Announcement

Collapse
No announcement yet.

drilling multi-hole cranks for easy pedal length options

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • drilling multi-hole cranks for easy pedal length options

    I've found a professional machinist (father of my daughter's friend) who says he can drill extra pedal holes in cranks for me like:
    http://www.unicyclist.com/forums/sho...rilling+cranks
    http://www.unicyclist.com/forums/showthread.php?t=93360
    http://www.unicyclist.com/forums/sho...rilling+cranks

    What lengths do you guys think would be best and/or possible?

    In preparation I bought new KH Moments Duals (165/137) (If I had read all the posts I probably would have taken KH Moments Single to not have the second chromoly insert and thus have more space).

    My plan was 2 additional holes for the Dual 165/137s:
    165/137/117/100 (20/17 : distance between holes)

    With 20mm distance from the 137 home, because most threads here say that the KH chromoly inserts are 20mm apart.

    But in the German forum, Cyc wrote that he would recommend a minimum of 21mm distance next to the chromoly inserts of the KH duals as he ran into problems trying 20mm (although if I understand right, he was able to do 20mm):
    Originally posted by Cyc
    Die Multikurbel war eine 165 und hat nun die Zusatzlöcher 145, 128, 111, 94. Ich würde empfehlen den Abstand zwischen Stahlbuchse des Originalloches und dem ersten Zusatzloch mindestens bei 21 mm zu belassen. Das ging bei mir gerade nochmal gut, aber wenn man beim Fräsen der Pedalsitze in die Stahlbuchse kommt, dann könnte es Probleme geben.
    http://www.unicyclist.com/forums/sho...0&postcount=28

    That would mean:
    165/137/116/99 (21/17)

    Any opinions/experience? i.e. is 20mm enough? I guess the problem is that if the distance is exactly 20mm and you space it at 20mm and are even 0.02mm too close then it could be a problem.

    So should I try?
    165/137/117/100 (20/17)

    OK, I know it's lots of personal preference, but what are some opinions on the lengths?
    I've been commuting for about 3 times a week for the last 6 months with 127mm for my 16km x2 commute and I have great control and also feel like I could go faster, so I think I could go a little shorter as my standard length for commuting. A few weeks ago I did the commute 2 times with 100mm cranks, and although I was in sum slower as I was not used to the pedals and struggled a bit with mounting, it felt fine and I think with practice it would be ridable.

    And for Munic I am presently riding 170mm (I found 150mm was too short, although that was months ago and I'm better not), but I think 165mm should not be such a big difference.

    Therefore:
    • 165 for Muni
    • 137 as "bailout" for commuting, when I'm dead, (or for fast XC)
    • 116/117 for commuting
    • 99/100 for fast commuting and practice

    Or is 99mm not really practical on a 36er? And/or should I go even shorter?

    Or should I exchange the duals for KH Moment Singles so I can do something more moderate:
    165-127-110 (38/17)
    or
    165-125-108 (40/17)

    I will see the maschinist this weekend and am hoping to try and set up an appointment beginning of the week.
    36" Nimbus Oracle, VCX 100/125/150, 200mm disc
    29+ KH, Maxxis DHR II 29x3, 127/150 Spirits
    Schlumpf (KH29) Duro Crux 29x3.25 137/117 Spirits
    26" Nimbus, Maxxis DHR IIx2.8, 117/137 Sprt
    19" Trials Impact Athmos
    20" Qu-Ax Profi Freestyle, 89mm VCX

  • #2
    Moment are not ideal for such machining because of thread inserts
    I made 3 holes cranks from Spirit 127/150 + additional hole at 110, this is perfect for my 36 Unguni
    http://monocycle.info
    http://www.leblogdumonocycle.fr/
    CITY XTP 26", MUNI KH26" & KH29", ROAD Oracle 32" and KH36"
    my goal : a 3 geared 29" to have only one uni for all kind of rides :-)

    Comment


    • #3
      Telescopic cranks similar to telescopic crutches would be nice. A row of holes in the outer sleeve with a pressured pin on the inner sleeve which would engage into a selected hole affording different length settings.

      I think it was Roger@UDC,UK, who designed the Nightfox unicycle with it's telescopic forks. Maybe he would use his genius to design telescopic cranks.

      Last edited by unibokk; 2015-03-27, 09:02 PM.

