Bike engine reverser

[v8ian]

Mulling things over about my lack of reverse using a bike engine, Now this is a IF question, If I used a sensible sized inertia starter motor, remove the bendix, and retrofit a larger shaft which I can fit a prop flange to. obviously the motor would be fixed to the chassis. energise the motor, and I should have a reverse, possibly use a variable resistor, I can have speed control too.
My thinking is if I do this the motor will turn into a dynamo, creating drag, which I don't really want, how can I isolate the it so It doesn't create drag, Is there a way to do this, isolate the brushes??

[Ryannn]

Z-Cars minis have a reverse, I don't know how they do it though. Might be able to find out by asking them?

[v8ian]

They run a big gear alongside a bike sprocket, and use a pre engaged starter motor, turns it into a bit of a harsh reverse,

[dodgerover]

Could you engage it via an electronic clutch like you would use for an aircon pump? Really you don't want it spinning at the time if at all possible, if it's suitably geared I can't see why it shouldn't work reliably.

[v8ian]

I can see what you are saying about the clutch, I'm not sure if I could get the gearing to suit, the od of the clutch pully is quite big. to get the gearing right I would need to reduce the dia by at least half, and not sure of the capability of the clutch, the clamping area is not great.
If I can use the motor inline, it sorts out quite a few packaging issues I have.

[andyborris]

I think if you ground the field (the windings inside), that stops it charging. Many race cars of the 1930's used to do this to make a little more power.

And I know of one race car (AC Supercobra) that used this system, a electric motor for reversing, which then charged the battery. But I suspect it was just a regs thing, car had move backwards to pass scrutineering, wasn't actually meant to reverse the car into a parking bay!

[Darkspeed]

Double switch a pre-engaged type - use the piggy back solenoid to engage the gear and then use another separate solenoid to switch the power - would be the same operation as your original idea.

Apr 17, 2014 17:17:13 GMT v8ian said:

They run a big gear alongside a bike sprocket, and use a pre engaged starter motor, turns it into a bit of a harsh reverse,

[chairchild]

speed control with a big-ass resistor simply wouldn't work how you'd want it to. By reducing the current with a resistor, you'd lose all the power of the motor, along with the speed (ie: it just wouldn't move the car at all)

Get a motor speed controller. They can be had amazingly cheap nowadays. They use a PWM signal to reduce the speed of a motor, whilst still allowing it full-fat current so it'll grunt the motor at near full torque

[colnerov]

Hi, I don't think you want the motor permanently engaged because it won't take the revs and the commutator is likely to fly apart. What about using one of the things they use to maneuver large caravans about, they are moved into contact with the tyres and then are controlled by a remote?

Colin

[adam73bgt]

The Honda Gold Wing has some form of electrical reverse gear on it, I have no idea how it works or whether it would be powerful enough to actually reverse a car though (although the GoldWing is a weighty thing)

[andyborris]

What size car are we talking about? I built a Yamaha R1 engined Sylva Phoenix, didn't bother with a reverser.

Did only weigh 432 KG though!

I think I read somewhere that the average car reverses less then 2 miles in it's total lifespan, no idea if this is a real fact though, got on ok without reverse in the Sylva, only had to push it backwards a few times, but then, never went shopping in it!

Miss that car, would love to know what happened to it, sold it to a guy in Germany.....disappeared without trace!

[dodgerover]

Apr 17, 2014 23:09:42 GMT adam73bgt said:

The Honda Gold Wing has some form of electrical reverse gear on it, I have no idea how it works or whether it would be powerful enough to actually reverse a car though (although the GoldWing is a weighty thing)

Pretty sure they work through the starter motor,

[MrSpeedy]

Apr 17, 2014 22:54:33 GMT colnerov said:

Hi, I don't think you want the motor permanently engaged because it won't take the revs and the commutator is likely to fly apart.

^^^ THIS

To get a reverse speed of say 2mph with the motor running at approx 2,500 rpm you'd need a considerable reduction ratio.

Multiply this back up for when the car is doing even 30mph and you'll be picking bits of exploded starter motor out of your for weeks!

[DWDarkWheels]

I'd say get over to the Locost Builders forum, It's a hot-bed of ingenuity, and this is just the sort of thing BEC builders have faced before.

[v8ian]

after a few purchases at wheels day today, a slight change of direction with the reverser is on the horizon, I will be hiding behind a mill and a large pile of swarf, the starter motor is probably a non starter (sorry), personally I think it would work, but after looking at a decent sized motor, I don't think I could get the shaft size needed thru the middle, I would not feel comfortable with less than a 25mm shaft, possibly machined from a piece of 75mm stock so I could turn it with a flange from one piece. and probably from a tough bit of steel too,

[Clamity]

A friend of mine for his kit car machined up an adaptor to take a starter and free wheeling clutch from a Honda (fireblade possibly, might have been something else). The motor has a planetary gearbox in the body and drives the clutch inner via a chain for roughly another 2:1 reduction. The clutch outer normally bolts up to a plate on the bike crankshaft with three short screws. I believe he made a similar plate to fit either the propshaft or one of the half shafts on his freelander diff.

Edit: ^^ Whoops, this is complete cobblers. The motor came with one of those clutches, but he couldn't use it as the motor would have been spun when the car was going forwards. He actually has some sort of solenoid clutch on it apparently.

[chairchild]

magnetic clutch from either an aircon pump, or merc supercharger?

Allows the perfect reduction ratio for whatever motor you choose, and can transfer a good few Bhp (if you go for the merc supercharger item - unsure about the aircon one in comparison). If it were mine, I'd possibly get a poly-v fanbelt pulley made to fit on the input of the rear diff, with the aircon pulley equipped motor fitted alongside the diff/propshaft. Once you're done reversing, just switch off the clutch, and totally isolate the drivetrain from the 'leccy motor