Dog Gear?

[greemly]

We've heard dog gears being mentioned in relation to winding up surgical tubing with a winch (as per Team 1114 in 2008). What is a dog gear/how does it work/where can you find one?

[EricH]

One of the best places to find one is in the middle of an AM Gen 2 shifter, IIRC. What it is is you have the teeth (which are rather large and square, in that case) on the side of the gear, along with a matching set on the side of the gear/wheel/whatever it's interfacing with. Pull it away, the teeth disengage.

[Jamie Kalb]

A dog gear is a mechanism for shifting. It rides on a shaft, preferably hex but I'm sure keyed works, too. The dog has three teeth on both faces that fit into pockets on the side of special gears. The trick is that there are two gears on the dog's shaft, one on either side of the dog, and the dog will engage one of them. The other one doesn't spin at all. You can slide the dog back and forth along the shaft to determine which gear it's driving.

Take a look at the AndyMark Super Shifter: http://www.andymark.biz/am-0114.html

[Matt382]

The AndyMark Supershift also uses a dog gear: http://andymark.biz/am-0114.html

Simbotics used a Dewalt transmission that does not backdrive, so they don't need to power the motor to hold it in place (this is important because you don't want to put power to the motor when the motor isn't moving). The Supershifters and the Gen 2 can backdrive, so you would need to further modify them so they don't backdrive if you wanted to do a winch like Simbotics did.

[Chris is me]

The idea behind 1114's winch is that once release is desired, you'd "shift" the dog gear, allowing the winch to free spin and release that nice stretched up surgical tubing you hopefully just wound up. Seemed to work for them.

[MrForbes]

We're thinking of making something similar, but using some pins or bolts sticking out of the side of the winch spool, and a pin thru the shaft. Have the shaft pin engage the spool pins, then pull the spool sideways to disengage. No prototype yet....sorry....

[wilmo]

In 2008, we used a Gen 2 servo shifter to a garage door spring (200 lbs. force or more to "crack it"). The AM shifters are GREAT at winch applications. Instead of winding up the surgical tubing itself, try winding up 550 cord (google it or ask any armed services member) to winch. It has a 550 lbs. breaking strength in a very small package with minimal stretch. One strand of it could fully tension our garage door spring. Also, check out spear gun elastic tubing as an alternative to surgical tubing. LOTS of elastic strength.

[Alex Cormier]

Originally Posted by Matt382

The AndyMark Supershift also uses a dog gear: http://andymark.biz/am-0114.html

Simbotics used a Dewalt transmission that does not backdrive, so they don't need to power the motor to hold it in place (this is important because you don't want to put power to the motor when the motor isn't moving). The Supershifters and the Gen 2 can backdrive, so you would need to further modify them so they don't backdrive if you wanted to do a winch like Simbotics did.

Really? I was thinking more of the opposite, as where you would want a motor that has the capability to be free spinning when the dog gear is not in contact and thus the cable system frees it self. Can you give me any further details about this? My first thought was to use one of the window motors and then second thought was a fisher price.

[Matt382]

Originally Posted by Alex Cormier

Really? I was thinking more of the opposite, as where you would want a motor that has the capability to be free spinning when the dog gear is not in contact and thus the cable system frees it self. Can you give me any further details about this? My first thought was to use one of the window motors and then second thought was a fisher price.

Sorry I meant that does not backdrive when it's in gear, so it can hold the winch in place. When you shift the gearbox into neutral, it will have to go the opposite way, to unwind.

[ttldomination]

Originally Posted by wilmo

In 2008, we used a Gen 2 servo shifter to a garage door spring (200 lbs. force or more to "crack it"). The AM shifters are GREAT at winch applications. Instead of winding up the surgical tubing itself, try winding up 550 cord (google it or ask any armed services member) to winch. It has a 550 lbs. breaking strength in a very small package with minimal stretch. One strand of it could fully tension our garage door spring. Also, check out spear gun elastic tubing as an alternative to surgical tubing. LOTS of elastic strength.

Hm...Why would you use a Gen 2 shifter as compared to a Gen 1 shifter? As far as I can tell, the only difference is the side plate. Is that an extremely large difference for the purpose of a releasing winch?

[wilmo]

Originally Posted by ttldomination

Hm...Why would you use a Gen 2 shifter as compared to a Gen 1 shifter? As far as I can tell, the only difference is the side plate. Is that an extremely large difference for the purpose of a releasing winch?

It dosent matter at all. We just had 3 sitting around from the year before (where large cim's were allowed) 2 went to the drive, one to the winch.

[de_]

Isn't there 2 inherent weaknesses in a AM shifter used as a release mechanism given the forces the kicker could be putting on the dog. There is a small 3/32 pin through the dog to connect it to the internal pull shaft. If you use the air cylinder connector, it has a tiny bearing with an smaller roll pin running against it. Last I heard both pins have occasionally broken using 26lbs of pull force with a 3/4 air cylinder. Now I hear people have to use 1.5" air cylinders to trigger a release. Surely those pins are going to break.

[jgannon]

Originally Posted by de_

Isn't there 2 inherent weaknesses in a AM shifter used as a release mechanism given the forces the kicker could be putting on the dog. There is a small 3/32 pin through the dog to connect it to the internal pull shaft. If you use the air cylinder connector, it has a tiny bearing with an smaller roll pin running against it. Last I heard both pins have occasionally broken using 26lbs of pull force with a 3/4 air cylinder. Now I hear people have to use 1.5" air cylinders to trigger a release. Surely those pins are going to break.

In 2007, we naively ran the 3/4" bore cylinders in our AM shifters at 60psi. The spring pins sheared before ship date. I'd estimate that we didn't shift them nearly as many times as a typical kicking system would be expected to fire, so I'm surprised to hear that people are doing this successfully. Has the design changed?

[AdamHeard]

Originally Posted by jgannon

In 2007, we naively ran the 3/4" bore cylinders in our AM shifters at 60psi. The spring pins sheared before ship date. I'd estimate that we didn't shift them nearly as many times as a typical kicking system would be expected to fire, so I'm surprised to hear that people are doing this successfully. Has the design changed?

You're supposed to shim the shaft so the dog can't actually touch the face of each gear. Not sure if you did this.

We've never sheared a pin after a few seasons of use; We later switched to bolts (which were actually weaker), and still haven't sheared any.

[ttldomination]

My team ordered an AM Shifter, Gen1, and we realized that there is no output shaft, but instead, there is an output sprocket. Now, the sprocket faces a lot of resistance to turning. Is there something that we can do to modify that? Should we try and order the supershifter? Or did you guys just use it like it came?