Commuter Booster - <1kg Friction Drive

[Kepler]

Good idea Hillhater, I will give that a go.

[adrian_sm]

Sounds like its all coming together. The geometry for your setup infront of the seat stays is quite different to the geometry of a setup behind the seat stays like mine. Definitely needs a smaller arc then what I use for my setup.

In relation to end stops, this will work ok and is how I originally did mine. However as Todd pointed out, its all or nothing. Also you will find the drive throws off the tire with quite a force and make a loud clunk every time you throttle off. Not a big deal, just anoying and the stop needs to be quite strong to survive the constant pounding.

Was thinking that the dead stops will have some give. Think metal on rubber, rather than metal on metal.

The damper arrangment solves this issue and has the added benifit of making the contact pressure progressive and as such inproves low throttle efficiency.

My original plan was to lightly spring load the drive against the at rest dead stop. Enough to hopefully stop it bouncing on to the tyre when not in use. But light enough to allow the start torque to pick up the tyre. The spring would then be helping with the progressive pressure pick up... Maybe.

But not sure if this is achievable. Hence mockup it up without the springs, dampening while I get my head around how these work.

However, what I am yet to find is the ideal damper material. All the rubber products I have tested so far have poor rebound memory and tend to get distorted under contant use. I am thinking a silicon rubber damper would be worth trying but havent had any luck finding a supplier of sheet between 10mm and 20mm thick and the right compression properties. If anyone could point me to a possible supplier, it would be much appriciated.

Silcon is good for compression set ~10-20% depending on grade. But has little to no strain rate hardening below 40s^-1. So it will end up just acting as a spring rather than a dampener. Easy to make a little mold to make whatever geometry you want too.

I was thinking more of a little rotary dampener. These work on having a non-newtonian fluid in a small radial gap. Cheap as anything. But dampens an equivalent amount for both engaging and disengaging the motor with the tyre.

An alternative would be a simple linear dampener. Imagine a leaky seal on a syringe, with a one-way bypass valve. This could give very little dampening for engaging with the tyre as the bypass valve allows air flow. Then when the tyre tries to kick the motor out, the valve shuts, the air must then go through the harder leaky valve, which will slow things down.

Heaps of other ways to achieve the same thing. But I sure don't want to have to add extra complexity unless I really need to.

- Adrian

[adrian_sm]

Distracted myself looking in to buying a mill, to make it easier to make the parts I need.
But ended up deciding I should be able to get away with just a drill press and hand tools for now.

In tweaking the geometry of the pivot point and arms I have found that I really need to get the pivot as close to the seat tube as possible, to give the mounting system as much adjustment as possible. This means that the current clamp I have is not suitable. So I thought I might have to make my own.

But I did stumble across these little gems. A couple of these would be ideal to mount the pivot block.
$19 http://www.hfutmpa.com/product_PROBLEM- ... LAMPS.html, or
$19 http://sellerby.com/good_7588_457359832 ... CLAMPS.htm


Or even cheaper.
$5.50 http://www.chainreactioncycles.com/Mode ... odelID=745
$4.10 http://www.wiggle.co.uk/p/cycle/7/DMR_H ... 220000003/


Now i just need to spend a bit more at wiggle to get free shipping

- Adrian

[adrian_sm]

Finally started cutting metal.
- Angle grinder to cut the 10mm plate to size.
- Drill press to make the holes.

Will get the shaft support bearing hole done properly at work.

I'll pretty it up once I do my first dry fit.

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- Adrian

[Kepler]

Well its going to strong being made from 10mm Ali thats for sure. I use 4mm Ali on my swing arms but I do need to make separate flanged bosses to hold the pivot shaft.

[adrian_sm]

Well its going to strong being made from 10mm Ali thats for sure. I use 4mm Ali on my swing arms but I do need to make separate flanged bosses to hold the pivot shaft.

No point skimping on the first prototype.

Update:

One of the annoying things about this build is that the shaft pokes out the wrong side of the motor for my needs.
To move the shaft requires a little bit of effort. For the little TGY AerodriveXp 90 SK Series 50-65 270Kv / 2100W this requires you to:

1 ) Get a replacement shaft with a circlip groove in at the end of the shaft.
Turnigy AerodriveXp 50-65 SK Series Shaft US$5.12
Or machine the groove in the original if you have access to a lathe.

2 ) Remove the circlip & washer

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3 ) Carefully pull the motor apart (note new shaft in centre of image)

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4 ) Measure shaft circlip groove location
- when putting th new shaft in it is important to have this groove in the same location.

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5 ) Undo the two shaft retaining grub screws
- GOTCHA #1: Make sure you remove both grub screws. I forgot and stuffed a motor because of it
- GOTCHA #2: The grub screws on my first motor used metric alan keys, the second motor uses something else.
[EDIT] Correction: it does use a 1.5mm allen key, just make sure it is a good one without crappy rounded edges.

