Bike motor

Thread Starter

beatsal

Joined Jan 21, 2018
169
I want to add a dc motor to my bike as an assist i.e. I like the exercise of pedaling but to pre-empt a heart attack would like an assist to climb slopes. Want to use a 60 W 12VDC Motor, may be with rergen. Looking for ideas on what battery, how to mount the motor etc.
 

Thread Starter

beatsal

Joined Jan 21, 2018
169
Thanks, so will have to use a 350W, wonder if 24VDC is OK? Any idea what Volts? Not interested in hub motor or kit, but only in dyi
 

MisterBill2

Joined Jan 23, 2018
7,007
Unless you get a hub-motor, adding an electric drive to a bike is mechanically a big deal. And I have no clues as to your mechanical skills, which matter a lot, unless you get one of the packaged setups where everything bolts on perfectly. You also need to decide how long you would be riding with assistance at any particular time. That will determine the battery capacity that you require. The size of the battery will then help decide where you would mount it. Where the battery is mounted will help decide where the control electronics get mounted. So there are quitea few choices that need yo be made at the start.
My idea is to have a wider set of gear ratios so that hills will not be a challenge at all. 15 speeds with a wide spread should certainly handle most situations.
I started this post before the 2 beore it arrived. But I took a while and so part of it is funny.
 

MisterBill2

Joined Jan 23, 2018
7,007
Now, 350 watts and not a hub motor. So a chain drive and externally mounted motor. You will need some welding ability as well as metalworking skills. To drive the rear wheel you ciuld get a disk brake hub and put the drive sprocket where the disk would normally go. Tghat would be strong and sanitary. And you can have the brake caliper grab the sprocket for stopping.
 

MrChips

Joined Oct 2, 2009
21,853
Let's assume that you are going to use power assist on a flat and not for start off, climbing hills or riding against the wind.
100W should be what is required. So aim for a 250W motor.
10A @ 12V = 120W

Determine your battery requirements.
A 12V 10Ah SLAB should give you a 1-hour ride at 120W.

Check on the internet what others have done with friction drive.
Old electric power saw to spare, anyone?
1600737946792.png

https://www.electricbike.com/the-diy-junkyard-e-bmx-friction-drive/
 

Sensacell

Joined Jun 19, 2012
2,596
Friction drives are very lossy, not good when you are trying to squeeze as much as you can from an undersized motor and battery.
 

MisterBill2

Joined Jan 23, 2018
7,007
My observation is that the HUGE problem with a front wheel drive is the big increase in the mass that turns as one rides the bike, and so the handling characteristic is totally different. In my opinion, RUINED. Thus I do not recommend such a setup at all.
But, if one wanted to try it, a much better scheme would be to put a coaster brake hub in front and drive that with a chain. Much more efficient than a friction drive and much easier on the tire wear. The second advantage is that when the drive is not driving there is no chain friction loss. Of course that can also be achieved by using a single-sprocket free-wheel hub, possibly more available.
 

Alec_t

Joined Sep 17, 2013
11,640
Friction drive isn't really so bad. Back In the 50's I rode to school on a push-bike with a bolt-on friction-drive petrol-engine. My first engine was a Velosolex (an earler version of this). I later had a rear-wheel drive engine (I never did know the brand). With both engines you started them by initially pedalling the bike, then engaging the 'clutch', which simply yanked the drive roller down onto the tyre. Surprisingly, in two or three years of cycling this never shredded the tyre or caused a puncture.
 

ElectricSpidey

Joined Dec 2, 2017
1,235
If you are doing this to avoid over exertion, you might want to consider what the added weight will do when on level ground.

Consider getting off and walking the bike up hills.
 

Chris65536

Joined Nov 11, 2019
225
I always thought it would be cool to motorize a bike through the regular chain. I have seen bikes where the freewheel is on the pedal sprocket instead of the rear wheel. This would let the motor power the bike through the rear sprocket, while your feet rested. And you could change gears to get the torque or speed that you need, depending on terrain. I think every E-bike I have ever seen has been direct drive.
 

MisterBill2

Joined Jan 23, 2018
7,007
I actually owned one of those rigs with the freewheel clutch on the one piece crank. I think that it was made in India, the bike was not up to Chinese quality standards and so I did not keep it. That setup certainly could work, and if one had it with a double front sprocket then the reduction could be very simple, just a second chain up to the motor sprocket. With a 3-piece crank system it would take a bit of custom machining to make it work, but it could be really a good setup.
As for the extra weight, would it really be more that 15 or 20 pounds? And if one is not racing would that really matter? Just shift to a lower gear and pedal on.
 

Thread Starter

beatsal

Joined Jan 21, 2018
169
Just wonder - suppose I attach a small sprocket wheel to a geared motor and mount the motor so that the sprocket wheel engages with the top of the chain, won't it work? The weight of the geared motor will help in the geared motor engaging with the chain. Some mounting brackets would do the trick. Any comments?
 

Thread Starter

beatsal

Joined Jan 21, 2018
169
I actually owned one of those rigs with the freewheel clutch on the one piece crank. I think that it was made in India, the bike was not up to Chinese quality standards and so I did not keep it. That setup certainly could work, and if one had it with a double front sprocket then the reduction could be very simple, just a second chain up to the motor sprocket. With a 3-piece crank system it would take a bit of custom machining to make it work, but it could be really a good setup.
As for the extra weight, would it really be more that 15 or 20 pounds? And if one is not racing would that really matter? Just shift to a lower gear and pedal on.
Thanks. A pic would be useful
 
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