MDS Bi-Motor design schema

Discussion in 'Performance Mods' started by JemmaUK, May 4, 2010.

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  1. JemmaUK

    JemmaUK Guest

    I have recently got into a relationship with someone who has two kids - doesnt drive and is a real fanatic when it comes to money. I have no problem with that as its fine with me since I am permanantly broke... but it got me to thinking...

    How to make a vehicle that can transport 4 people - at a reasonable speed - say about 25 cruise and 35 flat out but on the minimum of fuel... this is what I came up with...

    First prepare your ingredients...

    2 x second hand tandem bicycles
    2 x GEBE mounts (with or without engines as you are going to sell the engine it comes with anyway - so with would be better to make more savings)
    someone with welding expertise
    2 x 2.5 - 3hp water cooled engines (DDM does the G231PUM engine 3hp for example @ $235)
    1 x electric start kit for the above
    relevant cooling lines and radiator or header tank arrangement
    Fuel tank and ancilliaries
    2 x engine ignition cut out switches
    2 x one way bearings for GEBE mount clutches (78mm)
    1 x mobile phone fitted with GPS
    relevant lighting equipment (dynamo)

    So far so obvious right - well yes - its a simple matter of a 2/2WD long bike made from the two frames brazed together - GEBE belt drives front and rear and all the relevent GPS mounts and lighting being wired up.. but here is the trick...

    Chrysler and other car makers who use V8 engines currently have a trick called MDS which is where half the engine shuts down in order to save fuel, the idea being you dont need a 450hp V8 when you are traipsing along in a stream of traffic doing 30mph.. this makes the engine more efficient and saves fuel.

    So how about a similar system on a bike?

    This is my interpretation of it.

    Take your two wheezy aircooled 4 strokes or 2-stroke engines and put them up on ebay as new motors (which they are) and sell them... they arent needed.

    You need to get hold of some water-cooled 2/4 stroke engines - ideally both of the same manufacture and power since their power bands should therefore be identical. You will need a pressurised header tank cooling system (a teardrop type fuel tank *should* act as a decent header tank with a few mods) and the relevant tubing to connect the engines to the header or radiator. BOTH engines MUST be connected in series - IE coolant from one MUST run from one to the other... - temperature should be monitored carefully as well.

    Test this by running up one engine - and checking that when that one is at normal operating temperature the other is too. Check also that they are not overheating. This may take some fettling but the MDS on the bike depends on this.

    Normally small engines like this have a manual choke - and even if they dont they always run differently when cold - this you dont want....

    Connect the throttle cables of both engines up to one throttle so they are as syncronous as possible but connect up the kill switches separately - using make & hold switches (so that when you press the switch you kill the engine and it will stay like that - but when you release it the engine will restart if the bike is moving). That latter part is why you need the one way bearing in the GEBE clutch mounts so the engine(s) can be spun up from the bike being in motion.. - either that or you can just use two electric starters.

    At this point you need to decide which is the primary engine. Personally I would pick the front one - since FWD is better in bad conditions. Fit this with the electric start and wire appropriately.

    So far as the fuel supply goes it would be better to have one large capacity tank for both engines - with a clearly labelled fuel cut off for the secondary motor - because this is going to be turned off alot of the time - as well as one at the tank.

    The riding procedure is as follows:-

    1. usual cycle checks
    2. main fuel tap on
    3. choke and start primary engine with electric starter
    4. when engine warmed through - release choke
    5. with one or two people up on flat ground the single engine will pull you along at a fair speed no problem - the problem comes on hills and such - this is where MDS & paired throttle comes in.
    6. when more power is required the kill switch for the secondary engine is released to give electrical power to the secondary engine & the fuel tap turned to the appropriate position to supply fuel. At this point the engine should start (with help from our one way bearing) - importantly, at the same throttle opening and power as the primary one - instantly twice the power on tap.
    6a. it is suggested that this is not attempted at full power/full RPM, as primary engine damage may result from over-revving.
    7. when the destination is acheived both engines can simply be killed on the switches and the fuel taps switched off.

    It would be advisable that an adult be in charge of the fuel tap for the RWD engine unless some sort of remote activation device were to be fitted. It would also be advisable to upgrade the brakes.

    This system would result in a cycle that has the horsepower required for all tasks with all 4 up but can be flexible enough to be ridden with one or two people using only one engine saving anything up to 40% fuel (chrysler calculations based on their 300C MDS model).

    Any comments?

