Advice on seat yoke design

[Carl84]

Hi I am new to the forum , I'm not pretending to be an engineer. I'm an ex mechanic by trade and have an interest in engineering/ fabricating,I'm currently designing and building an adapted electric mountain bike with help from Freind's and brother in welding and machining trades which will be for my self (now a paraplegic) and would like some input or advice on the design of the seat yokes which will be connected to eachother by two tubes and will have a tilt function to allow for stability whilst negotiating off camber sections etc , The two yokes have been machined from 25mm thick 6000 series aluminium plate and I would like to know how much material we can remove without making it too week and failing also would it be better to remove material from both sides to create an I beam type cross section or one side ? The lighter I can get them the more range I will have on the battery, I weigh approx 68 kg and intend to use the bike for trail riding but would like some strength incase I do a jump if Im feeling brave , I need the front yoke to be no less than 15mm thick at the centre as it will house a spring for a detent mechanism, please see attached drawings and photos for reference and ,any input will be much appreciated, thanks Carl

 

[Carl84]

Please see attached photo

 

[Tmoose]

Sorry Carl, I'm lost.

Bicycle seat yoke didn't get much from Google.
Canoe seat yokes got more.

The second attachment is a sketch of a component that looks to me like the "triple clamp" of a telescopic fork. But being 400 mm/ 16" wide my first guess is it must be mounted with the long dimension running fore and aft or vertical. Or does it??

Is the mountian bike a three wheeler, like this ?

https://cdn.spinlife.com/images/product/61605.425906100822.webp

the photo ( first attachment) seems to have a possible wooden version of the seat yoke, but in the vicinity of a front fork or something, and running sort of perpendicular to a tire with a clamp and some rubber belts or straps.