speed and gear ratio, friction/chain drive questions

Discussion in 'Motorized Trikes' started by WENSIAW, Jun 10, 2009.


    WENSIAW New Member

    I am planning an extended cycling tour in rural part of China on my tadpole trike, pulling a trailer with my trike, and bringing 2 German Shepherd dogs with me.

    Since the ride will be over mountaineous region ranging from 6,000 feet to 15,000 feet, the dogs would be helping to pull during ascend, which I suspect could be as bad as 1:3 and enjoy the ride on the trailer during descend.

    I bought a Robin EH025 25cc engine today to convert the trike to power assisted, the 25cc engine is to comply with China's law for power assisted HPV which has to be less than 30cc.

    When the dogs are too tired to be pulling on ascend they will be sitting on the trailer. Our combined weight with luggages would probably be around 180kg, approx. 400 lbs.

    The trike is presently fitted with a 3 x 8 speed cartridge hub, and I intend to swop it to the Rohloff internal gear hub that is on my mountain bike now.


    1: What would be the optimal gear ratio for the Robin EH025 engine, probably running between 5,000 to 6,000 optimal rpm to be pulling a load of 400 lbs up the ascend with a gradient of 1:3, at whatever attainable speed.

    2. What would be the optimal gear ratio for the Robin EH025 engine to be cruising on reasonably flat terrain with a load of 400 lbs, at whatever maximum attainable speed. I do not need to have quick acceleration, I would pedal to overcome the inertia, I just need the engine to do the job of cruising comfortably when both human and dogs are too tired to pedal towards the end of the day.

    3. With the gear ratios decided, I would prefer a system that I can switch quickly when the trike is stationery, between low gear for ascending and high gear for cruising.

    I thought about friction drive and I can get a local machine shop to custom make a simple one that I can swap quickly between a bigger roller for speed and a smaller roller for ascend. However, one of the problems with the friction drive is that it doesn't work very well with knobbly tire, but I will need the knobbly tire, or at least semi-slick/knobbly for the terrain that I will be going through. Some of them would be just muddy terrain without asphalt, would it slip when they are wet and muddy? not to mention the amount of mud churn up by the tire that would stuck in the friction system.

    4. That leaves chain drive, I guessed the popular choices are Gebe and Staton. The Gebe does not allow me to change between 2 gear ratios, so it is out. The Staton, whilst it does not work like a 2-speed gearbox, I hope to use it as a reduction gear box, and considering the extended drive chain on the trike, my thoughts is to have the engine/gearbox mounted within the drive train and in that way I could also utilize the rear cassette/rohloff internal hub to achieve the multiple gear ratios for ascend/cruising.

    At present it is very much just thoughts and I am hoping to learn from those who have gone on these paths before deciding on the final solution.

    Last edited: Jun 10, 2009

  2. Happy Valley

    Happy Valley Active Member

    Seems like a well laid out planning stage. What's your timetable for prep?

    I'll start by mentioning the Robin and altitude. I've been in touch with R/S techs on the carburetor issues a number of times and the only adjustment on the stock carbs is re-jetting. I am told they are jetted from the factory for sea level.

    I hope you get a lot of response here, it promises to an informative thread.
    Three members here come to mind: Kerf has fabbed a two-speed Staton gearbox, Detonator tuning is currently working on a right-side to cassette chain drive and Alaskavan is an accomplished long distance trike builder.

    Maybe we can catch their attention. :D
    Last edited: Jun 10, 2009

    WENSIAW New Member

    Thanks Happy Valley for your encouragement :grin5:

    I was born in Malaysia but my grandparents were from China.

    The thought of cycling through some remote areas of China started about 3 years ago but unfortunately it remained as a thought without specific deadline, mostly due to my procrastinating nature but I am slowly getting ready and would certainly keep everyone inform if it materialised.

    I have gotten a reply from Gerald Pitts of Robin USA who has been most prompt and helpful that I need to modify the Robin EH025 with a high altitude kit 592-90110-00 for high altitude application.
    Last edited: Jun 10, 2009

    WENSIAW New Member

    Please accept my apologies that in sheer desperation on my first day on this site I did not look up for answers from the past questions and responses. Jawnn seems to have similar requirements, and I think one of loquin's answers may have also answered my question 1 & 2. If loquin or others who are familiar with torque and gear ratio calculation please help me to confirm my rough calculation.

    let me get on with it (considering engine powered and no other form of input such as pedalling or pulling):

    For ascend: perhaps my estimate of 1:3 may be too high, I am going to back down to 1:5, i.e. 20%, and if it gets any steeper the dogs and I would just have to get down from the trike and trailer and walk.

    Gradient: 1: 5 (20%)
    Total load: 200kg = approx. 400 lb
    Max torque of Robin EH025 engine: approx. 1Nm @ 5,000 rpm
    Max attainable speed at full load: 5 km per hour
    ratio of engine rpm to 26" wheel rpm: 1:130

    For flat (<5% gradient)

    Gradient: 1: 20 (5%)
    Total load: 200kg = approx. 400 lb
    Max torque of Robin EH025 engine: approx. 1Nm @ 5,000 rpm
    Max attainable speed at full load: 20 km per hour
    ratio of engine rpm to 26" wheel rpm: 1:33

    Were my very rough calculations correct?
    Last edited: Jun 10, 2009
  5. loquin

    loquin Active Member

    THat sounds about right. I did the calcs for a 400 pound load on a 14% grade, and you would need the Honda gsx50 (50cc, 2.5 hp, apx. 2 ft.pounds of torque) and a 40:1 reduction to get 10 MPH uphill.

