E-Trials bike input needed

If you read my Project #001 thread all the way through (which is not an easy task) then you know that I went through several "transaxles" as I called them. My mistake was in underestimating the strength that is needed in the bearings. You need strength that is greater than a bicycle hub (I was using a steel rear hub and altering it) and probably less than a one piece bottom bracket set of bearings. I ended up with some high precision sealed bearings and it's gone a couple thousand miles without complaints.

So just be sure to go with the highest quality sealed bearings or you will find yourself rebuilding it again and again. And with an expectation of wanting to maximize torque that means that the stresses will be at their highest.

It's surprising how much strength is required even because of a tiny little motor... (they can surprise you with how strong they are)

The RC motors are even more extreme as they put out so much power for how small they are.

(the pictures are too dark for me to see what you are doing very well)
 
The only real issue with using RC components (aside from the cost) for your situation would be the extremely low reduction needed. You would need roughly 50 to 1 to get down to a reasonable level for trials. That is doable, but would require 3 stages (from motor to wheel) for most RC motors. However, at that reduction, even 1500 watts would be CRAZY power! You would have snap wheelie heaven! You could run one of CNCAdict's 40 series outrunners (under $200) and gear it way down. That motor will put out 3kw in short bursts and is really small and light, as well as efficient.

I think you will be surprised how much torque you can get with a low reduction using an RC motor. My biggest worry would be breaking driveline parts. I would suggest one of the high strength trials chains and I wouls absolutely recommend using the left side disc brake flange on the hub to drive it. That would be the strongest solution.

Matt
 
I agree with the geardown part.

You know... we've been lazy with gwhy! and not done the math on what the actual gear ratio needs to be. At some point the actual math needs to be done.

By the looks of it those gears he's using will give about a 10:1 at best and that's just not going to get very far.

Your motors powerband looks like this:

MY1016Z3 Powerband.gif
...the goal is to be able to have the motor running at near 3000 rpms while doing the Trials pulses. Maybe pulse from 2000 rpm up to 3000 rpm. (this is assuming a 30 amp controller... and so if the unlimited current controller was to be used it would be different... but this is a place to start)

If you go here:

http://www.arachnoid.com/bike/index.html

...and plug in:

Wheel Diameter - 20 inch
Pedaling Cadence - 1000 (to avoid round off errors)
Front gear - 1
Rear Sprocket Teeth - 1

...then you get:

59.5 mph which if you divide by 1000 you get the speed you travel for each rpm of the motor.

0.0595 mph per rpm

Now we can look at 2000 rpm:

2000 rpm * 0.0595 mph per rpm = 119 mph (a little over geared? :lol: )

...which means if we really want to get down into the 5 mph to 10 mph range we will need a gear reduction of:

( 0.0595 mph per rpm / 5 mph ) * 2000 rpm = 24 to 1 geardown

A little less than 50, but it's a lot more than 10.

(note you could have done this in a more formal manner, but the online tools work good enough for ballpark estimates)

------------------------

Don't forget our torque chart:

file.php


...if you look at the torque at 2000 rpm it's about 3 Nm (assuming unlimited this time) which after the geardown becomes:

3 Nm * 24 = 72 Nm (at the hub) Red Line

At about 100 Nm you have to figure that many things begin to break on you, so even with this little motor you are getting close to the limits of the equipment.

Using a 30 amp standard controller you get:

2 Nm * 24 = 48 Nm (at the hub) Green Line
 
first reduction is 8:1 this drives a 10 tooth bike chain sprocket which in turn drives the back wheel I can go upto a 44 tooth chain ring mounted on the back wheel should i need to but that will be far to slow I found it will need to drive about a 28ish tooth sprocket on the back will give me about 5-6 mph and pull the bike up anything ( but would need to be a tad faster more like 10-15 mph )like without any mods to the controller. The hub on the back is a fixed hub ( screw on freewheel ) so it will be just as strong as running the drivetrain down the left ( I dont trust or like freewheel hubs :shock: I have seen so many brake unless you pay alot of $$ for a topclass one) if thats what you mean. The hub im using has a screw on disk mount so if you are saying that the torque will strip the theads on the right side then they will stip the thread on the left :cry: Which wont be clever :mrgreen:
 
gwhy! said:
first reduction is 8:1
this drives a 10 tooth bike chain sprocket
28ish tooth sprocket
Click to expand...
That's right there... 8 * 28 / 10 = ~24

Okay... so you got the gearing right. The fixed rear sprocket sounds good too.

