1972 Yamaha DS7

Redbird

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Shit started happening yesterday evening ;)

6:00p...
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9:00p...
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Had to stop and do some cleaning before the new bullet went in.
 

Redbird

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More stuff happened over the weekend...
New bullet in:
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Test fired said bullet:
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Started "un-engineering" the rear brake linkage:
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Quality Control Supervisor seemed unimpressed:
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Waiting on a new set of cables, and the bodywork will get rewrapped, but she should return to terrorizing the streets soon ;)
 

Redbird

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More stuff this weekend...

Got the rear brake "un-engineered".
Had a buddy weld a chunk of 1/8" flat stock onto the oem brake lever.
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After some measuring/test fitting/etc. I cleaned it down to what I needed.
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After more test fitting/verifying operation, I cleaned it down to only what I needed.
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And the final assembly (with a new lever and heel guard installed).
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While I was at it, I cleaned up some of the geometry on the shifter side, as well as installed a new lever and heel guard.
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The body got dropped of Friday for the rewrap.
I'm still waiting on the cables though. Seems the speedo cable is on backorder ::)
 

jpmobius

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Nice work using the stock brake linkage. You will find the pedal effort to be noticeably higher, but probably ok. If not, just make a new weld on arm that is longer and you can restore the stock throw and pedal effort. Your new pedal is a lot shorter than the very long stock piece. If you want to restore the stock performance, make the length ratio of the new rear set actuation arm to your weld on arm the same as the ratio of the new pedal to stock. Have to go from the pivot of each, not the foot peg location. (obviously the same point on the new rear set)
 

Redbird

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Mobius, thanks for the info. I'm no engineer at all, but i thought i was doing good by making sure the distances from pivot centerline to linkage mount was consistent. Is there a formula I can use to calculate the pedal effort ratio?

Fwiw, even with the screwed up setup on it before, i was able to lock up the rear brake. "Increased effort" doesnt mean much though. I never rode this bike with the oem peg/brake setup, so i have no basis for comparison.
 

irk miller

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I think he's referring to the shifter side. You want the shifter arm and the clip on arm to be parallel. That, plus longer length on the shifter arm will ease shifting.
 

jpmobius

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clem said:
That would be tough with that r6 shifter. I tried and wound up making one. Wouldn't that be more fun anyway?

Actually I was talking about the brake side, but the mechanisms are the same. And, in fact you are right that the shifter side will incur exactly the same issue. Again, this does not necessarily mean that there will be trouble operating it, but in my experience, the factory usually has things pretty close as their brakes and shifters are easy to use and quick to get used to. That means to me that if you have not experienced the bike in question in its stock form, building foot controls that mimic the throw and pressure of the stock set up is a good place to start. If you have used the bike in its stock form, and think it needs more or less of something, you can make changes reliably by using the stock set up as a guide. The shifter set up here looks great, however it will be considerably more difficult to shift than the stock setup. Why? because while the crank arms are the same length and parallel to each other, the shift pedal itself is far shorter. The result will be a much shorter throw at your toe, but a lot more force will be required. If you made a new pedal the same length as the stock one and moved the pivot for it back behind the peg like it is stock, the linkage you have would exactly mimic the stock set up for throw and power - minus the small losses from the mechanism itself which are largely negligible. As far as a formula goes, yes. If you keep the angles perpendicular, all you need to do is keep the ratios the same as previously mentioned. If your new pedal is 75% shorter than your old one, you simply need to make crank arms of different lengths with the same ratio. In this case, the driving arm attached to the pedal would need to be 75% as long as the driven arm on the brake spindle.

I found this old post I wrote a little while back discussing the same issue. Maybe it will help here - I think it was also an RD or R-5.

Rear-sets / Re: Rear-set leverage (or lack thereof)
« on: Oct 27, 2015, 13:59:39 »
There is rather a bit more to your shifter linkage than it would seem. Part of how it works in practice is the ergonomics of your foot peg and foot. On the other end, the mechanics of how the shifter mechanism (inside the transmission case) on any particular bike make comparing bikes directly impractical. On your bike, the shift pedal lever is quite long and the shaft it rotates on is actually behind the peg. It takes a fairly large amount of torque to operate the transmission which is ok because you have the leverage with the long pedal. Compare to a factory bike with a linkage like a CB400F. That bike has a very short pedal, and the crank arms are very short, parallel, and with some pretty sloppy rod ends to boot. Works fine on the Honda, but you would find it miserable if not impossible on the Yamaha. Why? Because the transmission itself takes greatly less force to rotate the mechanism. You can't conveniently alter the RD's transmission, but you can replicate the stock pedal's action and locate it in a different spot.