      Comment


      • #4
        To get a telescopic crank that was sturdy enough and had little to no slop would be very expensive I would think.
        "I used to watch Highway Patrol whittlin' with my knife..." - NY

        Comment


        • #5
          ..hmmmm titanium, that'd be awesome if it works!

          Comment


          • #6
            Yep, I think titanium would do the job. There might be some flex with titanium but in my case I'm thinking about road riding where there wouldn't be much side pressure on the cranks.

            If the sleeve tubes are a tight fit I think the slop would be minimal.

            It would be great not having to plan crank lengths before going for a ride. It's not just the hills. Sometimes a strong wind may suddenly start blowing in which case it would be nice to just adjust the crank length with ease.

            Also, telescopic cranks would, in effect, give you more ratio choices than the existing Schlumpf geared unicycle hub.

            One set of telescopic cranks would be worth several sets of normal one hole cranks and I would be willing to pay a fair price for them.
            Last edited by unibokk; 2015-03-27, 11:12 PM.

            Comment


            • #7
              I have already given considerable thought to variable length cranks. It certainly would not be done through telescoping. Far too weak for the forces involved.

              The effective length of the crank is the distance between the wheel axle and the pedal axle and there are other more practical ways to adjust this.

              Mount an ordinary crank offset from the wheel axle by thirty millimetres. If it were fully able to rotate about this point, the effective crank length could vary by up to sixty mm.

              In a practical construct the end of the wheel axle would limit the rotation because mounting the crank beyond the end of the wheel axle would result in a ridiculous Q factor. However the offset could be much larger to compensate.

              The intermediate positions could be pinned but ideally I would like to come up with a continuously variable position. Better still one that responded automatically to pedal pressure that could be set with a lever.

              I have contemplated such mechanisms. A forward only system with a sprng would be quite simple but the requirement to work on pressure in both directions seems intractable.
              Triton 36" + 29" | KH 29" | KH 26" | KH 27.5" Muni | Nimbus eSport Race 24" | Torker LX 24" | Qu-Ax Luxus 20" | Qu-Ax Profi 20" | KH / Impact 19" hybrid

              Comment


              • #8
                Originally posted by OneTrackMind View Post
                The intermediate positions could be pinned but ideally I would like to come up with a continuously variable position. Better still one that responded automatically to pedal pressure that could be set with a lever.
                Are you talking about a crank that would vary length while riding or one that could be adjusted and locked in place without removing and exchanging them?

                Comment


                • #9
                  Originally posted by DaUniGuy View Post
                  Are you talking about a crank that would vary length while riding or one that could be adjusted and locked in place without removing and exchanging them?
                  I originally started thinking of a system that could be adjusted without tools when stopped but the possibility of a dynamically adjustable crank length soon started to look like a very attractive possibility.

                  The stop and move system would be simple to build from ordinary cranks and some metal bar.

                  Take a crank and weld a short strong flat arm to the back if it. In the end of this arm, fix a stout pin cantilevered and parallel to the axle. I call the arm a "metacrank" for want of a better name.

                  Around the pin and rotating upon it, fit the crank interface of a hub and retain it. Now this "metahub" can be fitted with a range of ordinary cranks.

                  By rotating these cranks on the metahub we change the effective crank length. The extent of that adjustment is just a matter for geometry.

                  Another opposite arm (or even the original crank itself) on the metacrank retains a stay of adjustable length that joins the main crank. Altering the length of this stay changes the effective crank length.

                  Replacing the stay with small hydraulic rams could allow adjustment on the move if a suitable control system could be envisaged.

                  I expect the system also needs to synchronise the movement of both cranks. However the possibility of independently adjusting crank lengths could be considered. Perhaps it could be used like a trim knob to overcome camber thrust by having a longer crank on one side.

                  The control system could be designed to be pressure sensitive. Rider sets the pressure and the cranks change with the terrain to that pressure. Dampened of course.

                  A further possibility would be cyclic crank adjustment so the dead spots were traversed with effectively shorter cranks.

                  The change would feel wierd. Not only the length but the phase of the crank would be changing due to the geometry.

                  Lots to think about there. Anyone ever ridden with two different crank lengths? I would love to know what it is like.

