Rob Guyatt, designer and builder of RMG winches has answered to the challenge from the super-quick arm-winch camp by sourcing a new motor for the RMG280D (the most popular model for an IOM). The motor is about 15% faster than the previous model, while torque is about the same or slightly less.
Couple the new faster winch with a bigger diameter drum, which trades torque (force on the sheeting line) for speed, and Rob has been measuring sheeting times, using a typical 310mm travel, which are very similar to what is achieved with an arm-winch. Above the RMG 280D with standard 26 mm drum in the middle, 32mm drum on the left, and 42mm drum on the right.
Here's the latest from Rob's drawing board (well, CAD program...). A spring loaded drum ! If I understand correctly one spool of the drum is fixed (and could be a spiral spool), and the sheeting line is connected to this spool. The other spool is spring loaded and will take out any slack in the return line of an 'endless loop' type sheeting system. Especially useful if the sheeting spool is of the spiral type, since the amount of sheeting line travel per revolution is then variable, and the spring loaded spool absorbs this variability.
Here the new RMG is sitting in the Noux RC-tray. There's just about room for the largest 42mm drum (flange outer diameter is about 50 mm). There's a thumb-screw on the drum, but it's a bit too high - the lid won't go on like this, so perhaps I'll grind down the thumb screw to about half its height. I've also taped on some supports for the battery, and a 6-cell AA battery fits comfortably. The idea for the rudder servo is that it will hang in an L-shaped bracket from the vertical wall of the RC-tray, final design and wether it will be stiff enough is still to be confirmed.
Update 2007Feb14: Rob has now finalized the design of the spring-loaded drum design and is offering it for sale at www.rmgsw.comÂ
One thought on “A new, faster RMG”
Rob emailed me with some further comments.
The current RMG uses a Mabuchi RC280 motor. Thew new motors are by Graupner and there are two versions: speed 280, and speed 280 Race (the one I got on my new winches).
Rob also sent some test results:
Motor max torque max speed max output power
speed 280 15.4 kg.cm 3.6 rps 8.4 Watts
speed 280 Race 15.9 kg.cm 4.4 rps 10.7 Watts
This should be compared to measurements on a Hitec 5745 and an old Whirlwind which indicate that their output power is roughly 3.1 and 1.5 Watts respectively. The standard RMG 280D motor power is 8.4 Watts.
In terms of speed the Hitec 5745 does 140 degrees of rotation on about 0.35 seconds. An RMG (Race motor) using a 42mm drum will do 300mm of sheet travel in 0.52 seconds. These figures were measured at 6 Volts.
Production RMG winches with the new motors will be for sale when Rob has sorted out availability of the new motors.
I'd like to stress that these are Rob's preliminary measurements - if I find time to do some testing it would be nice to repeat these tests.
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