Mating motor to gear sprockets and H Bridge Circuit

[fitek]

Hehe, I'm packing in two questions for all of you guys:

1) I bought a BMC/PowerPack motor with a D shaft for my recumbent. I think the easiest way to hook this up to the wheels is to have a chain from one of the crank sprockets go to the motor, which will be mounted underneath the main tube nearby. I'll have to adjust the shifters so that the existing chain can't interfere with this new one.

That said, how do I get a chain on the D-shaft, and what kind of chain? A usual bicycle chain?

2) Anyone got a *decent* H Bridge circuit schematic? (not super over engineered and not half-assed) I have been reading through the posts in this forum and found discussion of some mosfets (IRF2907, IRFB4110, IRF4310...) and the use of Schottkey diodes and capacitors... Also, there is the Open Source Motor Controller, but it's got sooo many pieces that the materials cost quite a bit and I think I'll tear my hear out trying to build it. I'm a CS/E person, so if I try to make the circuit up on my own it will probably come out half assed.

Thanks!

 

[Rassy]

I think the easiest way to hook this up to the wheels is to have a chain from one of the crank sprockets go to the motor, which will be mounted underneath the main tube nearby.

I agree with the above statement. After ending up with a cheap trashed scooter, I purchased a $53 MB, made a simple BB bracket and used the batteries, controller, throttle, and chain from the scooter. It actually worked pretty good. There were only 3 little issues. I smoked the motor on the fairly steep hill to my house. I could only use the two outside sprocket wheels on the crank, because the two chains did not have enough clearance to be on adjacent sprocket wheels. And I really did not like to have to peddle whenever the motor was being used. And of course the Ebike bug bit me and my current recumbent trike and trailer setup represents about a $2000 investment.


Anyway, back to subject, If I were to do another project similar to yours, getting the motor and pedals on their own freewheels would be a high priority. Good luck with your project. enjoy

Hehe. Oh yeah, I didn't answer either of your questions.

 

[fechter]

I'd suggest using a Crystalyte controller with the BMC motor. If you want chain snapping power, you can modify it with better FETs.

A planetary reducer from a Currie USPD is supposed to fit on the D shaft BMC motor. This would probably the easiest route. The planetary has a #25 chain sprocket. This means you'd have to find a large #25 sprocket and attach it to one of the existing sprockets.

You still need to deal with the motor driving the pedals. Some kind of freewheel to prevent the pedals from being driven would be good.

 

[J Barrie Wilkinson]

I have built the configration you are proposing and as Fetcher suggested the Currie type planetary gear reducer does fit the D shaft. The BMC no load rpm is over 3000 depending on the voltage you run it at, so large reduction is necessary to run on a chain wheel. I mounted a #25 90t Currie scooter rear chainwheel to my chainring at the bottom bracket and got the smallest gear reducer chain wheel Scott McGregor at http://www.evdeals.com/ could supply. Scott can supply the planetary reducer, Crystalyte controller, and heavy duty #25 chain.

One drawback to this system is that you have to pedal when the motor is running and it can be got around by using a Vision freewheel crank.

The planetary reducer has a built in freewheel so you can pedal without the motor running, it is advisable to get the large size freewheel mod that Scott does, but not necessary.

JB

 

[fitek]

Thanks for the feedback!

I will look into the reducer after I post this.

Hopefully the non freewheeling crank won't be a problem because I'd prefer not to have a throttle on the handlebars, but rather provide assist when the user is pedaling. I'm not sure how I'd make that happen, but thats fine for now. I tried riding a bike with a throttle and I didn't like it.

I'm building my own controller. Part of the reason for building this bike was to have a reason to play around with a motor controller... just I want to play around with the code, not the circuit I just noticed the schematics posted as a sticky. I'll have to play with those.

I will have to hurry up and build this bike now as my upright was lent out to someone who left it out unlocked! Next to the Caltrain station. Just for a minute they said!

 

[fitek]

Good news, the person took my mother's bike instead of mine, as mine had a flat. It was a decent Japanese ATB however, so the wallet was equally hurt. But at least its not as big a sentimental loss

Question: are there problems with powerful FWD motors? Rear brakes don't work so well, the wheel skids easily, does the same happen with the front when accelerating?

 

[fechter]

Question: are there problems with powerful FWD motors? Rear brakes don't work so well, the wheel skids easily, does the same happen with the front when accelerating?

In a word, yes. It's not so bad on dry pavement, but on dirt or wet pavement it could be an issue. You can help by moving the batteries further forward.