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6 ) Press shaft out
- the shaft has an interfernce fit so will need to be pressed out.
- remember make sure both grub screws out removed, before pressing the shaft out.

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7 ) Press new shaft in to correct location
8 ) Replace grub screws
9 ) Reassemble motor
10 ) Replace circlip with washer

This will put the motor shaft out the other end, which allows the second pivot arm to support the motor via a bearing.

[adrian_sm]

Here is a quick snap of two different motors assembled to one of the pivot arms, prior to adjusting the shaft location. Damn weird grub screws
Sorry about the poor image quality.

The two motors are:
TGY AerodriveXp 90 SK Series 50-65 270Kv / 2100W
HXT 63-74 200kv Brushless Outrunner (Eq:5240)

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[Hillhater]

One of the annoying things about this build is that the shaft pokes out the wrong side of the motor for my needs.
To move the shaft requires a little bit of effort. this requires you to:

1 ) Get a replacement shaft with a circlip groove in at the end of the shaft.
Or machine the groove in the original if you have access to a lathe.
......

OR... you could just forget the circlip all together since this is not a axial loaded application, (like a prop pulling ?)..just supporting the motor .
The grub screws will keep the shaft located in this type of install .

Hey, wow, one mighty clean workmate !

[spinningmagnets]

After I have been cutting and grinding on one of these shafts, I am certain it would not be difficult to cut a new circlip groove where ever you needed. Perhaps put the shaft in a drill-press chuck to spin it slowly, and then hold up a hack-saw blade to the spot where you needed the groove?

Make sure to hold the blade so that if the blade gets grabbed and moved, that it is pulled away from you instead of stabbing your hand. I strongly suggest wearing a glove...I have many scars from when I did not wear a glove.

[adrian_sm]

OR... you could just forget the circlip all together since this is not a axial loaded application, (like a prop pulling ?)..just supporting the motor .
The grub screws will keep the shaft located in this type of install .

I was just worried that if I didn't have the alignment just right, there might be an angle between the motor, and tyre. This could try and drive the motor can axially when loaded up.

After I have been cutting and grinding on one of these shafts, I am certain it would not be difficult to cut a new circlip groove where ever you needed. Perhaps put the shaft in a drill-press chuck to spin it slowly, and then hold up a hack-saw blade to the spot where you needed the groove?

Make sure to hold the blade so that if the blade gets grabbed and moved, that it is pulled away from you instead of stabbing your hand. I strongly suggest wearing a glove...I have many scars from when I did not wear a glove.

Hmmm there's an idea.

You might even be able to just cut the groove without removing the shaft at all. Just bolt the motor down, spin it up, the cut the groove with the hack saw blade...

The main reason I didn't modify the original shaft was that I needed a second shaft for the main pivot anyway. The idea being that you reuse the motor shaft for the main pivot, and then use the new, readily available hobbyking shaft with the groove in the right spot for the motor.

This means anyone copying my design doesn't need to bother modify the shafts. Too easy.

[adrian_sm]

Correction:

The grub screws in the TGY AerodriveXp 90 SK Series 50-65 270Kv / 2100W are metric, and require a 1.5mm allen key.

Just not a crappy old one that has rounded edges.

I'll edit the post above to correct my misleading comment.

[spinningmagnets]

I just checked Fastenal's catalogue, and those shaft grub screws for the 50mm diameter motor are 'likely' to be M3-0.5 threads, since they are using the 1.5mm hex-wrench.
http://www.fastenal.com/web/products/de ... 818&ucst=t

That means if you took it out and wanted to just use a common socket-head bolt with a dab of loctite, the hex-wrench would be a bigger 2.5mm wrench, MUCH better. I don't know if that would cause an out-of-balance condition, so I won't throw away the grub-screw until I see if it works.

I noticed on the new 280-kV motor I just got, that the motor-shell screws (for the skirt bearing) are flush-head hex-sockets instead of the philips-head screws on the 250-kV motor I got a month ago. They use a 2mm hex-wrench. I hope they start using hex-sockets for all their fasteners.

Edit: just pulled out the shaft grub-screws on my Turnigy 63mm motors, the 250-kV and the 280-kV, there are two each, so no out-of-balance issue. The hex-wrench is a 2mm, and the diameter is 3.92mm, so they are likely M4-0.7mm, and could be replaced with cap-bolts that use a 3mm hex-wrench. I will check my local bolt supplier to verify.

[adrian_sm]

Update:

1) Motor Shaft
Photo of the new shaft installed in the correct location.

This will allow the motor to be supported on both sides.
On the mounting side with 4 screws, on the opposite side by a bearing in the pivot arm, supporting the shaft now that it protrudes.

