E-Trike Design: Balloon Tires vs Dedicated suspension

[amberwolf]

Great feedback - thanks! Not sure how I would implement a stabilisator on a trike.

same way you would on anything else. look at the links in that search and they show you how they work, so you could figure out how to add that to your design.

. Besides price / complexity issues, the main argument is the loss of cargo space: the whole back gearbox + suspension in the fully design sucks up nearly a third of useful cargo space.

this is part of why the sb cruiser is the way it is, and why it uses big heavy hubmotors in the rear wheels vs a central drivetrain.

i have ideas in the works to use a differential to drive the (still unsuspended) wheels from a single central motor, but it is complex because the diff axle can't go to the hubs of the wheels, or else it will make a bump in the middle of the cargo deck, or actually have to be in the middle of teh cargo area.

so if i use a diff, it'll go under the deck, between the wheels, but the deck will be below the axle line, and the deck frame will "hang" from the axles, like it does on my big mk iv / v trailer, and the raine trike for my brother. so the diff will be down between the rims, really, just enough off the ground to clear the usual things, since stuff like speedbumps/etc will automatically clear as the wheels will force that.

then the ends of the diff axle will go to chain sprockets, and short lengths of chain will then drive the wheel hubs; both will use the largest practical sprockets to keep tooth loading down, whcih will reduce wear and increase grip/torque transfer.

the placement of the motor itself will depend on what motor i use, but a big hubmotor is the likely type, mounted in the frame in front of the cargo box under the seat, in place of the igh that's there now, simply becuase i already have a few to try. probably no freewheels, as those would wear quickly or break at the power level expected.

the pedal drivetrian presently goes to the left wheel, but will change to go to the front wheel (kinda like the cycletruck or whatever it is that ups is using some places), with an igh in the front wheel, or as a jackshaft (like it is now) on the way up to the wheel.


anyway, just ideas you may be able to use.

 

[qwerkus]

i have ideas in the works to use a differential to drive the (still unsuspended) wheels from a single central motor, but it is complex because the diff axle can't go to the hubs of the wheels, or else it will make a bump in the middle of the cargo deck, or actually have to be in the middle of teh cargo area.

I see the issue - same here. But are you sure you'd gain any advantage by ditching the hubs in favor of a central motor ? If you use 4.3kg geared hubs, two of them actually weight only marginally more (about 500g in my calculation) than a mid drive + mounting support + reduction + tensioner + diff + axles + hubs, which also add a lot of part that can fail. Of course if you go for a rear pedal drive, you'd need that setup anyway, so the argument becomes irrelevant. But if you chose a fwd design of some kind, the simplicity of hub becomes more and more obvious, and you can use the space between the hubs to mount battery + controllers.

 

[amberwolf]

ditching the hubmotors would be to make stronger wheels, and lighter wheels, and easier to repair / replace / carry a spare i can just quickly install, for the very rare but very problematic flat or broken wheel from bad road conditions.

i could use larger diameter wheels (regearing between wheel and motor to compensate), which will give a much better ride over uneven surfaces than small diameter wheels the hubmotors require to operate well at high torque / low speed.

simplifies wheel mounting tremendously.

could even allow for single-ended axles (doing that for existing hubmotors i have would require complete redesign and rebuild of the stator supports and side covers; i have a thread for that from a year or two ago). but doing it for regualr wheels is pretty easy; i just start with hubs made for that, which i can make myself (since i generally build my own wheels) wiht very large diameter axle holes, very thick axles, good bearings, etc.


as you note, it adds complexity in other areas, and it also may negate serious motor braking (unless all the stuff from wheels to motor is really beefy).


fwiw, i originally went hubmotors in the first place to simplify all the broken crap i kept having on crazybike2's middrive...most of which was caused by the frame flexing enough under torque to allow chain derailments.

 

[adam333]

Nice trike design so far Qwerkus,

Here is my personal experience with trike suspension.

1- Suspension doesn’t help to keep the tires in better contact with the pavement most of the time. The regen ( with hub motor ) has decreased because of the amount of time the tire is bouncing in the air.

2- Heavy wheels kill the suspension efficiency.

3- My initial trike had no suspension at all and I could fell every single tiny crack in the road. After 60 min I had to stop because of the discomfort ( note that KMX's trike seat is not really soft from the start )

4- Adding the suspension was a lot of time and effort but in the end, it's worth it and I would never go back to an UN-suspended trike.

 

[ZeroEm]

Wondering what is the least amount of travel is needed on the front of a trike. I mostly want to get away from the vibration of all the small bumps. I try to avoid the pot holes but the smaller bumps just can not see flying up on them.

 

[amberwolf]

The little stuff at 20MPH, up to the driveway entrance lips (at <10mph), was absorbed reasonably well on SB Cruiser when I was using a Suntour XCT (XCV? cant remember) with 100mm travel. It was just a spring/polymer pogostick type.