Everything is looking okay so far.

It's good to have other people double check your math. :)
 
Ok put the speedo on to my cycle trials today and had a max speed of 12mph for the stuff i was doing today (just playing) I estimate a max speed of 18mph will be fine and very usable for cycletrials. Because I havent really fixed anything to my prototype bike yet I thought ( as I had a bit of spare cash this week ) I would buy a cheap RC setup (motor+controller) 2.5kw 200kv motor and a 110a controller ( as this will be the way forward for lightness and power ) just so I can get a reduction stage built and tested that will hopefully withstand the forces involved . The motor may well be way overkill ( or it might be rubbish as a motor/ESC cos it was cheap ) for what Im intending it for but it is a starting point ( for me :D ) to see what these little motors are like. I will still get my exsisting motor setup on the bike for some other test that I will like to do. The clutch thing was sort of what I was thinking in the first place but using a lockable variator ( CVT ) with a clutch setup but I have drawn some designs out on paper and I have come to the conclusion that I could not make it small enough to fit on a cycle ( wish I could :) ). A clutch/flywheel setup is a very good idea and would make very good use of a lot smaller motor/esc but as the RC setups are so small and powerfull I dont know ( yet ) if it would be a enhancement on the drivetrain .
 
You arrived on the scene at a good time. Six months ago there were only rumors about how much potential there is with RC motors and now the intesity of interest is very strong.

I think you are making a good decision to leap frog ahead to the RC motor. You were going to have to invent some sort of geardown anyway, so you might as well do it with an RC motor. You will have a few hurdles to clear with the RC motor compared to the standard brushed variety, but the result looks to be much better.

I'm going to finish up on my Project #003 with the motor I have since it has a built in geardown so that it's a simple bolt on part. (no additional gearing needed) But my next project will go with an RC motor.

Things move really fast in this hobby. :shock:
 
safe said:
I think you are making a good decision to leap frog ahead to the RC motor. You were going to have to invent some sort of geardown anyway, so you might as well do it with an RC motor. You will have a few hurdles to clear with the RC motor compared to the standard brushed variety, but the result looks to be much better.

I'm going to finish up on my Project #003 with the motor I have since it has a built in geardown so that it's a simple bolt on part. (no additional gearing needed) But my next project will go with an RC motor.

Things move really fast in this hobby. :shock:
Click to expand...

I hope its a good decision :mrgreen: , but for the price I bought the motor+esc for it would have been silly not to . Even if the motor/esc only last for testing purposes it will hopefully give me some benchmark results which will be worth the cost of the motor/esc. Only real problem is I will have a lot of parts that I have already bought now not being used ( spose theres always e-bay, would be nice to try and get some cash back on some of the stuff I have :D )
 
gwhy! said:
Only real problem is I will have a lot of parts that I have already bought now not being used ( spose theres always e-bay, would be nice to try and get some cash back on some of the stuff I have :D )
Click to expand...
You should see my garage. :lol:

http://endless-sphere.com/forums/viewtopic.php?f=6&t=1266

To give you an idea of how bad a terminated project can be you ought to read my Project #002 thread. All the parts and effort that went into that went to waste because I realized in the middle of the project that the future would be to comply with the Federal Ebike Law and that law requires pedals. I wasted my time building a "Missouri Only" ebike without pedals.

I have a bunch of parts that I've bought and have not yet used.