First, consider the difference in pedal length. If it took 10 lbs of pressure to select a gear with the stock pedal, and your new pedal is 75% as long, it now takes 13.3 lbs of pressure to do the same job. That is a big difference. With the same amount of rotation, the throw is shorter with the shorter pedal. So you trade throw for power. Longer pedal = longer throw = less effort. You can make up for this by adjusting the lengths of the two crank arms. If the driving arm is shorter, it will deliver more force than a longer arm. Keep in mind that this is the opposite situation of the pedal. There the leverage of the pedal applies a torque to the shaft. For the driving crank arm, the torque of the shaft results in force at the end of the arm. For example, if you you start with a 12 inch pedal and apply 10 lbs to it, you get 120 in-lbs of torque. If you have a 4" crank arm, 120 in-lbs/4 in = 30 lbs of force, and if the driven arm on your shifter shaft is also 4", you get 30 lbs x 4" or 120 in-lbs of torque again. So you get the same torque with the linkage as with just the direct connect pedal. But if you shorten the pedal to 9" you only get 90 in-lbs of torque with the same 10 lbs of foot pressure. To get the needed 120 lbs of torque, you need to add another 3.3 lbs. However, shorten the driving crank arm to 3" and you get 90 in-lbs/ 3 = 30 lbs of force, and when that is applied to the 4" crank arm on the shift shaft, you get back the originally needed 120 in-lbs of torque. So to maintain the same torque with a linkage, the crank arm lengths must have the same ratio as the change in pedal lengths. In this case, the 9" pedal is 75% as long as the 12" original, and the driving crank arm of 3" is 75% as long as the driven arm of 4".

Unfortunately, there is a problem. This situation ONLY happens when the crank arms are both parallel AND at 90 degrees to the connecting link. Consider the driving crank arm on a linkage with the connecting link above the pedal and shift shaft (like J-rods Honda in the previous post): At 90 degrees, the arm offers the least effort on the link. As the arm rotates clockwise, and the angle becomes less and less than 90 degrees, the force delivered to the link increases due to the inherent mechanical advantage. Similarly, the driven arm sees less and less effort applied to it as the angle between it and the link increases past 90 degrees. In a same length 90 degree parallel crank arm scheme these effects cancel out, but changing the arm lengths and their angles with the link can have a very noticeable effect on the performance.

This gets rather complicated, so consider it from a more basic perspective. Lets say you have your linkage built like the above example, 9" pedal, 3" driving crank and 4" driven crank. The crank arms are parallel, and at 90 degrees to the connecting link when the system is at rest. Assuming the transmission shifts equally easily for upshifts as well as downshifts, the linkage will also apply equal force for upshifts as well as downshifts. When you ride the machine, you find it is easier to downshift. Why? Probably because it is physically easier to apply more force down on the shift pedal than it is to lift it up. Here is one possible adjustment that will help the situation. Remove the driven crank from the shaft and rotate it one spline counterclockwise and lengthen the connecting link to match. Now the angle between the driven crank arm is less than 90 degrees. The angle between the driving arm and the link is still 90 degrees. When you lift up on the shift pedal, the driving arm delivers more linear force the more acute the angle with the link becomes. The driven crank arm on the other hand, has changed. Instead of the torque decreasing as the angle becomes greater than 90 degrees, the torque INCREASES as the angle gets closer and closer to 90 degrees. Maximum torque is achieved at 90 degrees. So upshifting is easier, and downshifting is harder. There is never a free lunch though, anything that gets you needing less effort gets paid for with greater travel or throw.

There is a great deal more to all this but hopefully this hits the high spots. I used to think quality rod ends/bushings/bearings was important. The shorter the crank arms, the greater the impact of sloppy joints. Slop in joints/bearings is fixed, and longer arms result in less rotation required to take up any slack. That said, sloppy joints (up to a point) is irrelevant for how well the system works. Even ridiculously sloppy setups seem to work great as long as there is no binding. Evidently your foot takes up all the slack and the trans can't tell the difference.

And finally, one last thing to consider: Your ankle rotates your foot on an axle that is in a different location than the axle your pedal rotates on. It has an effect on how you perceive the operation of your shifter.
 

Redbird

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Very interesting. Pedal effort never really occurred to me in that respect. I figured the lengths of the brake pedal/shift lever were dictated more by the ergonomics of the oem footpeg location, and less by operational effort. And basically what you're saying is, by keeping the driving arm consistent with the driven arm, I've applied the 2006 R6's rearset operational effort to the 1972 DS7's chassis/engine... correct?
It'll be a week or two before I get the bodywork back and I can actually ride the bike, but I can definitely do some math this weekend and see how far from the mark I am. I'll keep ya posted ;)

And that info deserves to be a "Sticky" on the rearset forum!
 

Redbird

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Update on the lever ratio situation.
On the brake side the R6 lever is 52% shorter than DS7 lever, and (as mentioned earlier) the crank arms are even at 100%.
The shifter side is much closer, with the R6 lever being 68% shorter than the DS7 lever, and the crank arms being at 77% (driving arm being shorter than the driven arm). Not sure I follow the calculation needed to determine how that effects the force needed though.
It'll likely be atleast another week before I get the bodywork back and am able to test ride.
 

jpmobius

where does this go?
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Easy. Except I'm not certain about what you mean by 52% shorter. I'll assume you mean the R6 lever is 52% as long as the original, in other words just slightly more than half as long of the original and that the R6 shift lever is a bit more than 2/3rds the length of stock. If that is the case, make the drive crank arm 52% as long as the driven crank arm on the brake, and the drive crank arm of the shifter 68% as long as the driven arm. Set the shifter linkage arms up parallel with the connecting rod at 90 degrees to start with - you can adjust the angles and rod length later if you want to change the behavior. Set the brake up the same, but before you do, fully engage the brake - at the brake itself so you can set up the linkage in the fully applied brake mode. You want the pedal to be in the position where you want your foot to be when you have the brake strongly applied. Then set up the linkage with parallel arms and 90 degree rod angles.
 

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