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2) Pivot Arm Bearing
Took that shaft support pivot arm to work to get the bearing mount machined. Still waiting on it.
I might just do it my self, with a 22mm hole saw and some lubricatant on the drill press.
If the size isn't quite right, I'll just loctite it in place.

If that works, the only tools anyone would need to replicate the design would be:
- angle grinder with cut-off disc to cut the aluminium plate to size (or hack saw if you are really patient)
- drill press & drill bits, to drill nice perpendicular holes (or handheld drill if you skills are better than mine)
- screw-drivers, allen keys
- M3 or M4 tap set, for grub screws in pivot arms to pivot shaft.

Next:
- pivot arm bearing mount
- waiting on seat-tube clamps to arrive
- make main pivot block to suit new seat-tube clamps
- sort out dead-stops, and springs
- ....

[spinningmagnets]

adrian_sm, I have recently tried a "nutsert" steel-thread connector, and I am very pleased with them.

I have been tapping threads into aluminum with a large 5-16"-18 tap, but for a smaller hole, I was very nervous, because I have broken taps inside holes that I needed and could not move to another spot. Hillhater reminded me about nutserts, and I tried a 1/4"-20, and it was very easy. Just drill a hole, do a dry fit to see if the location is perfect, then pull it out and use a smear of JB / Devcon epoxy-glue.

http://endless-sphere.com/forums/viewto ... 24#p323450

[adrian_sm]

Nutserts are great for sheet metal. Use them all the time at work. Almost used them on my first ebike to mount the batteries in the frame.

Not sure where you thought they would help on this drive. But I am aiming for a simple easy to install, bolt on type drive. Hence the seat-tube clamps.

The threaded holes I referred to in the previous post, are at right angles to the main pivot shaft for grub screws. This will hopefully keep the two arms aligned with each other. That was one of the reasons I went for 10mm thick plate arms.

- Adrian

[adrian_sm]

Updated CAD while I wait for the new DMR hinged clamps. So I can start planning the main pivot block.

First image is for the small 50-65 motor
Second image is for the bigger 63-74 motor

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[Hillhater]

Have you considered just making the clamp integral to the pivot block as it is looking like a machined part anyway ?
just bore it to suit the downtube dia, (looks like you are half way done anyway ?) .. split it, and use 2 clamp bolts.

[adrian_sm]

Hmmm looking at the CAD image above, I don't know why I don't just do this.
Probably easier, cheaper and stronger than the seperate OEM clamp.

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[adrian_sm]

Have you considered just making the clamp integral to the pivot block as it is looking like a machined part anyway ?
just bore it to suit the downtube dia, (looks like you are half way done anyway ?) .. split it, and use 2 clamp bolts.

Missed your post while I was busy updating cad. Was bloody obvious once I saw it. Hopefully I can find some time this long weekend, an extract myself from the kids long enough to do it.

[adrian_sm]

Amazing what you can get done with a couple of kid free hours in the shed.

Here is the new pivot block.

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[adrian_sm]

And a new side plate for the bearing side.

Note what happens when you guess the drill size for a tapped hole... a broken tap.

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[adrian_sm]

Dimple the shaft to take the torque to align the side plates.

Throw it together, chuck it on the scales..... and ......

707 grams or about 1.5 pounds.

Still need to add a few deadstops etc. But not bad.

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[adrian_sm]

Next step, get it on the bike and spin her up . But ....arrggghhhhh... a major flat and tire failure.
I just rode the bike to work yesterday. Inner tube must have let go, and blown the tire out over night.

Will have to get a new tire tomorrow.

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[spinningmagnets]

I really like your tube-clamp a lot! It would also be useful for battery enclosures, or any other frame-attachment problem. I really appreciate you showing the progression of how to make one, so that the two bolt holes are in perfect alignment. Great work! The design is very elegant and simple.

If someone had an oval or triangulated tube cross-section, you can fill the void with JB or Devcon (putting grease/wax on the frame till it dries, do one half of the clamp one night, the other half the next)

I broke a small drill bit a couple months ago (I have also broken small taps in the past) and based on an Endless-Sphere suggestion I recieved, I put it in boiling water, and the aluminum expanded more than the steel.

[Kepler]

Good work Adrian. Lots to like about your solution. I especially like the low parts count, something i am working really hard on at the moment with my drive.

The clamp looks good. Nice and simple and I really like how the clamp becomes the the pivot bearing. What type of material is it? I wonder how the tapped threads will go in the clamp? Need to put a fair bit of pressure on the clamp to keep it in place so I hope the threads are up to it.I am sure we will soon find out. If they don't hold, you always have the option of making the clamp wider and drilling the clamp hole right through above the pivot shaft then using nuts and bolts.

No road testing in sunny Melbourne today