Awesome idea for an e-pusher using part of BOB trailer

I was looking closely at how my Bob trailer is put together and I had a EUREKA moment, seeing a loose stem lying around.

a.) Removed most of BOB trailer from the fork attachment, by undoing the two bolts which hold the Bob platform to the Bob fork attachment, leaving the following part (which can be bought separately from the BOB people) as standalone, attached to BOB Nutz on my axles:

http://www.bobgear.com/accessories/accessory_popup.php?accessories_id=19

b.) The vertical piece of one inch steel rod at the very back is perfect to attach a quill stem (so it can still swivel - not too tight) as though it were a handlebar, leaving the quill part pointing backwards, away from the bike. If you attach a fork directly to the quill, and tighten it right up you have a backward facing fork ready to accept a front hub motor. You can put a pipe clamp around the vertical, under the stem surround to prevent slippage down, if the stem is loose around the vertical. So, you have 2 degrees of freedom of movement of the fork - up and down with the BOB part, and right and left turning, with the stem. Perfect. No rotational movement/twisting along the axis of the pusher which is undesirable.

This is very easy - I built the pusher in about 20 minutes - at least the basic idea. I tested it and it trailed great, and really sturdy. So now I just need to add the hub motor. The axis of the fork is level with the ground about 10 inches above the ground. The longer the quill, the further the e-wheel will be from the bike. Of course people have done this with the whole Bob trailer itself, which is good for carrying batteries, but I wanted a minimal pusher.

I was impressed by the simplicity of this idea and will be engaged in building and testing it, with a 20" geared brushed with Ping battery that I have.

Of course you would have to buy the part from the Bob people and the Bob nutz too. I made some Bob hitch pins myself.

Here is the final product:

View attachment Pusher.JPG

Cool idea, except, you may not have enough traction for hill climbing. As long as most of your rides are on fairly flat and smooth surfaces it might work. Even as I write this, it seems that if you were accelerating while turning and leaning there would be even less weight on the "patch" with centrifugal force also trying to swing the wheel out.

Good luck with your tests. Let us know how it works out, and show a picture of the completed setup.

Thanks Rassy. Food for thought. Perhaps I will need to get a longer quill and fashion a platform for the battery itself, to get more traction...oh wait! That's a Bob.
Hmm. I'll report back when its done.

fashion a platform for the battery itself, to get more traction...oh wait! That's a Bob.

Click to expand...

Hi Chvidgov. Your "BOB Fork Pusher Trailer" intrigued me more than I realized. I woke up this morning with possible solutions to what I consider the two problem areas. I have already decided to try one myself, since in addition to my two BOB trailers, I also have two new BOB forks hanging on the wall. Long story, don't ask.

For weight/traction issues I thought about the hitches used for travel trailers that distribute some vehicle weight to the trailer. To accomplish this I would attach a short length of (1") angle in a vertical position just ahead of the bike axle, using two u-bolts on the bikes rear triangle frame. This angle would hang below the axle level by a couple of inches. Then do the same thing on the BOB fork. Then attach a spring between these two angles, using eye bolts on each end. Now with the right spring and right tension you could transfer as much weight as desired from the rear wheel of the bike to the trailer wheel (and front wheel of the bike) In fact with enough tension you could lift the rear wheel off the ground. This would only have to be done on the left hand side.

Edit again: Don't even read the next paragraph. I didn't understand the initial post concerning the quill fork.
Edit: This paragraph is being redone, after looking at a stem:
For attaching the 20" fork to the BOB tube I would first cut off the stem so it all fit inside the tube. Then replace the original bolt with a threaded rod (or a slightly smaller diameter threaded bolt with the head down). Use a washer on the cut off end of the stem and a nut to tighten the sliding clamp within the fork. This can be done before the fork is inserted into the BOB tube. Then just add a large washer to the top of the tube and secure to an appropriate tension with a nylock nut. Hack off the extra part of the threaded rod (or not if you used the right length upside down bolt) and you're done.

Edit: I'm also thinking you could add a regular rear rack. You could attach the front of the rack to a bracket from the area where brakes are normally attached, and the rack would move with the fork. With a rack bag for the battery and panniers to cover the motor it would look like a pack mule. With a real quiet direct drive hub motor this would be a real stealthy rig.

I have thought about different push trailer arrangements, but I can't figure out what is meant by "quill stem". Is there any chance either of you could make a sketch?

Rassy, I thought about the load leveler arrangement too. An important feature on the 4 wheel implementation is that the tow vehicle has a suspension. There is a limited amount of weight I'd want to take off of the back tire. A better traction solution might be more batteries or cargo over the trailer tire.

That Bob trailer fork with the Bob Nutz is an attractive ready-made solution for hooking the trailer to the bicycle.

I tried my first trailer over at this thread: My project at mid-completion: It works! and I think the bob push trailer is a great way to power a bike! I can't wait to hear more about the ideas in this thread.

