Mounting Gearbox & Motor Aluminum Frame - Weld? Bond?

Hi,

I am planning to get one of Matt's drives and I think this deserves a separate topic. A 2kw to 5kw motor needs to be mounted very securely.

The possibilities are (if I'm missing something let me know):

• 
  Welding - Is any welding at all acceptable on an aluminum frame or swingarm?
  
  Bonding - is there any kind of bonding process that is strong enough?
  
  Fabricating a mount that is complex enough and fits the frame well enough that bolts or bonding would be secure. The fabrication might be expensive but this should work. Is there an easier solution?

Thanks!

Mitch

Race car roll cage mounting brackets may work. And theres brazing rod for ally to ally.

Are any of the frame tubes on the bike round? Because a solid clamp would be easy to machine out then. Even with a non-round tube, an approximatly shaped clamp could be turned into a precise clamp with some epoxy filler and a frame coated in a mold release agent/film.

my two bits,
Marty

Where do you plan to mount the drive Mitch? I've been keeping an eye on Matt's evolving design but I'm still not sure where it's intended to fit.

I'd suggest a combination of bolts and epoxy. Welding aluminum requires lots of skill. Not many guys are good at it.

Angle-iron makes a reasonable clamp on round and oval tubing. Just u-bolt around it.

Hold On!! I thought we were all in agreement that duct tape was by far the most elegant way to mount EVERYTHING!

I wonder if you got a hold of some carbon fiber clothe and epoxied it like you would fiberglass, it seems like you would have a very strong mount custom fitted to your frame after it dried. Without vacuum bagging it, you might lose strength to air bubbles, maybe two layers would be enough. I mean, if you don't have any duct tape, this could be an alternate.

I know he posted it somewhere, if you had the dimensions for the piece Matt already made, then you could use a block of wood to mock it up while you wait for the drive to arrive.

Hey, maybe thats a good name for Matt's drive:
ARRIVE

Just a thought...

Hi All,

im going to try to clamp mine, wont know exactly how until my bike is home and i have the box in my hand, however
initially im hoping for 2 clamps on the downtube, 1 clamp on the seatpost, but it depends on the rubiks drive flexibility
As far as angle iron brackets and welding go i won't be going anywhere near those for two resons, firstly i want to be able to take the unit off my bike (i have a crazy idea now to make the bike dual usable this time round) and secondly i dont see any other method worthwhile that isnt in keeping with the quality of the box itself? maybe it's just me being overly anal about astethics but to just lash it to the bike seems a bit like putting an engagement diamond on a zip tie to save money on the ring mount? :wink:

cheers,


D

Mitch,

I do not want to dominate your thread. So, hopefully this discussion will remain centered around your build, not another thread about my drive.

Anyway, if this question is purely related to mounting my drive unit, I can offer some advice;

#1 Welding aluminum is fine if it is TIG welded by a professional. I purposely used 6061 for its strength and weldability. I would prefer 7075, but that is not weldable. :wink:

My drive can be mounted with two different methods (tough to describe without a finished drive to show you). Both methods would merely require brackets welded to the frame, not the drive itself. The drive, then, gets mounted to those brackets (again, two different style brackets can be used and will be made by me and stocked).

#2 I am not a big fan of bonding unless there is no other option.

#3 Yes it could be bolted with fabricated brackets. There will be included mounts that should be easy enough to weld to the frame, drill and cut to fit existing points on the frame, or added to with other brackets that are welded or bolted to the frame.

I would tend to lean toward welding mounts to the frame or swaingarm. The drive can be removed at will. The only negative is a permanent change like that kills the resale value if you ever want to sell just the frame.

I hope that helps!

