@JohnActon posted:This probably applies to the 550, 555 as well as most other Mabuchi motors and their knockoffs. Each size comes in a multitude of different windings and their stall current at say 12v will vary with their static resistance which can run from under one ohm to over 50 ohms. At 12v a 50 Ohm static resistance motor will pull less than 1/4 amp at stall where a 1 ohm motor will pull 12amps. This is what that extra writing after 550, 550-xxxx is all about. It tells what winding is in the 550 motor frame. So if you know the current draw at a given voltage you can compute the static resistance or if you know the resistance you can compute the current draw at that same voltage. If you change the voltage the current will change at the same ratio as the voltage change as long as the resistance stays the same.
So Sid, if you have a dc power supply run that 555 at 6v ~ 8v for ten ~ fifteen minutes, with no load, to set the brushes. You can use the electronic E- unit that came in the J if you do not have a good dc power supply (or a battery charger if it has a 6v /12v switch at 6v don't run it in at 12v) Then measure the static resistance like I describe in the first message. Measure five or six times spinning the armature by hand between each measurement. Then average all your readings. if you measure 1 ohm that motor will pull 12A at 12V when stalled you can use it for a drill motor. If you measure 2 ohms it will pull 6A at 12v. If it measures 3 ohms it will pull 4A at 12V. 4 ohms gives 3A at 12v stalled. I know little about the Legacy boards however I bet their current capabilities are not too different than TMCC driver boards and most of them can handle an 8A stall for a short time. Train America Studios even had some 15A boards that could drive four 385 motors and survive a stall. If your 555 has a static resistance between 2 and 3 ohms you are likely OK if you use it with your Legacy driver board. Above 3 ohms you will be cutting into your maximum speed and power output that your driver board can supply. Though it is safe to use you just loose some top speed and a little pulling power. Most of the sellers in china do not give the stall current at rated voltage or the static resistance however Mops Electric on eBay does for most if not all the motors they sell. I sure hope your J has the 21:1 gearbox so much easier to deal with. The 42:1 gearbox alone makes a considerable amount of noise. One thought I keep having, though I have not personally tried, is a Pittman rated at 8~9v might get along well with that crazy gear ratio. It will be operating at the low end of it's torque curve and never heavily loaded even at 12v. That 42:1 gear ratio may eat rpm but it is a beast for torque at the wheels. j
I will try and do what you said just to see, but the ebay ad did say 11.7a stall current which is considerably high. My J does have the 42:1 gearbox, but I have done some things to make the entire chassis quieter which actually helped out a lot. I also don't plan to run the thing at a million speed steps. I am still going to buy a new motor, but will do some testing as you said.
