You could use six motors, but it would make the design more complected. Putting wheels and motors in a single line across the width of the 'bot makes for a wide bot. Or you could drive them with timing belts (like DPA, and mine!), but then you’ve still got a lot more work.
Driving three wheels by one motor on each side still results in a slip-steer, but I think it can be managed. I can even add Ackerman steering on both front and end! It can rotate in its own wheel base, so that’s not bad.
Navigation will not be limited to Odometry; I intend to use a compass, GPS and inertial references as well (big undertaking).
Bob in the HBRobotics club IS using six motors, and the motors are pivoted from the rear to give some ground compliance. Large piano wires give some suspension.
Stairs? Wow, keeping the CG as low as possible and the overall weight is pretty crucial for a task like that. I do have a 4wd rock crawler that easily manage stairs, but its not a robot though.
Well, DPA (David) manages to do it with J-Bot. My design is based on his team’s 'bot, so it’s reasonable that I can climb the stairs also. As long, as you say, the COG is low enough. I will have a higher COG.
Not really goal, but I think possible! (probably hard on 'bot).
@Alan,
Made it to FL on Sunday Aug 5th all in one piece with the wife and a final trailer load of stuff that we could not haul in the van.
Plan to renew work on my Traxxas E-Maxx after a short vacation in Key West next week.
I do have a six wheel skid steering home made rover that I tested out before moving from TX. I plan to replace the Sabertooth motor controller with a RoboClaw 15 and replace the center two wheels with motors with encoders.
You steer with six wheels? I wondered how that would work. I’ve seen Traxxas converted to four wheel steering, took a vertical plate in the rear between the bulkheads. I might do something similar front and rear to add four wheel steering to my 'bot. I haven’t figured out how to get the steering parts (I have) on the deck below the bulkheads, as I have belts and pulleys running between the bulkheads. That’s why a vertical plate to mount the components might work.
While I’d like to work it out now, my time would be better spent getting the axles finished up, and the wheels spinning! Maybe this weekend, or soon. I do want to have it moving by the next HBRobotics meeting!
I got the DN2800MT Mini-ITX motherboard running. I installed Windows XP PRo, and I will also split the partition and install Ubuntu 10.4. But first I have to get the network connection working. I’ve done several XPs, but they seem to move the menus around. Where did they hide it?
200 GB HD for now, but I’ll switch to a SSD after a while ($$$).
Enjoy your vacation! We’ll be going to Squaw Valley for our vacation in the next few weeks.
The 'bot has been on the ground and running, which lead to modifying the central bearing blocks, and adding machined brass washers to the tensioning blocks for the belts. So far, just under R/C control, but the central black box on the top is the ITX computer.
Next to last pix looks like a hexapod! Hence, the name HexaTraxx moose (Traxx is from the suspension components).
The suspension and wheels are Traxxas parts. I added all the chassis, timing belt drive train, dual motors, batteries, computers, etc.
The last pix above shows the split drive shafts, center bearing (two ball bearings), timing belt pulleys, and if you look really close, a bearing carrier that slips into the Traxxas bulkheads to carry a ball bearing. As the timing belts are strung between pulleys on 8" centers, there are tensioning pulleys mounted on a ball bearing supported and adjustable shaft between the pulleys on each side (see tensioning blocks in second pix above)
I considered designing and machining the suspension parts as well, but Traxxas has some nice parts! I started out buying the tires/wheels on E-bay, and after figuring out the Traxxas parts system, I soon figured out the suspension parts.
The tires, bulkheads, upper and lower wishbone suspension arms, wheel hub and universal drive shaft (between the suspension arms) are Traxxas. I think everything else is mine.
I made a Pan mount for my Robomagellan. It uses the LPA, a small disk, and some ABS (schedule 40 or 80) 3/4" pipe.
The disk (aluminum or PVC) is drilled with the standard “servo hub) hole pattern. the disk is glued into the cut off pipe coupling (cut off to leave a 1/10” deep step on one side).
