to rise up?

2. Turning the crab module might be a bit difficult with 2 wheels. If the wheels don't slip much, this will put backdrive on the drive system (since the wheels will want to spin when rotating the module). Make sure the turning unit and/or drive system will tolerate it.

3. I see the power is transferred using chains mounted horizontally. Are you afraid at all of the chains falling off? Might want to consider a chain tensioning mechanism.

21-01-2003 17:43

D.Viddy

This picture may help

The top sprocket is the drive sprocket, the lower one is the steering sprocket. The bevel gears are locked together with set screws tightened onto shaft flats. The fork and the widest shaft coming down on the outside are welded together. The driveshaft with the bevel gears on them are perfectly machined to no move, everything is spaced evenly with washers so there is no movement. When steering, the drive system is locked so there will be no back drive. The wheels only options are to slip. All of our chains will be tensioned with idler sprockets. The idlers will also force the chain 1/2 way around the drive motors. This means there will be more chain on the drive sprockets to prevents chain slipage.

21-01-2003 19:24

FotoPlasma

When rotating the module, I think I can see how the wheels would turn without being driven.

Is the motor going to be mounted vertically above the module?

With four of these, it's possible to use multiple motors to drive the wheels of multiple modules.

I can see a lot of different combinations. You can have multiple drive motors for 1, 2, 3 (not sure why you'd do this, but it's possible), or all 4 of the modules. The same goes for the rotation of the modules, either linked or independant.

Very interesting setup, to say the least.

21-01-2003 22:31

Madison

Re: This picture may help

How does it lock, exactly?

When you rotate the wheel module, the wheels will want to spin in opposite directions. Were they equidistant from the point of rotation, the torque applied to the drive shaft would cancel itself out. By that picture, however, it appears as if your point of rotation is not in the center. Thus, one wheel must travel a greater arc length than the other to complete a wheel module turn. As a result of that, one wheel will apply more torque to the shaft than the other and it won't balance out. This will back drive the motor and twist the shift.

It may be insignificant. It may not be. Just a head's up.

24-01-2003 00:08

sevisehda

You could put a tiny differential down there to solve the spin difference.

I saw something similar to this back in 2000. It had the bevel gears but only 1 wheel. The key was the wheel was angled in so the point of contact was on the axis on rotation. Customize bevels to achieve this of course.