Making a homemade electric bike frame from scratch

cribby546

cribby546

10 mW
Joined
Mar 6, 2014
Messages
31
Hi I was wondering If anyone had any tips they could give me involving making a high powered downhill electric bike, similar to the one made by phasor cycles. I have to make a powered vehicle for my year 12 project and can't say I have made many bike frames in my life. I have gone with a 2000watt hub motor and possibly 10-12 zippy lipo batteries, anything you can help me with would be great. :?: :?:
 
make a sturdy jig, it's a must to keep things straight when welding
if you can afford it go with 4130 chromo...good luck

KiM
 
Ive tried welding with chromoly and with the thin walled sheet material it blew holes in it to easily so I have opted to make the frame out of 1mm cold rolled mild steel sheet vs the previous .75mm chromoly sheet, I will have to make it thicker than the chromoly but it is a 33%weight difference and for the frame I'm making 20% will not be a huge lose and I have found that the cold rolled sheet is pretty rigid and it holds its shape well. I still don't know how to make a good jig, I've struggled with many plans for one and all of them either won't work or are to complex for the 26 week build and design time I have left.
 
Lots of good ideas here. Make sure you look into head tube angles, best bet likely finding a bike similar to what you want, and copying that angle. If nothing else, slip into a bike shop with an angle finding level, and find out what angles are used on nice DH bikes with the fork length you want to use.

Copy the headset angle, and the bottom bracket height off the ground, and you will likely end up with a frame that doesn't handle funny, or have the pedals too high or too low.
 
We don't have many bike shops that have downhill bikes as we don't have many hills, what is the general pedal height you would want for a downhill bike. At the moment I have used the measurements off the boxxer forks I am looking to get and the height under the pedals is about 5inches, I could get it between 4 to 6.5 inches off the ground by adjusting the swing arm pivot point, also I am using a 9.5 inch rockshox cage rc rear shock. Also I have already set the head tube angle at 66 degrees (apparently the best angle for a DH bike), if you would like me to post a drawing to better sort out the issues just ask.

Thanks :D
 
Here is a rough dimensioned drawing of the main frame i will admit I did like the phasor design because of the way they hid the batteries and the simplicity of the design, this is only a school project so if phasor are worried about someone making a similar designed bike I wouldn't put money on me making this more than once but if the phasor guys do have a problem with the similar shape, feel free to tell me i can change it(all the sizes and dimensions of the frame are my own just the style is similar). :shock:
 

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On thin steel brazing is a lot easier for the novice metalworker to learn than welding and you are more likely to get a good joint.

Welding is one of those skills that if you don't practice regularly you won't be very good at it and something like a bike frame is critical enough I would not recommend you entrust your health/life to a beginner self done job.

Why not cut and fit all your pieces and then take the entire lot to a skilled welder/brazer and have it done properly?

For making and fitting your joints there is a free online service that will make printable templates for coping your tubing pieces to each other, I've used this with good success. For the novice I would suggest a hacksaw and files, it's easy to get carried away with power tools and cut too far which then ruins your material.

http://www.metalgeek.com/static/cope.pcgi

On edit: I just realized your frame is going to be mostly sheet material, the welding heat is likely to warp the sheet considerably as you go so it will be necessary to weld a little here and a little there so as not to heat any particular part up too much. Definitely a job for a skilled fabricator/welder.
 
I Dont think Phasor will be too worried about a similar design. The Phasor frame originally started as a school project as well.

The side covers will form part of the structural integrity of the frame. Chain alignment has always been an issue on my Phasor being 100mm bottom bracket so something to keep in mind.
 
Jonathan in Hiram said:
On thin steel brazing is a lot easier for the novice metalworker to learn than welding and you are more likely to get a good joint.

Welding is one of those skills that if you don't practice regularly you won't be very good at it and something like a bike frame is critical enough I would not recommend you entrust your health/life to a beginner self done job.

Why not cut and fit all your pieces and then take the entire lot to a skilled welder/brazer and have it done properly?

For making and fitting your joints there is a free online service that will make printable templates for coping your tubing pieces to each other, I've used this with good success. For the novice I would suggest a hacksaw and files, it's easy to get carried away with power tools and cut too far which then ruins your material.

http://www.metalgeek.com/static/cope.pcgi

On edit: I just realized your frame is going to be mostly sheet material, the welding heat is likely to warp the sheet considerably as you go so it will be necessary to weld a little here and a little there so as not to heat any particular part up too much. Definitely a job for a skilled fabricator/welder.
Click to expand...


I have used both MIG and braze welding regularly. The bike is going to be laser cut by a professional but the joining and building of the frame has to be done by me at the school metalwork shop, the shop has every machine and tool needed. The only real thing I am worried about is how to make a simple frame jig which I can use to perfectly align the header, seat post and bottom bracket.

Heat warping won't be much of a problem because I have simplified the frame build by having the frame cut out as one big piece and then I will bend all the joins and seem weld the joins where the opposite sides meet.

