Wednesday, December 22, 2004
Stronger Servos for the Foot Motor
42oz/in foot motor 01
Keith Rowell Design
There was some concern from the beginning as to whether the feather weight servos would suffice for the foot motor, because it's the only motor that experiences the full weight of the robot during walking. The HighTek HS-55 feather servos are rated at 18 0z/in at 6V. http://www.servocity.com/html/hs-55_sub-micro.html Over powering might take it up to a higher torque, just before the magic smoke escapes.
Phillip FitzSimmons did a rough estimate of the forces needed to hold the weight of the bot on one motor and surmised that 15-18 oz/in wouldn't be enough. Not being able to find any servos in the same size format that had more torque, I ordered the next larger size. http://www.servocity.com/html/hs-81_micro.html An even stronger one is available in the same size format: http://www.servocity.com/html/hs-85bb__mighty_micro.html And one with metal gears: http://www.servocity.com/html/hs-85mg__mighty_micro.html
48pitch gears are available for this servo spline shaft too. I ordered a 18tooth pinion and 66tooth spur that will replace the ring and pinion used on the smaller motor. http://www.rcmodels.com/1002-9524.html http://www.robinsonracing.com/catalog/catalog.html
An 18 and a 66.
Metal ones are available
The smaller motor with it's smaller spine shaft required a tricky manuver to make the pinion fit. And it requires a pillow block to hold the pinion in place. The larger motor is much easier to fit because of these issues. I would still like to be pleseantly suprised to see the smaller motors carry the day. But I'm planning their replacement just in case they don't.
I'm also looking for travel cases for the knewt. It's overall size is 7x9x12". The pelican water tight case is ideal with the foam inserts but is expensive at over $100. http://www.all-pelican-cases-4-less.com/detail_pelican_1600.html If anyone has access to travel cases for lot less, please let me know.