Power Wheels ~ Bicycle

[ChamomileMotorbike]

Hi Guys, new to the forum, I had a question about creating a circuit for a new project I want to undertake.

While driving to work after the Hurricane this past week, I found two powerwheel children's toys in the parking lot of my work. Seemingly someone had just dumped them by the dumpster. Unfortunately they did not have the batteries in them but I figured let me grab the motors for a project I've had in mind for sometime. An Electric Bicycle. To my surprise inside the powerwheel toys there were two 12v 12,000 rpm motors connected to either rear wheel.

So now instead of an easy or common strap it to the frame and put a sprocket on it type project I'm trying to think if its worthwhile doing a dual motor setup. The best concept at this point is attaching both motors on the back of the bicycle on the little loading tray my schwinn bicycle has. Mount them there, facing either side of the bike, and chain drive down to the rear wheel where I'll have to figure out how to mount on either side.

It is a 10 speed bike so there are sprockets there to attach to. Now here come the questions.

I need to see if I can remove the sprockets that are there for the 10 speed, and place one on either side of wheel to be driven by the motors. Not sure if that's a reality.

The main question is, is it worth using two 12v motors for this project. Will it give any reasonable speed (say above 5mph)?
Will two 12v motors be considered a 24v system if I wire them in series? I hope to run it off of 2 motorcycle gel type batteries.
Lastly what should I look for as far as a controller, is it necessary or can I simply wire a rheostat into the circuit?

 

[ChristianCMcKay]

At 12,000 RPM, you'll definitely want some gear ratio. Hub motors for electric bicycles generally go near 250 - 350 RPM's depending on the size rim for the bike with smaller wheels having higher RPM's because less torque is necessary to move them forward at the same speed. Also, what is the power rating of the motor (watts). A normal bicycle motor will be anywhere between 250 - 1000 watts, however I believe legally they can only be 500 watts in America. At 250 watts, you should definitely be able to go 5 mph though.

Also, don't just wire a rheostat into the circuit. Motor speed is controlled by PWM.

 

[DerStrom8]

Hi Guys, new to the forum, I had a question about creating a circuit for a new project I want to undertake.

While driving to work after the Hurricane this past week, I found two powerwheel children's toys in the parking lot of my work. Seemingly someone had just dumped them by the dumpster. Unfortunately they did not have the batteries in them but I figured let me grab the motors for a project I've had in mind for sometime. An Electric Bicycle. To my surprise inside the powerwheel toys there were two 12v 12,000 rpm motors connected to either rear wheel.

So now instead of an easy or common strap it to the frame and put a sprocket on it type project I'm trying to think if its worthwhile doing a dual motor setup. The best concept at this point is attaching both motors on the back of the bicycle on the little loading tray my schwinn bicycle has. Mount them there, facing either side of the bike, and chain drive down to the rear wheel where I'll have to figure out how to mount on either side.

It is a 10 speed bike so there are sprockets there to attach to. Now here come the questions.

I need to see if I can remove the sprockets that are there for the 10 speed, and place one on either side of wheel to be driven by the motors. Not sure if that's a reality.

The main question is, is it worth using two 12v motors for this project. Will it give any reasonable speed (say above 5mph)?
Will two 12v motors be considered a 24v system if I wire them in series? I hope to run it off of 2 motorcycle gel type batteries.
Lastly what should I look for as far as a controller, is it necessary or can I simply wire a rheostat into the circuit?

I'm not sure why you'd want to connect your motors in series. Putting them in parallel would be much better. It'd be more efficient, and it would only take a single 12v battery.

Anyway, if you're looking to motorize your bicycle, you should definitely just use one of the motors. Otherwise, the second one will waste power and probably create drag on the first one, causing it to slow down, draw more current, and drain your battery faster.

Also, ChristianCMcKay is right--a rheostat will not control the speed of a DC motor. It will probably just burn out. You'd need a high-power PWM motor controller, which is somewhat difficult to find and/or build. I'd just use an on/off switch (momentary push-button would be my first choice) and a relay (to connect the batteries with the motor separately so you don't burn out the push-button).

I started building a motorized bicycle a while ago myself, using an automotive starter motor. I would have given anything to find motors like the ones you found! I have a blog here at ETO, but there's probably not enough information to go off of, considering my bicycle got stolen when I moved to Boston.

So my personal opinion: Stick with a single motor, two motorcycle batteries wired in parallel (to provide enough current to drive it), a push-button switch for the accelerator, and a relay.

Hope this helps!
Regards,
Matt

 

[ChamomileMotorbike]

Thanks!

Thanks for the replies, that definitely gives me a lot of help.
I still have to look up the wattage for the motors, I was looking for replacement parts hoping they would list it there, but to no avail. I'll triple check the motors themselves tomorrow.

