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?
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.
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
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.
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.
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…
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.
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.
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.
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?
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.
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?
We are designing a similar system since we don’t have room in our budget for 1 or 2 Super-Shifters. Unfortunately, I am having trouble understanding just one concept about this method of power transmission.
My understanding is that the power source (crankshaft) is connected to the output rod (driveshaft) by a pair of gears. The input gear is rigidly coupled to the crankshaft. The output gear is connected by a bearing to the driveshaft so it can rotate freely if the dog collar is not engaged. The dog collar is coupled to the driveshaft so that it rotates with the shaft, but can move axially to engage or disengage the output gear.
First, is my understanding of this system correct? Second, how can a piston push or pull the dog collar as it rotates on the shaft? In other words, I need to undestand the linkage from the piston to the dog collar.
Thank you very much in advance for any help you can provide.
This is about as far as we got on our Inventor design yesterday.
http://photos.project1726.org/albums/userpics/10010/normal_winch05.jpg
The black shaft is driven by the motor/gearbox. The pink spool has bushings which allow it to rotate and slide on the shaft. The light gray pin is pressed into the black shaft, it turns with it.
Not shown is the “fork” and it’s actuating pneumatic cylinder. The fork fits into the groove at the left end of the spool, and slides the spool along the black shaft to allow the two pins on the end of the spool to engage or disengage the other pin.
To wind the winch, the spool is slid by the cylinder/fork to the right to engage the pins, then the motor runs, then stops. The cylinder is energized the other way to disengage the pins, pulling the spool to the left, and allowing the winch to unwind suddenly.
This still in the design/fabrication stage, if you see any problems, please let us know!
i cant believe i didnt think of that one! haha
looks good. Only concern that i have is if your going to move the shaft, how to keep the spool in place?
and im curious, anywhere that sells doggears that we could use?
Is the motor or gear train that drives the winch backdrivable?
This one is. We need to get it built and see how it works. If the backdriving is too much to deal with, we’ll probably put a ratchet on it.