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 I have some free time tonight (What?) - Brandon Martus [more] |
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This design is outdated for my purposes as I've already moved onto its second revision, so I thought I'd post a screenshot here for everyone to see. It's nothing that hasn't been done before -- but I thought it might spark some conversation or better, ideas.
Of course, this is a two-speed, shift-on-the-fly solution that doesn't require a shifting transmission. I do realize that a shifting transmission is probably an easier way of achieving the same result if you're only looking for two-speed performance, though.
As with anything, this sort of design has its advantages and disadvantages.
No pictured are the chains and sprockets and the mechanism that engages the yellow block in the center -- typically a pneumatic piston. Also missing is the mounting solution for attaching this to a chassis (I turned the outer plating off for visibility's sake.)
This achieves two speeds by utilizing two wheel diameters. The inner, smaller wheels are a low-speed tank drive. The outer omniwheels are, of course, larger in diameter and geared up slightly to produce high speeds. The high-speed wheels are lowered via the four-bar linkages on each end.
This was made in Solidworks. If anyone would like a copy of the assembly and its parts, I'll see what I can do about getting them to you.
Questions, comments, concerns and criticisms are appreciated.
Discussion
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07-11-2003 09:04
patrickrd
Hey M.
Looks interesting! I actually haven't seen that type of drive-switching mechanism before, we (639) implemented a vaguely similar idea for 2002. I'm kind of confused exactly what it's intention is, maybe you can elaborate for my slow mind? For example, why are there two omniwheels? This would result in a robot with 4 omnis touching ground right? I'm also curious why the rollers of the wheels are slightly staggered. So yea, I'm just interested to hear a summary of what it does 
Hope you're enjoying Seattle!
- Patrick
07-11-2003 09:18
Gadget470
While I can't really say anything for the staggered rollers, I assume it's so that pressure is held closer to the drive rollers so there is less chance of slack being a factor working against the drive roller. Some kind of a pre-tensioner?
As for the omni wheels, their productivity is two fold (possibly)
When the yellow block connected to the dark blue frame actuates vertically, the Tank-Treads would be lifted and the omni wheels in place.
If each omni wheel is idependantly powered, the bot would be able to have omnidirectional motion and have a smooth 0º turning radius.
If each Omniwheel set is powered by one motor, the bot would not have omnidirectional motion, but would have the smooth 0º turning radius.
According to the description, the tank drive is for slow & high torque applications, while the omniwheels geared for fast lower torque applications. Example: Omni's to get to the objective first, then the tanks for holding it.
07-11-2003 13:45
Madison
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Originally posted by patrickrd Hey M. Looks interesting! I actually haven't seen that type of drive-switching mechanism before, we (639) implemented a vaguely similar idea for 2002. I'm kind of confused exactly what it's intention is, maybe you can elaborate for my slow mind? For example, why are there two omniwheels? This would result in a robot with 4 omnis touching ground right? I'm also curious why the rollers of the wheels are slightly staggered. So yea, I'm just interested to hear a summary of what it does Hope you're enjoying Seattle! - Patrick |
The high-speed configuration does have four omniwheels on the ground. This offers the advantage of a zero turning radius and it minimizes the force required to turn the robot -- allowing for maximum straight line speed. I also think it can powerslide through turns, which probably isn't useful, but still cool.
The omniwheel rollers aren't staggered for any particular reason. I've been exploring different ways of creating omniwheels that are easy to manufacture. What's shown is just one variation that's comprised of two 8-roller wheels offset and bolted together.
Of course, a team could replace as many of the omniwheels with regular wheels as they'd like.
The other large advantage here is that the wheelbase dimensions change when you shift speeds. The low-speed wheelbase is shorter than most other robot designs, meaning that the robot can exert more force while turning than a similarly geared drivetrain. Conversely, the high-speed wheelbase is larger than most other robots, making the robot more stable during direction changes at high speeds.
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