I have been looking at methods of making a shifting gearbox for next year, and have noticed the popularity of “dog” shifters this year. I’ve looked at specs of gearboxes such as 45’s, but have not been able to figure out how these work. If anyone would be willing to explain this to me, it would be greately appreciated.
Also, I was wondering if anyone can post some specs of any dog shifters you have…how to make them etc. I’ve read on some threads that some teams have made some simpler ones that do not require a high degree of machinging…if anyone has a design for something like this…that would be prefered.
I’m not really good with this stuff, but this is what i understand of it:
I have attached a photo of our tranny from 2003. It used a dog shifter to shift between high and low gear. This is the part to the right of the picture that is attached to the pnuematic cylinder. As you can see, there are pins on the radial part of this shifting mechanism. These are on both sides of it. When pushed by the piston eigher way, these pins are engaged with holes of the same pattern in the gears. This shifter is what is attached to the output shaft, while the gears themselves rotate freely on the shaft. Now you have 2 possible ways to drive the output shaft, by shifting the dog gear into “low” or “high” gear.
PS… forgot to mention… our tranny shifted between sprockets, not gears, if that was confusing at all
actually, in a dog shifting design, the gears freewheel on the shaft until engaged by the dog. so they need to be on bearings. The dog is rotationally fixed to the shaft. Via a key or something simillar, and slides across the shaft. This is the extent of my knowledge, though. except that you’d better have a beefy key if you’re doing it that way. greasing it up good should work, though.
i think you misunderstood me, i was asking about the shifting dog, not the gear, the shifting dog can’t be on a bearing like kevin said. Like tomman said, its kinda hard to tell how the technokrats GB actually works from the drawings so i wasn’t really sure what the shifting dog slides on.
The shifting dog has a hexagonal broach through the face. This allows it to fit on the hexagonal drive shaft, and slide to engage/disengage the gears. Since it’s hexagonal, you dont need a key or anything else to secure it from rotating in relation to the shaft.
The dog is bored w/ a hex like sumone above said and basically it sits on a hexagonal shaft (which has a hole bored in it) and which has a slot milled into it the dog has a pin going through the slot which connects to a pneumatic for sliding it back and forth.
There are several methods currently in use for dog shifters. The basic design uses a component rotationally fixed to the output shaft and allowed to move axially to engage a free spinning gear or gears. Several methods have been used to limit the rotational elements, hex rod in a hexagonal hole and a fixed keyed shaft fitted to an oversized keyway of the dog are most predominant. The engagement of the dog to the gear causes the gear to be fixed rotationally to the output shaft. The power from the motors is fed thru the gears and the shifter is used to select the proper gear ratio during operation.
Most manual transmissions use this method. Motorcycles are a prime example and also incorporate the dog into gears in order to save space and weight. The TechnoKats (45) dogs are design along these lines with three lobes fitting into three pockets. The Who’sCTEKS (716) uses a square dog fitting into a square hole. The TechnoKats use a rod thru the center of the output shaft with a pin at right angle to slide the dog back and forth. The Who’sCTEKS use an outside yoke to do this. Team Epsilon Delta (116) also uses the outside yoke for moving their sliding gear type shifter. In both cases lube between the shaft and dog is sufficient as the total movement is low.
Take a look thru the white papers for all these designs. The Who’sCTEKS ‘Dual Speed Shifter’ paper has drawings of the keyed shaft method using the square dog. A paper of the 2004 complete gearbox will be posted this summer.
(Tom, Team 195, I can clean up your files and post for you, PM me to discuss)
You can purchase “dogs” either from your local pet store, ar premade from a bearing supplier. They are used in a lot of applications, but not originally intended for shifting gears.
We had the Technokats style dogs made by a local machine shop for less than $50 each. We didn’t think we could broach the hex. We also didn’t know we could buy stock with the hex already from Small Parts Inc.
If you want some info on team 188 3 motor shift on the fly transmission that use dogs, go to http://www.team188.com and go to the ask tem 188 link. Ask if Tristan has the drawings of this years transmission and you might be able to see how we did ours.
In fact, I’m attempting to write up something about the gearboxes…maybe in a little while. (I do have some drawings of the dogs, in Pro/E format–I suppose they could be exported to AutoCAD or whatever else is necessary. Let me know, or just wait a bit for a write-up.)
In any event, our dogs were similar to those of the TechnoKats (and others), but we elected to go with two-jawed dogs, rather than three (like the 'Kats), because we did not have CNC milling available to us (or even a precise rotary table). They did not use the central pin-and-slot arrangement; instead, they were grooved around the outside, and engaged a sliding plate which shifted between two positions.
Thanks for everyones responses…some of these little comments have made things connect in my brain…and I think I have a pretty good grasp on how these dog shifters work. Thanks again.
Team 195’s tranny that year wasnt a dog shifter, it was a pin shifter. Similar but different… As for the slide we use whats called a rexnord bushing, its a hex bushing that slides easily on a hex shaft, if you want I can take a pic of it for you and get it to you maybe next week. My AIM s/n is snipr22 and syanc94ZJ if you have anymore questions about our transmission.