I didn't know what "quill" stem meant either, so I just googled it and it was just a standard stem with the 4 bolt handlebar attachment that BMX bikes use. They had a good picture of a stem which jogged my memory of how they work. I'm going to go edit my previous post concerning the steps required to attach a threaded rod to a fork.

Right about taking too much weight off the back wheel, but with a good adjustable spring you should be able to dial it in for just a few pounds, maybe using a scale under the rear tire to see what you are actually doing.

All of my experience with BOB trailers starts over today. I'll soon be 70 and I've decided to give up my two-wheel recumbent. My new Terratrike tadpole with an internal Nexus 8 speed just arrived at my house. I have a regular BOB Yak set up with a Bafang in a 16" wheel that will probably get me up the 20% grade on my driveway. I also have a 20" BD36 in an old style BOB (see my avatar) with a modified fork, but I want something shorter and quiet when I ride with pedal only guys. I've considered Matt's dual reduction system and a Bafang set up sort of like a Stoke Monkey, but I think this "BOB Fork Pusher Trailer" might be just the ticket. I'll start my own build thread when I get started on this project.

some pictures would really help understand what you guys mean. i had some ideas too about the active suspension idea. i don't have a bob trailer though so no fork to analyze.

Thanks for the quill stem clarification, I feel foolish for not having Googled it. That's a great use of easy to get parts chvidgov.bc.ca.

Another simple Ebob would be to use the Bob forks with a rear suspension piece turned upside down. You could drill out the straight tube (that holds the front derailleur) and use it as the pivot. That might give a little more structure to work with for a battery carrier.

chvidgov.bc.ca I think you've tapped a rich vein with your original post.

Here's a picture of a BOB fork with the tube just resting on a bucket.

Hi Guys...sorry for the confusion on the quill stem, should have explained what it was. Anyways, just the quill stem is all you need with the Bob fork attachment, to connect the fork of the e-wheel. And the force of the e-wheel is pushing them together in operation. The stem could go into a 1 1/8 chromoly pipe instead, and then perhaps the fork could be welded to that for a longer platform. In other words, the longer the fork steerer is, the longer the trailer would be. So you could build different ones for different purposes. I'm also thinking that there are existing canti-posts on the fork which could be used as attachment points for a battery platform. You have three points, those two posts and the bolt hole in the fork crown. That's a good starting point. Perhaps a drilled hole in the steerer/quill assembly could provide another attachment point and make the quill wedge solution fail safe. Anyways, just brainstorming. I will be fooling with this some more, and I've got the eparts for it on hand.

I don't suppose it would be an issue that the force of the e-wheel would be concentrated on the Bob-Nutz pins holding the fork assembly onto the Bob-Nutz...

Chris

Okay, now I get it, I think. Would like to see a picture of your first effort. I thought the bike fork stuck into the bottom of the BOB tube, so all my above stuff is pretty much BS. Remember, I am really old and really really slow.

When you apply power to the trailer wheel, it will try to lift the back wheel of the bike up (which is what puts pressure on the BOB pins), and that same force will try to lift the quill up, so you may need to fix your desired position for the quill with some sort of clamp under it and above it.

When I made my first BOB pusher trailer I worried that the pins might not be able to take it, but they are strong stainless steel, and none have ever shown any problems.

Wow,I'm going outside right now to look at my BOB trailer. I'll be following this thread with interest. I've been thinking of a pusher trailer for a while. I'd love to see something that would just hook up to any old bike to give people the feel of ebiking without any mods to their bike. Talk about the perfect mousetrap...

Yes...the fork is not stuck into the Bob Trailer fork tube. The stem grabs the vertical tube, somewhere in the middle of the tube, with pipe clamps around the tube, above and below the stem, and the wedge of the stem "gloms onto" the inside of the fork steerer when the stem bolt is tightened.

I like the idea, but be aware that intially it might not have much traction. This is one application where having heavy SLA batteries (on either side of the wheel?) would be a benefit. Can't wait for pics...

edit: Looks good! Its been added to the "push trailer revisted" list. http://endless-sphere.com/forums/viewtopic.php?f=7&t=13995

Success! I had an extra long stem cut from the folding stem of a parts-bike I had, about two feet long, and attached it to the vertical of the Bob fork. I put two bolts through the 20 inch fork (inserted inside stem assembly) and stem at the trailing end, and attached a P2A brushed geared motor with Ecrazoid 48V 500 watt controller and battery, with a longer throttle line to the fork, with torque arms. Tested motor, ran.

I found an old piece of 1/2 inch round lightweight steel tubing pre-bent in a triangle, from the back of an old office chair, and drilled holes in the two ends which screwed nicely onto the brake posts of the fork and formed a triangular platform, rather strong forward of the wheel, with another bolt through it and the stem. This is a very good start on a strong platform, and I velcroed on a big Nicad pack about 15 pounds onto the triangular platform with self-adhering velcro.