Matt

Could the gearbox be secured to the bottom bracket? If you make large 'washers' from 2mm sheet steel with the same ID as the BB shell they could be secured either side of the BB shell using the BB cups. The 'washers' could then provide mounting points for the gearbox (some form of torque restraint would be needed, but that's easy enough to do with a hose clamp or the like. Even better would be to find (or machine) a piece of channel that is just wide enough inside to fit either side of the BB shell, with holes cut either side through which the bottom bracket cups could be inserted. This would provide a rigid mounting point with a flat surface to attach the box. It might be necessary to replace the bottom bracket with a slightly longer version, but that's no big deal.

one concern there malc as you say is the width of the bb - i have a 127mm spline,the widest i could get.
The pic that Matt posted shows the gb has a width of 4" (is that right Matt?) and i dont think it will fit between the cranks, still i don't know if i need single or dual stage reduction yet so i'll wait and see how it goes with final measurements but may ask Matt for a special should it not work out.

Cheers,

D

To me it would depend on the bike I'm putting the drive on.. If you feel it's your ultimate bike, the one you plan on keeping for a good while, go ahead and have it welded, that can be made to look the nicest with the least effort.

A bike worth trading later, do some kind of semi permanent thing with clamping force most likely, at least if you plan on keeping the gearbox and motor.

A beater you are going to ride the wheels off and throw away go Fred Flintstone on it, just drill it through the big tube(s) and bolt on a plate or plate and angle adapter.

D,

The complete drive will come in a touch under 4 inches. I am desperate to get it to clear the cranks. Also, it can be made even narrower (much narrower) depending on the situation. Setup as a single stage, the drive could be as narrow as 3 inches. In two stage arrangement, the second stage could be setup 3 inches wide as well. However, in two stage guise, there would still be roughly 4 inches of width at the center jackshaft, but it could be as narrow as 3 inches at the output shaft.

Matt

recumpence said:

The complete drive will come in a touch under 4 inches

Click to expand...

Sounds as if mounting via the bottom bracket is a possibility then.

deecanio said:

one concern there malc as you say is the width of the bb - i have a 127mm spline,the widest i could get.

Click to expand...

Why do you need such a wide bottom bracket D? Is it needed to clear your battery box?

Hi All,

Malc, i took the widest one to clear the battery box as you guessed, i could have got away with a slightly smaller one but i didn't want to take the chance as i ordered it without the bike at home to measure, also i had to put the road crank on to get a large ring upfront (52t) and the cranks were a lot straighter than mine so again a wider bb was needed to clear the frame, the 127mm took care of both issues.

Matt, i'm gong to work out in my own thread all the gearing i need - do you know what the KV of the pletty is so i can begin to work out what i need - also i would love a slimmer drive, dependant on how im going to gear im hoping that i can use a single stage and then whatever reduction i need from the drive sprocket tothe rear?
I still want to utilise the space i have between the seatpost and rear wheel - can you make a special if i give you the dimensions at all? im hoping this is achievable as i have a plan for my own particular needs that means the gb would have to be custom, maybe we can use the same gears but adjust to fit? I was looking at the pics you put up the other week againand i finally think i know how its going to work - is it belt first stage and chain second? my guess is my pletty will have a pulley connected to the large pulley shown in the assembly and then the other end would have a small sprocket connecting to the large sprocket shown and then a freewheel sprocket on the opposite end of that as my final drive sprocket?

If i can work out the pletty kv i will know what speed that 48.4v gives me and then i can work out how to geardown for myself (i think) - then i can plan how big my reduction gears need to be and where i can put them, the more i look at the standard setup i dont think it will fit between my cranks but im sure we can work around that?

can someone tell me if i have 25" wheels (tyres included) what rpm would i need for a top speed of 30mph and 35mph respectively??? is there a calculator??

I hope Matt is not reading and thinking "messer" i still want a gb from you sir it's just that i may need something slightly of the standard model??

i will post up in my own thread with all my figures and then you guys can help me see if it's right


Cheers,


D

deecanio said:

can someone tell me if i have 25" wheels (tyres included) what rpm would i need for a top speed of 30mph and 35mph respectively??? is there a calculator??

Click to expand...

Created by JohnRobHolmes:

excellent, thank you Miles

Cheers,

D

MitchJi said:

Is there an easier solution?

