Instructables

Failed attempt at a tow bar for child's bicycle

Picture of Failed attempt at a tow bar for child's bicycle
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My daughter has been riding her two wheeler for close to a year, now.  She has a healthy trepidation about riding on, or crossing, "big streets;" and several of her friends have those overpriced "towing wheel" cycles (see the second picture).  The kind that can't be used for anything at all if they aren't attached to a grown-up's bike.  Well, she wants a towing bike, too. 

I'm not about to drop $300 when she has a perfectly usable bike already.  Instead, I tried to build a towing rig that can attach to both of our bikes, and can also detach, leaving both bikes fully operational.

DISCLAIMER This project did not work as intended. The trailing bike is not stable when towed, and falls to the side very easily, even without a rider. I have documented my work for completeness, but the device described here is not safe for use.

I do intend to keep working on this, and try to find a way to reduce the swivel and sway to make it safe and rideable. If I succeed, I'll update this Instructable accordingly.

Update: It turns out that there's an instructable which discusses modifying a commercial product that does exactly what I'm trying to do here. I need to study that I'ble more, to see if it can help me with my issues here.

 
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kelseymh (author) 1 year ago
UPDATE: Modified some of the steps today (6 September 2013) to reflect further attempts at making the project successful. They didn't work, but I've documented them here, replacing some of the previous pictures and parts items.
Lithium Rain10 months ago
I wonder if placing an additional "extension" of the tow bar higher up on the child's bicycle would help with stabilization? And/or shorting the length closest to the adult bike, placing the "bend" much closer (as in the commercial products).

Probably dumb suggestions since you're the physicist. :P
Maxus_Lu1 year ago
The idea is great and cost-effective.
I think to remove instability it is highly necessary to take the front wheel of the kid's bike OFF the road. It should be hanging in the air. Otherwise it will aim to move in it's own direction wile towed, being then thrusted downwards if the direction of the Kid's bike differs from the towing one.
Or you have to tow the front wheel itself, giving/dictating it the direction of movement. Something like in openproducts's picture.
And there was an instructable here somewhere with the sort of hanging bike-stand for the front wheel, that was attached to the adult's bike rear frame triangle and axis.
gav4god1 year ago
Have you tried attaching your trailing arm to the axels of the towed bike?
That should stabilize it and steer it as well.
wb8nbs1 year ago
I once made a two wheel trailer for my bike This required a flexible joint just under the seat. I used a steel plate welded to the seat, and a double strip of rubber cut from a tire tread attached to the trailer tongue. The rubber attached to the steel plate with a single bolt loose enough so the trailer could swing to either side in a turn. The rubber flexed enough to allow the bike to lean. Woked well. Put hundreds of miles on it with my 4year old son in the trailer.
kelseymh (author)  wb8nbs1 year ago
Yes, indeed! For a two-wheel (side-by-side) trailer, the flexible joint is critical. The trailer can't tilt to accommodate turns, ramps, bumps, etc., so you need some kind of swivel joint at the lead end.

The problem I've got is that for pulling a regular bicycle, that flex joint introduces too many degrees of freedom: the tow bar swings, the trailing bike fishtails, and my daughter gets a skinned knee or worse :-(
Lorddrake1 year ago
I think i see the problem in your design.

If you look at the store bought version there is no front wheel on it. it basically makes the back wheel of the parent's bike into the front wheel for the kids bike. In that way the kids bike will lean into the turns correctly and follow the progression of the parent's bike.

in your design you have the front wheel on the ground and the tow bar attached to the fork.
I think that if you were to elevate the front of the kids bike just enough to get the front wheel off of the ground and attach the towbar to the neck instead of the fork it would work better.
although you may need to redesign your articulation at the seatpost for better range of motion.

kelseymh (author)  Lorddrake1 year ago
Yup. I tried two different modifications: Raising the front wheel (by supporting the towbar on my end), and by using training wheels. In both cases the underlying issue raised its head: the friction of the "clamp" holding the towbar onto the neck of the trailing bike was not enough to overcome the torque from the rear wheel. The trailing bike would start to fishtail, and combined with the angle of the fork, would tip to the side and flop over.