    Jemma xx
    Last edited by a moderator: May 4, 2010

  2. roddy4477

    roddy4477 Member

    Greetings, I like everything about your idea,Except the putting two bikes together. I tried that and it would drive ok a low speeds on flat ground but because the frame is solid on a crowning road it puts you in the ditch. Only three wheels in contact. Perhaps you could have a front supension that would keep all four wheels on the ground. Check out my picture gallery and you can see what I tried.
  3. JemmaUK

    JemmaUK Guest

    Hence not using 4 wheels - I should have made that clear - the two frames are welded in the middle and the only wheels retained at at the very front and very back of the machine... which should solve that particular issues.

    Actually I did - 2/2WD - two wheels/two driven...

    All my bikes have been fitted with front suspension - I consider it a requirement - full sus I am not so sold on tbh

    Jemma xx
    Last edited by a moderator: May 4, 2010
  4. SimpleSimon

    SimpleSimon Active Member

    I like your thinking here, Jemma.

    I would like to raise a point, though. A three or four in line two wheeler raises some serious issue regarding frame design. By no means insurmountable, but issues. More importantly, if I am understanding your intent in this, you propose to couple two engines separated by several feet of space with a common cooling system in series fashion. Lot of insulated pessurized tubing and coolant weight to fill it there.

    Honestly, why not use one of those water cooled small engines tuned to run at its most economical rpm range turning an onboard generator feeding a LiPO battery pack powering drives both front and rear? I'd bet the weight would be similar if not less, and it gives you the advantage of a programmable control system that could readily incorporate an inclinometer, speed controls, and traction sensors to manage power distribution to both driven wheels as needed.
  5. 5-7HEAVEN

    5-7HEAVEN Guest

    So far, not so obvious.:detective:

    Jemma, your prototype four-passenger quadracycle is still not clear enough for me to picture. When you say your bikes will be welded "in the middle", are the frames side by side or one behind the other? Is this one lonnnng 2-wheeled four-passenger tandem bike? Will the frame sag? Will it flex and break or will you be needing a middle wheel?

    Brazing is DEFINITELY not strong enough. Methinks that connecting two long tandem bike frames in this manner is a fatality waiting to happen.

    I would imagine that a custom chromemoly frame ENGINEERED for this length and engineering problems would be necessary, for safety purposes.


    Will there be any anticipated problems in the turning radius? How about four riders of different weight and skills "leaning" into a unison?

    I have never heard of electric starter kits for water-cooled G231 engines? Do you have a link?

    Can you explain how your one-way bearing would work to start the engines?

    Where will your fuel tank be located? Will you be needing an electric fuel pump?

    Both engines do NOT have to be synchronized and should have separate throttle controls. I know from personal experience with my twin-engined cruiser "The

    Dragon Lady". They also do not have to be geared same or have the same power output.

    At 35mph flat out, this machine is TOTALLY unsafe. In fact, it is unsafe at ANY speed.

    How about braking? Are you going to "slap on" a couple of disc brakes?

    Your project, if done right, will cost thousands to complete.

    If constructed in a casual, flippant manner without no regard for engineering and safety issues, it will be a killing machine.

    I have a GREAT idea!

    How about two motorized separate tandem bikes?

    This project looks unsafe, in my opinion.:whistling:
    Last edited by a moderator: May 17, 2010
  6. 5-7HEAVEN

    5-7HEAVEN Guest

    The four-wheeled quadracycle looks to be MUCH safer, especially for riders of different size and skills.

    If you add two engines in the rear, THEN you will need synchronized throttle controls, same gearing and identical power output.

    If you add front drive and rear drive, you do NOT need synchronized throttle or equal power levels and gearing.
  7. 5-7HEAVEN

    5-7HEAVEN Guest

    I'm wondering how you are going to braze the rear dropouts to the rear bike's front fork?

    This project is not for someone who's fanatical about money and his partner who's permanently broke. I'm guessing it will cost $3500...and fail.:whistling:

    How's this idea!?:detective:

    Two used tandem bikes, each motorized. Their backup power...

    are the riders' legpower!

    Let's see...two used tandem bikes...$700
    Two GEBE kits with Subaru/Honda engines...$1400

    Lighting kit.....$150

    Two HD rear wheels.....$300

    Miscellaneous expenses.....$200

    Not included are the watercooled engines, coolant systems, mobile phone, GPS, professional framebending and welding, etc.

    That's $2750 for two used motorized tandem bikes, not including shipping to UK.