Pusher trailer build

[izpirkt]

I'm finally getting started documenting my electric pusher trailer build. I'm doing this for a thesis project for a design degree. I want to promote the vast amount of information and expertise that are on DIY forums like this one.

Since this is for a design project, I am not just building something that I will be able to use, but want a product with production potential that anyone, with experience or not, can use. I need to design a product for a user with less technical knowledge and tools than you guys here. I am thinking that it needs to be like an accessory that did not significantly change the bike itself. Something that will come off of the bike when you want to ride it yourself. For instance, on a mountain bike you don't necessarily want a 10lb motor unsprung in the front wheel when you are out popping roots. On a road bike, you may want the assistance for a commute to work, but then remove it for some exercise or training on the weekends.

The result of this narrowing of focus leads me to an electric pusher trailer. Pusher trailers have been around for a long time as a concept, and there are an amazing number, variety, and quality of builds on this site. However, there are few electric trailers on the market. They have never really caught on, and I think this is due to a focus on the die-hard cyclist, and not the general public that own an underutilized bike.

As far as geometry, I have seen some that attach to the seat post, but this may not be the best geometry. The closer the connection of the trailer is to the contact patch of the rear wheel, the less disturbing the mass is to deal with. There are a couple of trailers I've seen that attached to the lugs on both sides, but they were long cargo trailers. This would make city/campus/parking more difficult. I am leaning toward an extrawheel trailer. I am going to combine the lug mounted style with a hub motor to take advantage of the dynamics, and short length, and simple implementation.

 

[Rassy]

izpirkt, good luck with your trailer build. I think my total number of pusher trailers is about 10, some two wheel and some one wheel. All the one wheel trailers were connected to the bike with a BOB hitch, whether the trailer was an actual BOB trailer or not.

I found that for pushing my bike, a LWB recumbent, the shorter the trailer the twichier (is that a word?), it got. Even with the weight held down low, the trailer would make the bike unstable. The best pushers for a bike were either two wheel (i.e. two hub motors) trailers or long trailers such as a regular BOB trailer. I think the two wheel trailers worked good because they weren't affected much by the slight side to side motion created as the bike was pedaled and balanced.

I don't use any pusher trailers anymore because I'm so happy with my mid-drive that allows the motor to use the eight gears in the IGH. The mid-drive with the gears has eliminated all problems with hills, at least to 20% grade. I do use my BOB trailer in stock form to carry cargo when needed.

 

[izpirkt]

Rassy,
Thank you for that input. I'll be looking out for that "twichiness". The intention of my first build is to test the dynamics of the trailer. I expect to have to go through several rounds of re-building. I wonder if a collapsible trailer is possible. Extend to a long wheelbase while in use to smooth it out, and then collapse or fold to make fitting into a bike rack and locking up easier.

I have a pile of parts that I have scored from various sources. I found a 400w hub motor and controller:

I also just got a big pile of DeWalt batteries:

and for those, I need to solder up some BMS interface boards from kfong:

 

[izpirkt]

I also scavenged some dead bikes around campus to use for parts:

I'll get some images up soon of what I am planning to do with this mess of parts in my garage.

 

[Lock]

Pusher trailers have been around for a long time...

Just something fun for your files then... Bernardi, 1893:

LocK

 

[bctriker]

Here's my E-BOB.....crystalyte front hub laced into a 16" 50-305 Schwalbe Big Apple, EZEE 36V 9.6ah Lithium Ion batt and a 25a controller...........Sweet Ride, coupled with my Catrike Trail

 

[izpirkt]

Thanks for the pictures guys. The 1893 picture looks like a steam powered friction drive. Betcha that was loud.

Here's my E-BOB..

bctriker,that looks like a lot of fun! Was the e-BOB purchased, or built by you? The yoke on the front of the trailer seems to be built for a larger wheel, does this affect handling with the pivot further back? only the throttle and wiring are on the bike, right, the rest of the components are on the trailer?

 

[izpirkt]

I soldered up one of the boards from kfong, and went to test out all of the parts I got from ebay. The components are off of an old ebike called a "callisto" There is a 36V controller (brushed) and throttle. I can't find any information about it, and all of the parts are potted. It has a 31V LVC, which is turning out to cause problems. The motor is a Heinzman. From what I have heard, it is a really reliable brushed, geared motor.

I completed one board first because I wanted to see if it worked, and wanted to test out the controller and motor which I have never seen work. I hooked everything up, and the wheel actually turned!

It was really quiet, and hit about 200rpm unloaded. I think this is about 15 mph according to this chart: http://endless-sphere.com/forums/viewtopic.php?f=28&t=16114

The controller is turning out to be an issue because it is expecting SLA voltages. A 36V SLA battery bank will read well above 36 when fully charged, correct? The fully charged DeWalt batteries are only reading 33V at full charge, and when I spin up the motor, they drop to 31 pretty quickly. Therefore the charge meter on the throttle reads low and the controller cuts off the supply after a few seconds. As far as I know the DeWalt batteries can go as low as 24V without damage, so I have a ton of unused potential. I went ahead and finished the rest of the boards, and tried two batteries in parallel. It improved the time the wheel would spin, but still under a minute.

