Hi from a newbie

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Hi, I am in UK and building a recumbent trike. Been thinking of building one for about 3 years and finally doing it. I already built one frame with the steetring geometry done right, and rear suspension but the frame was too weak. I had 40mm x 30mm miod steel box section which was 1.2mm thick. I have now bought 40mm x 40mm x 3mm x 5ft long mild steel box section. Much stronger, but the box section is 5kgs (approx 10 pounds in weight. I have bought 2 of them. One for the main frame and some of the other length for the front cross piece. Can someone please tell me what the weight of an average recumbent trike frame would be. Is the box section I have too much overkill for the strength ?
Thanks in advance
 
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Hi, I am in UK and building a recumbent trike. Been thinking of building one for about 3 years and finally doing it. I already built one frame with the steetring geometry done right, and rear suspension but the frame was too weak. I had 40mm x 30mm miod steel box section which was 1.2mm thick. I have now bought 40mm x 40mm x 3mm x 5ft long mild steel box section. Much stronger, but the box section is 5kgs (approx 10 pounds in weight. I have bought 2 of them. One for the main frame and some of the other length for the front cross piece. Can someone please tell me what the weight of an average recumbent trike frame would be. Is the box section I have too much overkill for the strength ?
Thanks in advance
Hi Ian,
3mm is twice what you need (unless you weigh over 400 pounds ;)). Most folks use 40 x 40 or 38 x 38 at 1.6mm and that's plenty strong enough.
40 x 30 @ 1.2 should have been adequate IF oriented with the long side vertical. Did the tube bend or the joints rip-apart? If the latter, did you include reinforcing fillets/gussets?
Without being melodramatic or too much of a weight-weenie try to reduce the weight as it is just dead-weight YOU need to drag around (don't ask me how I know).
Was it an AZ bike plan you were building or a home-brew?
 
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Hi Ian,
3mm is twice what you need (unless you weigh over 400 pounds ;)). Most folks use 40 x 40 or 38 x 38 at 1.6mm and that's plenty strong enough.
40 x 30 @ 1.2 should have been adequate IF oriented with the long side vertical. Did the tube bend or the joints rip-apart? If the latter, did you include reinforcing fillets/gussets?
Without being melodramatic or too much of a weight-weenie try to reduce the weight as it is just dead-weight YOU need to drag around (don't ask me how I know).
Was it an AZ bike plan you were building or a home-brew?
Hi, It is just from my own head and variations of trikes I have seen on youtube and pinterest.
The tube I had bent like a banana. The cross bar for the front wheels, I made a mistake and made them longer side upwards instead of like the frame was (shorter side upwards) and they bent at the welds but in a twisting motion. If I had made it the same as the main frame, they could have bent back if hit a kerb / rock or something. I thought with them being short, there was sufficient strength. I was wrong. lol.

I was thinking of buying 2mm wall steel, but was thinking more on the stronger side. 3mm may be overkill but a 5ft length weighing around 8 - 120 pounds is heavier than I had thought. I might make a bearing bress with the stuff I have and buy some 1.6mm or 2mm. Thanks for the advice.
I have bought a tow ball drop plate to weld under the head sets so I can pit tow ball bolts through and weld them to the plates. They will be the axles. I have 2 x 24" tricycle wheels (I sold the tricycle axle on ebay) which take 14mm axles, but I am going to replace the sealed bearings in the wheels for 16 x 35 so the bolts will go through and the axles will be super strong.

I have put a pic of the first make attempt as my avatar. I hope you can see how I made the mistake. It also had 20" bmx wheels with 10mm axles. The axles are welded on the bottom of the head sets. I think they might still bend.
 
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Hi Emma. Thanks. I have built the frame now with what I have. It isnt too bad. Twice I welded the upright for the seat andsuspension. The piece was thin and I turned the welder powetr down. Needless to say, the weld didnt take. I forgot I turned the power down and didnt get hte penetration on the main frame. Now I am out of welding wire.
 

Radical Brad

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Welcome. and thanks for stopping by!

A lot has to do with the geometry of the frame as well. Do you have photos of failures and wins?
It's amazing what a well placed gusset or truss tube can do!