But it wasn't perfect, and anything other than basically road imperfections (like actual potholes, missing chunks of pavement, etc) were best avoided.... :/


The crown broke in the only crash I've been in, so now I'm using a doublecrown rigid fork (with doubled-up bicycle frame tubing for the stanchions, and a pedicab "crown kit" with steerer). It's not as bad as it might be on a regular bicycle, but the road vibrations still reach the bars thru the long tiller. (the seat is "suspended mesh" type, like a hammock, so my butt is saved from all that, except for the stuff over around 1/2" to 1", depending on it's shape, size, and my speed).

 

[MadRhino]

The little stuff at 20MPH, up to the driveway entrance lips (at <10mph), was absorbed reasonably well on SB Cruiser when I was using a Suntour XCT (XCV? cant remember) with 100mm travel. It was just a spring/polymer pogostick type.

But it wasn't perfect, and anything other than basically road imperfections (like actual potholes, missing chunks of pavement, etc) were best avoided.... :/

Yep, adequate suspension is not a matter of travel, as much as proper rebound control. With the weight of hub motors especially, most bicycle shocks and forks are not made with sufficient damper setting range. Thicker oil can improve this, but damper valve mod is best.

 

[amberwolf]

With the weight of hub motors especially, most bicycle shocks and forks are not made with sufficient damper setting range.

My trike is just a regular wheel up front (the "giant" hubmtors are in the small rear wheels).

 

[ZeroEm]

by Rassy » Mar 31 2020 2:07pm

There was a mention about cambered rear wheels to help with cornering. My current trikes are both Sun Delta X3-AX models, which have cambered rear wheels. It does help with cornering, but it doesn't prevent tipping. Never tipped over, but have raised the inside wheel off the ground which will happen on a delta and on a tadpole if you are going too fast for the corner.

The down side of cambered rear wheels includes lower load capacity and accelerated tire wear. The Sun EZ-3 USX also has cambered rear wheels and the original model was replaced with an identical HD model, and the only change I can see is 48 spoke wheels with wider tires.

One of my X3-AX trikes has 1.35 X 20 tires at about 60 PSI and the other has 1.75 X 20 tires at about 40 PSI on the same narrow rims. There is a definite difference in the ride quality, plus the wider tires do not wear as fast. When the current 1.35s wear out they will be replaced with 1.75s. If I could justify it I would replace the narrow rims with a wider rim and go to an even wider tire.

For my style of riding I would prefer non-cambered wheels, but I'm happy they are there when cornering at speeds over 20 MPH.

Thx Rassy, Going to go buy a pair of 1.75 X 20 for my fronts and was worried about narrow rims. Had 1.5 X 20 went to 1.3 X 20 fast but not enough traction and at 100 psi hard as rocks but getting a lot of miles out of them unlike the 1.5. Don't want to go to wide yet limited space to many mods.

I would like to try a 2" suspension travel (front) that would be stiff only respond to the worst bumps and not flex with normal riding. Something like the Cattrike.
I have rear suspension and it works great.

 

[The Speaker Guy]

Rear camber helped a lot on this trike. This has proved very stable, but needs a suspension. Tires were 2.5" CST, now replaced with Hookworms. 26" rear 24" front. We have had 6 adult males riding on this on flat ground. Don't ask ....

 

[momus3]

I like the second, simpler design, and my preference would be to go w/ balloon tyres. KISS. For my money, tyres ARE suspension. Ever get some of those solid, airless tyres on a bike? You'll destroy the rims in no time flat, and feel every pebble on the roadway. A hyper inflated tyre will beat you and the bike up. Not safe either. You need something that will absorb road irregularities, not go skittering in a curve or sudden maneuver. A large cushy or sprung seat is a good idea too.

I do agree that bike front suspensions are not designed for heavy hub motors, which is why I decided to put front suspension on my bike for comfort and safety, and nixed my original idea of going w/ a front hub motor. A front hub motor sure simplifies everything, but along w/ the suspension issue, it just makes more sense to have the rear wheel(s) power the bike, at least to me.

I'm making my Sun Traditional trike into an eTrike, and people here mentioned that stiffness was a definite factor in stability. Something to think about.

I've never been able to get an idea of what something will look like from 3-D modeling. Maybe a quick sketch on the back of an envelope. Once something starts getting built, I always see stuff that looked good on paper but didn't really work in the build.

 

[MadRhino]

High PSI doesn’t destroy a wheel, airless tires do, because a hit is not distributed around the wheel by the dynamics of gas. High PSI does affect traction and yes, the feel of the small stuff on pavement. High PSI does make you feel them even with proper suspension, that is made to absorb the bumps that would eventually lift a wheel off the ground and not the small irregularities of pavement. Suspension is for traction first, to keep the wheel in contact with the ground. Comfort is only a consequence. Lower tire pressure does help with comfort and grip, but not with keeping the wheel on the ground. A big, soft tire only makes a comfortable feel that is an illusion of suspension but once the wheel had lifted, the fatty tire will make it bounce back thus spending even more time off the ground. Up to 3’’ it is not that bad, but fat tires 4 or 5 inches are bouncers.