So, do I get another controller, or find some SLA batteries? What do I look for in a brushed motor controller? is reliability an issue? How do I hook up my throttle with the 6 or so wires?

 

[izpirkt]

I still haven't figured out the LVC issue with the controller. I did finally get 4 batteries in parallel, and it will run longer, but with any real torque on the wheel, the controller will trip. Any ideas on how to change the cutoff, or are there brushed controllers out there without one?

 

[jimw1960]

Sounds like you have two choices for the controller: (1) just buy a new one (36 v brushed motor controllers are fairly cheap) and hope it doesn't have the same low voltage cutoff problem; or (2) dig out all the potting and post some pictures; brushed controllers are not very complicated and should just be a matter of changing some resistance somewhere.

 

[izpirkt]

I ordered a brushless motor and controller from Cycle9. They came in last week.

It came with a 25A infineon controller that has a direct connection to a Cycle Analyst. I thought that the cycle analyst could change the LVC of the controller, but even if I set the CA to a 25V cutoff, when I load the motor, the controller will cut out. It is only pulling 4 amps, and I can't see the voltage sag b The BMS in the DeWalts are not tripping, so the only thing I can think of is the LVC on the controller.

How have you guys with the DeWalts dealt with this? the 33V max charge on the batteries is killing me.

 

[izpirkt]

I quick probe with the dremel tells me that removing the potting is not going to be possible. It is about an inch thick of metal-hard epoxy.

I don't know anything about controllers. If I google "36V brushed controller", I get some chinese options (http://www.virtualvillage.com/36v-5....html?utm_source=googlebase&utm_medium=shcomp), some robotic's options (http://www.pololu.com/catalog/product/760). What am I looking for other than 36V and reasonable amperage? Do most have an LVC, or not?

 

[jimw1960]

You can get one from electricrider.com here: http://www.electricrider.com/crystalyte/x-ct3625sd.htm

It could still have the same problem, though, since it is a 36v controller. Maybe a 24 volt controller would get you around the LVC problem on the 36 V controllers.

 

[jimw1960]

electricscooterparts.com has a variable voltage controller for 24 to 60 volt operation that does not have any LVC. http://electricscooterparts.com/hookup/SPD-601000Awiring.htm
Though it doesn't say specifically if it is for a brushed moter, I assume it is because it only has two wires going to the motor. You could call and ask.

 

[izpirkt]

electricscooterparts.com has a variable voltage controller for 24 to 60 volt operation that does not have any LVC. http://electricscooterparts.com/hookup/SPD-601000Awiring.htm
Though it doesn't say specifically if it is for a brushed moter, I assume it is because it only has two wires going to the motor. You could call and ask.

Excellent. Thank you. It is hard to find some of these sites if you don't know where to look. This never came up on Google.

 

[izpirkt]

The 24-60V controller seemed like it would solve my LVC problems, so I ordered one. I set it up on the workbench, and hooked up all 4 batteries.

high res link: http://www.flickr.com/photos/59120715@N02/5489106620/

I turned the throttle, and all I got was a blip at about mid twist. I tried again with a slow twist, and got a "groan" or "hum" after about 20 degrees of twist, and then nothing. The Cycle Analyst screen went blank. I let off the throttle, and the CA came back on. It seems like the BMS on the batteries is cutting out. I tried again, just barely twisting past the first hum, and with very careful increases, got the motor to spin all the way up. The active portion of the throttle is only about 20 percent, near the middle of the twist. It hums for about the first half of the active portion, and then quiets. The humming seems to be coming from the hub motor itself, and the inductor that is in between the batteries and controller.

The peak amperage on the CA reads just under 18 amps. This is seems to come right at the first power delivery to the motor. I should be able to get 80 amps out of the 4 batteries in parallel, so I don't know why they are cutting out.

Any ideas? bigger inductor?

 

[kfong]

It sounds like you are getting voltage spikes back into the Dewalts. They shut down when they see any abnormal spikes or current draw and need to be reset. Try winding more wires through that inductor to increase it's value. You can also add another one on the negative wire. The photo is hard to see. I'm not able to verify your wiring setup due to the resolution.

Looking forward to the pusher build, I've thought of building something similar to exend my range. I hate the idea of having to drive to the trails just to ride my ebike. A pusher would solve that problem for me, just lock it up once I get there. It would also be a great way to carry extra gear or groceries.

 

[izpirkt]

That photo was supposed to be a link to a high res version. Let's try this:

http://www.flickr.com/photos/59120715@N02/5489106620/

 

[izpirkt]

I think I figured it out. I had been using the BMS interface boards without the spacer that kfong sent along with them. This spacer puts force onto the PCB to make sure it stays against the contacts in the battery. The batteries would work without the spacer, sending a readable voltage. I thought the spacers were just there to prevent vibration loosening during road use, and would not be needed on the bench. However it seems that it is not just vibration that the spacers help with. I must have been pulling voltage out of only one activated BMS, (hence 20 amps) leaving the others to cut off on their own.