Brad
 
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.....as a point of reference, my trike is made from 1"x2" rectangular section, with less than 1mm wall. It has to be the design of the frame that's the problem, some pics here would help greatly. It's been said before - remember, you're building a trike and not a tractor!

PS - welcome to the forum :)
 
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I have placed pics into albums in the DIY builders gallery of both frames. I didnt take a pic of the bent frame as I cut it up ready for the new metal arriving.
 
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As you ad more, the frame will be more stiffer, but it depends on where and what you ad to the frame. From where you mounted the arms to the rear, will become stiffer as you ad mounting for a seat and a seat.
The front will probably become a bit shorter and for the front arms for the wheels, you can make triangles. Don't have to be big.

My frame got a lit stiffer when I added the seat and some extra parts in the rear to make it stronger.
I use 40x40x1,6mm steel tubing and used 20x20x1,6mm for the seat and round 12x1mm for extra suport.
It's the construction that makes it stiffer and stronger. A profile of that length is always full of flex.
 
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As you ad more, the frame will be more stiffer, but it depends on where and what you ad to the frame. From where you mounted the arms to the rear, will become stiffer as you ad mounting for a seat and a seat.
The front will probably become a bit shorter and for the front arms for the wheels, you can make triangles. Don't have to be big.

My frame got a lit stiffer when I added the seat and some extra parts in the rear to make it stronger.
I use 40x40x1,6mm steel tubing and used 20x20x1,6mm for the seat and round 12x1mm for extra suport.
It's the construction that makes it stiffer and stronger. A profile of that length is always full of flex.
My boom will be cut down to about 3 inches beyond the bottom bracket when I get one and fit it. That will sorten it and lose a bit of weight.
I cant do anything else to it yet as I need welding wire.
I am still mot sure if I will keep the 20" front wheels on or go 24" front amd rear. The rfear forks are off a 24" wheel mountain bike, but the wheel is a 26" MTB. I have one bottom, bracket but the crank is single with fixed pedal arms, like a bmx one. I have yet to buy a bike frame with the square shaft BB as I have a set of 3 cranks for one.
I have the brake levers off a tricycle I broke up for parts. The levers have the brake lock pins in so its like putting a hand brake on.
 
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Couple things worry me ?

Your front wheels don't look vertical
Your front wheel axles look like 9mm and not 14mm ?

I am not a tadpole builder so cannot comment of the first ?
The second it is possible you will bend/break those axles with the first enthusiastic corner you take ?
 
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.....a close up shot of your welds might also be helpful. Getting 2 pieces of steel to stick together is not the same as 'welding'. Another issue with the front wheels is they appear to be radially spoked, which results in a weak wheel in this application. If they are also 9mm axles, you'll have to find another set I'm afraid. All this is for your safety, a failure of the frame or wheels in heavy traffic could ...............well, I think you get the picture.
 

Radical Brad

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Yes, as others have said, the only 2 problems you ARE going to face are with the front wheels.
Radial spokes "may" hold up, but only if you weigh less than ~160 pounds, and don't race around the corners.

But anything less than 14mm axles will NOT cut it. This is certain.

The rest is looking good. Run a nice hot bead on your boom joint to get that flux out, and you are good to go.

Brad
 
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Ooops ?

I can't see any form of brakes on those front wheels ?

The trike needs brakes on the front wheels either disc or cantilever or even side pull.

If you put a brake on the rear wheel it should only be used as a drag brake if heavily loaded or a parking brake....
 
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Thanks for the tips and help. The wheels are the normal axles. They will be coming off. I have more gringing and cutting to do.
When I get some more welding wire, I will put a good weld bead around the axle joint to make sure it is strong.
Wheels. They are 72 radial spokes. They came off a stunt bmx. I bought the bmx off ebay as it had the stunt pegs on and I thought it would have the 14mm axles. I have two 24" rear wheels from a tricycle to go on. They go on a 13.5mm axle. I have to buy some bearings which are 35 x 16. I have a tow bar drop plate which I will cut and weld a towbar bolt to it for the axle. Waiting for the bolts to arrive in the post. It will be a 16mm axle.
Thewheels that are on are not true to the vertical but the new set up will be.
Brakes. I will be welding small L shape box section to the steering so it comes from level with the axle and out along thew wheel where I will put calliper brakes.
 
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