ARod1993
100 W
I'm pretty sure we've had a number of discussions about using internal gear hubs on mid-drive setups, and the general consensus seemed to have been that using an IGH laced into the rear wheel on a vehicle running a large RC motor (something like the Astro Flight 3220 or the Turnigy C80100) would be a terrible idea because it would involve putting far more torque through the hub than it was designed to put up with. Running some numbers through Wolfram Alpha, a 130KV C80100 produces 11N*m of torque at the shaft if you feed it 150A. Assuming you run it at 72V, you're going to need to gear it down by something like 15:1 to get a usable top speed (in this case about 51.5mph), which produces 165 N*m of torque going into the hub. If we're taking the Shimano Nexus 8 as an example, then it's taking 165N*m in, and in its lowest gear (0.527) is putting 313N*m back out through the wheel; that's somewhere on the order of two to three times more than what you want to put through it and (given the significant expense associated with a nice IGH) you don't really want your $200+ hub to be a six-month wear item.
That said, (in theory at least) it should be safe to use a nice internal gear hub in a high-powered RC mid-drive vehicle as long as you use it before the main gear reduction, as long as the high RPMs aren't a huge concern. If we take the same system that I mentioned before, a 130KV melon at 72V and 150A will only put 11 N*m through the hub input, and in the lowest gear you'd only be putting out 20-21 N*m; you'd then be free to use much sturdier chain and sprockets on the post-reduction portion of the drivetrain, making it possible to get a wide range of speed/torque combinations in a >5lb package for under $250. The only possible catch I could see with this would be wear and tear on the bearings and gears at stupidly high RPMs; in a human-powered setup most IGHs wouldn't be seeing more than 1-200 RPM in and more than 4-500RPM out. A 130KV C80100 on a 72V nominal system will be spinning at anywhere between 8K and 12K mechanical RPM; increasing the number of machine cycles per mile of use by a factor of 10-20 might lead to significantly accelerated gear and bearing wear. I'm not sure whether or not this is significant enough to be concerned about, and I was wondering if people had any experience using IGHs in this manner.
That said, (in theory at least) it should be safe to use a nice internal gear hub in a high-powered RC mid-drive vehicle as long as you use it before the main gear reduction, as long as the high RPMs aren't a huge concern. If we take the same system that I mentioned before, a 130KV melon at 72V and 150A will only put 11 N*m through the hub input, and in the lowest gear you'd only be putting out 20-21 N*m; you'd then be free to use much sturdier chain and sprockets on the post-reduction portion of the drivetrain, making it possible to get a wide range of speed/torque combinations in a >5lb package for under $250. The only possible catch I could see with this would be wear and tear on the bearings and gears at stupidly high RPMs; in a human-powered setup most IGHs wouldn't be seeing more than 1-200 RPM in and more than 4-500RPM out. A 130KV C80100 on a 72V nominal system will be spinning at anywhere between 8K and 12K mechanical RPM; increasing the number of machine cycles per mile of use by a factor of 10-20 might lead to significantly accelerated gear and bearing wear. I'm not sure whether or not this is significant enough to be concerned about, and I was wondering if people had any experience using IGHs in this manner.