Next installment in the Cromwell rebuild - Roadwheel's The roadwheels on the Cromwell are built up from plywood disks. They are wrapped in a cork/rubber composite material (McMaster# 94545K57) that provides cushioning. The bearings are Oilite bushings pressed into the wheels and ride on 1/2" axle bolts (lawnmower wheel bolts). The wheels have proven very durable and all ten are still on one piece. A minor issue is that the cork/rubber wrapping tends to come loose here and there but an reapplication of Goop adhesive fixes things up for several years. A less than minor issue is that the Oilite bushings and axles will collect gunk between them and tend to lock the bushing to the axles. When this happens, the wood wheels will start to turn on the bushing themselves. This isn't has bad as it sounds because I've learned that there's very little added friction of wood on Oilite versus Oilite on steel axle. Net result is no appreciable loss in function.
This is one of the axle bolts and a couple of bushings. Note the gunk that collects on the axle. This axle was actually cleaned a bit so I could remove the bushings off of it. A concern I had when I first built the Cromwell was whether any of the axle bolts would bend where the thread stops and the axle section starts. This proved not to be an issue, all the bolts where straight and true. <https://lh5.googleusercontent.com/-1PWWeVeNRFI/UpNkElU_E3I/AAAAAAAAAW0/Lanq5iDfPQc/s1600/2013-11-24+13.43.02-B.jpg> To address the bushing issue, I decided to re-bearing the wheels with the same 1/2" flanged bearings used in the hull that hold the suspension arms in place. On the right is an original wheel and the left modified with the new bearings. I'm thinking of using some sort of cap to cover the bearing to keep goo out. <https://lh5.googleusercontent.com/-A4x_e9o4ihU/UpNlChQPigI/AAAAAAAAAW8/E9at2yOLz5U/s1600/2013-11-24+13.40.29-B.jpg> To drill out the wheels for the new bearings required some very precise drilling. Do do this I made this jig that holds the wheels centered to the drill press. The wheels have a 5/8" though hole, so using a 5"8" bit, a hole was drilled into the plywood and a 5/8" dowel was glued into place. <https://lh6.googleusercontent.com/-BS6HYvYLjvA/UpNl2S0R4VI/AAAAAAAAAXE/2Ugbb9Px8rM/s1600/2013-11-24+13.42.03-B.jpg> A wheel on the jig being drilled out. <https://lh3.googleusercontent.com/-NLSsmsVFupY/UpNmGj19nBI/AAAAAAAAAXM/-ySNPiBnJCI/s1600/2013-11-24+14.09.58-B.jpg> Sometimes the cork/rubber wrapping gets loose. In this case, the entire piece was thrown off (actually a rare thing to happen). The old piece (which was saved at the battle field) has since been glued back on. In the past, I would have maybe glued new material on but I am currently out of stock on that item. <https://lh3.googleusercontent.com/-S8dMOqO0Q7o/UpNmYDB3xtI/AAAAAAAAAXU/H9M5nsQGFKc/s1600/2013-11-24+13.41.41-B.jpg> This particular wheel showed the most damage. It was located right before one of the rear drive sprockets. Note that only one internal side is worn. None of the other wheels showed damage as severe as this and most had very little wear. I'm guessing that something got wedged into the track at one point and ground this wheel a bit. This wheel is still perfectly functional and will be re-used. The damaged section is getting a liberal coat of Titebond II and it will be re-positioned at the center where it will experience the least lateral load. <https://lh5.googleusercontent.com/-A6l8hunuOt8/UpNm8gP_72I/AAAAAAAAAXc/MA-J9dxlVe8/s1600/2013-11-24+13.41.25-B.jpg> Next installment, suspension springing... Steve Tyng -- -- You are currently subscribed to the "R/C Tank Combat" group. To post a message, send email to [email protected] To unsubscribe, send email to [email protected] Visit the group at http://groups.google.com/group/rctankcombat --- You received this message because you are subscribed to the Google Groups "R/C Tank Combat" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/groups/opt_out.