So, with the spacers, I am not getting any blips, and managed to pull 50 amps! I can twist the throttle without having to nurse it along. Yeah! Now I've got some torque to play with!

 

[izpirkt]

Shoulda done it like kfong said in the first place!

 

[kfong]

Yeah, you definitely need the spacers. Without them they don't push up against the contacts. Very important to have.

 

[izpirkt]

So, in addition to the electronics portion of this build, I have also been working on hardware. I wanted to make a very short trailer, basically just a wheel. There was a caution from Rassy about short trailers being twitchy. I welded up an ugly prototype so that I could pull it around and feel some of the dynamics.

I started with a plate that clamps under the rear quick release on both sides of the bike. I needed an additional screw into the frame to prevent rotation of this plate. There is a weld nut on the plate to receive a bolt that will retain the trailer.

The trailer itself is a mash up of random donor bike parts. I've got the rear frame off of a cheap suspension bike, a head tube, and a set of forks. I stuck an old rear wheel in it so I would not have to risk my hub motor in case of major failure. It can move up and down by rotating around the bolts on the plate on the bike. It can rotate side to side on the head tube axis (between the green and gray colored parts)

The trailer followed smoothly and was unnoticeable most of the time. It came right behind me through tight turns and up and down curbs. Originally the tire was at full pressure, and I could feel it bouncing over every sidewalk joint. I couldn't feel much through the bike, but there was an annoying jolt I could feel through the handlebars. I stopped and let a significant amount of air out of the tire, such that I could deform it easily with my thumb. This really improved the bouncing, such that you could forget it was there. I think the whole setup might weigh 10 pounds.

Boy did I get some strange looks pulling up to a stoplight with this contraption hanging off the back of the bike!

 

[izpirkt]

I do have a couple of concerns about this setup. One is the fact that the trailer will probably behave differently with a significant load on it. The other is that at high speed when the trailer hit a bump it would fishtail a bit. When it landed it would snap back into place with a pretty good thump. When you watch the videos about the extrawheel, it is bouncing and twisting the whole time.

http://www.youtube.com/watch?feature=player_detailpage&v=6ijnEr1kn98

It seems that these trailers have been pretty well thrash tested, and come through all right. I need to test how they will react when powered. Is the bouncing going to really diminish their usefulness as a pusher?

I really like the idea of a short trailer because it will store and park much more easily. I hope to be able to get the wheel to fold up next to the rear wheel of the bike so that it can easily be chained. I'm wondering if an extendable frame would be the answer to this. It can be extended for use, and more capacity, and then compressed for parking and storage.

 

[Rassy]

Nice job on the test trailer. Be sure to make the adjustable frame pretty ridgid.

The old BOB trailer pictured below made a good pusher. This model with the 2 foot long Action Packer tote only got a little squirelly at speeds over 20 MPH or if heavy items were attached on top of the tote. (this was an actual BOB model with the tote, but I never could find any info on it. I cut the original fork off and replaced it with one from an old bike to accomodate a motor)

 

[izpirkt]

I did some welding this weekend, and attached two platforms to the sides of the trailer fork. These will support the batteries, to be bungied on top for now. Eventually they will hang underneath the platform, and it will be a shelf for carrying whatever load I need. I decided to invert the fork (mount it on the low side) to keep the mass as low as possible.

My first test run was today. I got the controller strapped on, batteries wired, and bolted the contraption onto the bike. I started with the 26" brushed geared Heinzman wheel, and took a couple of laps of the driveway. I found that over 10mph, the trailer would wag back and forth pretty severely. I could hear the trailer-bike connection rattling as the side to side motion translated to front to back motion on the connecting bolts. I added a couple of spacers and cinched it down tight on both sides. This removed the front to back play, but the joint would still turn to allow for pitch changes. There was a vast improvement in stability. However I could stand next to the bike and when I grabbed the seat and shook side to side, the wheel itself had play that contributes to the wobble.

I took it out on the road, and there was instant smilage! there is nothing like the feeling of a light pedal speeding you up a hill. The bike was steady at 15mph on flats, and would slow to 12 up hill, but I was pushing 750W if I did not pedal. The motor did not heat up to more than warm. There was more noise than I had hoped. It was like a big model airplane following me around.

I then swapped out the wheel for the 20" brushless.

This motor is dead silent. It does not have as much torque, but seems to be able to hit similar speeds. The silence is amazing. The smaller wheel seems to be more stable. Possibly since the weight is 3" closer to the ground, and the wheel is a lot stiffer side to side.

I'm considering whether to make the effort to make a trailer that is 6" shorter for the small wheel. I want something as compact as possible, but still stable.