I recently stumbled across a commercial product (the Trail-Gator) which does exactly what you describe: it lifts the front wheel up off the ground, with rigid clamps at both the lead and trailing bike. The few bad reviews it has on Amazon describe the same problem: fishtailing, with slippage at the clamp, and the trailing bike falling over.
Nice Instructable, thanks kelseymh for sharing your experiences. And a great discussion in the comments. It inspired me to test an idea I had on the shelf. Towing a child's bicycle should be possible by using its front wheel as a connector piece. The experiment turned out worse than I expected: the child would be thrown off its bike in the first curve. Read more on this unsuccessful proof of concept and the suggestions for further work in my Instructable 'Failed Project: Tow Child's Bicycle'.
Openproducts_-_bike_connector_failed_project.jpg
If she knows how to ride, I don't see the reason for the tow bar, tbh. But if she is set on being towed:
Why not install training wheels for more stability, and make a handle bar lock, so she can't steer, but can still hold on? (Im thinking a mix between an old steering wheel lock, and a bolt and eyelet lock).
kelseymh (author)  HelmutHound1 year ago
I tried the training wheels idea this morning; it didn't work. The trailing bike stayed upright for much longer, but still ended up flopping over. It appeared to me that it got "pulled" by the tow bar, so the next thing I want to do is replace the galvanized pipe with thin-wall conduit (EMT), which is much lighter in weight than pipe.
kelseymh (author)  HelmutHound1 year ago
Don't get me started :-) She can ride very well. However, crossing the "really big streets" (two or three lanes each way, traffic lights, multiple cars making left and right turns, etc.) is very intimidating. My expectation is that once we've done the tow-bar thing for a few months, she'll be "desensitized" to the traffic and better able to handle it on her on.

...Training wheels. Why didn't I think of that?!? That's probably just the right answer. They keep the back of the bike from flopping over; that's what they're designed to do. We still have her old ones, sitting in my "box 'o' stuff".
Kiteman1 year ago
I'd be tempted to extend the angled bar (currently 18" long), so that it can be clamped along the angled cross bars of the smaller bike's frame.

I might also be tempted to remove the front wheel.

The challenge would be to come up with a way to clamp bar rigidly to bike, yet also allowing quick removal once you're off the Big Road With Scary Cars.
kelseymh (author)  Kiteman1 year ago
You've hit exactly the challenge, Kiteman! It's coming up with a way to hold the main frame to the towbar (or somewhere), in such a way that it can't fishtail. Everything else seems to work fine.
Lightbulb!

*Insert* the tow bar!

Drill through the front of the frame, where the badge is, and insert a long rod. Further down the frame, drill through the lower cross-bar, and through the inserted rod.

A pin would then fasten the rod in place, which would, in turn, stop the forks turning. The new challenge is finding a rod stiff enough to work, yet thin enough that drilling the holes through would not weaken the bike too much.
kelseymh (author)  Kiteman1 year ago
I had actually thought of an even simpler version of that -- drill through the neck and stick a clevis pin through the hole. That ties the two telescoped pipes together (the fork and frame) rigidly.

When I started drilling a pilot hole (1/8") into the neck, first I got metal shavings, then I started getting this weird black powder out. So I stopped and investigated.

It turns out that the neck of the bicycle is more complex than that. Handlebars have a height adjustment. This consists of a long bolt which runs from the base of the handlebars all the way down to the bottom of the fork. The bolt is threaded through a heavy "rubber" bung inside the fork, and when you tighten it, the bung in pressed up against the inside of the fork tube. Loosen the bolt, and you can raise or lower the handlebars.

If I had continued drilling, I would have ended up putting a hole through the height-adjustment bolt :-(
:-(
Sketch:
20130822_154442-1.jpg
Oh! Another thought! Why not two bars that could swing out from your bike frame, and attach to her's? I'm thinking of something like a side car, then your only problem would be finding a way to slave her steering to yours! Would that work?
kelseymh (author)  HelmutHound1 year ago
That's a cool idea! Instead of tandem bikes, side-by-side. It's not what I've built, but definitely something to think about. ...I am going to try out putting the training wheels back on, and see if I can tow her bike safely.
Saad19981 year ago
I'd suggest that you should cut off the steering of the small bike and then attach the angled bar
kelseymh (author)  Saad19981 year ago
But that makes the small bike unrideable on its own.
DrRedu1 year ago
Have you tried attaching the bar to your rack with a u-bolt, and mounting the other end to the handlebars. This would lock in the steering, and stabilize both together. IMHO :)
kelseymh (author)  DrRedu1 year ago
Thanks! What I noticed was that the bar and flange on the trailing bike did lock the steering, in the sense that the front wheel and handlebars stayed straight, lined up with the lead bike. It was the rest of the trailing bike (the frame, seat, and rear tire) which pivoted around the front fork.

That's when I added the "handlebar clamp" (step 8) at the bottom of the handle bars. It "worked", in the sense that when I tried to turn the handlebars, they seemed "stuck." But the rest of the bike had enough torque to slip within the "clamp" and flop over.