DerStrom Thanks for the all the tips. Sorry to hear about your bike. I like the sound of the setup. The motors are identical so I was hoping they would work well together. My idea of getting it to 24v was thinking it would be more powerful together. Again, I'm green to this so I really don't know the theory behind electrical engineering enough to know.
The motors are surprisingly small, which made me concerned about their ability to handle the bike using just 1. I guess I may as well try one and then rig up a second if its necessary. The car starter idea sounds really good, that must have some wicked torque. How quick was that setup? 12v right?


The motors came attached to a grey plastic number which contain the gearing. I wondering whether I can maintain them and attach sprocket or belt drive setup to that. Its probably tuned to the small 12 - some odd - inch power wheel tires, not 20 something bicycle wheels so it may need tuning anyway.
The whole thing is new to me but I'm hear to figure it out and learn. I really gatta see if someone else tried doing the same thing.

 

[DerStrom8]

DerStrom Thanks for the all the tips. Sorry to hear about your bike. I like the sound of the setup. The motors are identical so I was hoping they would work well together. My idea of getting it to 24v was thinking it would be more powerful together. Again, I'm green to this so I really don't know the theory behind electrical engineering enough to know.
The motors are surprisingly small, which made me concerned about their ability to handle the bike using just 1. I guess I may as well try one and then rig up a second if its necessary. The car starter idea sounds really good, that must have some wicked torque. How quick was that setup? 12v right?


The motors came attached to a grey plastic number which contain the gearing. I wondering whether I can maintain them and attach sprocket or belt drive setup to that. Its probably tuned to the small 12 - some odd - inch power wheel tires, not 20 something bicycle wheels so it may need tuning anyway.
The whole thing is new to me but I'm hear to figure it out and learn. I really gatta see if someone else tried doing the same thing.

Two motors working together are only as powerful as the most powerful one. Though the motors may look identical, there will always be slight differences in them. Nothing can be exactly the same.

I never got to finish my bike, so I'm not sure how well it would have worked. The starter motor is a 12v device, yes. It's only designed to run in short bursts though, which makes it difficult to drive a bike. But it was all I had, so I thought I'd give it a shot I still plan to pick it up where I left off when I get a new bike, but that may be a while....

 

[()blivion]

You'd need a high-power PWM motor controller, which is somewhat difficult to find and/or build.

It's not that difficult. Maybe for a complete newbie that absolutely can't solder at all whatsoever. But most normal people can learn to do something like this without too much hassle.

View attachment 68518

 

[DerStrom8]

It's not that difficult. Maybe for a complete newbie that absolutely can't solder at all whatsoever. But most normal people can learn to do something like this without too much hassle.

View attachment 68518

I'm sorry, I assumed the OP was a newbie to electronics, but reading back he didn't really say anything of the sort

Anyway, as for the circuit, I have a couple reservations about it. The first is the "control" setup. A 5k+ pot on the control pin of the 555 timer will not give full, steady PWM. I'd sooner use a circuit like this one:

View attachment 68520

My second issue is the freewheel diode. I think it would probably require a lot more protection than just a single diode, especially considering the kind of current these motors probably draw. Also, finding high-power MOSFETS to drive it might be a problem, and will rack up the price a bit. I'd also put some extra protection across the FETs, since they're very sensitive to voltage spikes.

That's my $.02
Regards

 

[ronv]

I would try to retain the gear box if I could. Getting down from 12,000 rpm to something you can use will be a problem. I think 2 motors have twice the torque of one motor but will be hard to interface.

 

[()blivion]

I'm sorry, I assumed the OP was a newbie to electronics, but reading back he didn't really say anything of the sort

Actually... looks like he did say he was "green to electronics". Me assuming that he may know enough already was a bad call on my part. Sorry.

Anyway, as for the circuit, I have a couple reservations about it. The first is the "control" setup. A 5k+ pot on the control pin of the 555 timer will not give full, steady PWM. I'd sooner use a circuit like this one:

Using diodes to stabilize the timing is a useful possibility. And my circuit does vary in frequency from max to min, and also doesn't fully stop at min pot setting either. Both our circuits use a 555 as the timing element, so we can use whatever topology gets us the best results.

My second issue is the freewheel diode. I think it would probably require a lot more protection than just a single diode, especially considering the kind of current these motors probably draw.

They make some beefy diodes, Digi-Key Part Number 150EBU02-ND for example. Or 300U40A-ND if you don't mind spending $30 for just one part. I have used such things with great success. But we could use a TVS or something similar just as easily. Another possible option is making a circuit that feeds the freewheeling energy back into the battery pack. This would create regenerative breaking and eliminate the need for the protection altogether. In any case, if you leave the motor open as is shown in your schematic, the back EMF will almost certainly build up enough to murder the FET's.

Also, finding high-power MOSFETS to drive it might be a problem, and will rack up the price a bit.

