Drum
100 W
Hi all,
I am new to the world of EVs, although I have had a general interest in them for a long time.
In December I decided to make an electric minibike for my 3 year old grandson, and it worked so well that I decided that grandfathers should be allowed to have a bit of fun as well, and that I should build something for myself.
I discovered ES and have been lurking for a few months, reading lots and learning fast.
The amount and quality of information here is amazing, and I would like to thank everyone for their time in sharing their knowledge and experiences with the rest of us.
I started collecting parts to add to my existing collection of mountainbike parts left over from other builds, intending to build an electric trials bike, patterned on the Oset 20 but slightly larger, but also had a few other ideas ticking away...
One day, a small size Kona Stinky frame came up on Trade Me (New Zealand's equivalent to Ebay) with a damaged swing arm pivot, and that aligned with one of the other projects I was considering, so I put a low autobid on it, and ended up getting it for $21!
Soon after, I also scored a strong 24 inch back wheel at a good price, so the electric trials bike has been put on the back burner and a new project was born:
I had been studying the Oset 20, and was impressed by the simplicity of the drive system. With the motor mounted on the swingarm and a fixed drive ratio, there is very little to go wrong, and components can be chosen to be strong enough to handle quite a powerful motor.
The basic idea is to build a complete new swingarm for the Kona frame and pivot it on a shaft passing through the bottom bracket position of the frame. At the back of the swingarm would be holes to take a 12mm through axle for the hub of the 24" wheel, and in front of the wheel would be a platform or other mounting for the motor.
The motor would drive the back wheel through chain drive of a fixed ratio. If the motor spun too fast for a single reduction (e.g. GNG or the similar "big block" motor), then a double reduction would be needed, but Ideally I would find a low revving, torquey motor capable of driving the back wheel through a single reduction of chain. I am currently favouring the lower kV 48V, 1000W nominal "big block alternative" motor starting to be discussed in other threads under the "mid drive" topic. This would have a single reduction of DID 219 chain, say 15 tooth driver and 77 tooth driven sprockets as a starting point.
The swingarm would have brackets on top to take the standard Kona back suspension system, although the longer swingarm would require a stronger spring on the shock.
With no pedals, and using the bottom bracket as the swingarm pivot, I would have to find another place to mount the footpegs. My current plan is to weld footpeg pivot brackets to either side of the swingarm between 10 and 20% of the swingarm's length behind the bottom bracket. This would mean that the footpegs move up and down a bit as the back suspension works, but I think that as long as they were not too far back, this would be acceptable.
As with any project, each decision involves compromises, and each advantage may be partially offset by a corresponding disadvantage. In this project, the main disadvantage I see is the need for a significantly longer swingarm (it is looking like the back wheel will be 100 - 125mm further back than with the standard swingarm). This will load up the back suspension more, and the bike would probably be harder to ride around really tight hairpin corners on steep singletrack trails. On the other hand it would help keep the front wheel down under hard acceleration...
There will also be significantly more unsprung weight, but the motor will be as close to the forward pivot of the swingarm as possible, so it shouldn't be too bad.
Then probably add a fixed elongated seat rather than a saddle, partly as a safeguard against falling onto the back wheel if a foot slips of the footpeg..
It is starting to sound a bit more like an electric motorbike rather than an electric bicycle, but as most of the components would be bicycle based, and other "no pedal" bikes have been included in this forum I feel ok to post here.
I will try to figure out how to post drawings and photos, and post more information soon. Meantime, any comments are welcome.
Regards,
Dave.
I am new to the world of EVs, although I have had a general interest in them for a long time.
In December I decided to make an electric minibike for my 3 year old grandson, and it worked so well that I decided that grandfathers should be allowed to have a bit of fun as well, and that I should build something for myself.
I discovered ES and have been lurking for a few months, reading lots and learning fast.
The amount and quality of information here is amazing, and I would like to thank everyone for their time in sharing their knowledge and experiences with the rest of us.
I started collecting parts to add to my existing collection of mountainbike parts left over from other builds, intending to build an electric trials bike, patterned on the Oset 20 but slightly larger, but also had a few other ideas ticking away...
One day, a small size Kona Stinky frame came up on Trade Me (New Zealand's equivalent to Ebay) with a damaged swing arm pivot, and that aligned with one of the other projects I was considering, so I put a low autobid on it, and ended up getting it for $21!
Soon after, I also scored a strong 24 inch back wheel at a good price, so the electric trials bike has been put on the back burner and a new project was born:
I had been studying the Oset 20, and was impressed by the simplicity of the drive system. With the motor mounted on the swingarm and a fixed drive ratio, there is very little to go wrong, and components can be chosen to be strong enough to handle quite a powerful motor.
The basic idea is to build a complete new swingarm for the Kona frame and pivot it on a shaft passing through the bottom bracket position of the frame. At the back of the swingarm would be holes to take a 12mm through axle for the hub of the 24" wheel, and in front of the wheel would be a platform or other mounting for the motor.
The motor would drive the back wheel through chain drive of a fixed ratio. If the motor spun too fast for a single reduction (e.g. GNG or the similar "big block" motor), then a double reduction would be needed, but Ideally I would find a low revving, torquey motor capable of driving the back wheel through a single reduction of chain. I am currently favouring the lower kV 48V, 1000W nominal "big block alternative" motor starting to be discussed in other threads under the "mid drive" topic. This would have a single reduction of DID 219 chain, say 15 tooth driver and 77 tooth driven sprockets as a starting point.
The swingarm would have brackets on top to take the standard Kona back suspension system, although the longer swingarm would require a stronger spring on the shock.
With no pedals, and using the bottom bracket as the swingarm pivot, I would have to find another place to mount the footpegs. My current plan is to weld footpeg pivot brackets to either side of the swingarm between 10 and 20% of the swingarm's length behind the bottom bracket. This would mean that the footpegs move up and down a bit as the back suspension works, but I think that as long as they were not too far back, this would be acceptable.
As with any project, each decision involves compromises, and each advantage may be partially offset by a corresponding disadvantage. In this project, the main disadvantage I see is the need for a significantly longer swingarm (it is looking like the back wheel will be 100 - 125mm further back than with the standard swingarm). This will load up the back suspension more, and the bike would probably be harder to ride around really tight hairpin corners on steep singletrack trails. On the other hand it would help keep the front wheel down under hard acceleration...
There will also be significantly more unsprung weight, but the motor will be as close to the forward pivot of the swingarm as possible, so it shouldn't be too bad.
Then probably add a fixed elongated seat rather than a saddle, partly as a safeguard against falling onto the back wheel if a foot slips of the footpeg..
It is starting to sound a bit more like an electric motorbike rather than an electric bicycle, but as most of the components would be bicycle based, and other "no pedal" bikes have been included in this forum I feel ok to post here.
I will try to figure out how to post drawings and photos, and post more information soon. Meantime, any comments are welcome.
Regards,
Dave.