Click to expand...

I forgot who it was, but somebody used these kind of things: http://www.pegasusautoracing.com/productdetails.asp?RecID=269

18 seems like a fair deal to not have to machine from scratch.

thats more like it, not too expensive but easy on the eye,good find.


Cheers,

D

Hi,

I should have put this in the original post. What prompted me to post this was this email from a friend:

My thoughts are:
You cannot/should not do any additional welding to an aluminum frame. They are heat treated after their assembly welding, and any disruption of that causes a fault in the frame that can only be solved by re heat treating it, which no one will do. It would be better to devise a way to bond or clamp the motor to the frame. Steel is the only material that you can modify at will without incurring damage to the original construction technique.

Click to expand...

lawsonuw said:

Are any of the frame tubes on the bike round? Because a solid clamp would be easy to machine out then. Even with a non-round tube, an approximatly shaped clamp could be turned into a precise clamp with some epoxy filler and a frame coated in a mold release agent/film.

my two bits,
Marty

Click to expand...

Voicecoils posted this link for round "clamps":
http://shop.ebay.com/?_from=R40&_trksid=m38&_nkw=+two-piece+SHAFT+COLLARS

Here's one ($5.59):


Round clamps won't work for my frame/location. For builds where they do work they will be great except that for a 3-5kW motor I would either want tabs welded on the frame or clamps on more than one tube (both down-tube and seat-tube for example) to prevent any rotation. Generally welding tabs on the frame would be easier than fabricating brackets that connect to clamps on multiple frame tubes. The issue is can that be done without damaging the structural integrity of the frame?

etard said:

Hold On!! I thought we were all in agreement that duct tape was by far the most elegant way to mount EVERYTHING!

Click to expand...

Except that for a 3-5kW motor duct tape is overkill, don't you think?

recumpence said:

Mitch,

I do not want to dominate your thread. So, hopefully this discussion will remain centered around your build, not another thread about my drive.

Anyway, if this question is purely related to mounting my drive unit, I can offer some advice;

#1 Welding aluminum is fine if it is TIG welded by a professional. I purposely used 6061 for its strength and weldability. I would prefer 7075, but that is not weldable. :wink:

My drive can be mounted with two different methods (tough to describe without a finished drive to show you). Both methods would merely require brackets welded to the frame, not the drive itself. The drive, then, gets mounted to those brackets (again, two different style brackets can be used and will be made by me and stocked).

#2 I am not a big fan of bonding unless there is no other option.

#3 Yes it could be bolted with fabricated brackets. There will be included mounts that should be easy enough to weld to the frame, drill and cut to fit existing points on the frame, or added to with other brackets that are welded or bolted to the frame.

I would tend to lean toward welding mounts to the frame or swaingarm. The drive can be removed at will. The only negative is a permanent change like that kills the resale value if you ever want to sell just the frame.

I hope that helps!

Matt

Click to expand...

My intention was that this would not be focused on my build but the issue of mounting your drive (or any drive) on an aluminum framed bike, given that I was told it isn't safe to weld to an aluminum frame.

So is the friend who said its not safe to weld to an aluminum frame incorrect?

Or is it safe within certain limitations (like soldering batteries)?

Malcolm said:

I've been keeping an eye on Matt's evolving design but I'm still not sure where it's intended to fit.

Where do you plan to mount the drive Mitch?

Click to expand...

I think part of the intention is by making it as small and flexible as possible it can be adopted to a wide range of situations. No fault of Matt's but I think mounting is the biggest hurdle to using his drive and ending up with a quality build. I think the mounting for motors this powerful needs to be very strong. Either welded or very carefully fabricated mounts.