(the secret is to try to find alternative projects that the spare parts can be used on)
 
The cheap esc arrived today :D , ( 22ukp very cheap indeed :lol: for a 110a ) I will hopefully take delivery of the motor tomorrow. First impressions of the esc are ( bearing in mind I have no other esc's to compare it with :wink: ) its very well made, Heat sink seems way to small for any amount of sustained high current flow and the input caps ( 2 ) seem a little under value again for bursts of high current flow into a inductive load. So a few things that I think need to be altered on this esc are , I will increase the heatsink area ( Probably just force cool the heatsink with a small fan first off I dont what to spend to much time altering the hardware as the esc may well not perform very well anyway ) and add alot more capacitance on the input before I go trying to draw lots of amps through it. Other than that so far Im pleased with the cheap esc ( just hope it works when I connect it to a motor :? ) then some real testing to be done.
 
I have a rc motor, controller, and thottle controller I am just waiting for some belts and pulley's , not sure what I'm gonna do about batteries at the mo I think I will wait till I have all the hardware mounted on the bike and geared to what I think will work :D There's not much point putting a build thread up but I will take some piccys of the hardware when I have mounted it all on a bike :mrgreen: ,
 
ok I now have most of the stuff I need to start putting my prototype e-trials bike together I have just been looking at the 3 and 4 speed nexus hubs and they are not to badly priced but it would appear you need to buy the coaster/roller brake,fixing kit and shifter as a separate items I have a few questions have you got to have a the coaster brake installed for the whole hub to work ,is there a way of converting it to disk? if not I will have to use rim brakes. What do the fixing kit consist of ? and what is special about the shifter ? is there a way of making the hub a fixed hub? I have made the first stage reduction/motor mount which is 4.5:1 the plan is to drive a 219 13t sprocket to a 50t'ish sprocket on the bb coupled with a 26t'ish front bike sprocket driving a 44t'ish rear sprocket connected to a geared hub this should give me around a overall reduction of about 28:1 before any gearing within the hub so with a max of 5000 rpm from the motor should give me about 10mph with a 20" wheel (may go up to a 24"or 26" if there is enough torque ) when the geared hub is 1:1 do this sound about right to you guys? , I'm planning on having a additional rear sprocket of about 20t that can be used for commuting ( may not be needed ). This will be the starting point to see what gearing works best unless anyone can see any potentional problems. The bb sprockets needs to be as small as I can get away with for ground clearance . The motor I have is just a small one compared to what you guys are playing with its just a 2.4kw outrunner but it is a starting point :D .
 
Just thought I would post some pics of my very slow progress :roll:
leftside.jpg

rear.jpg

rightside.jpg

top.jpg


sorry about the quality of the pics ( note to self "must get a better phone" :lol: )

how do you upload pictures directly to this forum , is it possible ? ..
 
gwhy, stonking effort!!!!


i think the setup looks great 8) im hoping my pulley will sit like that on mine.
did you make the motor bracket yourself?, sorry im not up to speed with the thread yet :oops:

cheers,

D
 
Thanks D,
Yes made it myself with a fair bit of trial and error, the pulley fits in that space like a glove :) Im not putting a fw on this setup so its gonna be a small spocket straight onto the output shaft the bracket is also gonna be clamped to the cross bar also so there should be no way the thing is gonna twist, I have been playing around with my other frame with a similar setup but using only a 350w brushed motor and that is twisting on the down tube so I think you will have to put a bit of thought into mounting Matts drive as it may be a problem with twisting, but to be fair the gearing on both my bikes is only geared for a max speed of about 15-20mph so there is one hell alot of torque trying to make the bugger twist on both my frames :mrgreen:
 
lawsonuw said:
Good link Gwhy! Cool that a Preditor fits in the same space as the crankshaft on that engine. Wonder if the Preditor has more power than the engine it's replacing?

Lawson
Click to expand...

Mototrials bikes dont put out much at the back wheel only about 15-18bhp max so I think if they can ditch some weight for the bike ( which will be a problem as they only weigh around 75kg anyway ) it could be competitive for some small stuff trials.
 
recumpence said:
That Predator motor is good for 12 to 14kw bursts if the controller can handle it.

That is 15 to 20HP. :wink:

Matt
Click to expand...

Very interesting stuff, would love to see how it performs :D
 
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