    I really think you need to look at a nuvinci hub & staton's gearbox to make this thing work the way you want it too. (that way, the motor uses the rear hub as well) Even with the nuvinci, I'm afraid that the rs25 doesn't have enough guts to pull the load up the hill.

    WENSIAW New Member

    Thanks Lou for the confirmation.

    I am inclined to start with the friction system, which will be a quick and easy solution so that I can use it almost immediately, then upgrade it to the gear system when I have more time to think over the solution involving my Rohloff internal hub presently on my MTB.

    For the friction system, for ascend, the theoreotical friction roller diameter is 5mm (3/16"), and for cruising it is 20mm (3/4"). My main purpose of the powered trike is to help me during steep ascend. But 5mm (3/16") friction roller is definitely out of question, would most probably compromise with a 12mm (1/2") friction roller.

    Question is would 1/2" friction roller more prone to slipages than bigger friction roller?

    If so than I will have to have a simple chain/belt reduction gearbox and use a bigger friction roller instead.

    Upon completion of this simple friction roller system, the next step might be a 2-speed system involving a rocker system having 2 separate friction roller turning at different rpm for ascend and cruising.

    I haven't seen any existing 2-speed friction driven product on the market, is there any proven implementation that you have seen that I may refer?
    Last edited: Jun 10, 2009
  7. Happy Valley

    Happy Valley Active Member


    Let me point out this post by Simplesimon with some ideas on a two speed friction drive:

    That said, I do believe your initial thoughts on friction drive concerning the use in wet weather and the use with knobby tires will be substantial issues.

    It is possible to surmount the problem of wet weather use with the addition of an aggregate surfaced roller but if the terrain you'll be covering requires the use of aggressively treaded tires, friction drive will be less than ideal.
  8. Alaskavan

    Alaskavan Guest

    Interesting. I'm not a gear ratio guy. I work by trial and error. I will bow to Lou's superior understanding of the ratios and forces. I also agree with Happy, that rollers and wet weather would probably be a problem (Thanks Happy for pointing me towards this thread). I would add that an aggregate surface roller would probably result in serious tire wear, and the roller itself would probably wear smooth quickly (a week or 2). I don't know if that would be a problem for you. That being said, I initially mounted a friction drive on my trike, in part to determine the viability of the platform (the trike) itself, in part to desensitize the local police. Once I was convinced that the trike would be controllable, comfortable, etc., that's when I put a larger motor and chain drive on.

    Perhaps, if the NuVinci is not a possibility, you could create some way of running a Staton to a mid gear that could be changed quickly/easily?

    Go for gusto dude.
  9. bamabikeguy

    bamabikeguy Active Member

    What would be the category/penalty if you were outfitted with an engine around 50 cc? Would it then be classed as a moped?

    Because, in the interest of success, and especially in the pursuit of climbing steep highways in the Chinese outback, that would seem to be the more reasonable option.

    I haven't heard of the R/S 25 cc doing anything more than city puttering-around with a light weight rider.

    I don't mean to dampen enthusiasm, but having lugged maybe 300 pounds for 1,100 miles, with the R/S 35cc, I'm sure your route will be a LOT tougher.

    WENSIAW New Member

    Thank you Happy Valley, the link is really useful, turned out to be very similar to the sketches that I have for the 2 speeds. Then believe it or not within the link there is also another link to a chain drive, which was also what I have in mind too for my second phase, but I haven't check the space behind my trike seat to assess viability of mounting the engine there, nor I have the guts like Alaskavan to saw his greenspeed into 2 :sweatdrop:

    WENSIAW New Member

    Alaskavan, thanks and hat off to you for your courages move to saw your trike into 2 ;-)

    WENSIAW New Member

    well, laws are never clearly defined in China, it is a deliberate act, not incapability.

    I get really ****ed off for such encounters, when I am right I would take the opportunity to tell the authority off, but when I am in the wrong I would miss all the fun of telling them off, would I?

    You are absolutely right about a bigger engine would do the job better, but then it gets into the argument that the whole point of powering bicycle is that one still wants and enjoys pedalling... otherwise we would have leave the deposit for the moped instead.

    If not for the tinkering fun I think to transplant the complete rear end of a gas powered scooter, including engine, transmission, wheel and rear suspension would make the most sense, but then where is the fun? :devilish:
    Last edited: Jun 11, 2009
  13. bamabikeguy

    bamabikeguy Active Member

    I was lucky when I lost my gas cap that the closet town had a Robin/Subaru dealer, $7.10 replacement. Else I would have had to seek out a place selling Kawasaki generators, (it happened before, on a Tanaka) $18.00.

    Hope you take a list of repair spots in the area you are about to travel, just in case !!

    Good luck, and keep posting here as you continue the project, it will be fun.

    Will they hassle you regarding photography?

    (With my knack for getting lost, if I tried such an adventure, I'd cross right over the North Korea border without knowing it.)
  14. Will Snow

    Will Snow Member

    I was reading with interest about your plans for a trip over the mountians in China.

    What kind of drive did you end up using? Maybe by now you have completed the trip, If so, would like to hear how it turned out.
  15. 5-7HEAVEN

    5-7HEAVEN Guest

    JMO, you should be able to do the trek with Robin-Subaru, NuVinci, 2 dog power and pedal poweri, if it's not a race against time. Keep a length of rope so you can help pull the trike.

    I would not consider friction drive for long distance.

    would you consider using a 35cc Robin engine with a 25cc Robin decal?

    Why are you bringing two large dogs with you?
    Last edited by a moderator: Jan 23, 2010