Ready to ride, I cautiously went out on the street and started off with the e-pusher. It ran great with no particular handling issues. I wasn't surprised, as it is shorter than a regular Bob trailer on it, and has more weight, and the BOB is known to work itself as an e-pusher, particular with the weight low to the ground and as far forward as possible. I took it up to about 20 mph, and then kicked in my <other> motor and boosted to about 30 mph. Not bad for a twenty inch wheeler, Giant Revive. Good enough for a first test! Overall, I would say that the whole assembly is close to thirty-five? pounds 10 for motor, 15 for battery, and about 10 for fork, platform bolts and stem/fork attachment, and that seems to confer enough traction in general - no fish-tailing was observed on cornering. Went up some small hills in the neighbourhood. I will send a picture tomorrow - company's coming.

So I just need to work on fixing a nice aesthetic basket for the platform, although just having the battery pack and controller would be fine. Something in wicker from Chinatown.

And its easy to get your <normal> bike back. Which happens to be an ebike!

Using a regular, short stem, would put the e-wheel rim only about 15 inches from the back of the regular bike wheel rim, so the config would be shorter, with less room for a platform for batteries.

On further thought I have come to the conclusion that a bike quill stem, say on a junked bmx, is a wonderful universally available throwaway "connector" enabling flexible assembly of steel tubing and bicycle forks in various combinations. It's not hard to envision making a two wheeled model of trailer this way, using two stem/fork combos attached to a long "handlebar" which forms the end of a two wheeled bike trailer platform. This notion would seem to better than a lot of existing "instructables" on how to make a bike trailer, which grapple with the issue of attaching the wheels to the platform. I'm going to see if I can make a two wheeled cargo trailer for under 20 bucks with recycled forks and stems and some scrap handlebars, with no welding involved.

And yes, I did enjoy tinker toys when I was a kid

On further testing, I discovered an issue with handling, in that when the bike is standing still, if I turn very sharply, the front of the trailer, where the stem is attached to the Bob fork attachment tends to dive to the floor, especially with a Ping 15Ahr on the "platform", on which I have affixed a basket. I'm hoping this isn't a major issue at speed on turning, I will have to test it some more. I found that if I put a rope from my bike rack to the top of the Bob vertical post and snugged it up enough, turning was still enabled, but it prevented this diving behaviour. I imagine this a problem with most single wheel trailers though.

spinningmagnets said:

I like the idea, but be aware that intially it might not have much traction. This is one application where having heavy SLA batteries (on either side of the wheel?) would be a benefit. Can't wait for pics...

edit: Looks good! Its been added to the "push trailer revisted" list. http://endless-sphere.com/forums/viewtopic.php?f=7&t=13995

Click to expand...

I experienced a considerable lack of traction when I went from SLA to LIPO on my pusher trailer. It was most noticeable in the tire wear. I put my pusher build to rest when I only got about 150 miles out a new tire.

Bubba

Yes, I went for a ride yesterday in wet conditions, and noted a considerable wheel spin/non-traction on a hilly section. So this implies that putting the batteries on the bike is not a good idea, unless there is lots of cargo on the pusher. If you have cargo then you would need to move the battery to the bike to create room. Or put the cargo on the bike and leave the battery on the pusher. So, I am seeing some of the tradeoffs with this idea now.

Been out of town since last Tuesday, but did go to a Goodwill store in Eugene, Oregon. They had a lot of bikes, but their bike selection was poor. Found a child's 16" with a four bolt quill stem and a 20" for the fork. The four bolt cap was for a 7/8" handlebar, but it was alloy so I was able to file it out to fit the 1" BOB tube.

Here's a picture of the forks bolted together with one of my BD36's. Thanks again chvidgov for the idea.

Edit: I have started my own build thread here:
http://www.endless-sphere.com/forums/viewtopic.php?f=6&t=14106

How's the handling on your creation, Rassy? That is exactly what I had in mind for a shorter pusher using a stem/fork combo. I imagine you will be putting a rack over the wheel?

It will be a while until I get to a road test. It's wet and windy here on the Oregon coast this week. Instead of a rack on top, my first test will be with a 20AH LiFePO4 over the fork between the trailer wheel and the BOB post. See my link in my previous post for more details as I get to them. Because I'm using a tadpole trike instead of a bike I don't expect any stability issues, unless it falls apart.

It should work well on the trike. Between your recumbent, bob trailer and pusher, all of which I also have (Sun Ez CX for me), and the wet weather here in Victoria, I think we we are on parallel trajectories. I will probably need a trike in about 15 years too judging from my new "neck crick"! Good luck!

I love that idea too. I was thinkin' maybe pedelec would help keep the motor more in sync and help reduce wheel spin? Has anyone used a BOB trailer behind a bike with a rear hub motor? I'd like to use a BOB pusher to help with hills. I'm looking at trikes for the same reason(neck problems). So thanks for being the test pilot.

Rassy: How do you like the new tadpole trike compared to the older delta trike design? (hope i'm not taking this too far off track :? )

I was thinking of a delta trike from http://www.lightfootcycles.com because of the great storage capacity and their straightforeward engineering approach. Mounting a hub motor to the rear wheel would be easy on these trikes, no stub axle to worry about.