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Unread 30-12-2015, 00:35
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Re: [FTC]: Experience with new REV servos?

Quote:
Originally Posted by madz View Post
It's a 12-tooth gear (https://www.servocity.com/html/32p_f...etal_gear.html) meshed with an 84-tooth, so I mis-typed (it's a 7:1 gear ratio -- 1314 oz-in total) mounted with an Actobotics channel and ball bearings for the larger gear.
Yes, that's a lot closer to what gear inefficiencies could cause a problem. A second servo would put you back into solid territory assuming the NeveRest numbers were right.

Here I found an issue. The Servo wants 2A near stall (that is, when delivering maximum torque). While the programmer does not list a maximum current, it is powered by 4 AA batteries, apparently in series, as the output is nominally 6V. This means that the output current of the programmer is limited to the current of one AA battery. When drawing 2A, a fresh alkaline AA battery drops to an average of about 1.25V. This will reduce the peak torque. Using a second servo (with a second programmer) should resolve the issue. Alternately, you may be able to figure out a way to use D cells or parallel AA cells with the programmer to bring the current draw for each cell down to about 1A, which will give 1.4A for 2x AAs, or probably a bit more for D cells.

Also check the current capabilities of the 6V circuits on your regular robot control system. (I'm not familiar with the FTC systems.) Is it up to delivering 2A here, plus whatever else you will need at the same time?


Quote:
Originally Posted by madz View Post
Thank you for the advice, and we'll check the speed and torque (and swap the programmer batteries) tomorrow!

We are thinking about adding a 2nd servo to the other side of the large gear to double the torque. Servo City is closed this week, though, so we can't get another one of those small gears, yet.
As I stated above, this might work if you also use a second programmer. The key is probably getting 2A at a full 6V total to the servos.
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Last edited by GeeTwo : 30-12-2015 at 00:40.
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