Switching to my build:
I tentatively plan to have a "structural" fender fabricated out of aluminum. About 1/4" thick. Then mount the fender to the swingarm chainstays and what would be seatstays except that they are on the swingarm. Probably a couple of braces attaching to the hub bolt. The fender would be fastened on both sides so it should be pretty immune to twisting. Then I have the whole sweep of the fender from chainstay to the top of the wheel to use for mounting. Fender is not heat treated so welding mounts to it should be fine. The issue is how to fasten it to the swingarm. Welding on tabs on both the swingarm and the "fender" would be easiest but the swingarm tubes are pretty small so I don't want to weaken them (they are square or rectangular). Having some brackets fabricated that would clamp to the swingarm and bolt to corresponding tabs on the fender would work but more complicated and expensive.

While proof reading this before posting I got an idea that I think should work well. Use some square tubing that is just large enough to fit over the swingarm tubing. Split it down the middle and remove enough material that it makes a tight fit when clamped together. Weld tabs on both halves of the tubing so that bolting the tabs causes the tubing to clamp tightly on the swingarm tubing. Either bolt through those tabs for mounting or weld more tabs on for mounting.

If I don't like where the GB/Motor end up with the stock wheelbase (without the rearwheel, fender, GB or motor its pretty hard to tell ) I might move the rear wheel back by either extending the swingarm ( a 2" to 4" extracycle) or by having a new swingarm fabricated. Extending the swingarm would require even more extensive fabrication or welding.

So there is no miracle product named Alumibond? :lol:

Your friend is correct in one sence, and over-reacting in another sence.

I have some first hand knowledge of this. I was also assuming someone would bring up the issue of welding to an already heat treated frame. Before I go into the ins and outs of this, allow me to give my experience in this;

In 1991 I hand build a freestyle bicycle frame that was featured in the october 1992 issue of BMX Plus under the heading "Project Homemade" (you can Google it and still find info on the artical). That frame was made from some donor parts off an old 70's vintage Race Inc. frame. I used the head tube, bottom bracket tube, and rear dropouts from that frame. I did a HUGE amount of research into the issue of heat treating the frame especially considering the fact that freestyle bikes get a LOT of abuse. I was told by Alcoa and Mountain Cycle that heat treating is not needed if one of a couple factors are present;

#1 If the frame is overbuilt. The heat treating would not matter if the welded area is stronger than required.

#2 The welding is done in a relatively non-stressed area.



Here's my understanding of it;

Heat treating is important to maximize the strength of a frame while minimizing weight. A complete frame can be made without heat treating if the frame is overbuilt (hard to qualtify how much overbuilding is needed). If anything is added to an already heat treated frame, that does not make that spot srtificially weak. What it does is affect the heat treating in that localized area. It slightly reduces the durability if that area. However, that affect is normally minimal.

I built my freestyle frame and beat the crap out of that thing for years on the pavement (jumping down stairs and other harsh treatment). I couldn't believe the abuse it tolerated and I never heat treated it. At the time, I worked at a welding shop and went over this in detail with our TIG welder and got the green light to proceed with the build.

I would say on a typical mountain bike frame with suspension, those frames are so overbuilt, you should not have any issues. Also, you can go a bit on the safe side and make sure you gusset the area to add some more material to guarantee strength.

Lastly, I run into so many people who are alarmists on this kind of thing. My experience is that this is not a big deal. It is merely a slight reduction in durability in taht localized area. Make sure the welded area is gussetted and there is no problem.

Matt

Hi Matt,

Thanks!

That is exactly the type of information I was looking for. The reason I made it a separate topic is that this information should be of interest to a wider audience than users of your GB.

Hi Matt,

recumpence said:

Mitch,

#1 Welding aluminum is fine if it is TIG welded by a professional. I purposely used 6061 for its strength and weldability. I would prefer 7075, but that is not weldable. :wink:

Matt

Click to expand...

One more question. Where are bicycle frames normally on the weldability scale? More like 6061 or 7075?

Thanks Again!

Mitch

Almost all bike frames are 6061. Those that aren't (like my recumbent) are 7005. 7005 is the highest quality aluminum that is weldable. 7075 is not weldable (or not weldable in a decent enough manor to be worth doing). It is fantastic to machine, though.

Matt