I don't think it's a problem. You can easily get 100's of Amps @ 12v with just a few FET's. I have just two FET's controlling a 300~400 Watt 12v DC motor right behind me as I type this and it works perfectly. And the FET's I used are nothing special, I recovered them from an old motherboard. If the OP specifically purchased switches with the application in mind, he could get better matched parts and maximize power-cost ratio. Just the FET's would probably cost less that $20 and would provide more than enough power.

I would try to retain the gear box if I could. Getting down from 12,000 rpm to something you can use will be a problem. I think 2 motors have twice the torque of one motor but will be hard to interface.

I agree, using the gear box to some extent can be very useful. And I also agree that two motors would be better than one *IF* it can be made to work mechanically. Two motors that are drawing the same amount of electrical power will be making twice the mechanical power of a single unit, as is necessary to be in accordance with the First Law of Thermodynamics. But it is a big "if". To make them work together mechanically, rather than expend mechanical energy fighting each other would require a variable gear system, similar to what you would find in a snowmobile. Another option is to have precision torque gauges on each motor, and vary the electrical power to each independently so that the torque matches at all times. This quickly becomes electronically difficult, and such torque gauges are quite pricey.

The whole problem is analogous to attaching two switch mode power supplies together in parallel and making them share current evenly. If there is even a small difference in the two motors RPM(voltage), then torque(current) will get lost going from one motor into the other and not add to the systems mechanical power. Even using the two independent tires will give problems because they are mechanically coupled together though the ground.

This isn't going to be something easy for the OP to get around I don't think. For simplicity's sake I would just go with one motor and over power it. Most simple electric motors are solid as a rock electrically will put out just about as much power as you can throw into them without problems.

How I do/did power plant to mechanical interfacing for all my bike projects/plans is use a direct interface to the tire it's self, rather than try to integrate something into the gear/chain. This gives you a great step down plus has the added benefit of a safety slip clutch in the event things should bind. But most of my projects involved attaching small gas engines to bicycles. And even a good 2 stroke chain saw engine will only get up to about 8k RPM. So even with my method but an electric motor, the OP may still need a gear box of some kind.

 

[DerStrom8]

Actually... looks like he did say he was "green to electronics". Me assuming that he may know enough already was a bad call on my part. Sorry.



Using diodes to stabilize the timing is a useful possibility. And my circuit does vary in frequency from max to min, and also doesn't fully stop at min pot setting either. Both our circuits use a 555 as the timing element, so we can use whatever topology gets us the best results.



They make some beefy diodes, Digi-Key Part Number 150EBU02-ND for example. Or 300U40A-ND if you don't mind spending $30 for just one part. I have used such things with great success. But we could use a TVS or something similar just as easily. Another possible option is making a circuit that feeds the freewheeling energy back into the battery pack. This would create regenerative breaking and eliminate the need for the protection altogether. In any case, if you leave the motor open as is shown in your schematic, the back EMF will almost certainly build up enough to murder the FET's.



I don't think it's a problem. You can easily get 100's of Amps @ 12v with just a few FET's. I have just two FET's controlling a 300~400 Watt 12v DC motor right behind me as I type this and it works perfectly. And the FET's I used are nothing special, I recovered them from an old motherboard. If the OP specifically purchased switches with the application in mind, he could get better matched parts and maximize power-cost ratio. Just the FET's would probably cost less that $20 and would provide more than enough power.



I agree, using the gear box to some extent can be very useful. And I also agree that two motors would be better than one *IF* it can be made to work mechanically. Two motors that are drawing the same amount of electrical power will be making twice the mechanical power of a single unit, as is necessary to be in accordance with the First Law of Thermodynamics. But it is a big "if". To make them work together mechanically, rather than expend mechanical energy fighting each other would require a variable gear system, similar to what you would find in a snowmobile. Another option is to have precision torque gauges on each motor, and vary the electrical power to each independently so that the torque matches at all times. This quickly becomes electronically difficult, and such torque gauges are quite pricey.

The whole problem is analogous to attaching two switch mode power supplies together in parallel and making them share current evenly. If there is even a small difference in the two motors RPM(voltage), then torque(current) will get lost going from one motor into the other and not add to the systems mechanical power. Even using the two independent tires will give problems because they are mechanically coupled together though the ground.

This isn't going to be something easy for the OP to get around I don't think. For simplicity's sake I would just go with one motor and over power it. Most simple electric motors are solid as a rock electrically will put out just about as much power as you can throw into them without problems.

How I do/did power plant to mechanical interfacing for all my bike projects/plans is use a direct interface to the tire it's self, rather than try to integrate something into the gear/chain. This gives you a great step down plus has the added benefit of a safety slip clutch in the event things should bind. But most of my projects involved attaching small gas engines to bicycles. And even a good 2 stroke chain saw engine will only get up to about 8k RPM. So even with my method but an electric motor, the OP may still need a gear box of some kind.

You've got some good points there ()blivion, but things are still rather complicated. I guess it's up to the OP now whether he thinks the costs are reasonable and the setup won't be too complex.