Snow blower motor backpedaling?

[lphung]

Hi,

I am a mentor of a rookie team this year and we tried to use the snow blower motor from AndyMark to drive an arm on our robot:
http://www.andymark.com/Motor-p/am-2235.htm

However, the load on the motor seems to be too heavy and causes to motor's shaft to turn in the opposite direction of our desired input. In general, I do not expect the direct transmission to be reversible with worm gears (I would even suggest that if there is no inputs on the worm gear, the output shaft should not technically move). Do you have an explanation regarding why the motor would be "backpedaling"?

Thanks.

[MrForbes]

Do you know what ratio the worm gear is? It has to be pretty steep to prevent backdriving.

[lphung]

Thanks for the quick reply.

I don't know what is the ratio of gear is, but I would assume that it would be between 20:1 and 30:1. What would be a reasonable ratio that would prevent back driving?

[klhutchi]

We tried direct driving 2 snow blower motors for our extension arm as well, unfortunately we had the same issue. The motor was very under powered and didn't lift the arm well and when it did the motion was very quick, not quite controllable. We eventually scrapped the idea of using these motors and are now using a single CIM motor with a gearbox articulate.

Our arm was a box of 1in-1in 80-20 extrusion about 16 inches long and 14 inches wide, If you are sticking with the snow blowers make sure the arm is pretty light maybe box extrusion or even PVC.

http://team-paragon.org/wp-content/u...Motors-571.pdf
This link has a list of motors and power ratings, the snow blowers are one of the weaker ones on the chart

[Chris is me]

Worm gear drives aren't magic. They don't prevent back driving other than to the extent that they create friction. The worm gear drives that do not backdrive are actually just remarkably inefficient reductions.

The motors that come with integral worm gearboxes are some of the lowest power options available to teams. Hanging and holding arms in the air takes a lot of power. Consider other options.

[lphung]

Thanks for the replies. I appreciate it