Since i am making the frame 100mm wide will the chain still run smoothly even though to is at an angle :?:

And I will get it checked out by an engineer before I try and jump it off any mountains...
 
Since i am making the frame 100mm wide will the chain still run smoothly even though to is at an angle :?:

And I will get it checked out by an engineer before I try and jump it off any mountains...[/quote]

Go for a 160mm rear dropout and a motor to suit. I'm even using a motor with a 135mm width in the 160 mm dropout with spacers and it's working well.
 
I have already ordered a kit from dillenger electric bikes, its is made for 135mm dropouts but he said it could easily be widened so I will have to wait a few weeks for the hub motor to arrive so I can get the maximum possible dropout width measurements right. it should be close to 160mm if I try to widen it.
 
Running the frame 100mm wide, you'll likely need to make the rear end a 1 speed. I found the chain line was fine on my build with a 135mm spacing rear and a 100m bottom bracket shell.

There are some great threads from people who have built their own frames in the photo's section of the forum. Read them through and you may get some answers to questions you didn't even know to ask.

Good luck with the build. Post some pics as you go.
 
I have just got the frame back from laser cutting and it looks great will post a photo of it later but do you think 1mm thick cold rolled mild steel sheet would be strong enough for the frame because it does feel a bit flimsy in its flat state but i was just wondering if it would be strong enough when I weld it up which will make it more rigid, any tips or concerns you have could you please tell me thanks. :?: :?: :?:
 
I just got the frame back from laser cutting, it looks so good and I am going to start bending it this week. heres a photo of it.
And I also forgot to add that it only cost $90 to get the frame material and laser cut which I thought was pretty reasonable. :eek:
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Do you have access to a bending machine then?
Be sure to do everything as a mirror image, then any discrepancy that comes about will be dead center. Same with the welding if you do it yourself. It gives a degree of cancellation if you play it right. Cancellation of the warping that is.

You might want to trace that shape into another sheet incase it does go wrong for you. Cutting that out wouldn't take long at all with a jigsaw. You could even make two, as the second is generally better. Having learn a lot from the first.

It would be nice to see all the accounting for this. It is something many of us might like, if we could simply farm all the work out. You might even get a few donations for the plans :)
 
here is the frame bent up, it looks like its gonna work. :D :D :D
The sides match up perfectly i just hadn't taped them up to make them looks symmetrical when i took the photo's...
 

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I was wondering if anyone had any tips or advice on how I should go about welding the frame the sheet is 1mm thick cold rolled sheet. We have oxy, MIG and TIG welders in the workshop. :?: :?:
 
Ive chosen to to TIG welding but since I have started practicing I have run into some issues, I am finding that because the sheet is so thin (1mm) i can get a good bead going it is just at the end of the weld I am finding it difficult to stop the ends from blowing out. I have tack welded the frame together and it is looking and feeling really strong but I am more worried about welding in corners, simple flat joining welds are easy it is just when you've got two sheets at right angles to each other that it makes it tough to weld I haven't found a easy way to fig the inside corners, any tips would be greatly appreciated.

Here are some photos of Some practice welds and the frame tacked up (without the head and seat tube).
And the practice sheet did warp a lot due to me doing very long beads...(won't do that on the real project)
 

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Some of the cheaper Tig welders lack control at lower currents, I have used a 3 phase 350a Miller ac which is far more controllable on extremely thin materials than the single phase 200a ac machine I have at home. If I am suffering with it blowing through at the end of a weld I pull the torch away very fast to extinguish the ark instead of letting off on the pedal as that causes a flare which does the damage. But the single phase machine is fine on everything else, its just 1mm and lower where I need to whip the torch away at the end.
Doing this can cause HF emissions though, it used to set the workshop burgular alarm off!!

I agree that aluminium is much more difficult, if your struggling with ally I find the answer is usually get your torch further away and use more power! People who have learnt on steel tend to get too close! its a hard habbit to break!
 
TIG is tricky. I designed my frame using thicker tube so I could MIG it instead.

Something you could do is take a scrap piece of material and tac weld it under the ends, sticking out past the end of the joint by a n inch. That way you have a backing where you're likely to blow through. when you're done, you can grind off the extra
 
I have mig too but how much nicer a tig weld is. Totally diferent league. It is always good to learn. I suggest experimenting with settings. Mine is also sophisticated acdc, its 220 but gives out 240amps at 40% duty. I dont know pulling torch away, I just let the buton go and tig gradually reduces current and blows argon to cool the material. All settings could be adjusted within ms. Perhaps most tricky part for me is settings. When settings are spot on it is half the job done
 
Ive TIG welded alot of thin material (down to .7mm car body plate) and my advices would be to use a good currentsetting, a fresh electrode tip, good support for your body and have the materials you are gonna weld together joined with minimal gap. It is much easier to weld thin plate if you dont have to fill much gap at the same time.

I also use stainless steel additive material to "calm down" the weld if there are no special requirements on material properties.
 
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