                  One way or another I am sure this is a way forward in unicycling. I think 100 to 175 Zoom cranks could catch on.
                  Triton 36" + 29" | KH 29" | KH 26" | KH 27.5" Muni | Nimbus eSport Race 24" | Torker LX 24" | Qu-Ax Luxus 20" | Qu-Ax Profi 20" | KH / Impact 19" hybrid

                  Comment


                  • #10
                    Originally posted by OneTrackMind View Post
                    I have already given considerable thought to variable length cranks. It certainly would not be done through telescoping. Far too weak for the forces involved.
                    .

                    I think for road riding, the telescopic cranks would be fine. Chromoly telescopic tubular cranks would be another option. Chromoly tubular cranks are already used by bmx riders. My BMX GT Performer came fitted with chromoly tubular cranks and they are strong and rigid and I've had no problems with them.
                    Last edited by unibokk; 2015-03-28, 10:10 AM.

                    Comment


                    • #11
                      The elusive adjustable crank discussion...

                      This comes up every once in a while, and there have been riders who made various versions. I cant find the one that has the knee joint as described by onetrackmind, but i'll keep looking.

                      Here's a telescopic set that Nathan Hoover was playing with:

                      http://www.unicyclist.com/forums/showthread.php?t=31218
                      "A properly ridden unicycle is like an object in orbit: constantly falling but never landing." -Diogenes

                      Comment


                      • #12
                        Thanks for your post, jtrops. Nathans experiment is very encouraging and his telescopic cranks look really solid.

                        Comment


                        • #13
                          Originally posted by unibokk View Post
                          Thanks for your post, jtrops. Nathans experiment is very encouraging and his telescopic cranks look really solid.
                          it was 10 years ago and since this nobody launched a similar system in the market ... Dual or Triple holes cranks is the easiest and lightest solution
                          http://monocycle.info
                          http://www.leblogdumonocycle.fr/
                          CITY XTP 26", MUNI KH26" & KH29", ROAD Oracle 32" and KH36"
                          my goal : a 3 geared 29" to have only one uni for all kind of rides :-)

                          Comment


                          • #14
                            Originally posted by bouin-bouin View Post
                            it was 10 years ago and since this nobody launched a similar system in the market ... Dual or Triple holes cranks is the easiest and lightest solution
                            Quite true. All of the adjustable cranks I've seen look very heavy. Not to say that you couldn't make some of the designs lighter, but at what cost?

                            What I'd like to see is a triple hole crank with zero offset, and built in quick release pedal mounts. That way you could quickly swap between sizes without tools. The mounts would give a little offset to the pedal position, which would be consistent at each length.
                            "A properly ridden unicycle is like an object in orbit: constantly falling but never landing." -Diogenes

                            Comment


                            • #15
                              back to topic

                              Interesting ideas here, and yes, I've contemplated the same thing, more of a long channle slot running vertical along the pedal with a click-in mechanism with fixture points every so often, maybe with a spring to pull out and move. Anyhow just ideas...

                              However, you guys haven't given many real answers to my concrete project. The only real answer being here:
                              Originally posted by bouin-bouin View Post
                              Moment are not ideal for such machining because of thread inserts
                              I made 3 holes cranks from Spirit 127/150 + additional hole at 110, this is perfect for my 36 Unguni
                              Due to a shipping mishap, I actually do have both KH Spirit Dual 165/137 and KH Moment Dual 165/137 cranks (i have to send one back).

                              Prior to bouin-bouin's comment and based on some other older threads where people drilled Moments (either to save weight or for multi-length crank options), I thought the Moment was the better (or rather only) choice as it's stronger and easier to drill as it's straight.

                              Can you really safely drill the Spirits? Or are they hollow somewhere? I'm wanting to use them for road and 36er Muni, no trials, but they still have to be pretty strong.

                              And I know it's a lot of personal preference, but still looking for opinions at to which holes for cranks lengths and why?

                              Moments with 165/137/116/99 (21/17)
                              or
                              Spirits with 165/137/120/103 (17/17)
                              36" Nimbus Oracle, VCX 100/125/150, 200mm disc
                              29+ KH, Maxxis DHR II 29x3, 127/150 Spirits
                              Schlumpf (KH29) Duro Crux 29x3.25 137/117 Spirits
                              26" Nimbus, Maxxis DHR IIx2.8, 117/137 Sprt
                              19" Trials Impact Athmos
                              20" Qu-Ax Profi Freestyle, 89mm VCX

                              Comment

                              Working...
                              X